A Reef Manager’s Guide to

CORAL BLEACHING

Paul Marshall and Heidi Schuttenberg
ii

The designation of geographical entities in this book, and the presentation of the material, do not

imply the expression of any opinion whatsoever on the part of GBRMPA, NOAA, IUCN or other

participating organisations concerning the legal status of any country, territory or area, or of its

authorities, or concerning the delimitation of its frontiers or boundaries.

The views expressed in this publication do not necessarily reflect those of IUCN, US EPA or other

participating organisations.

This publication has been made possible in part by funding from the US National Oceanic and

Atmospheric Administration and IUCN - The World Conservation Union.

Published by: Great Barrier Reef Marine Park Authority,Townsville, Australia.

Copyright: © 2006 Great Barrier Reef Marine Park Authority

Reproduction of this publication for educational or other non-commercial

purposes is authorised without prior written permission from the copyright

holder provided the source is fully acknowledged.

Reproduction of this publication for resale or other commercial purposes is

prohibited without prior written permission of the copyright holder.

Unless otherwise noted, photographs are copyright GBRMPA.

National Library of Australia Cataloguing-in-Publication data:

Marshall, Paul, 1969

A reef manager’s guide to coral bleaching.

Bibliography.

ISBN 1 876945 40 0

I. Coral reef conservation. 2. Coral reef ecology. 3. Coral reefs and islands.

I. Schuttenberg, Heidi, 1973-II.Title.

639.972

Cover design

and layout by: AECgroup

Available from: Great Barrier Reef Marine Park Authority

2-68 Flinders St, PO Box 1379,Townsville, Qld 4810, Australia

Tel: +61 7 4750 0700, Fax: +61 7 4772 6093

Email: info@gbrmpa.gov.au

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E-mail: books@iucn.org

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A catalogue of IUCN publications is also available.

Or contact the authors:

p.marshall@gbrmpa.gov.au or heidi.schuttenberg@jcu.edu.au
iii

A Reef Manager's Guide to Coral Bleaching

Paul Marshall

Great Barrier Reef Marine Park Authority

Heidi Schuttenberg

US National Oceanic and Atmospheric Administration (NOAA)

with major contributions from:

Jordan West

US Environmental Protection Agency

and

Ray Berkelmans

Australian Institute of Marine Science

David Bizot

NOAA's National Marine Sanctuary Program

Billy Causey

Florida Keys National Marine Sanctuary

Herman Cesar

Cesar Environmental Economics Consulting

Loke Ming Chou 

National University of Singapore

Chris Hawkins

University of Massachusetts at Amherst

Ove Hoegh-Guldberg

Centre for Marine Studies (University of

Queensland)

Jessica Hoey 

Great Barrier Reef Marine Park Authority

Melanie McField

WWF / Smithsonian Institution

Nadine Marshall

School of Tropical Environment Studies and

Geography, James Cook University

Jeff Maynard

Great Barrier Reef Marine Park Authority

Peter Mumby

Marine Spatial Ecology Lab at Exeter University

David Obura 

CORDIO (Coral Reef Degradation in the 

Indian Ocean)

Rod Salm

The Nature Conservancy

Naneng Setiasih

WWF Climate Change Program 

Shelia Walsh

Scripps Institution of Oceanography

Additional contributors listed overleaf
iv

Greta Aeby

Hawaii Institute of Marine Biology 

Ken Anthony

Centre for Marine Studies, University of Queensland

Richard Aronson

Dauphin Island Sea Lab

Rohan Arthur

Nature Conservation Foundation, India

Andrew Baird

ARC Centre of Excellence for Coral Reef Studies,

James Cook University

Robert Buddemeier

Kansas Geological Survey and Department 

of Geography, University of Kansas

Steve Coles

Bishop Museum 

Nancy Daschbach

NOAA's National Marine Sanctuary Program

Lyndon De Ventier

Australian Institute of Marine Science

Terry Done

Australian Institute of Marine Science

Mark Eakin

NOAA's Coral Reef Watch Program

Udo Engelhardt

Reefcare International Pty Ltd

Mark Fenton

Environment and Behaviour Consulting

William Fisher

Gulf Ecology Division, US Environmental 

Protection Agency

Steve Gittings

NOAA's National Marine Sanctuary Program

Andrea Grottoli

Department of Geological Sciences,

The Ohio State University 

Lynne Hale

The Nature Conservancy

Lara Hansen

WWF Climate Change Programme

Jim Hendee

NOAA's Atlantic Oceanographic and 

Meteorological Laboratory

James Innes

Great Barrier Reef Marine Park Authority

Tim McClanahan

Marine Programs,Wildlife Conservation Society,

New York

Laurence McCook

Great Barrier Reef Marine Park Authority and 

Pew Fellows Program in Marine Conservation

Kirsten Michalek-Wagner

Great Barrier Reef Marine Park Authority

John Nevill

Marine Conservation Society, Seychelles

Magnus Nystrom

Department of Systems Ecology, Stockholm University

Arthur Paterson

NOAA's National Ocean Service International Office

Joe Schittone

NOAA's National Marine Sanctuary Program

Lida Pet Soede

WWF Marine Program

Glenn Ricci

Coastal Resources Center, University of Rhode Island

Kristin Sherwood

The David and Lucile Packard Foundation

Will Skirving

NOAA's Coral Reef Watch Program

Al Strong

NOAA's Coral Reef Watch Program

Kristian Teleki

International Coral Reef Action Network

David Wachenfeld

Great Barrier Reef Marine Park Authority

Additional contributions from:
v

Acknowledgements

Production of this book has been made possible through financial support from NOAA's

Coral Reef Conservation Program and IUCN - The World Conservation Union. We are

particularly indebted to Roger Griffis and Arthur Paterson of NOAA and Carl Lundin and

Kristin Sherwood of IUCN for their guidance and support, which has been instrumental to

realising completion of this guide.

We are grateful to the vast array of people–reef experts from a diversity of places and

disciplines–who have so willingly shared their thoughts and experiences with us in the

compilation of this guide.Those who provided substantial input or detailed reviews have been

recognised as contributors.

Many others have played less obvious, but equally important roles. In particular, we wish to

acknowledge the energy and vision of the Organising Committee for the workshop entitled

'Coral Reefs, Climate Change and Coral Bleaching', held in Hawaii in June 2003. Organised in

response to resolutions passed by the US Coral Reef Task Force, the thoughtful presentations

and engaging discussions generated by the workshop formed the foundation for

development of this product.The Committee was comprised of Kacky Andrews, Barbara Best,

Rusty Brainard, Billy Causey, Roger Griffis, Lara Hansen, Andy Hooten, Karen Koltes, Paul

Marshall, Tanya Maiava, Heidi Schuttenberg, Eileen Shea, William Skirving, Alan Strong and

Jordan West.

Development of this publication would not have been possible without the support of

many organisations and individuals. Within NOAA, support from the National Marine

Sanctuary Program and the NOS International Programs Office, in addition to the Coral

Reef Conservation Program, was critical to completing this document. We are grateful to

the staff of those programs who worked under tight deadlines to allow the timely release

of this product.

The senior management of the Great Barrier Reef Marine Park Authority have inspired and

facilitated many of the ideas and experiences that underpin the guide. We particularly

acknowledge the leadership and support given by Virginia Chadwick,Andrew Skeat and David

Wachenfeld.We are also grateful to Sara Trenerry, Jo McIntosh, Catherine Collier and Katrina

Goudkamp of GBRMPA for their assistance with the production of this book.

Distribution and application of this guide has been enhanced by a collaborative effort to

promote implementation of local management strategies to restore and maintain coral reef

resilience. We are grateful to the organisations whose logos appear on the back cover for

their support in this endeavour.The contributions of Rod Salm, Stephanie Wear,Alison Green,

Scott Smith, Nina Hadley and Elizabeth McCloud of The Nature Conservancy have been

particularly valuable in this effort.

We are also grateful to Britta Bierwagen of the US EPA, Michael Murphy from NOAA, and

Clive Wilkinson of the Global Coral Reef Monitoring Network for their logistical support.
vi

Foreword

The biological diversity and productivity of coral reefs underpins the welfare of many societies

throughout the world's tropical regions. Coral reefs form the foundation of dive tourism

industries, support fisheries and are important to cultural traditions.They play an essential role

in buffering coastal communities from storm waves and erosion, and they contain a largely

untapped wealth of biochemical resources.Tens of millions of people depend upon reefs for

all or part of their livelihood1, and over a billion people rely on reef-related fisheries

worldwide2.

With coral reefs providing such essential services to humans, the prospect of their continued

widespread degradation is of concern. Pollution, habitat destruction, disease and unsustainable

fishing have now led to declines in reef condition throughout the world.Against this backdrop

of conventional stresses, the threat of mass coral bleaching has recently emerged, leading to

what has been widely acknowledged as a 'coral reef crisis'3, 4.

Mass coral bleaching has affected hundreds to thousands of kilometres of reefs simultaneously.

It has caused stress, and in many cases extensive coral mortality, to nearly every coral reef

region. In 1997-98 alone, mass bleaching is estimated to have caused over 90 per cent coral

mortality to 16 per cent of the world's coral reefs5, 6.While strong initial signs of recovery have

been observed in some locations, many will take decades to fully recover7.

Scientists agree that tropical seas will continue to warm over coming decades, increasing both

the probability and severity of mass bleaching events8-11. These scenarios pose particular

challenges to coral reef managers, not the least because the main cause of mass coral

bleaching–anomalously warm sea temperatures–is largely beyond their control.Yet, managers

can play a critical role in helping reefs survive the threat of coral bleaching. Managers are in a

unique position to increase our understanding of the phenomenon of coral bleaching, to take

meaningful action during a bleaching event, and to develop strategies to support the natural

resilience of reefs in the face of long-term changes in climate.

Because of increasingly strong collaborations between reef managers and scientists, strategies

are being developed to directly address the threat of coral bleaching. Management needs and

preliminary strategies were first documented in 2000, when the IUCN published

Management of Bleached and Severely Damaged Coral Reefs12. In 2002, the US Coral Reef Task

Force called for a collaborative effort to identify actions local managers could take to address

the impacts of climate change and mass bleaching on coral reefs. In response, three US

government agencies (the National Oceanic and Atmospheric Administration, Environmental

Protection Agency, and the Department of the Interior) convened an international workshop

entitled 'Coral Reefs, Climate Change and Coral Bleaching' in June 2003. This workshop

significantly advanced thinking about the strategies that could support managers in their

efforts to respond to coral bleaching.
vii

Around the globe efforts have now begun to improve the prospects of coral reefs by:

(1) identifying resilient areas and enhancing their protection, such as in Palau; and (2)

implementing strategies to support ecosystem resilience. The Australian Government

has implemented strategies to improve the protection of Australia’s Great Barrier Reef,

including an integrated catchment management scheme and a new comprehensive

zoning plan that protects unique areas and biodiversity, and includes 33% of the Great

Barrier Reef in no-take areas. Further initiatives to build resilience principles into

practical management of coral reefs and other marine ecosystems are under way,

including efforts in Florida, USA.

This guide builds on these recent initiatives by bringing together the latest scientific knowledge

and management experience to assist managers in responding effectively to mass coral

bleaching events. It synthesises science and management information, explores emerging

strategies, and informs the ways managers deal with the complex human dimensions of these

issues. Importantly, this guide is designed to provide pragmatic, science-based suggestions for

adaptive management in this time of change.We commend it to reef managers worldwide,

and hope that the experience of implementing the ideas within will further advance scientific

knowledge and the practice of coral reef management.

The Hon Ian Campbell, MP 

Minister for the Environment 

and Heritage 

Australia 

Vice Admiral Conrad C. Lautenbacher Jr,

US Navy (Ret.)

Under Secretary of Commerce for 

Oceans and Atmosphere

USA
viii

ACKNOWLEDGEMENTS v

FOREWORD vi

1. MANAGING FOR MASS CORAL BLEACHING 2

1.1 MASS BLEACHING AS AN EMERGENT ISSUE 4

1.1.1 What is mass coral bleaching? 6

1.1.2 Trends in mass bleaching and coral reef condition 8

1.1.3 Socioeconomic and management implications 8

1.2 A STRATEGY FOR MANAGEMENT 9

1.2.1 Opportunities to minimise mass coral bleaching impacts 10

1.2.2 Integrating resilience into broader reef management 13

2. RESPONDING TO A MASS CORAL BLEACHING EVENT 16

2.1 DEVELOPING A BLEACHING RESPONSE PLAN 16

2.2 PREDICTING MASS CORAL BLEACHING 18

2.2.1 Climatic conditions 20

2.2.2 Sea temperatures 21

2.2.3 Coral bleaching thresholds: how warm is too warm? 25

2.3 ASSESSING ECOLOGICAL IMPACTS 27

2.3.1 Techniques for bleaching assessment 32

2.3.2 Special considerations for bleaching assessment 39

2.4 ASSESSING SOCIAL AND ECONOMIC IMPACTS 44

2.4.1 Socioeconomic impacts of mass coral bleaching 44

2.4.2 Measuring socioeconomic impacts from mass bleaching 49

2.5 IMPLEMENTING MANAGEMENT MEASURES DURING BLEACHING EVENTS 52

2.5.1 Managing local stressors: recreation, water quality, fishing 52

2.5.2 Impeding the causes: light, temperature, mixing 55

2.6 COMMUNICATING ABOUT MASS BLEACHING 56

2.6.1 Strategies 57

2.6.2 Frequently asked questions 65

2.6.3 Resources 67

3. BUILDING LONG-TERM REEF RESILIENCE 70

3.1 RESILIENCE 70

3.1.1 Defining resilience 71

3.1.2 Factors that confer resilience 72

3.2 IDENTIFYING RESILIENT CORAL REEF AREAS 74

3.2.1 Characteristics of resilient coral reef areas 75

3.2.2 How to identify resilient areas 75

3.3 USING MARINE PROTECTED AREAS TO INCREASE RESILIENCE 85

3.3.1 Selecting MPA sites in the context of mass coral bleaching 86

3.3.2 Managing MPAs in the context of mass coral bleaching 86

CONTENTS
ix

3.4 BROADER MANAGEMENT INTERVENTIONS TO INCREASE RESILIENCE 87

3.4.1 Guiding principles 91

3.5 REEF RESTORATION STRATEGIES 93

3.5.1 Considerations for reef restoration strategies 93

3.5.2 Restoration methods 95

4. CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES 98

4.1 WHAT IS CORAL BLEACHING? 98

4.1.1 The coral-algal symbiosis 98

4.1.2 The causes of coral bleaching 99

4.2 FACTORS THAT CONFER RESILIENCE TO CORAL BLEACHING 100

4.2.1 Factors that influence resistance 100

4.2.2 Factors that influence survival 105

4.2.3 Factors that influence recovery 107

4.3 CAN CORALS ADAPT TO CLIMATE CHANGE? 109

4.3.1 Future climates 109

4.3.2 Can corals keep up? 111

4.4 REEFS AND PEOPLE IN THE FUTURE 113

4.4.1 Ecological implications 113

4.4.2 Social and economic implications 116

5. ENABLING MANAGEMENT – A POLICY REVIEW 120

5.1 CORAL REEFS 120

5.2 CLIMATE SCIENCE 122

5.3 BIOLOGICAL DIVERSITY 122

REFERENCES 124

GLOSSARY OF TERMS 134

ACRONYM LIST 138

APPENDIX 139
x

Figure List

1.1. How to use this guide 3

1.2. Global trends in the extent and severity of mass bleaching 5

1.3. Stages in mass coral bleaching 7

1.4. Opportunities for management intervention 10

2.1. Environmental conditions and information sources used to estimate bleaching risk 19

2.2. NOAA HotSpot map for the eastern hemisphere for 20 February 1998 22

2.3. NOAA degree heating weeks (DHW) map for the eastern hemisphere for 

31 March 1998 23

2.4. The relationship between the intensity and duration of heat stress and the risk and 

severity of mass bleaching 24

2.5. Bleaching thresholds for Kelso Reef in the central Great Barrier Reef, Australia 26

2.6. Key variables for describing the extent and severity of a bleaching event 43

2.7. Target audiences and strategies for communicating about coral bleaching 56

3.1. Coral reef ecosystem resilience to mass coral bleaching 71

3.2. Decision tree for identifying resilient areas for increased management based on past

responses to heat stress and bleaching 76

3.3. Principles for building resilience into MPA design 85

4.1. A generalised hierarchy of coral susceptibility to bleaching 101

Table List

2.1. Examples of tasks from four categories of bleaching response actions under 

three different resource scenarios 17

2.2. Climate variables and their influence on bleaching risk 21

2.3. Management questions and ecological assessment techniques 33

2.4. Recording the severity of bleaching of coral colonies 39

2.5. Recording the proportion of corals affected by bleaching 39

2.6. Criteria used by the GBRMPA to distinguish between 'minor', 'moderate' and 'major' 

mass bleaching events 41

3.1. Characteristics and information sources for predicting the relative bleaching resilience

of candidate reef sites 80
MANAGING FOR MASS

CORAL BLEACHING
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

2

1. MANAGING FOR MASS CORAL BLEACHING

The need for a management response to mass coral

bleaching is now well established3, 11, 13. The incidence

and severity of mass coral bleaching events has

increased continuously over the last two decades. As

a result, almost every reef region in the world has

now suffered extensive stress or coral mortality4, 5.

Observations of these past impacts and studies of

expected future trends have prompted leading

researchers and managers to declare that coral reefs

are in 'crisis'3, 9. In keeping with this, the scientific

community has suggested that the impacts of mass

coral bleaching events, in combination with those

from chronic local stressors, will largely determine the

condition of coral reefs in the next 50 years11, 13.

While the need for management has become clear, identifying practicable and effective

management responses has proven challenging. Traditional management approaches that

focus on minimising or eliminating sources of stress are not applicable to coral bleaching.

Coral reef managers are unable to directly mitigate or influence the main cause of mass

bleaching: above average water temperatures. This makes mass bleaching a uniquely

challenging environmental management problem.

This guide presents a range of strategies for responding to the threat of mass coral bleaching.

Importantly, A Reef Manager's Guide does not aim to offer a ‘cure’ for mass bleaching and

related impacts. Rather, it draws from a significant and

growing body of research striving to develop methods to

support the ability of coral reef ecosystems to survive

and recover from bleaching events (Section 1.2).

Therefore, the Guide reviews management actions that

can restore and maintain ecosystem resilience, including

strategies for developing the knowledge and support

that are critical for effective management action.

Figure 1.1 provides an overview of the structure of the Guide.The figure illustrates how

management strategies are organised around those implemented in response to mass

bleaching events (Chapter 2), and those aiming to integrate resilience into long-term

management (Chapter 3). Chapter 2 outlines strategies for prediction (Section 2.1) and

detection (2.2), assessment of ecological (2.3) and socio-economic (2.4) impacts,

management interventions (2.5), and communication (2.6) during mass bleaching events.

Chapter 3 discusses how to apply resilience concepts by identifying areas resilient to

mass bleaching (3.2), adapting marine protected area design (3.3), implementing broader

management measures (3.4), and considering restoration options (3.5). Reviews of the

science (Chapter 4) and policy (Chapter 5) that support these management

recommendations are also provided.

Mass coral bleaching has affected large

spatial areas in every coral reef region in

the world and is expected to be a major

factor determining future coral reef

condition over the next 50 years

From a management perspective,

mass coral bleaching poses a

unique challenge in that its main

cause – above average water

temperatures – is beyond the

control of local reef managers
Support reef resilience

Increase chance of reefs

surviving future warming

4. Science

5. Policy

3.3 Design and manage

MPAs to maximise resilience

3.4 Manage local stresses

to increase resilience

3.1 Identify factors

that confer resilience

3.5 Restore damaged reefs

2.3 Assess

ecological impacts

2.4 Assess social and

economic impacts

2.5 Identify management

interventions

2.6 Communication

BLEACHING

EVENT

2.1 Predict seasonal

temperatures

and bleaching risk

2.2 Establish early

warning system for 

coral bleaching

1. Understand climate

and bleaching risk and

implications for reefs 

3.2 Predict future

resilience

3

MANAGING FOR MASS CORAL BLEACHING

Figure 1.1 How to use this guide

A Reef Manager's Guide to Coral Bleaching is organized around

the strategies that managers can implement as a short-term

response to mass coral bleaching events (Chapter 2) and to

support long-term coral reef resilience (Chapter 3).

Background information on the science (Chapter 4) and

policies (Chapter 5) that support these management

recommendations are also provided. While these actions

cannot ‘cure’ the problem of mass coral bleaching, they offer

managers a systematic response to current and future

bleaching events that aims to support ecosystem resilience.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

4

This guide attempts to capture the current state of knowledge about managing reefs during

a time of changing climate and increased frequency of mass coral bleaching events. More

than providing an ‘answer’ to how best respond to mass bleaching, the full potential of the

guide lies in the new ideas and collaborations that it is designed to inspire. With that in

mind, readers are encouraged to share their experiences of applying the methods and

strategies herein, so that a future edition of this volume might be even more useful.

1.1 Mass bleaching as an emergent issue

The number of regions reporting mass coral bleaching has increased substantially in recent

years (Figure 1.2).The implications of mass bleaching received global attention in 1997-98,

when increased sea surface temperatures associated with El Niño resulted in extensive

bleaching of the world's reefs6, 14, 15. Prior to this event, coral bleaching was often considered

a local problem–someone else's problem–resulting from localised stresses. The event of

1997-98 distinguished mass coral bleaching from localised events by the global extent of its

impacts across reefs and reef regions of different condition, composition and geography. It

is attributed to causing mass mortalities of corals to many reef regions16, in total 'destroying'

an estimated 16 per cent of the world's reefs15.

This event fuelled scientific curiosity about the causes of mass bleaching events and the

implications of these events for future coral reef condition. Comparisons of expected sea

temperature increases with derived bleaching thresholds suggest that the frequency and

severity of mass bleaching events is likely to rise significantly10, 11 and at a rate substantially

faster than that at which coral reef ecosystems are expected to adjust10, 12.This implies that,

should tropical seas continue to warm, coral reef ecosystems are likely to undergo

significant changes.These changes include losses to biological diversity and coral cover8 as

well as economic losses to the fisheries and tourism sectors13.They also highlight the need

to integrate mass bleaching phenomena into management efforts aimed at sustaining the

value of coral reef ecosystems.
MANAGING FOR MASS CORAL BLEACHING

5

1998

2006

Figure 1.2 Global trends in the extent and severity of mass bleaching

The extent and severity of mass coral bleaching events have increased worldwide over the last decade.

Prior to 1998 mass coral bleaching had been recorded in most of the main coral reef regions, but many

reef systems had not experienced the effects of severe bleaching. Since 1998 coral bleaching has become

a common phenomenon around the world. Every region has now experienced severe bleaching, with many

areas suffering significant bleaching-induced mortality.

No bleaching

Low bleaching

Moderate bleaching

Severe bleaching

Severity unknown
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

6

1.1.1 What is mass coral bleaching?

Although they cover less than 1 per cent of the earth's surface, coral reefs have deposited

limestone structures that are home to an estimated one-half to two million species16.

Ultimately, the ability of coral reefs to support such productivity largely depends on the

symbiotic relationship between corals and microscopic algae, zooxanthellae, which live

within their tissues. Corals are strongly dependent on their zooxanthellae, which provide

up to 90 per cent of their energy requirements17. However, stressful conditions can cause

this relationship to break down, resulting in dramatic decreases in the densities of

zooxanthellae within the coral tissue. Because the

zooxanthellae also provide much of the colour in a

coral's tissue, their loss leaves the tissue transparent,

revealing the bright white skeleton beneath and giving

the coral the appearance of having been 'bleached' (see

Box 1.1).

Box 1.1 What happens during

coral bleaching?

The productivity of reefs is ultimately attributable

to the symbiotic relationship between the coral

polyp and its dinoflagellate algae, known as

zooxanthellae, which live packed within the

coral's tissues. Under normal conditions, the

zooxanthellae perform photosynthesis and

provide energy-rich compounds to the coral

animal. However, under conditions of increased

temperature, the algae are unable to process

incoming light without releasing harmful oxygen

radicals, similar to those involved in aging. When

this happens the coral-algal relationship is

disrupted and the zooxanthellae either

degenerate in the tissue or are released from the

tissue. Consequently, the bright white coral

skeleton is visible through the unpigmented

tissue, making the corals appear 'bleached'.

At a local scale, many stressors may cause corals to bleach, including storms, disease,

sedimentation, cyanide fishing, herbicides, heavy metals, and changes in salinity and

temperature18. The primary cause of regional, or mass, bleaching events is increased sea

temperatures8, 9, 13, 18-20. Sea temperature increases of 1-2oC above the long term average

maximum are all that are required to trigger mass bleaching9, 23. Both the intensity and

duration of temperature anomalies are important in determining the timing and severity of

bleaching responses. Higher temperatures can cause bleaching over a shorter exposure

time, while lower temperatures require longer exposure times. While temperature is the

trigger for bleaching, light also influences the severity of bleaching impacts24.

Under normal conditions microscopic

algae, called zooxanthellae, live inside the

tissues of the coral animal and provide up

to 90 per cent of the coral's energy

requirements

© Kirsten Michalek-Wagner

Corals appear white or 'bleached'

when the coral animal ejects the

colourful microscopic algae that live

within its tissues as part of a

response to stressful conditions
MANAGING FOR MASS CORAL BLEACHING

7

The types of conditions that cause the rapid warming of waters characteristic of spatially

extensive bleaching events often coincide with calm, clear conditions that increase light

penetration. For this reason, shaded corals are likely to bleach less severely than corals

exposed to normal light levels during heat stress.

Bleached corals are still living and, if stressful conditions subside soon enough, zooxanthellae

can repopulate their tissues and the corals can survive the bleaching event (Figure 1.3).

However, even corals that survive are likely to experience reduced growth rates25, 114,

decreased reproductive capacity26, and increased susceptibility to diseases27. Bleaching can

cause the death of corals if stresses are severe or persistent. In many cases, bleaching events

have caused significant mortality of corals (>90% of corals killed)7.

Zooxanthellae 

in coral tissue Zooxanthellae expelled 

from tissue

Dead skeleton covered in 

filamentous algae

Water temperature increases

Heathy coral Bleached coral Dead coral

Prolonged temperature stress

Water temperature returns to normal

Days - Weeks

Days - Weeks

Weeks - Months

Zooxanthellae

Coral polyp

Healthy coral 

Bleached coral 

Dead coral 

Figure 1.3 Stages in mass coral bleaching

During mass coral bleaching, water temperature increases above a critical threshold, typically over a large

area. Under these stressful conditions, corals begin to lose their zooxanthallae, eventually appearing

'bleached'. At this stage, the bleached corals are still living and, if stressful conditions subside soon enough,

they can regain their zooxanthallae. In this case, corals can survive, but are likely to suffer sub-lethal impacts,

such as reduced rates of growth and reproduction and increased susceptibility to diseases. However, should

temperature stress continue, corals are likely to die.Where mass coral bleaching causes high levels of coral

mortality, these ecosystems typically take years to decades to recover.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

8

1.1.2 Trends in mass bleaching and coral reef condition

The global reach of the 1997-98 bleaching event has raised serious concerns about the

future of coral reefs.To determine the threat posed by future bleaching events, researchers

have compared known temperature thresholds for coral bleaching with projected sea

temperature increases under various climate change scenarios.These studies have shown

that sea temperatures may soon regularly exceed bleaching thresholds, making severe

bleaching events an annual occurrence on many reefs worldwide9, 28.The projected levels of

temperature stress also exceed the values known to cause major coral mortality28-30.

Corals and coral reef ecosystems exist in a wide range of environmental conditions,

suggesting that they have some capacity to adapt to changing sea temperatures. In the

Arabian Gulf, corals do not bleach until they reach temperatures 10oC higher than summer

maxima in cooler regions within the same species' range11. However, the projected rate and

magnitude of temperature increase will rapidly exceed the conditions under which coral

reefs have flourished over the past half-million years11, and there is growing evidence that

corals will be unlikely to adapt fast enough to keep pace with even the most conservative

climate change projections9, 23, 28.

The implication of these conclusions is that the rate and extent of mass coral bleaching is likely

to increase in the future, causing further degradation to coral reef ecosystems9

. As a

consequence, there is likely to be a shift towards reef communities that have lower biological

diversity and less coral cover, and are dominated by coral taxa that are either resistant or

inherently resilient9, 11, 31. Corals and coral reefs have survived massive changes in their physical

and chemical environment over the past half-million years,

and they are unlikely to disappear altogether, even under

extreme climate scenarios. However, the condition of

reefs and the ecosystem services that they provide are

likely to significantly deteriorate as a result of coral

bleaching over the next few decades to centuries.

Chapter 4 presents a more detailed discussion about the

science related to coral reefs and mass bleaching.

1.1.3 Socioeconomic and management implications

It is well documented that coral reef degradation can result in socioeconomic losses

through impacts to fisheries, tourism, and other ecosystem services, such as shoreline

protection32-36. The extent to which mass coral bleaching affects people is determined by

several variables, including the extent to which bleaching results in coral mortality, the ways

in which human communities use the reef areas that have been affected, and the flexibility

of human communities to shift their dependence off coral reefs when ecological

degradation occurs.These variables may provide a useful focus to management and policy

efforts aiming to reduce the impacts of mass bleaching on dependent human communities.

For example, knowledge about levels of resource-dependency among local fishing

communities can help policy-makers select response strategies following severe bleaching

that will not only minimise economic impacts, but also be consistent with social and cultural

values and practices.This, in turn, maximises the likelihood that those affected will support

the management initiatives, increasing their sustainability.

Mass coral bleaching events are

expected to increase in extent and

severity, causing losses to

biological diversity and coral cover

as well as economic losses to the

tourism and fisheries sectors
MANAGING FOR MASS CORAL BLEACHING

9

Some studies have documented or predicted considerable economic losses because of

mass coral bleaching. For example, a study on the 1998 mass bleaching event estimated a

loss of US$700–8200 million in net present value terms for the Indian Ocean37. Importantly,

it is expected that the timing and extent of economic impacts will be closely related to the

severity of mass bleaching events.The total costs of severe bleaching globally over a 50-year

time horizon are estimated at over US$84 billion in net present value, using a three per

cent discount rate38. For moderate bleaching, this number is US$20 billion38. In the Great

Barrier Reef in Australia, bleaching-related reef damage is predicted to cause losses to the

tourism industry alone of between US$95.5 million and $293.5 million by 202028.

Another central consideration in documenting and managing for mass bleaching is the

complexity of these systems. In particular, managers are realising that it is important to

consider the cumulative impacts of simultaneous threats to coral reefs. Efforts have been

made to document the specific socio-economic losses that result from mass coral

bleaching31-35. These studies demonstrate the difficulty of isolating the effects of single

phenomena against a backdrop of multiple influences and the adaptability of human

systems. They also identify a number of confounding factors that make it difficult to isolate

impacts related to bleaching from ecological degradation due to other natural disturbances

(for example cyclones), changes in fishing practices, and changes in tourism visitation

resulting from geopolitical issues (such as terrorism)37.While these complex interactions are

challenging, they may also provide opportunities to strengthen the resilience of coral reef

ecosystems and the human communities that depend on them.

1.2 A strategy for management

Our understanding of mass bleaching suggests that the future condition of coral reefs will

be largely influenced by two factors: (1) the rate and extent of sea temperature increases9,13

and (2) the resilience of coral reef ecosystems11, 39, 40.The rate and extent of warming will

determine the window of opportunity for reefs to adjust through acclimatisation,

adaptation, and other ecological shifts. For example, fewer and less intense temperature

anomalies will reduce the frequency and severity of bleaching events, and slower rates of

warming will allow more time for reefs to recover between events that do occur. These

relationships mean that the effectiveness of broader efforts to address the rate and extent

of warming will have significant implications for local management initiatives28, 40.

However, such efforts are largely a matter for national

and international policy and lie beyond the scope of this

volume.The focus of this guide is on the second factor:

What actions can local coral reef managers implement

to restore and maintain the natural resilience of their

coral reefs.

The future condition of coral reefs 

be largely influenced by two factor

(1) the rate and extent of increase

temperature stress and (2) the

resilience of coral reef ecosystems
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

10

1.2.1 Opportunities to minimise mass coral bleaching impacts

Four successive conditions determine the ultimate impacts of mass coral bleaching

following a regional heat stress event, and each can be considered a potential focus for

management action, as shown in Figure 1.4. The first condition, bleaching resistance,

determines the extent to which corals within the area of a regional heat stress event are

bleached. If corals do bleach, the second condition, coral tolerance, determines the extent

to which corals either die or regain their zooxanthellae and survive. If there is widespread

coral mortality, the third condition, reef recovery, determines the extent to which the coral

reef ecosystem is able to recover and maintain the characteristics of a coral-dominated

ecosystem. Finally, if the coral reef ecosystem remains degraded, then the fourth condition,

human adaptive capacity, determines the extent to which human communities will

experience negative socioeconomic consequences.

Figure 1.4 Opportunities for management intervention

Four conditions determine the outcome of stressful temperatures for coral reefs: bleaching resistance, coral

tolerance, reef recovery and human adaptive capacity. Each of these is influenced by a suite of factors that,

in combination, determine the resilience or vulnerability of the system. Factors that can be influenced by

local management actions are highlighted in green. Factors shown in black cannot be changed through local

management interventions, but can be incorporated in the design and placement of management initiatives

to enhance ecosystem resilience. Adapted from Obura (2005)88.

Bleaching

Protect resistance

determined by

Environmental factors

Intrinsic factors

No bleaching

Survival

Build tolerance

determined by

Coral health

Exposure

Intrinsic factors

Promote recovery

determined by

Connectivity

Herbivory

Water quality

Recruitment

Support human adaptive capacity

determined by

Economic diversity

Supportive policy

Capital and technology

Human resource skills

Mortality

Recovering 

ecosystem

Opportunities for

management

Time/effort/resources for recovery

Strong reef-based 

economy and society

Socioeconomic

decline

Socioeconomic

adaptation

Unhealthy ecosystem

Healthy coral

HEAT
MANAGING FOR MASS CORAL BLEACHING

11

Each of these conditions is influenced by a suite of factors that affect the resilience or

vulnerability of these systems. Factors vary in the extent to which they can be changed

through management interventions, their relative influence, and the scale (coral, ecosystem,

or human community) at which they are expressed. Factors that can be influenced by local

management actions are highlighted in green in Figure 1.4. Factors shown in black cannot

generally be changed by management interventions; however, both types of factors can be

incorporated into management strategies. Black factors can be utilised in the design and

placement of management initiatives. Green factors can be changed by management

interventions in order to promote system resilience.

The remainder of this chapter briefly describes opportunities to minimise the impacts of

mass bleaching events through strategies that promote the first three conditions: bleaching

resistance, bleaching tolerance, and reef recovery. These concepts form the basis for the

management interventions presented in Chapters 2 and 3, and the science behind them is

discussed in detail in Chapter 4. The fourth condition, human resource dependency, is

considered further in Section 2.4.

Strategies for promoting coral resistance. Environmental

and intrinsic factors are likely to be the main influences

on whether or not corals bleach23. The effects of coral

bleaching are characteristically patchy, with different

types of corals and corals in different locations frequently

showing different responses during a bleaching event18, 118.

Local environmental conditions are important because

shading or exposure to cooler waters can reduce the

risk of bleaching.The individual history and genetic composition of both the coral animal and

its symbiotic zooxanthellae also influence resistance to bleaching79. 80. Section 3.2 discusses

how knowledge of these factors can help managers identify corals or reef areas that are

likely to be more resistant to mass bleaching. Once identified, management measures can be

implemented to minimise localised threats to these areas, thereby creating a network of

refugia to 're-seed' reefs more susceptible to bleaching (see Sections 3.3-3.4).

Strategies for promoting coral survivorship. The difference

between significant coral survival and coral mortality

during mass bleaching events equates to the difference

between years and decades in terms of reef recovery

time (see Box 1.2). For this reason, promoting coral

survival during bleaching events is likely to be a particularly efficient focus for management.

Well-established ecological principles suggest that reducing or eliminating other stressors

to coral can be important for increasing coral survival during temperature-related bleaching

events (see Section 2.5.1). When bleached, corals effectively enter a period of starvation

due to the loss of their energy-providing zooxanthellae.The condition of a coral when it

enters this stressed state is likely to determine its ability to endure a bleaching-induced

'famine'41 long enough for temperatures and zooxanthellae densities to return to normal.

Identifying and protecting coral r

areas that are naturally resistant 

temperature-related bleaching ca

help to create a network of refuge

're-seed' areas damaged by mass

coral bleaching

Reducing or eliminating other

stressors will be an important

factor in increasing coral survival
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

a b c

Photos of the reef at Pelorus Island on the Great Barrier Reef during and after severe bleaching-induced

mortality. (a) This large stand of Goniopora, or daytime coral, was completely bleached during the

summer of 1998. It died shortly after. (b) Despite healthy conditions and effective control of algae by

herbivores, only the earliest stages of recovery were evident by 2002. (c) There was good coral

recruitment by 2004, but full recovery is likely to take decades.

© Paul Marshall

12

Above a certain threshold of sea temperature, however, heat stress may cause direct

physiological damage to corals, exceeding any nutritional concerns and leading to death9.

Both environmental and intrinsic factors are important in determining the extent to which

this happens. As before, local environmental factors have an important influence on the

amount of heat stress to which a coral is exposed. Similarly, intrinsic factors, such as

genetics, influence the threshold temperature at which a coral dies, with some species able

to tolerate higher temperatures than others.These factors contribute to patterns of natural

resilience that can be built into management planning (Sections 3.2 and 3.3).

Box 1.2 Recovery after bleaching mortality

Reefs suffering high coral mortality require a time-consuming recovery process of

recolonisation by coral larvae and asexual reproduction (such as by fragmentation) of

corals that survived the event. Even under ideal conditions, coral recovery is slow and may

take decades. Importantly, successful recovery depends on many conditions including the

presence and sufficient connectivity of 'source' reefs to generate new larvae, good water

quality that allows spawning and recruitment to succeed, and both strong herbivore

populations and good water quality to ensure suitable substrate is available for new coral

recruits. The ecological requirements for successful coral reef recovery highlight the

importance of considering management of local and global stressors together, since they

interact to determine outcomes for reefs.
MANAGING FOR MASS CORAL BLEACHING

13

Strategies for promoting reef recovery.There is ample evidence that coral ecosystems in good

condition will recover from mortality more successfully than will degraded ecosystems.

Healthy reef ecosystems are better able to provide the conditions required for the

recruitment, survival and growth of new corals after established corals have been killed by

bleaching11, 42, 44. Recovery requires a source of new coral recruits and suitable substrate for

the settlement and survival of larval corals. Good water quality, an abundant and diverse

community of herbivorous fishes, and high coral cover are key aspects of ecosystem quality

that facilitate recovery44, 45. Ecological modelling and empirical observations have indicated

that the original extent of coral cover and the abundance of herbivorous fishes are two of

the most important factors determining future reef condition under scenarios of repeated

mass bleaching31, 46, 47. Therefore, management of local

fisheries, water quality, and tourism strongly influence

both the rate and success of recovery and future coral

reef resilience. Biological diversity and connectivity

among reefs are also important considerations that

promote reef recovery39. These factors are discussed

further in Section 3.1.

1.2.2 Integrating resilience into broader reef

management

Although often discussed in isolation, the

interactions between local and global threats

will define the future of reefs9, 11, 13. The

cumulative impacts of multiple, simultaneous

threats, are at the heart of key management

questions. Understanding the complexity of

the threats facing coral reefs is particularly

important for: maximising cost-benefit when

determining where management efforts

should be focussed; making credible

predictions about the effectiveness of

management interventions aimed solely at

local stressors; and assessing the ability of coral

reefs to continue to provide goods and services of value to humans under plausible climate

change scenarios. From a management perspective, the interaction of local and global

stressors can be considered from two perspectives:

1. How can control of local stressors be used to increase reef resilience? 

2. What does the additional threat of mass bleaching mean for management of

'traditional' coral reef issues, such as water quality, fishing, and tourism?

Healthy reef ecosystems are bett

able to provide the conditions

required for the recruitment, surv

and growth of new corals to repla

those killed by bleaching

In the Great Barrier Reef in Australia, bleachingrelated damage is predicted to cause losses to the

tourism industry alone of between US$95.5

million and $293.5 million by 2020
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

14

Based on projections of future ocean warming, corals

are likely to be closer to critical thresholds, making them

even more vulnerable to local stresses. This is likely to

translate to a reduction in resilience suggesting that

managers may need to re-evaluate the adequacy of

current approaches to management of coastal

developments, water quality, fisheries, and tourism. In particular, reef managers should

consider the potential costs and benefits of restricting the timing or intensity of activities in

order to minimise sources of additional stress to corals and associated organisms, especially

during bleaching events. Other management implications are discussed in Section 3.4.

Corals will become more vulnerable to

local threats as oceans warm and

corals are confronted with global and

local stressors at the same time
RESPONDING TO A MASS

CORAL BLEACHING EVENT
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

16

2. RESPONDING TO A MASS CORAL BLEACHING

EVENT

This chapter outlines five actions managers can take to prepare and respond during

bleaching events. Many of these actions aim to help managers develop and communicate

reliable information about the impacts of a mass bleaching event.These strategies do not

provide a 'cure' to mass coral bleaching. However, managers have found that implementing

these actions during and after bleaching events can improve the overall effectiveness of

coral reef management. Specifically, managers can gain and maintain critical support from

decision-makers and other stakeholders by raising awareness and advancing scientific

understanding about the patterns and impacts of coral bleaching and the importance of

ecosystem resilience to the future of coral reefs.

2.1 Developing a bleaching response plan

Like any contingency plan, developing a 'Coral Bleaching

Response Plan' allows managers to respond more

effectively during the rapid onset of a mass bleaching

event. At its most basic level, the plan should identify

the goal of the response, specific steps that will be taken

to meet the goal, and resources required to implement

the response. Plans can be created to meet the needs of any reef manager, taking into

account available resources, staff capacity, management authority, and the characteristics of

local coral reef systems.Table 2.1 provides some examples of activities that can be included

in bleaching response plans depending on available resources.

The Great Barrier Reef Marine Park Authority (GBRMPA) Bleaching Response Plan

provides another example (Appendix). The GBRMPA plan includes procedures for

prediction, ecological assessment, and communication of mass bleaching impacts. These

procedures consist of routine, responsive, and strategic tasks. Routine tasks occur

throughout the summer season, whether or not there is a bleaching event. For example,

routine tasks include the monitoring of environmental conditions and frequently updating

assessments of bleaching risk.

Responsive tasks are only implemented if a bleaching event occurs. Responsive tasks include

rapid assessment of ecological impacts and increased communication activities, which can

include briefings for both senior managers and the media. Because it can be difficult to

decide exactly when a bleaching event has started, the GBRMPA plan outlines specific

thresholds that trigger each type of responsive task. For example, when bleaching

thresholds are exceeded at multiple sites, a structured aerial survey is undertaken to

determine the spatial extent and severity of bleaching in the region.

Responding to a mass bleaching

event is a demanding task with

numerous challenges; managers who

have planned in advance for events

will have an advantage
RESPONDING TO A MASS CORAL BLEACHING EVENT

17

• Check NOAA Coral Watch reports

• Volunteer network to detect the

onset of bleaching

• Volunteer network to estimate the

severity of bleaching, as well as

report coral types affected 

• Timed swims

• Take steps to protect herbivore

populations and water quality

through appropriate actions (eg

facilitating community-based

protected areas, installing latrines,

limiting land-clearing, etc)

• Talk to community members and

local media about mass bleaching

• Brief senior decision-makers

• Meet with key stakeholders, local

media, and colleagues

• Send email updates

• Check NOAA Coral Watch reports

• Check local weather forecasts

• Initiate sea temperature monitoring

program using in situ loggers

• Develop and monitor reef-specific

bleaching temperature thresholds

• Volunteer network to estimate the

severity of bleaching, as well as

report coral types affected

• Manta tows

• LIT/Belt transects

• Take steps to protect herbivore

populations and water quality

through appropriate actions (eg

implement fishery regulations,

address harmful land-use practices)

• Consider restricting potentially

stressful impacts from coastal

development and recreational use

during periods of high water

temperature

• Brief senior decision-makers

• Meet with key stakeholders, local

media, and colleagues

• Send email updates 

• Check NOAA Coral Watch reports

• Work with local weather

forecasters to develop forecasts of

conditions likely to induce bleaching

• Initiate sea temperature monitoring

program using in situ loggers 

• Establish stations for real-time sea

temperature measurement

• Develop and monitor reef-specific

bleaching temperature thresholds

• Volunteer network to estimate the

severity of bleaching, as well as

report coral types affected

• Aerial Surveys

• Video Transects

• Socioeconomic impact studies

• Take steps to protect herbivore

populations and water quality

through appropriate actions (eg

implement fishery regulations,

address harmful land-use practices)

• Consider restricting potentially

stressful impacts from coastal

development and recreational use

during periods of high water

temperature

• Brief senior decision-makers

• Meet key stakeholders, local media,

and colleagues

• Send email updates 

• Update websites

• Make informative publications

readily accessible to the public 

• Offer seminars

• Develop and implement an

education program for local schools

Low Medium High

Resource Availability

Table 2.1 Examples of tasks from four categories of bleaching

response actions under three different resource scenarios

Early warning system (Section 2.2)

Impact assessment (Section 2.3-2.4)

Communication (Section 2.6)

Management interventions (Section 2.5)
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

18

2.2 Predicting mass coral bleaching

The strong relationship between temperature and the onset of mass bleaching allows

managers to estimate the risk of coral bleaching based on forecast and observed climatic

conditions and sea temperatures.This ability allows a manager to be the source of timely

and credible information about bleaching risk for decision-makers, stakeholders and the

media. Additionally, it provides important information needed for impact assessment and

management responses. This section describes the key

approaches available to predict the probability and

severity of a mass coral bleaching event during high risk

bleaching periods, when sea temperatures reach their

annual maximum (see Figure 2.1).

The strong relationship between

temperature and the onset of mass

bleaching allows managers to

estimate the risk of coral bleaching 

Strategic tasks may be taken at any time to strengthen a bleaching response or support

long-term coral reef resilience (see Chapter 3). Strategic activities can include building

capacity, securing funding, raising awareness, developing professional networks to exchange

information, establishing policies that support bleaching response, or implementing

management initiatives to increase protection for or restore factors that confer resilience

to the system.

The remainder of Chapter 2 provides detail of the actions that can be taken as part of a

comprehensive response to a mass bleaching event. Managers may wish to take ideas from

these sections for their own bleaching response plans.
RESPONDING TO A MASS CORAL BLEACHING EVENT

19

CORAL

BLEACHING

Environmental

Conditions

Information

Sources

Regional warming trends

(eg EL Nino)

Above-average summer

temperatures expected

Regional Climate

Forecasts

Seasonal Weather

Forecasts

Short-term Weather

Forecasts

NOAA Coral Reef Watch

Satellite Imagery

In situ Temperature

Loggers

Observations

and Reports

 ~

Frequent or prolonged

hot, still, cloudless weather

Above-average sea surface

temperatures

Persistent above-average

water temperatures recorded

Figure 2.1 Environmental conditions and information sources used to

estimate bleaching risk

Mass coral bleaching is preceded by environmental conditions that can be tracked to provide managers

with an effective early warning system for bleaching events. In orange and red, these conditions are

described hierarchically from general situations that may suggest an increased risk of bleaching to specific

circumstances that correspond to a high risk of bleaching. Readily available information sources are listed

to the right of each environmental condition and further described in the text.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

20

2.2.1 Climatic conditions

Large-scale climate patterns. Sea temperature is the most reliable predictor of the

occurrence and severity of large-scale coral bleaching events9, 18, 19. An understanding of the

factors that influence sea temperature has the potential to enable managers to predict the

probability of occurrence and severity of a bleaching event. In theory, the relationship

between climate patterns, seawater heating, and mass bleaching should provide a

mechanism for such predictions. In particular, the weather patterns associated with

phenomena such as the El Niño Southern Oscillation or the Pacific Decadal Oscillation can

be associated with regional and local warming sea temperatures48. A dramatic example of

the potential influence of large-scale climate patterns is the 1997-98 global mass bleaching

event, which was associated with an extreme El Niño event.

Despite the importance of large-scale climate patterns in determining local conditions,

precise predictions of bleaching risk remain difficult. Many local and regional factors also

affect the rate and duration of sea temperature increases, including regional ocean currents,

cloud cover and winds. The interplay of local, regional and global factors make it important

that managers do not place too much emphasis on using single variables, such as ENSO, as

their only measure of bleaching risk49. The extent to which the complex interactions of

different oceanic and atmospheric phenomena can be incorporated into predictive models

for coral bleaching will vary from place to place depending on climate dynamics and the

knowledge and expertise of local forecasting systems.

However, precise predictions are not necessary for many management applications. Reef

managers may still get a very useful indication of whether their region is likely to experience

increased heating in coming months based on climate predictions. For example, the El Niño

Southern Oscillation (ENSO) index is used to indicate the probability of above-average air

temperatures, and extent to which the monsoon trough will develop (which affects cloud

cover and winds) over the Great Barrier Reef (GBR).These seasonal forecasts are used by

the Great Barrier Reef Marine Park Authority to assess the likelihood that conditions

conducive to anomalous warming of the waters are going to occur in or around the Great

Barrier Reef.

Managers may find it useful to discuss the effects of climatic factors on sea temperatures

with local oceanographers, meteorologists and other scientists. For locations where links

between climate and sea temperatures are known, reports and information on large-scale

climate phenomena can be a useful aid to predicting bleaching risk. An example of a useful

source of information is the ENSO Reporting Centre, which provides ENSO forecasts

through email updates and a comprehensive website:

www.cpc.ncep.noaa.gov/products/analysis_monitoring/enso_advisory 

Weather. Weather patterns also provide a useful indication of whether bleaching risk is

increasing or decreasing. Longer-term predictions, such as seasonal forecasts, can be used

to assess the probability of weather conditions that contribute to increasing sea

temperatures occurring over timescales of weeks to months. For example, seasonal

outlooks for the hot season that predict above-average air temperatures and decreased

storm activity indicate that there is an increased probability of conditions that can lead to

stressful sea temperatures.
RESPONDING TO A MASS CORAL BLEACHING EVENT

21

Shorter-term predictions, such as weekly weather

forecasts, indicate whether sea temperatures will

increase or decrease in coming days and weeks.The risk

of mass bleaching is higher when forecasts are for high

air temperatures and extended periods of clear skies,

low wind and neap tides50. In contrast, forecasts for

stormy conditions with cooler air temperatures, high

cloud cover and strong winds indicate that sea temperatures may stabilise or decrease over

the coming week. Table 2.2 summarises the major climatic variables that are known to

influence sea temperatures and thus the risk of a mass bleaching event occurring.

ENSO

Air temperature

Cloud cover

Wind

Tidal currents

El Niño conditions increase sea temperatures in the Indian and central to eastern Pacific Oceans,

and may increase the chances of stable hot conditions in the atmosphere in some reef regions. La

Niña conditions may increase temperatures in the western Pacific.

Hotter air temperatures enhance the warming effect of the sun.

Low cloud cover increases heating of surface waters. However, middle to high level cloud cover

acts as a shade and lessens the heating effects of the sun.

Low winds increase heating of surface waters. However, strong winds (and waves) have the ability

to mix water to great depths, which reduces surface water temperature. A change in wind direction

resulting in cooler winds can also dramatically reduce surface water temperatures.

Strong tidal currents coincident with spring tides increase mixing and reduce temperatures of

surface waters.

Climate

variable

Implications for bleaching risk

Table 2.2 Climate variables and their influence on bleaching risk 

2.2.2 Sea temperatures

Once atmospheric conditions suggest the development

of unusually warm conditions, measurements of sea

temperatures provide a more direct indication of the

potential for mass coral bleaching. Temperature stress

can be monitored using satellite imagery and in-water

instruments.

Satellite imagery. Coral Reef Watch, a program of the US National Oceanic and

Atmospheric Administration (NOAA), has developed three tools that analyse satellite

imagery to assess the likelihood of mass coral bleaching events.These products are freely

available over the Internet, and include: HotSpot maps, degree heating week (DHW) maps

and Tropical Ocean Coral Bleaching indices.

The risk of mass bleaching is high

when weather forecasts are for hig

temperatures and extended period

low wind and low cloud cover

Unusually high seawater temperatu

are the most direct indicator of

bleaching risk and can be monitore

using 'HotSpot' images produced f

satellite data by NOAA or by local, 

water temperature loggers
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

22

Figure 2.2 NOAA HotSpot map for the eastern hemisphere for 

20 February 1998 

The colour of the grid cells represents the temperature anomaly in degrees Celsius, as indicated in the

legend along the bottom of the map.Temperature anomalies of 1-2oC extending over a period of days to

weeks should alert managers that a medium to high risk of bleaching exists.

HotSpot and DHW maps are global to regional images that display the intensity and

duration of unusually warm sea surface temperatures (SSTs) using remotely sensed data.

Both the intensity and duration of heat stress are important factors in predicting the onset

and severity of a mass bleaching event. HotSpot maps show the intensity of temperature

anomalies with a colour gradation (Figure 2.2). A temperature anomaly is calculated as the

difference between the observed sea temperature and the highest temperature expected

for a specific location, based on long-term monthly averages. It provides a useful reference

point that shows the extent to which current temperatures vary from those that the corals

are accustomed to experiencing that time of year. Because different geographical locations

vary in their average water temperature, an anomaly of 2oC could mean an actual

temperature of 28oC in the Galapagos, but it could mean 34oC in the Red Sea. Despite the

differences in absolute water temperatures, conditions are likely to be equally stressful for

corals in both locations because the sea temperature anomaly is the same. Anomalies of

only 1-2oC can cause mass bleaching.

DHW maps combine the intensity of temperature anomalies, found in the HotSpot maps,

with the duration of exposure to provide a composite picture of accumulated temperature

stress over the last 12 weeks (Figure 2.3). One DHW is equivalent to one week of SSTs

1oC greater than the expected summertime maximum.Two DHWs are equivalent to two

weeks at 1oC above the expected summertime maximum or one week of 2oC above the

expected summertime maximum. At four DHW, the Coral Reef Watch program issues a

Coral Bleaching Alert that a mass bleaching event may occur. Current research on the GBR

suggests that other aspects of a thermal regime, particularly the rate of heat stress

accumulation, can also be useful indicators of bleaching risk.
RESPONDING TO A MASS CORAL BLEACHING EVENT

23

Figure 2.3 NOAA Degree heating weeks (DHW) map for the eastern

hemisphere for 31 March 1998

Both the intensity and duration of heat stress are important factors in predicting mass coral bleaching, and

the DHW maps combine this information into a composite unit of accumulated temperature stress over

the last 12 weeks. One DHW is equivalent to one week of SSTs that are 1oC greater than the expected

summertime maximum. At 4 DHW, conditions have become stressful for corals, and bleaching events

become likely. Severe stress and possibly mortality is likely to occur at 8 DHW50. In this figure, the colours

correspond to the number of DHWs indicated in the legend along the bottom of the map.

DHW maps are updated every 3-5 days, allowing managers to track the development and

persistence of temperature anomalies around coral reefs and to estimate bleaching risk.An

automated email system sends managers Satellite Bleaching Alerts when stress levels are

reached. All products are currently based on SST over a 50 x 50 km grid, and NOAA is

improving this product to a grid size of 7 x 7 km. In many cases, the surface temperature

measured by satellites can be used as a reliable indicator of the temperature of sub-surface

waters (>1 m depth), depending on the extent of mixing. When anomalies are large or

persistent, in-water instruments (described below) can complement regional satellite

information and provide a more detailed account of local conditions.

The NOAA Coral Reef Watch program also developed a Tropical Ocean Coral Bleaching

Indices web page to provide additional near-real-time information for 24 reef locations

worldwide. For each reef site, the closest 50 km satellite data is extracted and listed on the

indices web page.These data include: current SST, DHW, climatology, links to regional maps

(such as ReefBase), SST time-series, satellite surface winds and retrospective data. Visual

warnings are provided for each site when conditions reach levels known to trigger

bleaching in vulnerable coral species.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

24

Direct measurements. Direct measurements of water temperature complement satellite

imagery by providing data that are of higher spatial and temporal resolution. These

measurements can be used to ground-truth remotely sensed surface temperatures.They

can also provide measurements at multiple depths to establish a depth-temperature profile.

Particularly for small reef areas with complex oceanography and strong mixing gradients,

in situ measurements can help refine bleaching thresholds.

Local sea temperatures can be monitored using in situ instruments that either require

manual download or are equipped with remote data transfer features. Simple, stand-alone

temperature data loggers are now readily available and affordable. Data from several

popular brands can be quickly and easily downloaded in-water by a diver.Where resources

are available, weather stations with telemetry systems can be used to provide real-time

data on a full range of variables that influence bleaching, such as air and water temperature,

wind, current and irradiance.

Figure 2.4 The relationship between the intensity and duration of heat

stress and the risk and severity of mass bleaching

Directly measuring water temperatures can provide a more detailed account of local conditions to complement

regional satellite information about temperature anomalies and bleaching risk. Predicting bleaching risk from inwater measurements requires an understanding of the exposure likely to trigger bleaching in the local area.This

graph shows the general relationship between the size of the heat stress (vertical axis), how long it lasts

(horizontal axis) and the onset of bleaching. Actual bleaching thresholds will vary by location based on typical

ambient conditions and the sensitivity of the dominant coral reef species present.

Time (weeks)

Unbleached

Bleached

Dead

0123456

1

3

4

2

0

Temperature anomoly ( oC)
RESPONDING TO A MASS CORAL BLEACHING EVENT

25

2.2.3 Coral bleaching thresholds: how warm is too warm?

Interpreting bleaching risk based on direct measurements of sea temperature requires an

understanding of the exposure likely to trigger bleaching responses.As introduced in Chapter

2.2.2, the risk and severity of mass bleaching is directly related to both the intensity and

duration of exposure to unusually warm sea temperatures. Figure 2.4 illustrates the concept

of bleaching thresholds based on temperature and exposure time. This section describes

three approaches that can be taken to identify mass bleaching triggers: average high

temperatures, past bleaching events and experimental observations. Since the composition of

coral communities change, colonies acclimatise and species adapt in response to repeated

thermal stress events, triggers can drift over time for particular species or regions; thus,

bleaching thresholds should be reviewed regularly and revised as necessary.

Thresholds based on average maximum temperatures. The simplest approach, and the one

used to create NOAA's HotSpot and DHW maps, is to compare temperatures against the

average maximum temperature in order to calculate a temperature anomaly. Observed

temperatures should be compared against average high temperatures for the same month.

For example, sea temperature measurements taken in July are compared against the

average high temperatures observed in July over the previous ten or more years.Where a

long history of local temperature records is not available, managers may be able to derive

long-term averages from satellite data sets.These data sets may be available on the Internet,

or can often be provided upon request by the coordinators of satellite-derived sea

temperature data, such as NOAA, or the Australian Commonwealth Scientific and

Industrial Research Organisation (CSIRO). Once managers know the long-term average

temperatures, it is a relatively simple matter to record current temperatures (using a

regularly checked logger or real-time weather station) and compare this with the long-term

average.Anomalies should be calculated on a daily or weekly basis and summed to provide

a measure of the accumulated exposure to temperatures above the normal maximum.This

simple index gives the number of degree heating days or weeks (DHDs or DHWs) for a

particular period. NOAA issues a bleaching warning for monitored areas once heat

exposure is greater than four DHWs50. This indicates that stress levels are high, and

managers should consider initiating rapid assessments of reef condition, or at least

heightening awareness in a volunteer network used to detect the onset of bleaching

(Section 2.3). Anomalies of 1-2oC for days to weeks can induce coral bleaching in many

susceptible species, and should alert managers that medium to high risk of bleaching exists.

Thresholds based on past bleaching events. Estimating bleaching thresholds in this way

requires reliable records of when coral bleaching did and did not occur in previous years

at reefs within the area of interest. Bleaching records are then matched up with

temperature records in order to compare the average maximum temperature of bleaching

years with that of non-bleaching years. The bleaching threshold falls between the lowest

temperature for bleaching years and the highest temperature for non-bleaching years,

taking both the intensity and duration of exposure into account. Depending on the

resolution of past observations, this analysis may be carried out at either regional or local

scales. An example of a detailed estimation of local bleaching thresholds for Kelso Reef in

the Great Barrier Reef, Australia52 is described in Box 2.1. A regional-scale analysis of

bleaching thresholds has also been completed for the Indian Ocean region51.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

26

Box 2.1 Estimating bleaching temperature thresholds for Kelso Reef,

GBR,Australia 

Experience on the Great Barrier Reef indicates that threshold curves of reefs with similar

communities and species vary with latitude and, more precisely, with local ambient

temperature regimes.This correlation suggests that reefs have adapted or acclimatised to

local conditions and reinforces the need for locally specific bleaching thresholds for use in

an early warning system. Such time-temperature bleaching threshold curves are not

species-specific, but, if field observations are based on early signs of bleaching, are usefully

biased towards the sensitive members of the coral community.

In this example for Kelso Reef (Figure 2.5), cumulative exposure times and temperatures

are shown for four consecutive years, one of which coincided with mild bleaching (1998).

This graph shows the period when the warmest average daily temperatures were

recorded (December to March).Average daily temperatures near the maximum summer

range were summed to produce a cumulative frequency distribution of days and

temperatures at increments of 0.1oC.The shaded area between the 1998 curve and that

for the warmest non-bleaching year (1999) indicates the potential area in timetemperature space in which bleaching could occur. The predicted bleaching curve (bold

solid line) was estimated by weighting the mean on a four-point scale according to the

intensity of bleaching52.

Figure 2.5 Bleaching thresholds for Kelso Reef in the central Great

Barrier Reef,Australia

Coral bleaching thresholds can be calculated on the basis of temperature records and observations

about the onset and severity of bleaching over several years.The shaded area in this graph shows the

predicted bleaching threshold as the cumulative exposure falling between the coolest bleaching year

(1998) and the warmest non-bleaching year (1999). From Berkelmans (2002)52.

Temperature (oC)

 28.6 28.8 29.0 29.2 29.4 29.6 29.8 30.0 30.2

Geometric mean of

1998 and 1999 curves

Weighted mean of 1998 and

1999 curves = bleaching curve

70

60

50

40

30

20

10

0

1996

1997

1998

1999

Kelso Reef

Cumulative exposure time (days)
RESPONDING TO A MASS CORAL BLEACHING EVENT

27

Thresholds based on experimental data. This approach is the most resource intensive and will

likely require collaboration with scientists to collect detailed experimental observations.The

approach, developed by Coles and Jokiel53 and applied more recently by Berkelmans52 (See box

2.1), involves exposing corals to different water temperatures in a laboratory situation and

recording how many days are required for corals to show visible signs of bleaching at each

temperature.Time-temperature bleaching threshold curves derived in this manner can provide

the basis for detailed predictions about when bleaching may become evident in select species

from particular locations. Care should be taken in applying data obtained from these

observations to other species or locations. If the species selected for study are common,

relatively sensitive, and from locations that are representative of the wider area, the thresholds

can be useful predictors of bleaching within larger jurisdictions.

2.3 Assessing ecological impacts 

Managers must rapidly assess the extent and severity of mass bleaching in order to make

timely and effective management decisions (Section 2.5) and communicate the situation to

others (Section 2.6). Reef users, other stakeholders, the media, and senior government

officials will want to know: 'How bad is it? What are the impacts to the reef?' and 'What will it

mean for the local stakeholder community?'.Thus, we now turn to a discussion of approaches

for assessing the ecological (Section 2.3) and socioeconomic (Section 2.4) consequences of

mass bleaching events for coral reefs and for the stakeholders who value the ecosystem

services those coral reefs provide.

Coral reef monitoring protocols have been developed for a wide range of skill levels, ranging

from Reef Check for volunteers to the comprehensive Survey Manual for Tropical Marine

Resources developed by the Australian Institute of Marine Science (AIMS) and the Global

Coral Reef Monitoring Network54 for reef scientists and managers. Since mass bleaching is

transitory in nature, the decision about when to conduct a rapid assessment of bleaching

impacts and which protocol to use may have significant implications for the survey results

and for any conclusions made from those results.

Experience from around the world during previous bleaching events has led to the

development of strategies that can help with such timing concerns and other monitoringrelated decisions.The WWF, the WorldFish Centre and the Great Barrier Reef Marine Park

Authority (GBRMPA) have compiled these experiences into A Global Protocol for Assessment

and Monitoring of Coral Bleaching55. The protocol can be downloaded from the ReefBase

website (www.reefbase.org) by searching the online literature database, or by contacting the

authors. The protocol aims to provide detailed guidance for planning and implementing

bleaching assessments under a range of resource settings, while ensuring that data are useful

and readily integrated into a global database of coral bleaching impacts.
Designing and implementing a coral bleaching

monitoring program – Bali Barat National Park

Coral reefs of Bali Barat National Park

Bali Barat National Park contains the most significant

area of coral reefs in Bali, and is a focal point for reef

conservation in Indonesia. It is a major destination for

reef-oriented tourism and contains the only reefs in the

region that are under formal protection. Nevertheless,

these reefs are at risk from a variety of human activities

such as (illegal) destructive fishing, nutrient inputs and

anchor damage, and the threat of coral bleaching. The

area suffered a crown-of-thorns starfish (Acanthaster

plancii), or COTS, outbreak in 1996-97 and was affected

by mass coral bleaching in 1997-98.

The role of WWF

The WWF is the lead partner in efforts to study, manage and protect the coral reefs of Bali

Barat National Park. The damage observed by the WWF during the 1997-98 coral bleaching

event lead to renewed concerns about the sustainability of these reefs under existing

management regimes. In particular, the WWF was concerned that the added pressure of climate

change would make the reefs particularly vulnerable to existing levels of dynamite fishing, water

pollution and poor anchoring practices.

In response to these concerns, the WWF collaborated with experts from the Great Barrier

Reef Marine Park Authority (GBRMPA) and the International Centre for Living Aquatic

Resources Management (ICLARM) (now WorldFish Centre) to develop a coral bleaching

monitoring program for Bali Barat National Park.The resulting program was designed to detect

coral bleaching and assess the extent and implications of any bleaching events, yet be

implemented with minimal resources. Furthermore, in order to evaluate the importance of

various factors in conferring resilience to coral bleaching, the program aimed to monitor the

condition of local reefs from 2003 to 2006.The information from this program will be used to

assess and improve the effectiveness of management strategies to mitigate bleaching-induced

impacts and to protect coral reefs in the area, as well as to raise awareness about coral

bleaching and climate change.

The Coral Bleaching Monitoring Program

This WWF Monitoring Program was designed to use existing staff expertise and resources, and

to require only modest on-going funding.The WWF uses web-sourced El Niño predictions and

NOAA HotSpot maps to assess the risk of bleaching each season. These remote data are

backed up with measurements of local temperature obtained using low-cost temperature

loggers that are installed at key sites and downloaded regularly (ideally weekly during the

bleaching season) by WWF staff or their colleagues in the local tourism industry.

The WWF has also established a network of reef users to provide an early warning system for

bleaching or other indications of stress on the reef.This program, called KEYS, 'Keep your Eyes

on the Reef', encourages professional and recreational reef users to report any observations of

coral bleaching at the sites they frequent.

CASE STUDY 1

© Naneng Setiasih

Bali Barat Monitoring Team
Reports of possible bleaching received through the KEYS program trigger a field check by the WWF

Bali coral reef team.This team consists of staff with appropriate SCUBA diving skills and a mix of

scientific training,ranging from Masters Degree to no formal university degree.The team was trained

in coral bleaching assessment skills during a four-day workshop run by external experts.The team

leader runs regular refresher and calibration sessions to ensure skills are maintained within the team.

The WWF team works closely with local tourism and fishing businesses in the area, receiving

assistance from local reef guides, and cost-effective access to dive boats and equipment.

If field checks indicate that a bleaching event is occurring,

WWF launches a full bleaching assessment survey. This

entails a rapid survey of all sites, using timed swims to

determine the general severity and extent of bleaching

within the Park and surrounding areas.This is followed by

detailed monitoring of core sites, using the line intercept

technique (LIT), permanent quadrats and a

complementary study of tagged colonies.These methods

have been chosen because of their widespread use,

standardisation and, consequently, ease of comparison of

results with other reef regions. Importantly, they can be

implemented without the need for expensive equipment

or high levels of expertise. Detailed monitoring is done

regularly on a semi-annual basis as part of a four-year program designed to provide essential

baseline data to document the longer trends in reef condition within the Bali Barat National Park,

and to help understand the importance of coral bleaching relative to other threats affecting the area.

So far,WWF Bali has completed three baseline monitoring surveys (in February and October 2003,

and March 2004).There was no bleaching event recorded during those times.The data indicate a

trend that implies coral cover is recovering after the impacts of COTS and coral bleaching during

the period 1996-98.

Establishing a network of coral bleaching monitoring programs. Parallel programs are being developed

to assess the socio-economic impacts of coral bleaching and mortality, and to identify and promote

strategies to mitigate the socio-economic impacts arising from coral bleaching events.

The Bali Barat National Park Coral Bleaching Program is one element of an integrated program

being developed by the WWF. The program is designed to understand, document and mitigate

climate change impacts on coral reefs worldwide.A network of areas with similar programs is being

established and will include Bunaken National Park (Indonesia), American Samoa (USA), Batangas

(the Philippines) and Tubataha Marine Park (the Philippines). Linkages with additional areas are also

being explored, including with Ujung Kulon National Park (Indonesia), Cendrawasih Marine Park

(Indonesia) and the Great Barrier Reef Marine Park (Australia).

For more information about the Bali Barat National Park Coral Bleaching Program, and related

regional initiatives, contact:

Naneng Setiasih

WWF Climate Change Program, Bali, Indonesia

nsetiasih@wallacea.wwf.or.id

Monitoring on the reef slope at

Bali Barat National Park

© Naneng Setiasih
Community participation in monitoring coral

bleaching events on the Great Barrier Reef –

BleachWatch

The Great Barrier Reef Marine Park has experienced two major coral bleaching events in recent

years (1998 and 2002). These have dramatically increased awareness of the threat posed by

coral bleaching to the Great Barrier Reef ecosystem. Increasingly, reef users, the general public,

the media and senior decision-makers are looking to reef managers to provide timely and

credible information about the impacts and implications of coral bleaching.

However, resource limitations in conjunction with the size and remoteness of many reef areas

can be a substantial challenge for reef managers wishing to detect the onset of bleaching and

monitor bleaching-related impacts. Reef users can play an important role in assisting managers

to keep an eye on the reef during periods of high bleaching risk. In the Great Barrier Reef region,

a program to facilitate active community involvement in monitoring coral bleaching events has

been created. This program, called 'BleachWatch', provides an early warning system for coral

bleaching and forms part of the Great Barrier Reef Marine Park Authority's (GBRMPA's) Coral

Bleaching Response Plan.

The BleachWatch program acts as an important source of information for managers, and also

has an important outreach and communication function. Two different programs,

'BleachWatch-Professional' and 'BleachWatch-Community' have been developed to engage

the range of reef users.

CASE STUDY 2

BleachWatch participants are provided with a Monitoring Kit. The kit includes a neoprene wrist band to assist

with coral identification, a laminated reference sheet, survey form and instructions
The BleachWatch-Professional program is designed for regular reef users, predominantly

tourism professionals or marine park rangers who visit a particular reef on a regular schedule.

This program is an opportunity for marine tourism professionals to establish an understanding

of the coral community at their sites, with the assistance of coral reef ecologists at the GBRMPA.

A short monitoring form, which takes about 10 minutes to complete, is provided to participants.

Monitoring kits, provided by the GBRMPA, also comprise a waterproof reference key and

instructions.The program has been designed with the tourism professional in mind, and allows

monitors to go about their everyday work, be it guiding snorkel trails or diving, while taking a

mental picture of their 'home reef' with the help of the waterproof reference key. Once back

on the vessel, staff members fill in the monitoring form and send it back to the GBRMPA at no

postage cost. In return for the monitors' efforts, the GBRMPA analyses the information and

provides monthly site reports, collating the data into an informative poster that can be displayed

for the education of both staff and tourists.

The BleachWatch-Community program is designed for incidental observations made by reef

visitors who make only occasional trips to the reef. Tourists, students and scientists can all

contribute to this program by submitting reports via the GBRMPA website. A printer-friendly

form is also available to help visitors record observations while they are visiting the reef. Reef

visitors are encouraged to submit their data using the online form, and are reminded that a

report of no bleaching can be just as important as a report of bleaching.

Information collected through the monitoring form includes:

(a) weather information (wind speed, cloud cover, water temperature)

(b) site information (reef name, type of reef habitat, depth surveyed)

(c) coral cover and community composition (such as dominant coral types)

(d) bleaching information (percentage of coral affected, severity of bleaching, types of growth

forms affected).

Participants in both programs are encouraged to report observations prior to and during a

coral bleaching event, so that the condition of the reef can be determined and monitored over

time. This information provides an important early warning system for managers, indicating

where coral bleaching is occurring and how severe it is. The BleachWatch program has been

extremely successful in enabling community members to participate in monitoring the Great

Barrier Reef and to improve their knowledge about coral bleaching, and reef ecology in general.

Reef managers benefit by gaining an early warning of coral bleaching.

For more information contact:

Johanna Johnson

Great Barrier Reef Marine Park Authority,Townsville,Australia

bleachwatch@gbrmpa.gov.au
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

32

Bleaching impacts may be assessed by way of: (1) volunteer and community-based reports,

(2) broad scale assessments and (3) site assessments (Table 2.3).These approaches involve

different techniques of data collection by different types of teams with different levels of

detail and expertise required. Each approach has advantages and disadvantages in terms of

cost, ease of mobilisation, and training required; yet each approach yields information of

interest to managers and stakeholders.The choice of assessment approach will depend on

the nature of the management questions posed, the nature of the manpower available to

do the work, the amount of resources available, and the type of data needed for analysis. A

brief overview of the three types of approaches follows. Table 2.3 briefly describes a variety

of techniques used in the three approaches and provides a summary for each of the

management questions they address, the pros and cons of each technique, and the nature

of the data that they provide. An example of how these techniques have been combined

into a coral bleaching monitoring program for Bali Barat National Park in Indonesia is

described in case study 1. For more in-depth information on how to use these techniques,

the reader is directed to A Global Protocol for Assessment and Monitoring of Coral Bleaching55.

2.3.1 Techniques for bleaching assessment

Volunteer and community-based reports. In many cases, stakeholders come into more

frequent contact with the reef than do managers. A key goal of a volunteer monitoring

program is to take advantage of these 'extra eyes and ears' to rapidly detect the onset of

bleaching and support timely management decisions. Another benefit is the opportunity

provided by such programs to inform stakeholders about the impacts of mass bleaching

and to engage them in coral reef management issues. Often, people feel helpless during

mass bleaching events. Volunteer monitoring programs provide a means for community

members to help by acting as reef stewards, thereby heightening public awareness of

bleaching impacts and of climate change in general. An example of a volunteer bleaching

program is the GBRMPA's BleachWatch program, described in case study 2.

Key elements of a community-based bleaching monitoring program are:

• establishing and maintaining a network of reef users to provide casual and regular reports

of bleaching status at reef sites.

• developing and distributing an appropriate assessment protocol and datasheets for

participating reef users to use to report reef conditions and coral bleaching.

• encouraging regular reporting of both bleaching and non-bleaching observations.

• providing regular and useful feedback to volunteers about their data.
RESPONDING TO A MASS CORAL BLEACHING EVENT

Monitoring by volunteers • A network of volunteers

is established to report

on conditions at their

sites and assess whether

or not and to what

extent bleaching is

occurring.Volunteers

might include tourism

operators, community

members, students,

NGO staff, scientists or

enforcement officers.

• The University of

Queensland has

developed a colour

chart system to help

volunteers*.

• Cost-effective method

for determining if

bleaching is occurring

and the extent of

bleaching, potentially

over a large area.

• Depending on volunteer

training, data may be

quite subjective.

• Presence/absence of

bleaching at one or

multiple sites.

• Indication of bleaching

progress and severity.

33

Technique Description Advantages/

disadvantages

Data

collected

Volunteer and community-based reports

Timed swims • Observers swim in a

straight line or

'wandering' path within

the depth range

selected. Swims are

broken into fixed time

units, (i.e. 2 minutes).

• An example of the use

of timed swims to assess

bleaching is found in

McClanahan et al

(2001)56.

• Table 2.4 provides a

simple index for rapidly

estimating the

proportion of colonies

affected.

• Requires expertise to

identify corals to at least

the genus level.

• Capacity to be

performed in remote

locations.

• Does not require access

to aircraft or landing

strips.

• Provides greater

resolution of reef

characteristics than do

aerial surveys.

• Useful for selecting

representative sites for

more detailed surveys

• Suitable for detailed

coverage of smaller

areas or for sparse.

sampling of larger areas

• More time spent diving

and associated costs.

• Percentage of live coral

cover.

• Dominant coral types.

• Percentage of coral

bleached.

• Average severity of

bleaching.

Broad-scale assessments

Table 2.3 Management questions and ecological assessment techniques

• Is bleaching occurring?

• Where is it occurring?

• What proportion and types of corals are affected, and how badly?

• What is the total area (of a large reef ecosystem) affected by bleaching?

• How severe is the bleaching? 
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

34

Manta tows • An observer is towed

behind a boat at a slow

and constant speed.

Tows are broken into

fixed time intervals,

usually 2 minutes, during

which time observations

are made.

• Most suitable for reef

areas between 10-100

km2

.

• Detailed guidance is

provided in English et al

(1997)54methods

developed for surveying

COTS are applicable.

• Table 2.4 provides a

simple index for rapidly

estimating the

proportion of colonies

affected.

As for timed swims, but:

• Allows efficient coverage

of larger areas.

• Requires boat and

manta tow equipment

(can be made

inexpensively).

• Limits opportunities for

detailed inspections.

• Not suitable for reefs in

deep or low-visibility

locations.

• Percentage of live coral

cover.

• Dominant coral types.

• Amount of coral

bleached.

• Average severity of

bleaching.

Technique Description Advantages/

disadvantages

Data

collected

Broad-scale assessments (cont)

Aerial surveys • Observers fly in planes

over large reef areas to

determine if bleaching is

occurring and to assess

bleaching extent and

severity. Data are

collected by visual

observation or by aerial

photography.

• To be reliable, conditions

must include:

1. Coral cover >10

per cent.

2. Clear shallow water

over reefs; low tide is

best.

3. Good visibility; no high

clouds or rain.

4.Wind <15 knots.

• Flying height is

determined by data

collection method; low

altitudes are preferred

for visual observations

(ie 500 ft) and higher

altitudes (2000–10 000

ft) for photography.

• Particularly useful for

assessing bleaching over

large or remote areas of

100s to 1000s of km.

• Require specific

conditions of reef cover

and visibility.

• May substantially

underestimate the

impacts of bleaching.

• Requires funds and

availability of suitable

aircraft.

• Percentage area

bleached or proportion

of reef sites bleached.

• Estimates of proportion

of corals bleached and

severity of bleaching.

Table 2.3 (cont)
RESPONDING TO A MASS CORAL BLEACHING EVENT

35

Line intercept transects

(LIT)

• The observer swims along

a transect recording the

transect distance at every

point where the type of

organism or substrate

changes, and the level of

bleaching for each.

• Table 2.4 provides a simple

index for categorising the

severity of bleaching.

• Various schemes for

classifying reef organisms

have been developed for

different levels of expertise.

• Widely used for assessing

benthic reef communities.

• Reliable and efficient.

• Allows observers with

limited experience to collect

useful information, although

some training in coral

identification required.

• Requires little equipment.

• Is limited to addressing

questions about relative

abundance (cannot

determine number of

organisms or proportion of

organisms bleached).

• Relative abundance of

organism groups.

• Proportion of cover

bleached and severity

of bleaching.

Technique Description Advantages/

disadvantages

Data

collected

Site assessments

Belt transects • Transect tapes are laid as

in the LIT method; the

observer records the

identity and severity of

bleaching of every sessile

invertebrate within a set

distance on both sides of

the transect tape.The

width of a belt transect is

normally 0.5 m or 1 m.

• Table 2.4 provides a

simple index for

categorising the severity

of bleaching.

• Various classification

schemes have been

developed for different

levels of expertise.

• Reliable.

• Does not necessarily

require experienced

observers, although

some training in coral

identification required.

• Requires little

equipment and is

relatively simple.

• Particularly useful for

assessing the proportion

of coral colonies that

are affected by

bleaching.

• Less suitable than LIT

for collecting data on

relative abundance, and

more time-consuming.

• Type, abundance and

density of individual

organisms.

• Proportion of corals

bleached and severity

of bleaching.

Table 2.3 (cont)

• What are the local impacts of a mass bleaching event?

• What percentage of corals have survived or died from bleaching?

• What kinds of corals were most affected by bleaching?

• Has the species composition or diversity of a reef changed due to a bleaching event?

Video transects • A diver swims along the reef

above a tape measure,

recording on an underwater

video camera the reef

community.The video

footage is analysed back in

the laboratory.

• The footage analysis should

identify all bleached

organisms and the severity

of the bleaching responses

(Table 2.4).

• Provides a permanent

visual record of the reef

community, and reduces

time required in the field.

• Requires relatively

expensive equipment,

trained analysts to collect

the data, operate the

video-analysis equipment

and software, and

interpret the footage.

• Percentage cover of

organism groups.

• Proportion of cover

bleached and severity

of bleaching.

• Recovery rates.

• Nature of shifts in

species composition.

A variety of coral monitoring methods are presented and statistically evaluated for their effectiveness in reference Brown et al (2004)57

* More information on the University of Queensland Colour Charts is available at: www.coralwatch.org
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

36

Broad-scale assessment. When designing a program to

assess a mass coral bleaching event, managers will want

to begin with an overall picture of the situation.Timed

swims, manta tows, and aerial surveys are techniques

that help managers get a general sense of the spatial

extent and severity of a mass bleaching event.The most

appropriate technique will depend on the size of the area that a manager wishes to survey.

In-water techniques are relatively inexpensive and can provide detailed information about

conditions on the reef including: assessment of the proportion of live coral cover and bare

substrate, proportion of corals affected by bleaching, types of corals bleached, and both the

severity of bleaching and amount of recently dead coral. They can also be useful for

identifying sites representative of larger areas of reef. These are often the most useful

locations for more detailed ecological surveys of coral bleaching impacts.

However, in cases of very large or remote

coral reef areas aerial surveys may be the

best option for conducting assessments in

the relatively short time window available

to assess the impacts of a coral bleaching

event (typically 1-2 months after peak

temperatures). In very large reef areas

such as the Great Barrier Reef Marine

Park, which spans 350 000 km2

, aerial

surveys are the only feasible method for

assessing the full spatial extent of

bleaching. While aerial surveys have

distinct advantages in such circumstances,

the observations made should be

interpreted with caution.

Points to consider when using aerial surveys include:

• Aerial surveys will be most effective in locations where reefs have high live coral cover

and bleaching is moderate to severe.

• Aerial surveys of bleaching extent will be most accurate for shallow (5-10 m) reef

communities on horizontal surfaces.

• Results of aerial surveys should be interpreted with the understanding that they do not

distinguish reefs that have low coral cover from reefs on which corals have already

suffered major mortality due to bleaching.

One way to address the above issues is to conduct site assessments at key selected

locations in order to 'ground-truth' the interpretations that may emerge from aerial survey

data.The next section discusses site assessments.

Aerial surveys of mass coral bleaching events can be the

best option for conducting broad scale assessments in

very large or remote coral reef areas

Timed swims, manta tows and

aerial surveys are techniques that

help managers get a general sense

of the extent and severity of a

mass bleaching event
RESPONDING TO A MASS CORAL BLEACHING EVENT

37

Site assessment. Site assessments help managers

understand not just the extent and severity of mass

bleaching, but also its impacts on the reef.These more

detailed assessments are used to ground-truth broadscale assessments of bleaching severity, and to provide

a more thorough understanding of bleaching response

patterns and any observable long-term impacts of the

event. Specifically, they enable managers to directly

assess the extent to which corals are recovering or

dying because of the bleaching event.

Ideally, site assessments are conducted before and after bleaching events so that the results

of these surveys can be compared; however, this is not always possible. Whenever site

assessments can be repeated 6-8 months after the bleaching event, and in subsequent

years, they can provide answers to questions about how the bleaching event has affected

the reef ecosystem, such as:

• Did bleaching result in changes to the species composition on the reef? 

• Are corals differing in the rate of bleaching or the rate at which they either die or regain

their zooxanthellae? 

• Overall, how quickly is the reef recovering? 

Line intercept transects (LIT), belt transects, and video transects are common methods for

conducting detailed site assessments. In all three methods, tape measures are laid out along

the reef to provide replicate transects. Deciding where to position transects is important.

Survey sites should be partitioned into two or more depth zones (for example the upper

reef slope and lower reef slope), and transects laid randomly within the depth ranges

specified.Therefore, in many cases transects will be positioned parallel to the reef crest.The

length and number of replicate transects should ideally be decided based on pilot studies

that assess the level of variation in the reef community in the survey area. Often, however,

time and resources do not permit pilot studies. In these cases, a general rule of thumb is

to use 20 m long transects, with a minimum of three (ideally five or more) for each depth

zone at each site. More patchy or variable reef communities will require longer or more

transects. Another way of minimising the effect of high variability in a reef community is to

use permanent transects.These are marked out on the seabed with metal stakes or rods,

so that the tape measure can be placed in the same location during subsequent surveys.

Advances in GPS technology make returning to the sites relatively easy. More detailed

guidance on the use of transects to survey coral reef communities can be found in the

references54, 55, 57.

Line intercept transects (LIT),

belt transects and video

transects are common methods

for conducting detailed site

assessments – these can help

managers interpret broad-scale

surveys and understand the

impacts of bleaching on the reef
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

38

Observers record different

information for each of the

three techniques. When

using LITs, the observer

notes changes from one

benthic life form (plant or

animal growing attached to

the seabed) to another

along the transect. In

contrast, when using belt

transects, the observer

records every organism

within a set distance on

either side of the transect,

usually 0.5-1.0 m. Though

more time intensive, belt

transects cover a greater

area of the site than LITs can.Therefore, managers choosing to implement this method

can better assess the proportion of coral colonies that are affected by bleaching and can

evaluate differences in bleaching response that may be linked to colony size.

When using video transects, a diver uses an underwater video camera to film the reef

community either along a measuring tape or using a standardized swim time. The video

footage is analysed back in a laboratory. This approach can also be achieved using a still

camera (digital or film), which can reduce the expense associated with video equipment.

Still camera or video footage has the advantage of providing a permanent record of the

bleaching event and potentially allowing for more accurate data analysis. However, both still

camera and video data are costly, and the results are not available until after laboratory

analysis is complete. Because information is needed quickly during a mass bleaching event,

it is often useful to complement video footage with observations taken while in the water

(for example by rapid in-water surveys55). This information becomes the basis for

communicating the extent of bleaching impacts on affected reefs until the laboratory

analysis is completed.

Data collection during LIT and belt transects can be

tailored to the experience level of the observer. The

benthic life forms are normally characterised using a

broad taxonomic classification (such as class or family

level) or morphological categories (for example

branching, massive, etc.), or a combination of both. However, when the expertise of the

observer permits, more detailed classification of organisms (to genus or species level) is

preferred.Taxonomic detail allows for ease of comparison between reefs and reef regions

during far-reaching events when bleaching impacts are being assessed by numerous

agencies and researchers.

A diver completes a rapid survey of bleaching in Bali Barat National Park

(Indonesia) as part of an ongoing coral bleaching monitoring program

described in case study 1

© Naneng Setiasih

Data collected by LIT and belt

transects can be tailored to the

experience level of the observer
RESPONDING TO A MASS CORAL BLEACHING EVENT

39

When applying any of these methods to a mass bleaching assessment, observers will also

record the extent to which benthic life forms are bleached.While the focus of such surveys

will usually be the hard and soft corals, observers should also record the bleaching category

of any organism that appears to be bleached, such as clams, anemones or sponges. For

results to be comparable between observers and locations, descriptions of bleaching

severity should be based on widely used indices. A Global Protocol for Assessment and

Monitoring of Coral Bleaching55 recommends a simple index for categorising the severity of

bleaching within reef organisms (Table 2.4), and for estimating the proportion of corals

bleached within a survey site (Table 2.5).

0

1

2

3

4

No bleaching evident

Partially bleached (surface/tips); or pale but not white

White

Bleached and partly dead

Recently dead

Category Description

Table 2.4 Recording the severity of bleaching of coral colonies

0

1

2

3

4

<1

1–10

10–50

50–90

>90

Category Per cent

Table 2.5 Recording the proportion of corals affected by bleaching

Description Visual assessment

No bleaching

Low or mild

bleaching

Moderate

bleaching

High bleaching

Extreme bleaching

No bleaching observed, or only very occasional,

scattered bleached colonies (one or two per dive).

Conspicuous bleached colonies seen occasionally, but

vast majority of colonies not bleached.

Bleached colonies frequent but constitute less than half

of all colonies.

Bleaching very frequent and conspicuous, most corals

bleached.

Bleaching dominates the landscape, unbleached colonies

not common.The whole reef looks white.

2.3.2 Special considerations for bleaching assessment

There are a number of considerations that a manager should be aware of when assessing

mass bleaching events.The manager must be skilled at recognising when a mass bleaching

event is occurring, deciding when to survey, and describing the severity of bleaching

accurately.The following questions are helpful for providing guidance in these areas:
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

40

How do I know whether what I am seeing is mass

bleaching? Minor bleaching or paling of corals is a regular

occurrence in many reef areas, and bleached colonies

can be seen scattered throughout shallow coral

communities during the peak of summer. More severe

bleaching is sometimes seen within small reef areas due

to localised stressors, such as flood plumes. Corals can also appear bleached when they are

suffering the effects of coral disease or outbreaks of Acanthaster plancii, the crown-ofthorns starfish (COTS). It is important for reef managers to be able to distinguish between

these various phenomena and recognise when an actual mass bleaching event is occurring.

Mass coral bleaching is visually very distinctive, but determining whether bleaching or some other stress is

affecting individual corals can sometimes be difficult. (a) Bleaching is usually distinguished by the way it affects

entire colonies or large sections of colonies similarly.The effects of coral predators, such as (b) crown-of-thorns

starfish and (c) drupella snails can often be recognised by patches of bare skeleton adjoining patches of live,

healthy tissue. (d) Coral diseases can also be sometimes mistaken for the early stages of mass coral bleaching.

Disease takes many forms, but the effects of disease are often characterised by a strong line separating live and

dead parts of a coral, or by rapid erosion of the surface structure of the coral, as shown here.

The proportion of corals affected

and their spatial distribution

normally distinguishes mass

bleaching events from minor

bleaching or other disturbances

a

b c d

© Heidi Schuttenberg (d)
RESPONDING TO A MASS CORAL BLEACHING EVENT

41

Reef managers are often asked to distinguish between 'minor' and 'major' bleaching events.

The proportion of corals affected and their spatial distribution normally distinguish mass

bleaching events from localised bleaching. The early stages of a bleaching event may be

limited to the bleaching of more susceptible species of corals and be confined to shallow

reef areas. However, at the height of a mass bleaching event, large proportions of the coral

community will be visibly affected. Obvious signs of bleaching will extend below the reef

flat, to include the reef crest and slope, and will span sites throughout a region.

Furthermore, the majority of corals will be at least pale (category 1 in Table 2.4), with many

to most completely white (category 2).The proportions of bleached corals might be lower

during a mild bleaching event or if the coral communities are dominated by more

bleaching-resistant species. In these cases, managers can be confident that a mass bleaching

event is occurring if signs of bleaching are being observed at reefs throughout the region.

Rarely will the effects of a bleaching event be patchy within an otherwise uniform reef

habitat, such as might occur when outbreaks of coral disease or coral predators (such as

COTS or Drupella) move through a reef community.

The distinctions used by the GBRMPA (Table 2.6) to distinguish between minor, moderate

and major bleaching events are based on general criteria that can be adapted to local needs

and used when providing summary overviews of the severity of a bleaching event.

• reliable reports of low coral bleaching (1–10% of colonies completely white) from multiple

sites from multiple locations spanning at least two GBR sectors; or

• reliable reports of mild bleaching (10–50%) from a few sites only, scattered throughout the

GBR or concentrated in only one sector.

A 'minor' bleaching event shall be declared if there are:

Table 2.6 Criteria used by the GBRMPA to distinguish between 'minor',

'moderate' and 'major' mass bleaching events

• reliable reports of moderate coral bleaching (10–50% of colonies completely white) from

multiple sites from multiple locations spanning at least two GBR sectors; or

• reliable reports of severe bleaching (>50%) from a few sites only, scattered throughout the

GBR or concentrated in only one sector.

A 'moderate' bleaching event shall be declared if there are:

• reliable reports of severe to extreme bleaching (>50% of colonies completely white) from

multiple sites spanning multiple sectors.

A 'major' bleaching event shall be declared if there are:
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

42

When is the best time to survey? Where managers have

the resources to do 'pre-bleaching' (baseline) surveys,

they should ideally be done just before the time of year

when bleaching is most likely to occur.This works to

minimise the chance that changes in the reef community

due to other disturbances might be mistakenly attributed

to a subsequent coral bleaching event.

The timing of 'during-bleaching' surveys is more difficult to determine. Ideally, bleaching

surveys should be done at the peak of bleaching, when the bleaching is at its worst and

before corals begin to die or regain their zooxanthellae. However, the timing and spatial

pattern of mass coral bleaching can be highly variable from year to year. The onset of

bleaching is influenced by numerous factors, including the extent and duration of

temperature anomalies, variability in local oceanography, and variation in the types,

abundance and distribution of corals.The most efficient and reliable means of determining

if a bleaching event is actually occurring is via direct reports from people who regularly

visit the reef. By monitoring both the levels of heat stress (Section 2.1) and the

development of the bleaching event (via regular site visits or reports from reef users),

managers should be able to estimate when bleaching is at its peak and implement

bleaching surveys accordingly.

‘Post-bleaching’ surveys are ideally done once bleaching is fully resolved (that is, all corals

have either recovered their normal colouration or died). In practice, for most situations,

assessments of the level of mortality will be reasonably accurate if they are done between

three and six months after the onset of bleaching. Post-bleaching surveys run the risk of

underestimating levels of mortality if they are done too soon after bleaching is observed. If

done too late, they can overestimate the impact of bleaching by including mortality caused

by other sources.

How can I determine whether long-term changes on my reef are due to mass coral bleaching

or other causes? Ongoing monitoring is required to document the long-term ecological

impacts of coral bleaching and other major disturbances on reef ecosystems. It is necessary

to track changes in reef communities over longer time frames (several years to decades)

in order to estimate the probability and rate of recovery, increase the ability to determine

the cause of changes in reef condition, and evaluate the effectiveness of management

strategies. Maintenance of long-term monitoring programs will enable managers to detect

gradual changes in coral community structure that may occur because of bleaching and

mortality and to maximise their ability to attribute chronic impacts to particular stresses,

including coral bleaching. Monitoring on an annual or semi-annual basis should be

complemented with additional surveys timed to detect the occurrence and impact of coral

bleaching at long-term monitoring sites. The data from such targeted surveys will help

managers determine the relative influence of coral bleaching on the long-term dynamics of

coral reef ecosystems.

Ideally, bleaching surveys should

be done at the peak of bleaching,

when the bleaching is at its

worst and before corals begin to

die or regain their zooxanthallae
RESPONDING TO A MASS CORAL BLEACHING EVENT

43

Characteristic of

bleaching event

Variable

Regional extent

Regional severity

Site

severity

Proportions of reefs or reef area

that show signs of bleaching

Distance or area spanned by reefs

that show signs of bleaching

Average proportions of coral

colonies or coral cover that show

signs of bleaching in area surveyed

Average severity of bleaching of

corals within area surveyed

Relative resistance (based on

hierachy of susceptibility Figure 4.1)

of corals showing signs of bleaching

Figure 2.6 Key variables for describing the extent and severity of a

bleaching event

These five variables are useful in describing the extent and severity of a mass coral bleaching event and

in describing the impacts of bleaching to a particular reef or site. Reporting these variables based on the

widely used indices presented in Tables 2.4 and 2.5 is helpful for analysing and comparing different

bleaching events.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

44

2.4 Assessing social and economic impacts 

The effects of mass bleaching events extend beyond their impacts on coral reef organisms.

Coastal communities throughout the world's tropical regions depend on coral reefs for a

range of ecosystem goods and services, including fishing, tourism, shoreline protection and

recreation35, 36, 58, 59. Deterioration in the quality of coral reefs due to disturbances, such as

coral bleaching, reduces the reef's ability to provide these commodities and opportunities,

resulting in social and economic impacts. Importantly though, social and economic impacts

can also arise from management strategies designed to sustain coral reef quality.

Reef managers, policy-makers and communities that understand the relationships people

have with the adjacent coral reefs will be able to better identify both the impacts of a mass

bleaching event and any impacts associated with management strategies. This knowledge

can be used to design management strategies that maximise environmental outcomes

while minimising negative impacts on people. Specifically, impact assessments can:

• identify the potential social and economic impacts of mass bleaching

• integrate local knowledge with technical expert knowledge

• evaluate the social and economic costs and benefits of various coral bleaching

management strategies

• increase public involvement in the monitoring of bleaching impacts.

2.4.1 Socioeconomic impacts of mass coral bleaching

The nature and magnitude of social and economic impacts resulting from coral bleaching

will be influenced by the level of dependency coastal communities have upon coral reefs.

Economic impacts may take various forms, including decreased income, reduced business

efficiency and decreased business confidence and investment. Social impacts of bleaching

might include effects on people's lives (such as how they work, play, and interact), their

culture (shared beliefs, customs, values and language) and their community (for example its

cohesion, stability, character, facilities and services).

Coral bleaching events can have direct impacts on human uses of reefs by reducing the

aesthetic qualities of reef sites that are important for tourism, and by decreasing the

abundance or availability of fish stocks (an example of these impacts is described in case

study 3). As a result, the major reef uses likely to suffer direct social and economic impacts

from coral bleaching are tourism (diving, snorkelling, and charter) and fishing (commercial,

recreational, indigenous and subsistence fisheries). An assessment of the economic impacts

of mass coral bleaching in the Indian Ocean is described in case study 3.

Tourism impacts. The socioeconomic impacts of mass bleaching on tourism depend on the

awareness level of tourists, the severity of coral reef degradation, and coastal community

reliance on coral reef condition.Although the ecological impacts of coral bleaching can be both

rapid and visual, many of the social and economic impacts can be subtle or gradual. For

example, a study of tourists visiting the Philippines found that, generally, visitors had a low

awareness of mass coral bleaching; the result being that these businesses did not experience

any immediate losses as a result of a bleaching event60.Socioeconomic work in Palau found that
RESPONDING TO A MASS CORAL BLEACHING EVENT

during a mass bleaching event, the

white or pastel colour of the coral

improved the aesthetic appeal of

dive and snorkelling sites for some

tourists61. This highlights the fact

that many tourists may be

currently unaware of the negative

ecological implications of

bleached corals.

Should coral bleaching lead to

mortality, however, the declines in

reef quality become very difficult

to ignore. As a result, the

satisfaction of divers and

snorkellers visiting a site that is

deteriorated because of coral

bleaching is likely to decline, with

possible implications for visitation

rates, and consequent impacts on

tourism businesses. Economic

impacts on dive-oriented tourism have now been documented following coral reef

damage caused during the 1997-98 bleaching event in Tanzania, the Maldives, Sri Lanka and

the Philippines62.

In the long-term, the extent to which coastal

communities depend on coral reef condition

will determine whether declines in reef quality

due to coral bleaching translate into economic

impacts. In some situations, tourism businesses

have shown resilience to changing conditions.

For example, a combination of issues, including

coral bleaching, over-fishing, and tourism-related

damage were perceived to have decreased the

quality of reefs in the Philippines, causing a

decline in occupancy of local hotels by divers

from 80 per cent to about 10 per cent over 15

years60. The tourism industry recovered partly

through a shift from reef-oriented dive tourism

to 'honeymooners'. This less reef-oriented

market segment now forms over 50 per cent of

the resort bookings in the area60.

45

Coral mortality resulting from bleaching events can have direct

impacts on human uses of reefs by reducing the aesthetic qualities

of reef sites that are important for tourism and by decreasing the

abundance or availability of fish stocks. Degraded reef condition

can also have more subtle social impacts on communities by

affecting customs and values, and community cohesion or stability

© James Oliver

The socioeconomic impacts of mass bleaching on

tourism depend on the awareness level of

tourists, the severity of coral reef degradation,

and the industry's reliance on coral reef

condition. Some studies have shown tourists to

be unaware during bleaching events or even to

feel that the white or pastel colour of the corals

improved the visual appeal of the site. Should

bleaching lead to mortality, however, the declines

in reef quality become very difficult to ignore and

can impact the type and number of divers

choosing to visit the site
Economic analysis of coral bleaching 

in the Indian Ocean

The 1997-98 mass coral bleaching event had severe ecological consequences for Kenya,

Tanzania, and the Seychelles, with each country estimated to have lost roughly 40-50 per cent

coral cover. A two-phase study, undertaken as part of the Coral Reef Degradation in the

Indian Ocean (CORDIO) project, estimated economic losses resulting from the mass

bleaching event. Results suggest that, five years after the event, economic impacts are most

noticeable in the tourism sector38. Results describing the economic impacts on fisheries

incomes were inconclusive.

The study estimated tourism welfare losses by combining the results of a 'Willingness To Pay'

(WTP) survey with estimates for coral recovery. The WTP survey found that tourists were

willing to pay US$98.70 extra per holiday in the Seychelles, US$87.70 in Zanzibar and US$59.00

in Kenya in order to experience healthy coral reefs.Applying a conservative estimate that corals

should recover at a linear rate over a 20-year period, and assuming that WTP relates linearly to

recovery, the study estimated welfare losses in 2001 of US$9.7 million for the Seychelles, US$6.4

million for Mombasa, and US$5.4 million for Zanzibar. Net present values of these annual

welfare losses over a 20-year time period with a 10 per cent discount rate shows considerable

potential welfare losses: a total of US$71.5 million for the Seychelles, US$47.2 million for

Mombasa, and US$39.9 million for Zanzibar.

Related studies showed that tourism losses could vary significantly between locations. A 2000

study by Cesar et al34 found that, in the Maldives, tourism growth was cut by only one per cent

as a result of coral mortality.This is despite significant declines in reef condition (live coral cover

decreasing from 50 per cent to less than five per cent).The small loss in tourism is likely to be

explained by the successful shift made by operators in the Maldives toward other types of

tourism, 'honeymooners' in particular. In addition, with double-digit annual international growth

in the number of certified divers, and the relative proximity of the Maldives to the European

market, this archipelago is guaranteed a fresh supply of relatively inexperienced divers. New

divers are mainly interested in large, charismatic marine creatures (large fish, sharks, turtles, etc.),

which are readily visible in the Maldives due to low reef fishing pressure. By comparison, a 2000

study by Westmacott et al12 found a 19 per cent drop in dive-related tourism to Zanzibar due

to severe coral bleaching, corresponding to an estimated 10 per cent reduction in total tourism

arrivals.The difference in measurable changes in tourism between the Maldives and Zanzibar is

particularly interesting. One possible explanation is that the breadth of the tourism sector in the

Maldives enabled a shift in tourism focus (from diving to beach-oriented holidays, for example)

that minimised declines in total tourism revenue.

The impact of mass bleaching on fisheries in these nations was far less clear.While fish species'

composition changed (in some cases considerably) overall yield and income for fishers did not

change significantly. This suggests that fishers are targeting other species to compensate for

bleaching-related declines in their normal target species. The influence of coral bleaching on

overall fishery trends were difficult to identify because market price and fishing effort were being

influenced simultaneously by other factors during the same period. For example, one study150

found that catch per fisher decreased by around 25 per cent in Kenya in concert with estimated

decreases in biomass on fished reefs. However, at around the same time as the bleaching event

CASE STUDY 3
there was a 16 per cent increase in the number of fishers. Because these impacts coincided it

was difficult to identify the reason for the decline in fish catches. Furthermore, despite an

increase in the abundance of herbivorous rabbitfish on fished reefs following bleaching, the

number of rabbitfish recorded in fishing catches declined due to changes in fishing pressure and

target species.

These studies illustrate the difficulty in identifying the impacts of coral bleaching on fisheries.

There are complex relationships between habitat quality, fish abundance, community

composition and fishing pressure. Coral mortality resulting from bleaching can affect reef

communities in two different ways. On one hand, coral mortality increases the opportunity for

algae recruitment, which can lead to increases in primary productivity and consequently in the

biomass of herbivorous fishes. However, coral mortality also leads to decreased habitat

availability for fishes as waves, currents and bio-erosion reduce dead coral skeletons to rubble.

This leads to reductions in fish diversity, and, for some species, dramatic declines in abundance143.

From a fisheries perspective, the impacts of coral mortality associated with coral bleaching are

likely to depend on the type of fishery, and the relative importance of increases in algal biomass

versus decreases in habitat complexity for the resident fish community. However, fisheries,

especially those characterised by small-scale operations, can be highly responsive to changing

conditions, and shifts in fishing effort and species targeted can readily confound impacts of

changes in abundance of fish populations related to coral bleaching events. More research is

required to improve our understanding of the direct and indirect impacts of coral bleaching on

fish communities, and on associated fisheries. Such information is essential for the development

of management strategies that aim to sustain coral reef ecosystems and dependent fisheries in

the face of future coral bleaching events.

For more information contact:

Herman Cesar

Cesar Environmental Economics Consulting

herman.cesar@ivm.vu.nl

Lida Pet-Soede

WWF Indonesia-Wallacea Program, Bali, Indonesia.

lidapet@attglobal.net 
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

Fishing impacts. Time lags can be

expected between a coral bleaching

event and associated social and

economic impacts in fishing industries.

Studies have documented changes in

fish populations as a result of bleachingrelated ecological degradation63, 64.

However, studies have had difficulty

demonstrating how changes in fish

stocks have translated into changes in

fishery yields or fishing income

following coral bleaching events. In

these cases, the adaptability of many

fishers, and the confounding influences of other multiple influences on subsistence and

commercial fishing have complicated efforts to understand the impact of bleaching on

fisheries. For example, shifts to other target species, changes in net size, and the effects of

market prices and other disturbances such as typhoons or upwelling events all serve to mask

the possible effects of coral bleaching. However, deterioration in reef quality is likely to have

lasting impacts on the sustainability of fishing pressures, even if they are not readily apparent.

More comprehensive social and economic monitoring, with adequate baseline data, may be

required to properly assess the impacts of coral bleaching events on fishing38.

Indirect impacts. Coral bleaching may also have indirect effects on local and regional

communities through their social and economic links to the fishing and tourism industries.

Reduced prosperity of these industries can potentially lead to a multitude of flow-on effects

to other elements of the community, ranging from local schools, accommodation providers

and food stores, to hardware and fuel suppliers65. These subtle but important effects can

have ramifications for the stability of regional and coastal communities.

Management strategies designed to protect reefs from coral bleaching may also indirectly

affect people and industries by constraining the way people interact and access the reef.While

unintended, these restrictions can have significant and lasting social and economic impacts. For

example, management initiatives to protect herbivorous fishes from over-exploitation may

substantially limit the ability of fishers to pursue their traditional target species. While some

fishers in some regions may be in a position to compensate for such restrictions by switching

to other species or even to other activities such as tourism, many may not. Understanding

these effects will allow management initiatives to be more effective and equitable.

Social and economic resilience. Given the right circumstances, humans are able to adapt to a

changing environment. Understanding what factors influence people's capacity to be resilient

to change in quality or access to a natural resource is a key focus of current research66.

Knowledge of a community's capacity to respond to change can strengthen management

interventions and assist in predicting the longer-term social and economic impacts of coral

bleaching.This adaptive capacity may vary significantly between developing island nations and

developed countries with large land areas that vary in their dependency on coral reef

ecosystems and in the diversity of their economies.

48

Fishing is an important use of coral reef resources, providing

income and food to millions of people worldwide

© Udo Engelhardt
RESPONDING TO A MASS CORAL BLEACHING EVENT

49

2.4.2 Measuring socioeconomic impacts from mass bleaching

Managers are likely to have a range of socioeconomic questions related to mass coral

bleaching. Some of these are likely to be:

• What are the types of social and economic impacts likely to be experienced due to a

bleaching event?

• Who is likely to be affected?

• What are the characteristics of people and industries potentially affected?

• What opportunities exist to minimise the direct effects of a bleaching event?

• How can management responses to bleaching be designed to minimise impacts on reef users?

Answers to these questions may help managers decide if, for example, a contingency fund

for tourism operators should be established. Reef managers may wish to work with local

communities to identify strategies to promote alternative business opportunities or

facilitate access to other resources. Broader-ranging strategies, such as creating subsidies to

change land-use practices, or strengthening regulations for land clearing, agriculture, and

development may also be considered.

A framework for assessing bleaching impacts. Formal assessment of socioeconomic impacts can

help managers to understand, predict and assess the impacts of change on individuals, families,

communities and societies. In some instances, social and economic variables may already be

monitored on a regular basis to assist with other aspects of reef management, and managers

may wish to incorporate a bleaching element into these studies.

The science of measuring and understanding socioeconomic impacts has developed

rapidly in recent years, and there are now guidelines for assessment programs. Properly

implemented, socioeconomic impact assessments can be valuable tools in a reef

manager's approach to minimising the impacts of coral bleaching events. While available

resources may limit a manager's ability to complete comprehensive assessments, the

impact assessment framework described in Box 2.2 can still provide important guidance

for collecting relevant information.

This useful framework for socioeconomic impact

assessments comprises six generic steps: scoping,

profiling, prediction, evaluation, mitigation and

monitoring67. Depending on the resources available and

the goals of the assessment, not all steps may need to

be completed to the same degree. If the main concern

of the manager is to identify the main types of impacts,

a scoping study may be adequate. In other contexts, it

may be highly desirable to quantify all of the

community-scale impacts, requiring the manager to

complete each step of the assessment framework.

Assessing the character and

significance of socioeconomic

impacts resulting from mass

bleaching can help managers

communicate the importance of

healthy coral reef ecosystems

and develop strategies to

minimize impacts on affected

people and industries
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

50

Box 2.2 A social impact assessment framework 

Formal socioeconomic impact assessments generally follow a six-step process. Each of

these steps is described below in relation to coral bleaching. Familiarity with these steps

can help managers identify realistic goals for social and economic impact assessments,

and can provide guidance when developing collaborative assessment projects.

Scoping involves identifying the goals, issues and methods for the assessment of the

potential impacts that might be expected to result from mass bleaching events.The goals

of the assessment will determine the social and economic variables that need to be

collected.Wherever possible, a well-developed community involvement program should be

integrated into the process.A scoping study conducted in consultation with the community

may help identify goals important for the whole community with respect to coral bleaching.

Community involvement not only provides important information for the development of

the assessment, but also provides opportunities for the community to be informed about

coral bleaching and involved in the management response. Suitable representatives from

the local community, fishing industries (commercial, recreational and subsistence), tourism

industries and traditional users should be engaged at this stage. Common methods for

scoping include broad-scale workshops, industry-specific workshops, qualitative interviews,

key informant surveys and desktop-analyses, or a combination of these.

Profiling describes the existing social and economic environment in which impacts are

likely to occur. This step should identify the variables and indicators that describe the

vulnerability or resilience of people and communities to bleaching events. Profiling provides

baseline data about a community and can be carried out any time prior to a bleaching

event. Such data provide bases for comparison should managers wish to set up a social

and economic monitoring program to quantify the impacts of future bleaching events.

Sectors of the community that should be profiled are normally identified in the scoping

part of the study.Typically, profiling is achieved using standard survey techniques, although

secondary sources such as census data may also be useful.A recent guide, SocMon68, is an

excellent reference to help with profiling surveys. An example of the use of profiling to

characterise a commercial fishing industry prior to the implementation of various

management actions is provided by a Guide to the Fishers of Queensland65.

Predicting social impacts requires information collected during the profiling exercise to

describe potential social and economic impacts. The probabilities, magnitude and

distribution of impacts are also described in this section. Indirect impacts can be assessed

by identifying and quantifying links between direct and indirect reef users. Prediction can

also include quantification of the spatial links between the resource and reef users, and

the subsequent economic and social links between users and the rest of the community.

This information provides a basis for predicting the social and economic consequences of

alternative management actions, such as various locations for 'no fishing zones'. Predictions

may also be qualitative, with the results of the profiling exercise being assessed based on

broad discussions with the community. Historical records may be important to access

during this stage. Any prior change in the quality of the coral reef in the past–and any
RESPONDING TO A MASS CORAL BLEACHING EVENT

51

associated social and economic impacts that occurred–may be indicative of how a

dependent community may respond to a bleaching event in the future. Historical

records may also provide some information on the cumulative nature of social and

economic impacts.

Evaluation is a process that determines the acceptability of potential impacts. This

process should involve considerable public involvement since there are often significant

differences between interest groups in how impacts are evaluated. For instance, reef

managers may decide to implement a suite of Marine Protected Areas (MPAs) to assist

reefs in their recovery from bleaching. The design and placement of the MPAs will have

varying social and economic impacts, dependent on their location and size.The evaluation

phase allows reef managers to assess the impacts associated with alternative proposals.

This phase is initially conducted as a desktop study, but it is crucial to 'ground-truth' the

results by querying those people likely to feel the impact. Transparency in evaluations is

important if the community is to feel confident that impacts likely to affect them have

been considered and understood.

Mitigation focuses on minimising impacts. The aim of this section is to develop

management strategies that maximise the resilience of reefs, while minimising the social

and economic impacts. Again, this step requires extensive community involvement in the

design of strategies. Conflicts between user groups in their expectations for management

concessions can be minimised with good community engagement.

Monitoring can enable reef managers to detect the onset of and changes in social and

economic impacts associated with coral bleaching. In addition, a monitoring program will

help detect unforeseen impacts, and assess whether mitigation strategies are working as

intended. Reef managers may already have survey programs in place to address other

goals of marine park management. Where there are existing programs, managers may

wish to add components that can determine if the predicted impacts of coral bleaching

events are occurring.

Special considerations. While the structured approaches described here provide a solid

framework for assessing bleaching impacts, managers should be aware of issues that

impeded the progress of past impact assessments and discuss them with researchers when

developing appropriate projects. As noted in the previous section, a key issue is separating

the influence of mass bleaching from the effect of other disturbances and from other

stressors. For example, studies estimating the economic impacts of the 1997-98 bleaching

event on fisheries in the Indian Ocean region found that changes in fisheries effort and gear

type made it difficult to isolate bleaching impacts given the data available. Similarly, several

studies have found that significant decreases in tourism due to international terrorism

attacks complicated attempts to identify changes in tourism associated with the

degradation of coral reefs37, 60, 69. Challenges also arise when reef degradation results from
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

52

multiple sources. Coral reefs in Con Dao, Vietnam,

experienced almost 100 per cent mortality in 1998 as a

result of a typhoon followed by mass bleaching15.

Because mortality resulted from the combined influence

of both events, it is unclear how much of the

subsequent socioeconomic impact should be attributed

to the mass bleaching event. By discussing these issues

during project design, managers will be able to extend

the scope and limitations of research results, as well as

fine-tune studies toward the most managementrelevant directions.

2.5 Implementing management measures during 

bleaching events

The current section considers whether any meaningful actions can be taken during mass

bleaching events to reduce negative ecological impacts. While above-average sea

temperatures are outside the control of reef managers, other factors that influence coral

reef resilience to mass bleaching events are amenable to management (also see Section

3.1.2). Ecosystem condition, which influences coral survivorship during mass bleaching events

and reef recovery after bleaching-related mortality, can be maintained and improved by

effective management of local stressors40. However, it is the physical conditions–temperature,

light, and mixing–that principally determine whether corals bleach in the first instance.They

also play a key role in determining the probability of mortality during bleaching events.While

these factors are not amenable to intervention in conventional management approaches,

concern about the future of coral reefs is driving new thinking about ways in which

bleaching risk might be mitigated. The following

strategies for management intervention are based on

emerging ideas that mostly have yet to be tested.

Some may turn out to be fruitful initiatives, especially

those aimed at reducing local stressors; however, most

should be considered experimental and undertaken in

the spirit of adaptive management.

2.5.1 Managing local stressors: recreation, water quality and fishing

Physical damage from snorkelling, diving and boat anchoring. The temperature anomalies that

trigger coral bleaching events place substantial stress on coral colonies, even before there

are any visible signs of bleaching70. Once a coral is bleached, it is in a state of extreme stress,

with reduced capacity for feeding and maintenance of essential physiological functions, such

as injury repair and resistance to pathogens18, 23, 27, 71. Snorkelling, diving, and boat anchoring are

all activities that can cause physical injuries to corals if not carefully managed.A coral stressed

due to bleaching is likely to be less capable of recovering from physical injuries due to these

activities. Repair of even minor tissue damage may be hindered while the colony is in a

stressed condition, increasing the risk of infection or overgrowth by competing organisms71.

A key challenge in assessing the

socioeconomic impacts of mass

bleaching is separating out the

influences of other stressors and

changes in resource use – managers

should discuss these issues with

researchers during project design

to focus studies in the most

management-relevant directions

Bleached corals are in a state of

extreme stress and therefore less

resilient to local stressors, such as

physical damage from recreation,

degraded water quality, or pressure

from fishing activities
RESPONDING TO A MASS CORAL BLEACHING EVENT

53

Although the principles

behind these theories are

well established, there have

not been any direct studies

of the effect of bleaching on

a coral's response to

physical injury. However, reef

managers may wish to

explore the costs and

benefits of minimising

activities that could expose

stressed corals to increased

risk, especially in highvisitation tourism sites.

Water quality. Degraded

water quality affects various

life stages of corals45, 72,

making it likely that it

exacerbates the effects of

coral bleaching42. Acute

increases in sediment and

pollutants, associated with coastal development or dredging, deliver additional stress to

corals that must clear sediment from colony surfaces, wasting precious physiological

resources. Corals stressed from mass bleaching are likely to be less effective at defending

against invasion by microalgae or at competing with macroalgae71.Additionally, nutrient inputs

can significantly reduce coral recovery after bleaching-related mortality45 (Section 4.2.3).

Snorkelling, diving, and boat anchoring (shown here) are all activities that

can cause physical injuries to corals if not carefully managed. A coral

stressed due to bleaching is less capable of recovering from physical

injuries due to these activities

© Heidi Schuttenberg

Short-term increases in sediment and pollutants associated with coastal development or dredging cause

additional stress to corals that is likely to increase the effects of coral bleaching. Limiting particular coastal

activities during bleaching events could reduce damage to coral communities, while also reducing the risk

that the developer will be held responsible for any coral mortality that could be due to bleaching
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

54

In light of these implications, managers may wish to consider the timing of coastal activities

during periods of increased temperature stress. Limiting particular coastal activities during

bleaching events could reduce the risk of damage to coral communities that could result

from negative interactions between stressors such as turbidity and temperature41. Such a

strategy could also reduce the risk that developers will be held responsible for any coral

mortality that could be due to bleaching.

Fishing activities. Herbivores play a critical role in facilitating recovery of coral reefs after

major disturbances (see also Section 4.2.3). In many locations, the grazing activity of

herbivores is essential to the maintenance of substrate suitable for coral recruitment42, 45. For

this reason, should a bleaching event result in substantial coral mortality, a reef manager may

wish to consider implementing short to medium term initiatives to protect the herbivore

function that is necessary for the reef to recover.This is most relevant in underdeveloped

countries where herbivorous fish populations are under threat from fishing pressure.These

initiatives are most likely to be effective if they are done in partnership or consultation with

relevant stakeholder groups. Ideally, restrictions would be maintained until significant

recovery is evident or until there is other evidence that adequate settlement substrate can

be maintained despite fishing pressures.

Herbivores play a critical role in facilitating recovery of coral reefs after major bleaching events by maintaining

suitable substrate for coral recruitment. Should a bleaching event result in substantial coral mortality, managers

may wish to work with local communities to implement short- to medium-term initiatives that protect the

herbivore function necessary for the reef to recover

© Heidi Schuttenberg
RESPONDING TO A MASS CORAL BLEACHING EVENT

55

2.5.2 Impeding the causes: light, temperature and mixing

Light. Ultraviolet light is known to be a key factor in coral bleaching73, and small-scale

experiments have shown that reducing intensities of UV light have reduced the incidence

or severity of bleaching24. These observations suggest that shading moderate sized areas

during periods of greatest temperature stress may reduce the amount or severity of

bleaching. However, practical considerations involved in implementing a shading strategy, as

well as the potential for unwanted side effects, make this proposal particularly challenging.

Small to medium-scale experimental tests of this strategy would be best accomplished

through close science-management partnerships.

Temperature. Although water temperatures are not amenable to management intervention

at large spatial scales, there may be potential for temperatures to be manipulated in some

localised circumstances. In situations where high water temperatures are due to the solar

heating of shallow or contained water bodies, relatively small volumes of cool water may

be adequate to maintain temperatures below critical bleaching thresholds for at least some

species. Deep water adjacent to such sites may provide a readily available source of cool

water. This strategy may become increasingly appealing at high use tourism sites should

coral reefs continue to degrade because of temperature-induced stress. The feasibility of

this idea has not been thoroughly investigated to date, and no field tests are known.

Mixing. The amount of water exchange around a coral colony during thermal stress has

been hypothesised to influence the severity of bleaching74. Increased water flow is thought

to increase the flushing of toxins that are the by-products of the cellular processes which

lead to coral bleaching. Therefore, it is possible that increased flushing of toxins through

greater water circulation around coral colonies may

reduce the severity of bleaching or at least delay the

onset of bleaching. If greater mixing could be achieved,

it is likely that the amount of damage from a thermal

stress event could be reduced.The role of water flow in

determining the impacts of thermal stress on corals is

still being studied, and the practicality of this concept as

a strategy for management intervention has not yet

been explored or tested.

It seems unlikely that interventio

aimed at reducing temperature a

light are practicable except at a v

small spatial scale, such as at

discreet, highly valued tourism sit
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

56

2.6 Communicating about mass bleaching

Mass coral bleaching is a visually spectacular phenomenon with potentially severe implications

for the health of coral reef ecosystems, the enjoyment of visitors, and the prosperity of

individuals and businesses that depend on the reef. For these reasons, bleaching is an issue

that attracts strong interest from the public, the media, and policy/decision-makers. In

response, managers will want to provide up-to-date and informative answers to important

questions about mass bleaching events and related impacts. Preferably, managers will

proactively engage their target audiences (Figure 2.7) in discussions about mass bleaching and

the actions that are needed to build coral reef resilience.

COLLEAGUES

THE MEDIA

COMMUNICATING

ABOUT CORAL

BLEACHING

REEF USERS

SENIOR MANAGEMENT

DECISION-MAKERS

INDUSTRY/COMMUNITY

NEWSLETTERS

COMMUNITY INVOLVEMENT IN

SURVEYS ETC

COMMUNITY MEETINGS

EMAIL GROUPS

WEBSITES

TELEPHONE

EMAIL LISTS

WEBSITES

CONFERENCE/SEMINARS

MEDIA RELEASES

PRESS CONFERENCES

CONTACT KEY JOURNALISTS

BRIEFINGS

MEETINGS

Figure 2.7 Target audiences and strategies for communicating about coral

bleaching

Mass bleaching attracts strong interest from the media, reef users, senior decision-makers and management

colleagues because it is visually spectacular and has potentially severe implications for the health of reef

ecosystems. Effectively communicating with these audiences will increase support for coral reef

management responses.
RESPONDING TO A MASS CORAL BLEACHING EVENT

57

A communication strategy for responding to mass bleaching might have three aims:

(1) Gain support from supervisors and constituencies to respond to mass bleaching in the

short and long term

(2) Engage stakeholders in a two-way communication about the extent and severity of

bleaching and actions that can be taken to build reef resilience

(3) To work with the media to raise awareness of mass bleaching events and their impacts

among the general public.

This section outlines strategies for working with target audiences–senior decision-makers, reef

users, the media and colleagues–and provides examples of answers to common questions

about mass bleaching events. It also identifies available resources for outreach and education.

2.6.1 Strategies

In working with any audience, managers are advised to take an approach that is clear and

well thought out, proactive, solution-oriented, balanced, and respectful of political constraints.

In communicating about mass bleaching, it is important that managers maintain the trust of

their supervisors and the credibility of their reputation. Managers should be aware of political

and social sensitivities and operate within organisational constraints. Managers also need to

resist temptations to over-dramatise issues or events in

order to meet the expectations of the press. This is of

particular importance when bleaching is patchy and

tourism operators are wary of the condition of their

frequently visited sites becoming highlighted in the media.

Lost credibility due to exaggeration of facts or

presentation of premature conclusions can be costly and,

sometimes, impossible to regain.

Whether made up of supervisors, stakeholders, or the media, audiences are likely to be

more receptive when they feel they are being consulted early and presented with options

or useful information.When people feel attacked or helpless to solve a problem, they may

become frustrated or angry, disengage in the discussion, or actively try to cover-up the

issue. For this reason, over-dramatisation and focus on negative scenarios can be destructive

to efforts to address the threat presented by coral bleaching. Instead, managers should

enter discussions with a clear, balanced presentation of key issues and solutions, including

specific recommendations for how any given audience can help. Specific suggestions are

provided below.

Decision-makers. Senior managers, policy-makers and

political leaders usually have responsibility for

organisational priorities and allocation of funding and staff.

Information about mass coral bleaching and its

implications for the reef ecosystem, reef users and the

wider community should be conveyed to decisionmakers.This will ensure that coral bleaching is recognised

as a management priority and incorporated into any

relevant management decisions and strategies.

In working with any audience,

managers are advised to take an

approach that is thought-out,

proactive, solution-oriented,

balanced, and respectful of

political constraints

When briefing senior decisionmakers, managers should strive t

provide information early and to

suggest actions that can be take

in response to the bleaching even

such as rapid impact assessmen
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

58

In working with senior decision-makers, managers should strive to provide information

early and to clearly articulate actions and solutions that can be implemented in response

to mass bleaching events.A coral bleaching response plan is ideal for this purpose. The plan

should outline a course of action and identify/estimate the resources required to

implement it (see Section 2.1). In addition to immediate response actions, decision-makers

should be informed of broader efforts that can be implemented to build coral reef

resilience (see Chapter 3).

Formal briefings ensure decision-makers stay well informed and should be delivered in the

lead-up to the bleaching-risk season and during major bleaching events. Written briefs

should provide timely updates on the pending or current situation, and its environmental,

economic, social and political implications. During a bleaching event, briefings are essential

to ensure that senior management learn about significant developments prior to any

public release of information.This is critical if institutional credibility and political support

are to be maintained for the bleaching response as well as for any broader efforts to

address mass coral bleaching. Overall, managers should aim to put senior decision-makers

in a position where they can say, 'We know what's going on, and we are working hard to

address the situation'.

Reef users. Reef users, such as recreational and commercial fishers, divers, and tourism

operators, are likely to have a strong interest in the health of the reef and any major

disturbances.They are among the groups most likely to be affected by any change in the

quality of the reef, and may be key supporters of any efforts to mitigate localised stressors

that reduce resilience or exacerbate the impacts of a bleaching event.

In working with reef users, managers should strive to foster a two-way exchange of

information. Reef users can often assist the manager in understanding the status of

bleaching at their site, and can provide anecdotal information on the sea temperatures, tidal

conditions, and cloud cover that preceded the event. This information will allow the reef

manager to better communicate the extent and severity of mass bleaching throughout the

reef ecosystem, its effects, and its implications.Working together in this way can help raise

awareness, build 'grass-roots' support for strategic management goals, and develop a

shared understanding of the need for any short-term management actions. This is of

particular importance because short-term actions may require restrictions on the types or

levels of activities in order to minimise damage to the reef. The experiences of managers

working with the diving industry in the Florida Keys National Marine Sanctuary (case study

4) and local fishers in Kenya (case study 5) are examples of using two-way communication

during mass bleaching events to build support for broader management measures.

A community-based monitoring program not only provides valuable information about

conditions on the reefs (see also Section 2.3.1), but also acts as an important and engaging

communication tool. Involvement can convert a sense of helplessness into one of

commitment to identifying and implementing practical actions. Reef users who are willing

to contribute to community-based reporting programs are often the individuals and

organisations who are leaders within the stakeholder community, and are ideal conduits for

communication with the larger community.Their commitment to their industry or group,
Building collaborative partnerships with reef users

during bleaching events – Florida Keys National

Marine Sanctuary

Collaboration between reef users and managers can significantly improve the capacity of

managers to respond rapidly to bleaching events.In the Florida Keys National Marine Sanctuary

(FKNMS), the periodic occurrence of mass coral bleaching has provided an opportunity for

coral reef managers to initiate valuable collaborative partnerships with dive operators.

During coral bleaching events in the 1990s, managers of the FKNMS involved dive

operators in the early phases of their management response to coral bleaching. As soon

as managers were aware that conditions were developing that could lead to coral

bleaching, they communicated their concerns, and the scientific basis for them, to the dive

operators. The managers used the HotSpot maps and degree heating keeks maps

provided by NOAA to communicate the state of knowledge about the causes and

predictability of coral bleaching.

Dive operators are often the first reef users to observe the early stages of coral bleaching.

Dive operators and their customers are well placed to assist reef managers to monitor the

extent and duration of bleaching, and of any secondary impacts that follow. As well as

providing early observations of bleaching, divers and dive guides can assist managers in

ground-truthing predictions of conditions known to cause bleaching, derived from remote

sensing technology (such as satellite data).

The accuracy of the managers' predictions in the 1990 and 1997-98 mass coral bleaching

events improved their scientific credibility with dive operators. The fact that coral reef

managers could use remote sensing data from satellites combined with meteorological

observations to predict coral bleaching events caught the attention of dive operators.This

made it possible for managers to gain a mandate for responsive actions, such as research

and monitoring, as well as education and outreach. Dive operators were also able to put

in place measures to minimise visitor-related impacts on coral reefs stressed by bleaching.

While dive operators routinely caution their customers against coming into contact with

corals, the bleaching events provided another opportunity for operators to emphasise the

vulnerability of corals to human activities.

In this case, bleaching events provided an opportunity for managers to form collaborative

and mutually respectful relationships with a major segment of the tourism industry in the

Florida Keys.These relationships have been maintained beyond bleaching events, and they

continue to provide benefits in dealing with other management issues in the area.

For more information contact:

Billy Causey, Superintendent 

Florida Keys National Marine Sanctuary, Florida, USA

billy.causey@noaa.gov
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

60

as well as to the reef, also makes them valuable partners in collaborative efforts to

understand the problem and to devise appropriate solutions.

A community-reporting program can range in complexity from periodic face-to-face

meetings and simple phone networks, to specially prepared surveys, with on-line reporting

forms and summary reports. It is important that the primary mechanism for information

exchange is appropriate to the target group.Active involvement will only occur if managers

reach out and demonstrate a genuine interest in the knowledge and concerns of the

stakeholders. Ongoing commitment from reef users to a reporting program will depend

on their sense of the level of appreciation and utility of the information that they provide.

For this reason, feedback is an important ingredient in the success of a communityreporting program. Managers should design active and transparent mechanisms for

communicating to reef users how their information is being used.This may include regular

dialogue by phone, email, or formal written summaries of conditions at the reporting site.

In addition to community monitoring programs, a number of strategies can be used to

share information with reef users about mass bleaching. Managers should select the

strategies most appropriate to their stakeholders, which may include speaking at

community meetings, using local or industry newsletters, email updates, and the use of

appropriate websites.

The mass media. A mass coral bleaching event is visually

dramatic, attracts strong public interest and therefore, is

highly likely to be considered newsworthy. Managers

must be prepared to engage with the media in order to

respond to questions and inquiries and, ideally, to utilise

the media proactively as a communication tool. Good

media coverage can significantly advance efforts to

increase awareness about coral bleaching and create support for management initiatives.

Professional training in media engagements can be extremely valuable in helping managers

to maximise the value of media coverage.

Taking an active lead in interactions with the press will allow managers to influence the

agenda of discussions and avoid being forced into a defensive position. There is value in

meeting with the media before a mass bleaching event to educate, provide contacts, and

offer resources. Media statements should be released as soon as new and significant

information becomes available and senior decision-makers have been briefed. Managers

should consider drafting generic media releases that can be annotated with the current

facts and quickly released at key points throughout a bleaching event, such as when:

• conditions develop that indicate a high risk of coral bleaching

• a significant bleaching event occurs (describing spatial extent and general severity) 

• the bleaching event has concluded (describing coral mortality and ecological impacts).

Good media coverage can

significantly advance efforts to

increase awareness about coral

bleaching and create support for

management initiatives
RESPONDING TO A MASS CORAL BLEACHING EVENT

61

Managers should consider making available high-quality images for use by the press. Pictures

of mass bleaching are available free of charge from many Internet sites including those listed

in Section 2.6.3. High-quality still images of coral bleaching, especially those that have a

strong human-interest element (for example a scuba diver or sea turtle in foreground) are

often greatly appreciated by the print press. Similarly, television journalists will often be

grateful for high quality underwater video footage. The provision of usable images helps

foster a good working relationship with journalists, and increases the chance that media

reports will highlight the manager's perspective on the issue. Where they exist, managers

should work with in-house media experts to ensure that information is packaged

appropriately for use by the different branches of the media, while maintaining key

messages and factual correctness.

Although a well-prepared manager will usually be able to ensure accurate representation

in press articles, there is always the risk that journalists will ask questions about issues that

are politically sensitive to the management organisation.This is particularly true when the

topic is coral bleaching, as journalists will frequently make links to politically sensitive issues.

When a manager is speaking as a representative of an organisation, it is important that he

or she has a clear understanding of the organisational protocols for interacting with the

media.Working within organisational protocols is important to the manager's professional

development and helps ensure access to future media engagements, one of the most

powerful tools in the manager's response strategy. It is equally important to the

achievement of effective public communication to maintain the trust of the journalist by not

appearing evasive. Clearly defining boundaries prior to

any media engagements will enable a manager to

provide detailed and accurate information about the

issue, while ensuring future opportunities to speak as a

representative of the organisation. Strategies to deal

with pointed questions on sensitive topics should be

developed, and may include referring the journalist to a

more relevant authority, such as climate scientists, the

national meteorology or climatology agency, or a nongovernment organisation.

Colleagues. Communication should be a collaborative endeavour, and will be most

successful when done in close cooperation with colleagues, partner organisations, and

other constituencies. Scientists and non-government organisations (NGOs) can be valuable

partners in efforts to understand and communicate the effects of coral bleaching events,

and to develop, communicate and implement potential mitigation strategies. Colleagues and

fellow staff from within the manager's organisation are often overlooked in communication

programs. Collegues are an extremely important audience for updates on bleaching

conditions, as they will be major conduits to key sectors of the wider community for

information about coral bleaching.

To achieve good results with the

media, managers can consider

meeting with reporters before

bleaching starts, developing pres

releases with key facts, sharing

quality images, and developing

responses to questions about

sensitive topics
Involving fishermen in monitoring of coral reefs

affected by bleaching in Kenya

The Kiunga Marine Reserve (KMR), in northern Kenya, is the site of a highly successful

participatory monitoring program.The reserve designation allows traditional resource use

including fishing, and artisanal fishers have been key participants in the program.The Kenya

Wildlife Service (KWS) manages the reserve, while the WWF jointly operates a

community-oriented project to raise awareness of the need for management in the area.

The Coral Reef Degradation in the Indian Ocean (CORDIO) program gives technical

assistance and partial funding for coral reef and fisheries monitoring.

Over its nine years of operation, a mix of fishers,WWF staff, KWS rangers, fisheries officers

and researchers from the Kenya Marine and Fisheries Research Institute have participated

in the monitoring program. It has been one of the largest annual activities in the KMR area

that focuses exclusively on marine issues. This has given the monitoring program a social

and communications prominence that has served to raise awareness of environmental

issues in general, and particularly of the primary threats to coral reefs in relation to both

climate change and fisheries.

The Kiunga Marine Reserve is one of the 'last frontiers' for fishing in Kenya, being protected

by its remote location and harsh conditions. However, pressure has steadily increased from

fishing communities to the south, repeating the common pattern from other parts of Kenya

of invasion by migrant fishers from already depleted areas that use destructive fishing

practices. Fishers resident within the reserve area have had a varying understanding of the

extent to which these factors threaten their future livelihoods, with some welcoming and

working with the newcomers as they bring immediate economic gain, while others have

resisted change due to awareness of the longer term threat.

During the El Niño event of 1998, over 90 per cent of corals in the predominantly shallow

reefs of the reserve bleached and died.The white corals were clearly observed by fishers,

but their significance was not apparent due to the common belief that corals are 'stones'

and therefore dead (the local name for coral is 'stone'). The participatory monitoring

program offered a direct avenue for explaining the implications of the bleaching event to

fishers.The threat posed to the local reefs by coral bleaching (a completely external threat)

was used to emphasise the need to manage local threats, primarily recent increases in

destructive fishing practices within the reserve.

Fishers were provided with information to help them understand the value of minimising

local stressors so as to increase the capacity of reefs to regain their productivity in the face

of threats beyond their control (such as climate change). In subsequent years, repeated

sampling on the same reefs helped the monitoring team to appreciate the slow rate, and

variability of recovery of coral communities.

In 2002 a program of coral transplantation was started, and seized upon eagerly by the

fishers who were keen to attempt to rehabilitate reefs that showed little recovery. The

CASE STUDY 5
fishers were warned that true rehabilitation would not happen with only transplanted

corals, but the project provided an opportunity for them to get involved in a direct

conservation intervention.The exercise has served to draw parallels between the practises

involved in growing and caring for corals with those central to the indigenous farming

culture: raising crops and animals, and watching over their slow growth and survival in a

harsh environment.

The culmination of the first seven years of coral reef monitoring was a stakeholder

workshop in May 2004 to develop the beginnings of a zoning and fisheries management

plan for the Kiunga Marine Reserve. Fishers and marine reserve staff that have participated

in the coral reef monitoring program have become key resource people in promoting the

need for conservation management, and in facilitating the inclusion of their communities in

planning stages.The leaders of the monitoring teams played a strong and active role in the

workshop. Since the monitoring program was based on traditional fisheries zones and

taxon names, presentation of reef health results was based on familiar geographic and

ecological concepts to local communities.

For more information contact:

David Obura

Coral Reef Degradation in the Indian Ocean (CORDIO), Mombasa, Kenya 

dobura@cordioea.org

The monitoring team for the Kiunga Marine Reserve includes fishers,WWF staff, Kenya Wildlife Service rangers,

fisheries officers and researchers from the Kenya Marine and Fisheries Research Institute, coordinated by David

Obura from CORDIO (front right)

© CORDIO
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

64

In working with colleagues, managers should strive to

foster a mutual exchange of information and coordinate

response and communication efforts. Effective

communication channels should be established to share

information and facilitate working partnerships.

Collaborating on the development of response

strategies can set the stage for partnerships of mutual

benefit, as well as maximising consistency in methods

that can facilitate comparison of results between sites and regions. An analysis of successes

and failures can offer valuable learning opportunities, and shared experiences can rapidly

accelerate collective improvements in knowledge and in the capacity to respond to

bleaching events.

Methods for sharing information range from formal websites and email list-servers to

informal phone calls or seminar presentations. Briefings about current conditions and the

relevant management activities can be provided before and during bleaching events.

Where the technology is readily accessible, email reports or websites are a rapid, costeffective and far-reaching mechanism for disseminating information about 'current

conditions' during bleaching events. Email reports can be sent to pre-existing email

discussion groups or new lists can be generated and opened to self-subscription.Websites

can be inexpensive to produce and need not require a high level of technical skill. The

flexibility of a website enables the manager to present a range of information and

photographs through separate, but linked, documents and to provide links to other sites

of relevance (such as partner organisations).

Communicating with colleagues can help

managers better understand and

respond to mass bleaching events –

methods for sharing information range

from formal websites and email listservers to informal phone calls or

seminar presentations

Communication between managers and stakeholders is a critical element of an effective response to coral

bleaching

© Paul Marshall
RESPONDING TO A MASS CORAL BLEACHING EVENT

65

2.6.2 Frequently asked questions

While many of the questions that come up when talking to people about mass bleaching

are predictable, they can be challenging to answer briefly and without technical jargon.This

section provides examples of answers to eight common questions.

Q1: What is coral bleaching?

A1: Coral bleaching occurs when corals become stressed. Under stressful conditions, such

as above-average water temperatures, pollutants or other stressors, the important

relationship between corals and the microscopic algae that live within their tissue

breaks down.These tiny algae, called zooxanthellae, provide corals with most of their

energy requirements, as well as giving them their characteristic bright colours.When

this relationship breaks down, the algae are expelled from the tissue, which then

becomes transparent, allowing the white coral skeleton to be clearly visible. As a

result, corals turn noticeably white, giving them the appearance of being 'bleached'.

Q2: Is coral bleaching bad for corals?

A2: Coral bleaching is a serious issue for corals. Mass bleaching events, caused by unusually

high water temperatures, can lead to extensive coral mortality if temperatures are

high enough (1-2 o

C above long term summer maxima) for 4-8 weeks. During the

worldwide bleaching event in 1997-98, coral bleaching caused catastrophic mortality

at many reefs, including those around the Seychelles, Palau, Maldives and northwestern Australia. However, bleached corals do not necessarily die.While many reefs

have experienced mortality from coral bleaching, corals on many other reefs that have

experienced mass bleaching events have suffered only minor levels of mortality.

Providing warm temperatures do not persist for too long, zooxanthellae densities can

return to normal. However, even corals that survive bleaching can suffer side effects,

such as slower growth, lower rates of reproduction and increased risk of disease.

Q3: What causes mass bleaching?

A3: Many different stresses can cause corals to bleach, but mass coral bleaching occurs

when water temperatures become unusually high. When temperatures become too

high, the microscopic algae that live within the coral tissue are no longer able to cope

with high light levels. As a result, they begin to produce molecules that are toxic to

the coral, leading to their expulsion from the tissue.

When large areas of the ocean warm to unusually high temperatures, bleaching can

affect corals over hundreds or even thousands of kilometres constituting what is

known as a 'mass bleaching event'. High temperatures are projected to occur with

greater frequency in many parts of the world over the century, leading to concerns

that mass coral bleaching events will become an increasingly frequent and severe

threat to coral reef ecosystems.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

66

Q4: What will the impacts be to the affected reefs?

A4: Mass bleaching is a serious threat to coral reefs.While reefs are under pressure from

many sources, few stresses have the potential to cause severe damage over such large

areas. The unusually warm conditions that trigger mass coral bleaching can affect

hundreds or thousands of kilometres. In these situations, extensive areas of coral reef

can be severely stressed and potentially damaged. Importantly, the effects are not

limited to corals. Damage from bleaching has the potential to affect all of the animals

and plants that are part of the coral reef ecosystem, potentially impacting on reef

biodiversity and the health of the entire ecosystem.

Q5 Why should people care about mass bleaching?

A5: Reefs that are damaged by coral bleaching are less appealing to tourists, they are less

able to support fishing industries, and they may provide less shelter to coastal

communities from storms and ocean waves. Recovery of degraded reefs can take

decades, and the social and economic impacts can be long lasting. In Australia, for

example, one study has estimated that coral bleaching on the Great Barrier Reef could

cost the regional economy approximately US$100-300 million over 20 years28. In

addition, reefs damaged by coral bleaching have lowered biodiversity and, quite simply,

are less beautiful.

Q6: What does the future hold? Will mass bleaching events continue to be an issue?

A6: Reefs face a very uncertain future. Many are already under threat from land-based

sources of pollution, recreational over-use and destructive or unsustainable fishing.The

additional stress of mass bleaching events puts coral reefs at greater risk than ever

before. Moreover, the threat of coral bleaching is expected to increase in coming

decades. Climate scientists predict that the world's oceans will continue to warm,

meaning that the frequency and severity of mass bleaching events is likely to increase.

The abundance and vigour of corals is likely to decrease, with a potential shift to a

predominance of algae rather than corals.This could have flow-on effects throughout

the entire ecosystem, impacting on the full diversity of flora and fauna and the

industries and societies that depend on healthy reefs. It is important to recognise that

reefs are unlikely to disappear even under extreme climate change scenarios, but they

will deteriorate in their ability to provide the ecosystem goods and services upon

which human societies have come to depend.

Q7: Can anything be done about mass bleaching?

A7: Mass bleaching events pose a real challenge because there is little a reef manager can

do to directly alter the climatic conditions that can cause coral bleaching. However,

there are things we can do to help prevent and respond to bleaching. It is clear that

reef managers can help build and sustain healthy reefs, and those healthy reefs may be

better able to cope with the effects of coral bleaching than degraded reefs. Other

stresses reduce a reef's ability to survive bleaching, and can delay or prevent recovery

following severe bleaching events. Concentrating our efforts on managing the stresses

that we can control, such as water pollution and overfishing, will help support the

natural resilience of our reefs, and help maximise their chances of survival in the face

of climate change and increasing human pressures.
RESPONDING TO A MASS CORAL BLEACHING EVENT

67

Q8: What can our listeners/readers do to help?

A8: Listeners/readers can help by becoming more involved in the management and

conservation of coral reefs. These precious ecosystems are under unprecedented

pressure and need every bit of help they can get. People who visit the reef regularly

can help by reporting coral bleaching if they see it. We have a website/information

kit/contact person to help members of the public learn about coral bleaching, how to

recognise it on the reef, and how to report it.

2.6.3 Resources

There are a number of resources available to help managers to integrate bleaching-specific

elements into management and to communicate with stakeholders about mass bleaching.

There are many excellent resources available on the broader subject of coral reef

management. The list below, includes resources that specifically relate to mass coral

bleaching events.

• The Nature Conservancy (TNC) and partners have produced a multimedia CD-ROM

toolkit entitled: Reef Resilience: building resilience into coral reef conservation. This Reef

Resilience (R2

) toolkit (www.reefresilience.org) provides resource managers with cuttingedge strategies and tools to lessen the impacts of coral bleaching and conserve reef fish

spawning aggregations. The toolkit is designed to help practitioners begin to build

resilience into coral reef conservation programs so that their reefs might better survive

mass bleaching events in the future.

• ReefBase (www.reefbase.org) is a global information system for coral reef conservation

and management developed by WorldFish Centre, Penang, Malaysia. It provides managers

with monitoring data and advice on coral reefs, and stores all records from the Global

Coral Reef Monitoring Network (GCRMN) and Reef Check.Worldwide coral bleaching

reports, maps, photographs, and literature are available on the website, and bleaching

reports can be submitted online for inclusion into the databases.

• The Great Barrier Reef Marine Park Authority (Australia) (www.gbrmpa.gov.au) has

developed a volunteer program called 'BleachWatch' to encourage dive operators and

other regular users of the reef to monitor for bleaching in areas they frequently visit.

Similar programs have also been developed for use in Bali Barat National Park (Indonesia)

and the Florida Keys National Marine Sanctuary (USA). BleachWatch kit materials, such

as an armband showing degrees of bleaching and reporting forms printed on waterproof

paper are designed specifically for these types of reef users so that they can easily note

and report any bleaching with minimal inconvenience to their normal operations. The

GBRMPA website is also a source of information and images relevant to coral bleaching.

• The Coral Reef Alliance (www.coralreefalliance.org) hosts the International Coral Reef

Information Network library online. Bleaching papers, briefing sheets, reports and other

information can be accessed online.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

68

• The National Oceanic and Atmospheric Administration (NOAA) Coral Reef

Conservation Program (www.coralreef.noaa.gov) provides a number of tools and

resources related to coral bleaching events such as Coral Reef Watch (CRW).

Coral Reef Watch provides three tools that analyse satellite imagery to assess the

likelihood of mass coral bleaching events. These products are freely available over the

Internet, and include: HotSpot maps, degree heating week maps, and Tropical Ocean

Coral Bleaching Indices. Other tools and information are available through NOAA's

Coral Reef Information System (www.coris.noaa.gov).
BUILDING LONG-TERM

REEF RESILIENCE
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

70

3. BUILDING LONG-TERM REEF RESILIENCE

There is widespread agreement that increasing coastal populations and projected increases in

sea temperatures will continue to increase pressures to coral reefs, and that the need for

effective coral reef management has never been greater9, 11, 13, 23, 28, 31, 42, 47. Management efforts

that increase reef resilience will play a critical role in determining the future of coral reefs by

allowing species to adapt and adjust before irreversible damage occurs75. The concept of

resilience is based on well-established scientific principles, and its use in strategic management

of coral reefs offers insights and approaches that are becoming increasingly critical for the

protection of these complex ecosystems.

In the context of mass bleaching, resilience can be thought of as the integrated result of

coral resistance to heat stress, coral survival during bleaching, and reef recovery after

bleaching-related mortality (Section 3.1). Managers can take active steps toward restoring

and maintaining the long-term resilience of coral reef ecosystems. Managers can support

coral reef ecosystem resilience in two ways: (1) by incorporating existing resilient areas

into management design; and (2) by implementing strategies to either reinstate or protect

factors that confer resilience, such as good environmental conditions, biological diversity,

and connectivity.

Incorporating resilient areas into spatial networks for reef management requires knowledge

of the location of resilient reefs.There is an emerging knowledge of how to identify and classify

these areas (Section 3.2).

Factors that confer resilience can be reinstated or protected using a range of conventional

management strategies that focus on management of local stressors. MPAs can be used to

manage direct threats to reefs, such as those that may result from fishing and recreation

practices (Section 3.3). Broader management approaches, such as watershed management

and integrated coastal management (ICM) can manage indirect threats to reefs, such as

those resulting from coastal developments and agricultural land use (Section 3.4). In some

cases, restoration measures may also be appropriate to increase overall resilience (Section

3.5). While there may already be management action directed at localised issues such as

fishing, pollution and recreation, controls may need to become more conservative given

predicted increases in the frequency of bleaching events9

.This section explores ideas about

coral reef resilience and the management actions that can build resilience in the context of

mass coral bleaching.

3.1 Resilience

Coral reef ecosystems are highly dynamic systems that

have evolved to cope with a wide range of disturbances.

While a resilient system will have the best chance of

coping with future threats, human influences have

eroded the natural resilience of many coral reef

systems, reducing their capacity to cope with

Two ways of supporting coral reef

ecosystem resilience are (1) by

incorporating existing resilient areas

into management design and (2) by

implementing strategies to either

reinstate or protect factors that

confer resilience, such as good

environmental conditions, biological

diversity, and connectivity 
BUILDING LONG-TERM REEF RESILIENCE

71

disturbance. Strategies aimed at rebuilding and supporting the resilience of these systems

are the best investment for ensuring that reefs can continue to provide the goods and

services upon which humans depend11, 76.This section introduces the concept of resilience

and describes the factors that confer resilience on coral reef ecosystems.

3.1.1 Defining resilience

Ecosystem resilience relates to the ability of the system to maintain key functions and

processes in the face of stresses or pressures by either resisting or adapting to change76, 77.

For coral reef ecosystems, resilience characterises the capacity to maintain the dominance

of hard corals and/or to maintain morphological diversity, rather than shifting to a

predominantly algal state or a single coral morphology. Resilience also includes the potential

of the system to reorganise and build its capacity to adapt to change78. As an example, a

resilient coral community might suffer significant coral mortality from a bleaching event, but

reorganise so that the community composition shifts toward different coral species that

provide similar habitat and are more tolerant to coral bleaching.

Figure 3.1 Coral reef ecosystem resilience to mass coral bleaching

Ecosystem resilience relates to the ability of the system to maintain key functions and processes in the face

of stresses by either resisting or adapting to change.The resilience of coral reef ecosystems to mass coral

bleaching can be thought of as the integrated result of coral ‘resistance’ to heat stress, coral ‘tolerance’ during

bleaching events, and reef ‘recovery’ after bleaching-related coral mortality.‘Resistance’ determines the extent

to which corals either withstand exposure to heat stress or bleach. Once bleached, tolerance determines

the extent to which corals either survive the bleaching event or die. When coral mortality is high, reef

recovery determines the extent to which the system either re-establishes coral dominance or remains

degraded. Coral resistance, coral tolerance, and reef recovery are determined by a number of factors that

can be broadly grouped into four categories: (1) ecosystem condition, (2) biological diversity, (3) connectivity

between areas and (4) local environmental conditions. Implementing actions that either protect or

strengthen these four resilience-conferring factors can help coral reef ecosystems survive predicted increases

in the frequency and severity of mass coral bleaching events. Adapted from Obura (2005)88.

Bleaching

Resistance

No bleaching

Survival

Tolerance

Recovery

Mortality

Recovering 

ecosystem

Unhealthy ecosystem

High

High

Low

High

Low

Low

Healthy coral

HEAT
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

72

In the context of mass bleaching, resilience can be considered as the capacity of the coral

community to resist, survive, or recover after recurrent bleaching events (Figure 3.1). A

resilient reef may suffer significant coral mortality during a bleaching event, but will maintain

key system characteristics (structure and function) through rapid recovery and

reorganisation, relative to less resilient reefs. The capacity of coral reefs to recover from

disturbances will become increasingly important if the frequency and severity of bleaching

events increases. Reefs with lowered resilience are more likely to suffer serious and longlasting impacts from coral bleaching events.

In a broader context, the cumulative effects of global and local stressors will determine the

long-term resilience of coral reef ecosystems. While both global and local stressors can

support or degrade the factors that confer resilience on reef ecosystems, local stressors

are much easier to manage in the short term.These resilience factors are discussed below.

Implications for the management of local stressors are discussed in Sections 3.3 and 3.4.

3.1.2 Factors that confer resilience

Factors that influence the resilience of coral reef ecosystems can be grouped into four

categories: (1) ecosystem condition, (2) biological diversity, (3) connectivity and (4) local

environment. Each of these categories includes attributes that can strengthen resistance,

survival, and recovery from mass bleaching as well as recovery from other types of

disturbances.

Ecosystem condition. Ecosystem condition includes coral condition, coral cover, water quality,

and fish abundance. These attributes influence survivorship during mass bleaching events

and recovery after mass bleaching events or other disturbances. Corals that are stressed or

in poor condition, as indicated by low lipid levels, suppressed immunity, or high levels of

stress metabolites, may be less likely to survive the stresses associated with coral

bleaching41. Coral cover, water quality, and fish abundance are critical factors determining

reef recovery through their influence on a range of processes including: larval supply,

availability of substrate for settlement, coral recruitment rates and survivorship of juvenile

corals (see Section 4.2.3). Management efforts that effectively strengthen ecosystem

condition are likely to play a major role in facilitating recovery processes in reefs affected

by climate change47.

Biological diversity. Biological diversity plays an important

role in determining resilience, especially through the

influence of genetic diversity within species and species

diversity within ecosystem functions. These attributes

influence coral resistance to bleaching, coral

survivorship during bleaching, and reef recovery after

mass bleaching mortalities or mortalities from other

disturbances. In particular, genetic variation in

zooxanthellae may play a role in influencing resistance to

mass bleaching79. Genetic differences between corals also strongly influence the outcome

of bleaching events, with coral type being a major determinant of a coral's susceptibility to

bleaching and the rate at which it can recover from bleaching80.

Coral condition, amount of coral

cover, water quality, and fish

abundance are attributes of

ecosystem condition that are likely

to play a major role in determining

coral reef ecosystem resilience to

climate change
BUILDING LONG-TERM REEF RESILIENCE

73

The importance of these sources of diversity becomes increasingly significant over time as

reef ecosystems are repeatedly exposed to thermal stresses. When a diversity of species

fulfils a function (for example branching corals providing habitat for small fish), the loss of a

single species will not lead to loss of the function. This functional redundancy is a key

characteristic of resilient systems81. Biological diversity also plays a practical function in

protecting ecosystems from future threats through maximising the diversity of responses11.

A system is less prone to collapse when key functions are performed by multiple species

that respond differently to stress or disturbance events. Like functional redundancy,

response diversity minimises the chance that any one disturbance will eliminate all

organisms performing a key function.

The importance of biological diversity in conferring

resilience is well illustrated by the role of herbivores in

coral reef ecosystems. In a case study from Jamaica82,

overfishing had prevented herbivorous fishes from

playing a significant role in controlling algal growth. At

that point, the herbivory function, which works to

ensure the availability of substrate suitable for new coral

recruits, was dependent on the sea urchin, Diadema

antillarum. Subsequently, a disease epidemic killed most of the urchin population, leaving too

few herbivores in the system to adequately remove algae. When a major storm caused

widespread damage to coral communities, unchecked algal growth prevented substantial

recovery of corals.These reefs have remained algal-dominated for decades. Overfishing and

reduced functional redundancy made the system highly susceptible to disturbances and led

to a phase shift towards an algal-dominated system with a substantially lower capacity to

provide ecosystem services to humans. If a diversity of herbivores had been present and

fishing pressures better managed, the system would have been protected through

functional redundancy and less prone to collapse.

Connectivity. The capacity of a system to recover or

reorganise following a disturbance is an important

element in determining resilience. Connectivity plays a

central role in determining this potential as it influences

the likelihood that damaged reefs will be replenished by

'seed' reefs or refugia. In the context of resilience, it is

important to realise that connectivity is more than larvae drifting in largely unmanageable

ocean currents. Much of the connectivity in reef ecosystems depends on intact and healthy

non-reef habitats, such as inter-reef hard bottom communities or seagrass beds83. These

non-reef habitats are particularly important to the maintenance and regeneration of

populations. They will become increasingly critical as reef systems spend greater time in

recovery mode due to severe and more frequent disturbance events, such as temperaturerelated coral bleaching. Management efforts that provide effective protection for each of

the critical habitat types will play a key role in restoring and maintaining the capacity of the

coral reef system to adapt to increased frequency and severity of mass coral bleaching.

Biological diversity confers resilie

because different species are like

respond differently to stress and

disturbance events, increasing th

chance that some species will su

and continue to perform key

ecosystem functions

Connectivity plays a central role i

determining coral reef ecosystem

resilience as it influences the like

that damaged reefs will be replen

by 'seed' reefs or refugia.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

74

Local environment.Variation in the local environment can

determine exposure to heat stress, light levels, or

current speed – factors that influence resistance and

tolerance to bleaching. For example, exposure to heat

stress will vary depending on location within the reef

(such as reef flat compared to reef slope) or, at a larger

scale, a reef's orientation with respect to upwelling. In some situations, shading from cliffs

or mountains along the shoreline can reduce light levels and decrease bleaching risk. In this

context, topographic complexity can play an important role in determining the amount of

variation in the local environment of corals.This further increases the imperative for reef

managers to protect species diversity and thereby minimise the chances of reducing

variation in the local environment. The role of local environmental factors in resilience

makes it a useful feature for identifying resilient areas, as discussed in the next section.

3.2 Identifying resilient coral reef areas

The severity of bleaching responses varies between

reefs during mass bleaching events19 118. Identification of

areas that have historically had high resilience to

bleaching provides the basis for a network of refugia to

underpin resilience-based management of the reef

ecosystem. Refugia serve as a seed bank to facilitate the

recovery of areas with lower natural resilience, and will

play a central role in networks of protected areas

designed to maximise ecosystem resilience.

The identification of resilient areas as an ecosystem management strategy is already being

applied in various locations around the world. Examples of resilience-based management

initiatives include projects in Palau (A. Smith, pers. comm.), the British Virgin Islands (S.Wear,

pers. comm.), Belize (S.Walsh and M. McField, pers. comm.), the Seychelles (J. Neville, pers.

comm.),Yemen84, and the Maldives (G. Dews, pers. comm.).The experiences gained from

these initiatives will help to refine knowledge and develop additional protocols for the

identification of resilient areas.The outcomes of these early tests of resilience management

strategies will also provide important information about the extent to which the factors

that confer resilience on an area will remain consistent over time.

The Nature Conservancy, together with a group of partners, has developed a Reef

Resilience (R2) Toolkit to help managers develop and apply resilience principles for managing

coral reefs39.This section draws from the R2 toolkit to review the features that characterise

resilient reefs (Section 3.2.1), and to outline how to identify areas of high resilience 

(Section 3.2.2). Managers are directed to the R2 toolkit or website (www.reefresilience.org)

for a more detailed discussion of how to identify resilient areas and incorporate these areas

into MPA design.

Variation in the local environment can

determine coral reef exposure to heat

stress, light levels, or current speed

– all factors that influence coral reef

resilience to bleaching

Identifying coral reef areas that are

resilient to mass coral bleaching and

protecting these areas from localised

stressors offers the potential to

create a network of refugia that can

replenish other areas that are more

vulnerable to bleaching
BUILDING LONG-TERM REEF RESILIENCE

75

3.2.1 Characteristics of resilient coral reef areas

Patterns of past bleaching responses, mortality and reef recovery provide insights into an

area's resilience to mass coral bleaching events. Based on evidence from the literature and

systematically compiled observations from researchers in the field, a number of factors that

correlate with resilience to coral bleaching have been identified40. Resilience to bleaching is

associated with features that:

• Reduce sea temperature stress, eg localised upwelling, proximity to deep or cooler water 

• Increase water movement in order to flush harmful toxins, eg topographic features such as

narrow channels, strong currents

• Screen corals from damaging radiation, eg high island shading, reef shelf shading, aspect

relative to the sun, or water turbidity

• Indicate potential pre-adaptation to temperature and other stressors, eg highly variable

temperature regimes, regular exposure at low tides, history of corals surviving

bleaching events

• Indicate strong recovery potential, eg abundance of coral larvae or strong recruitment

• Improve coral larval transport to the site, eg connectivity with source reefs

• Maintain a favourable substrate for coral larval recruitment, eg diverse community structure

present, healthy and stable populations of herbivores.

3.2.2 How to identify resilient areas

There are two broad approaches to selecting reef areas that are likely to be resilient to

mass coral bleaching: (1) identifying areas based on their response to past incidents of

anomalous sea surface temperatures and (2) predicting areas based on the presence of

characteristics expected to confer resilience.

Identifying resilient areas from past responses.The response of corals and reef communities

during previous bleaching events can provide important pointers to sites that may be

inherently resilient to coral bleaching.There is uncertainty about the extent to which past

patterns will be repeated during future mass bleaching events, and data should be

interpreted carefully. In addition, identifying sites that display a demonstrated resilience to

bleaching requires reliable information about levels of heat stress during bleaching events,

and knowledge about the extent of bleaching for sites of interest. Figure 3.2 (based on

Done et al85) provides a decision tree for identifying areas to target for management

based on their resilience to past sea temperature anomalies.

A site's potential resilience is one of several factors that should guide decisions relating

to the selection of areas for increased management. The first step in a management

planning process is to identify candidate sites based on conventional criteria for site

selection.The eligibility of sites for protection should be evaluated on the basis of social,

economic, ecological, regional or pragmatic criteria86.The criteria used should be carefully

chosen so that the selection process meets the specific objectives of the planned

management regime.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

76

Figure 3.2 Decision tree for identifying resilient areas for increased

management based on past responses to heat stress and bleaching

(adapted from Done et al85)

Coral reef community response during previous bleaching events can provide important pointers to sites

that may be inherently resilient to coral bleaching. If a site warrants increased management protection

based on conventional social and ecological selection criteria (see Salm et al86 for further discussion

about selection criteria), its potential resilience can be assessed by first evaluating its historical exposure

to heat stress. A site that has not experienced previous exposure to stressful temperatures may be

resilient to mass bleaching, depending on the reasons for its good luck. A site that has been exposed to

stressful temperatures may still be resilient to mass bleaching if it has been tolerant to the bleaching

event and exhibited high levels of coral survival. Finally, sites that suffered high coral mortality during past

bleaching events may still be resilient if the site has demonstrated a good rate of recovery (years rather

than decades).

Site may 

be resilient

Site is likely 

to be resilient

Site is likely 

to be resilient

Potentially

resistant

Potentially

resistant

Likely to be resitant

(low exposure risk)

Resistant or

tolerant corals

Site is likely 

to be resilient

Site is unlikely 

to be resilient

Unknown if site

is resilient

(don’t include the site)

High recovery 

potential

Good Poor

Reef recovery?

Low recovery 

potential

Probably intolerant corals or subject

to intense exposure 

Has site experienced serious bleaching

or heat stress? 

Good luck

Don’t know No Yes

Good oceanography Low High

No Yes

Reason?

Does site meet social and ecological criteria?

Impacts of bleaching?
BUILDING LONG-TERM REEF RESILIENCE

77

At each of the candidate sites, heat exposure and past bleaching responses should be

evaluated. Sites should initially be divided into those that have experienced serious bleaching

or heat stress previously, and those that have not. Current information about thermal stress,

presented as sea surface temperature anomalies, is now readily accessible to most reef

managers through the NOAA HotSpot program, freely available on the Internet (see Section

2.2.2). HotSpot maps (50 x 50 km) visualise differences in exposure to thermal stress at a

larger spatial scale.This can be readily supplemented with reef-scale measurements obtained

from direct temperature readings with thermometers or inexpensive data loggers. Local

bleaching thresholds can then be refined by maintaining temperature records and correlating

measures of thermal stress with observed bleaching responses.

It is revealing to examine possible reasons for some reefs having no recorded history of

anomalously high water temperatures. If sites have low risk of exposure to high water

temperatures because of their oceanography or other physical characteristics, they may prove

to be resistant to bleaching in the future. In examining the reasons for low exposure, it may

be useful to question whether the feature conferring resilience in the past is likely to remain

unchanged in the future. For example, shading from cliffs is unlikely to change but currents

may shift under various climate scenarios. However, in many cases it may not be possible to

identify the mechanisms or characteristics that have resulted in a site being spared exposure

to heat stress. In other cases, it may not be possible to ascertain whether a site previously

experienced heat stress. In both of these situations, the resilience of the reef community to

bleaching has to be assessed using other criteria, such as community composition and

recovery rates following recent disturbances. Managers should consider implementing a

monitoring program at these sites to document their response to any future episodes of

thermal stress.

The next step is to examine the response of reefs that are known to have experienced

thermal stress in the past. Reefs that have suffered only minor coral mortality during previous

anomalies are likely to be populated by corals that are resistant to bleaching, or that have a

high tolerance for bleaching.These reefs are probably sites of high resilience, unless they were

only exposed to minor stress. If the latter is the true case, then it is difficult to predict whether

they are likely to be resistant or tolerant to more extreme temperature stresses in the future.

Determining the thermal history of reef sites can be difficult, especially if managers do not

have access to historical satellite-derived or in situ temperature data. However, even in

remote locations there may be long-term temperature monitoring programs being run by

researchers or other organisations (such as meteorological or shipping agencies). Local

knowledge should also be sought and collated, as some regular reef users, such as tourism

operators and fishers, have an intimate, longer-term perspective about the conditions on their

reefs that can help deduce the occurrence of anomalies.

The remaining category of sites includes those that have suffered substantial mortality

following exposure to stressful temperatures. The rate of recovery at these sites provides

important information about their resilience. Damaged sites that show high rates of recovery

are resilient. Sites with low rates of recovery are not resilient, unless the causes of slow

recovery can be identified and remedied by management action.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

78

Predicting areas of resilience. In many instances, it may not be possible to assess the response

of reef sites to thermal stress.This may be because bleaching has not occurred in the past,

or because there is not sufficient information about either the exposure of different sites

to high sea temperatures or its effect on reef organisms. In these cases, reef managers may

still be able to include bleaching resilience in their management plans by identifying areas

that are characterised by factors that are known to contribute to resilience.

Section 3.2.1 outlines a set of key characteristics that have been identified from

observations of the characteristics of reefs that have proven resilient to past bleaching

events, or have been derived from general principles of coral community dynamics.The R2

Toolkit provides detailed guidance and data sources for gathering information about these

characteristics. Table 3.1, adapted from R2, summarises information sources that can be

used to assess these characteristics and, thus, predict site resilience to mass bleaching.The

role of these characteristics in conferring resilience to mass coral bleaching events is

explored below.

1. Cool water. Some sites may have consistently cooler

water due to upwelling or proximity to deep water.

Local bathymetry, regional and local currents and

prevailing winds may all play an important role in

reducing the temperature of water bathing a reef. Case

study 6 describes research that is developing

hydrodynamic models of Palau to predict future sea

temperatures in order to identify areas that may be protected from mass bleaching

by cooler waters. Some researchers have suggested that currents may not be a

reliable source of long-term resilience because climate change may result in new

current patterns87.

2. Shading. Some reefs may also be protected from bleaching stress by shading where

sun exposure is limited by topographic or bathymetric features. Reefs shaded by cliffs

or mountainous shorelines may be at reduced risk of bleaching. While many reef

areas are unlikely to be associated with features that can provide shade, fringing reef

complexes around steep-sided limestone or volcanic islands, such as occurs in Palau

and the Philippines, may have many shaded sites.

3. Screening. Unnatural levels of sediments and excessive phytoplankton growth from

nutrient-enrichment can stress and kill corals. However, naturally turbid conditions

may filter or screen sunlight, providing a measure of protection for corals exposed to

anomalously warm water. Ongoing research suggests that organic matter in turbid

areas may absorb UV wavelengths and screen sunlight. Corals at these sites may be

less susceptible to bleaching. However, turbid conditions are often sub-optimal for

coral reef development, and biological diversity may be low in these areas.

4. Resistant and tolerant coral communities. Knowledge about the composition of

coral communities can also help predict sites that are more resilient to bleaching.

Observations during past bleaching events from around the world indicate that

The R2 Toolkit identifies five

characteristics thought to confer

resilience to mass coral bleaching:

cool water, shading, screening,

resistant coral communities, and

high recovery rates
BUILDING LONG-TERM REEF RESILIENCE

79

certain types of corals are generally more resistant to bleaching than others80. If a

site is dominated by resistant species, then any temperature-induced bleaching is

likely to be less severe (Box 4.1 in Section 4.2 shows key coral groups in order of

bleaching resilience). Similarly, certain corals appear to be able to survive in a

bleached state for an extended period and are, therefore, less likely to die even if

they bleach.While less work has been done on bleaching tolerance, it appears that

corals with a massive morphology and thick tissue, such as those from the families

Poritidae, Favidae and Mussidae, have greater tolerance to bleaching118.

Another observation is that different colonies of the same species can vary in their

bleaching response, and one mechanism that has been identified for this variation

is differences in the types of zooxanthallae hosted within the coral tissue79. Case

study 7 describes work being done on the Mesoamerican reef to assess the

importance of stress-tolerant zooxanthallae in determining the severity of

bleaching as part of a broader initiative to identify potentially resilient areas.

5. High recovery rates.The ability to recover, and the rate of recovery, after a mass

bleaching event is another relevant characteristic of coral reef resilience. Sites that

recovered well from previous disturbances, such as storms, are more likely to

recover quickly from bleaching events. Where recovery rates are not known,

managers can infer a site's capacity for recovery by evaluating whether conditions

are conducive to coral recruitment and survival.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

80

1.Cooler due to upwelling or proximity to deep water

• Consult nautical almanacs, charts, local fishers, online NOAA resources1, and University of Hawaii2 website to identify and

assess exposure to regional and local currents. Look at the location of islands and reefs to infer how prevailing currents

might cause mixing and water-cooling.

• Local studies that release dye, use drogues, or release drift cards or floating instruments can give some information on

surface current movements.

• Conduct shipboard studies of underwater and surface currents. Use oceanographic models of water movements.

2. Protected by shading

• Check topographic maps of islands and mainland coasts indicating likely areas of shading. In particular, look for high, steep

islands and coasts with cliffs. Mapping of the ocean floor and the topography of the reef can be used to describe the aspect

(angle to the sun) of particular reef faces.

• Direct observation of shading-by snorkellers and divers, from boats, or by time-lapse photography or video-can be used to

quantify sun exposure. Correlation with the presence or absence of bleaching in shaded locations during or after a bleaching

event can also indicate the impact of shading.

• Use a network of light meters to measure and correlate sunlight exposure over time with bleaching and mortality patterns.

3. Protected by screening by suspended particles and dissolved matter 

• Use satellite imagery, aerial photos, or direct surveys to identify areas with consistently lower water clarity.

• Measure suspended sediments and turbidity along transects with a Secchi disc, turbidometer, or other instruments.

• Take scientific measurements of sunlight penetration and quantitative measurements of CDOMs.

4a. Coral community dominated by bleaching-‘resistant’ corals

• Compile existing data or local knowledge about composition of coral communities at candidate sites. Identify dominant coral

groups and give them a bleaching resistance ranking based on Box 4.1.

• Conduct surveys of coral community composition at candidate sites and assess relative dominance of coral types known to

be more resistant to bleaching.

• Conduct physiological studies of dominant corals at candidate sites to measure likely resistance indicators, such as

zooxanthellae type and photoprotective pigments.

4b. Coral community dominated by bleaching-‘tolerant’ corals

• Compile existing data or local knowledge about composition of coral communities at candidate sites. Give dominant coral

groups an indicative bleaching tolerance ranking based on morphology (massive > encrusting > branching/tabular) and

tissue thickness or 'fleshiness'. Corals with good capacity for heterotrophic feeding should be assessed as having higher

bleaching tolerance, where this information is known.

• Conduct surveys of coral community composition at candidate sites and assess relative dominance of coral types known to

be more tolerant of bleaching (using criteria above).

• Conduct physiological studies of dominant corals at candidate sites to measure likely tolerance indicators, such as tissue

condition (lipid levels) and heterotrophic capacity.

5. Demonstrated strong recovery 

• Use existing data or local knowledge to identify areas with a good mix of old and young corals. Previous studies or

anecdotal observations may help identify reefs that have rapidly recovered from other disturbances such as storm damage

or COTS (Acanthaster) outbreaks.

• Undertake field surveys to identify those places where coral cover and species diversity quickly recovered following an

earlier known bleaching event. Use point, line or quadrat survey methods to measure changes in coral cover and community

composition following bleaching- induced mortality at candidate sites.The presence of high numbers and diversity of early

coral recruits, and the prevalence of conditions known to be conducive to survival and growth of young corals, can also

indicate strong recovery potential.

• Develop models to predict recovery capacity from ecological dynamics that include recovery-supporting processes, such as

larval supply, connectivity and physico-chemical conditions that enhance coral survival and growth.

1 www.noaa.gov/

2 www.soest.hawaii.edu

Table 3.1 Characteristics and information sources for predicting the

relative bleaching resilience of candidate reef sites

Availability of information sources will depend on level of resources or expertise, and are divided into low, moderate

and high resource requirements.
A major research program to improve predictions of 

coral bleaching in Palau

A collaborative program involving experts from The Nature Conservancy, the US National

Oceanic and Atmospheric Administration (NOAA) and the Australian Institute of Marine

Science is taking a detailed look at the role of sea surface temperature (SST) in major

bleaching events. The goal of the project is to improve predictions of coral bleaching in

Palau, but the knowledge gained from the study will be valuable to other regions.

Modelling patterns of thermal stress

One of the major environmental stresses that cause bleaching of corals is heightened water

temperature. Over 98 per cent of solar radiation energy is absorbed within the top four

metres of the water column.This heat will stay at the top of the water column unless there

is a mechanism to mix it with the cooler water below.Vertical mixing occurs in regions of

relatively strong horizontal currents; these can be associated with surface winds, large-scale

currents (for example the Gulf Stream) and tides.Therefore, extended periods of cloudless

summer days with low winds and low currents create conditions known to induce

bleaching events.

Hydrodynamic models can be used to predict SST patterns for a future, severe, mass coral

bleaching event. Thus, they provide an excellent tool for managers, particularly when

designing Marine Protected Area networks. Hydrodynamic modelling can also assist in the

investigation of other issues that relate to the coral reef ecosystem. Connectivity with

biological events (for example coral/fish spawning) and human activity (such as sewage

outfall and pollution accidents) can be monitored and/or predicted.

Calibration and validation of the hydrodynamic models for the Palau project will be carried

out by comparison of the model results with in situ data. Seventy instruments were

deployed across the Palau lagoon to record data for a five-month period, from August 2003

to January 2004. The instruments included current meters, conductivity sensors,

temperature profiles and pressure gauges. Atmospheric conditions were recorded during

the same period using a dedicated weather station. In addition, vertical profiles of

conductivity and temperature with depth were measured three times at several locations

during the study.

One of the most important inputs to a high-resolution hydrodynamic model is the

bathymetry. Since there was no reliable source of high-resolution bathymetry for Palau, this

project endeavoured to generate one.This was achieved by merging a global bathymetry

data set with satellite-derived depth data, and validating these with a series of transects

collected from small boats.
CASE STUDY 6

Studies of bleaching events on the Great Barrier Reef, Australia, have demonstrated how

the hydrodynamics during a coral bleaching event can be predicted with reasonable

accuracy.The methods used in this study will be used to increase our understanding of

the climatic and physical conditions conducive to rapid seawater warming to help

understand the process of heat dissipation within lagoonal and barrier reef systems. It is

expected that the study will highlight the importance of micro-environments, local

topography, and reef hydrodynamics in determining the severity of bleaching during

periods of anomalously high sea temperatures. In addition, during the Palau study,

additional research is being undertaken to further develop the technology and capacity

to predict coral bleaching events.

For more information contact:

Scott Heron

NOAA's Coral Reef Watch Program

Scott.Heron@noaa.gov 

Will Skirving

NOAA's Coral Reef Watch Program

William.Skirving@noaa.gov

Rod Salm

The Nature Conservancy, Hawaii

RSalm@tnc.org

Bathymetry map developed for Palau by merging global bathymetry data with

satellite-derived depth information
Understanding patterns of bleaching in the

mesoamerican reef – a collaborative effort to support

resilience-based management

Bleaching on the Mesoamerican Reef

The Mesoamerican reef includes the longest barrier reef in the western hemisphere, with

a diverse array of associated reef types.The core of this reef system, in Belize, did not suffer

a major bleaching event until 1995, when approximately 10 per cent of colonies suffered

at least partial mortality155. More recently, there have been dramatic declines in live coral

cover attributed to the 1997-98 bleaching, including severe mortality on nearly 100 per

cent of central lagoonal reefs and 50 per cent of 12 fore-reef sites studied. These losses

have been associated with the combined effects of bleaching and a hurricane156, 157. Several

regional threat assessments have identified the increased frequency of coral bleaching

events associated with climate change as a primary threat to the region158, 159.

A collaborative program

In response to concerns about the future of this reef ecosystem, the WWF, The Nature

Conservancy (TNC), the Wildlife Conservation Society (WCS) and Scripps Institution of

Oceanography are collaborating in an attempt to understand the variability in responses

observed during past bleaching events.These agencies hope to determine whether this may

provide a basis for resilience-based management of the region. This work will use TNC's

Reef Resilience (R2) Toolkit to help design and field-test a conceptual model of reef

resilience.The model will be based on natural variations in key environmental conditions

and incorporate the latest research on reef connectivity.

Understanding the characteristics that

actually confer resilience on any given

reef will provide managers with specific

targets for conservation. It will also

provide one of the key criteria in ongoing

efforts to develop and implement a full

representational analysis of the region's

Marine Protected Areas network. A

variety of approaches will ultimately be

needed to address this issue, but one

novel avenue currently being studied by

Scripps and the WWF involves the

characterisation of the abundance and

distribution of zooxanthellae in various

reef habitats. Furthermore, knowledge

about zooxanthellae distributions will

assist managers to decide whether this

approach could play a role in the design

of management strategies.

Coral bleaching can be highly variable, even within a

single coral colony

© Melanie McField
CASE STUDY 7Variability in coral bleaching

Different coral species can vary substantially in their response to thermal stress,

independent of zooxanthellae type80.Yet, different colonies of the one species can also vary

in their bleaching response, and one mechanism that has been identified for this variation

is differences in the clades of zooxanthellae hosted within the coral tissue. Different clades

of zooxanthellae respond differently to stress, leading to patterns of coral bleaching that

often cannot be explained by coral taxonomy alone160. Experimental bleaching of corals and

studies of the distribution of zooxanthellae suggest two potential explanations for the

observed patterns of bleaching161, 162. The first is that corals may resist bleaching by

associating with stress tolerant zooxanthellae.The second suggests that corals may be able

to survive future bleaching events by repopulating with stress-tolerant zooxanthellae162, 163.

Monitoring to understand resistance to bleaching

Beginning in 2003, researchers from the Scripps Institution of Oceanography and from the

WWF, Belize, began surveying the presence of stress-tolerant zooxanthellae within reefs

and in adjacent reef habitats. One theory that emerged from this survey is that the amount

of bleaching that occurs at each reef may be influenced to some extent by the prevalence

of stress-tolerant genotypes of zooxanthellae. Identifying the patterns and sources of

zooxanthellae diversity will provide information on the role of zooxanthellae composition

in determining the effects of thermal stress on coral communities, which may assist

managers to evaluate the potential resilience of different sites.

Using research to help managers support reef resilience

Following bleaching events, researchers and managers will work together to assess the

importance of stress-tolerant zooxanthellae in determining the severity of bleaching during

future thermal stress events. Combining the monitoring of zooxanthellae diversity with

other key factors for reef resilience will allow managers to better understand what makes

a specific reef resilient. In turn, this will help them adapt management strategies so that the

focus is on protecting those factors most important for maintaining reef resilience.

For more information contact:

Sheila Walsh

Scripps Institution of Oceanography (SIO) 

s1walsh@ucsd.edu

Melanie McField

WWF Smithsonian Institution,Washington, USA

mcfield@wwfca.org
BUILDING LONG-TERM REEF RESILIENCE

85

3.3 Using Marine Protected Areas to increase resilience

Marine Protected Areas (MPAs) can help build coral

reef resilience by supporting and enhancing the factors

that confer resilience: good coral reef condition,

biological diversity, connectivity, and favourable local

conditions. Traditionally, principles of MPA selection,

design and management have not specifically addressed

the threat of mass coral bleaching89.This section considers the additional considerations that

are relevant to MPA site selection (Section 3.3.1) and management (Section 3.3.2) in the

context of mass coral bleaching.

Expected increases in the extent

and severity of mass coral

bleaching warrants the inclusion 

additional, resilience-related

criteria in MPA site selection

Figure 3.3 Principles for building resilience into MPA design

The Reef Resilience (R2) Toolkit, developed by TNC, identifies four key principles to help incorporate coral

reef resilience into MPA design (www.reefresilience.org).
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

86

3.3.1 Selecting MPA sites in the context of mass coral bleaching

Expected increases in the extent and severity of mass coral bleaching warrants the inclusion

of additional, resilience-related criteria in MPA site selection (Figure 3.3). Importantly, the

resilience principles outlined here are meant to build on existing MPA selection criteria and

design principles, not to replace them. Existing MPA planning approaches, including

appropriate stakeholder engagement strategies, remain essential for defining conservation

objectives, identifying threats and determining management strategies to address these

threats. The intention of these additional resilience principles is to enhance the role of

selected sites in contributing to improved resilience of the ecosystem.

1. Representation and replication. Sometimes called 'spreading the risk', this principle

recommends that, in the uncertain context of climate change, MPA network design

should aim to replicate a range of reef types and related habitats. Section 3.1.2

describes how protecting biological diversity confers resilience to coral reefs. This

principle aims to maximise biodiversity as a way of increasing the chance that among

these species and habitats there will be enough survival and recovery to maintain

functional coral reef ecosystems.

2. Refugia. The refugia principle aims to take advantage of coral reef areas of natural

resilience, as identified in Section 3.2. In the context of mass coral bleaching, refugia can

serve as 'seed banks' or source reefs for less resilient areas. For refugia to serve this role,

they must be effectively protected from local stressors, such as anchor-damage, over-fishing

or pollution, and thus are high priority for increased management attention.

3. Connectivity. Connectivity plays an important role in coral reef resilience by promoting

recovery after mass coral bleaching events and other disturbances (see Section 3.1.2).

Implementing this principle in MPA design involves considering prevailing currents and

adjacent non-reef areas. Linking MPAs along prevailing, larvae-carrying currents can

replenish downstream reefs, increasing the probability of recovery at multiple coral reef

sites. Adjacent non-reef areas are important to connectivity because they can become

important staging areas for coral recruits as they move between reefs and into new areas.

4. Effective management. Coral reef ecosystems in good condition are better able to survive

and recover from mass bleaching events (see Section 3.1.2). This principle refers to

effectively managing local stressors at a site in order to optimise coral reef condition. High

coral cover, abundant fish populations and good water quality are all elements of coral reef

ecosystem health that support recovery.To implement this principle, MPA selection should

give priority to sites where levels of resource use and effective management can help

maintain these supportive attributes.

3.3.2 Managing MPAs in the context of mass coral bleaching

Once sites are selected for inclusion in an MPA network, managers must decide on the

management objectives and management regime for each protected area. Again, in the

context of mass bleaching, management can increase reef resilience by strengthening or

taking advantage of factors that confer resilience: good coral reef condition, biological

diversity, connectivity and favourable local conditions90, 91. Marine Protected Areas are
BUILDING LONG-TERM REEF RESILIENCE

87

particularly suited to managing direct threats to coral reefs, such as those from over-fishing

and recreational overuse or misuse. While MPAs can assist in addressing indirect threats,

such as land-based pollution, achieving this goal usually requires broader management

activities (see Section 3.4).

A high-level objective of MPA management in the context of resilience should be to

protect fish abundance, with an emphasis on herbivorous fishes.The role of herbivores in

maintaining conditions that are conducive to coral recruitment and survival3 makes their

protection critical for reefs subject to increasing sea temperatures (see Section 2.5.2).While

some level of harvest may be sustainable, the importance of herbivores to future reef

resilience means that managers should carefully manage fishing activity to ensure adequate

levels of herbivory are sustained (a conservation objective), and not merely to ensure a

sustainable or maximum harvest (a fisheries objective)11.

Managing the impacts of recreational use of MPAs is another way managers can support

the resilience of reef ecosystems. Recreational activities can result in physical damage from

diving and boat anchoring, and from release of nutrients and combustion products from

vessels (see Section 2.5.2). Where MPAs have been established to protect important

bleaching refugia, even localised stresses associated with recreational activities may pose a

significant threat to resilience. MPA managers should carefully control snorkelling, diving and

boat usage to minimise stress to corals, especially during or following a bleaching event. In

most cases, these are sites within MPAs and/or sites with high visitation rates. While MPA

managers may already have regulations and best-practice guidelines in place, measures to

ensure users avoid imposing additional stresses during periods of temperature stress should

be considered.

3.4 Broader management interventions to increase resilience

Many managers have a range of authorities and tools that can be used to protect resilient

reef areas from local stressors and to increase coral reef resilience.These include fishery

regulations, tourism permitting, coastal development regulations and watershed

management. Expected increases in the frequency, spatial extent and severity of mass coral

bleaching events will have implications for effective application of these traditional

management tools. At present, these implications are largely understood as conceptual

principles that will benefit from refinement with additional experience and research. The

approach taken by The Republic of the Seychelles following the 1997-98 mass bleaching

event, described in case study 8, is a good example of how these principles can be put

into practice.
CASE STUDY 8Identifying resilient areas for improved protection of 

Coral Reefs of the Seychelles

Responding to the devastating impacts of coral bleaching in the Seychelles

The Republic of the Seychelles, located in the western Indian Ocean between 4o and 11o

south of the Equator, was one of the areas most severely affected by the global mass

bleaching episode of 1997-98. In this area, sea temperatures exceeded 30oC for several

months. Coral mortality due to bleaching was extremely high, with declines of 85-95 per

cent in the cover of structurally dominant branching corals (Acropora and Pocillopora) on the

reefs surrounding the inner granitic islands of the group.These islands, Mahé, Praslin and La

Digue, are home to 95 per cent of the population of the Seychelles.

In the Seychelles, coral reefs are particularly important to social and economic sustainability.

Following the 1998 event, the Government immediately initiated a collaborative program to

facilitate and promote the recovery of damaged reefs, and to identify focal sites for future

conservation efforts.The program focused on rebuilding the resilience of reefs in the region.

The Seychelles Marine Ecosystem Management Project (SEYMEMP) was established to

facilitate the recovery of coral reefs, guide the management of existing marine protected

areas (MPAs) and develop strategies to improve the protection of reefs against future coral

bleaching events, or other negative impacts. Major aims for SEYMEMP included:

• assessment of the impacts of the 1997-98 coral bleaching event on corals and associated

fish communities

• identification of areas resistant to bleaching, and of areas that have demonstrated strong

recovery

• investigation of factors that could interfere with coral reef recovery and the development

of tools and strategies to promote recovery of degraded reefs.

Some sites are showing signs of resilience

Detailed ecological monitoring of benthic transects since the 1997-98 coral bleaching event

have identified reef sites that are demonstrating good recovery. These sites are showing

strong trends in the increase of hard coral cover, increasing from an average of less than five

per cent to 15-20 per cent in six years.This compares to an average of 10 per cent cover

Sailing and other reef-oriented tourism activities are an important use of coral reefs in the Seychelles

© Udo Englehardt
after six years for all sites combined. Hard coral diversity has also shown strong signs of

recovery at these sites, with many now having a significant proportion of the species typical

for the region. Significantly, however, the reefs of the Seychelles were affected by bleaching

events again in 2003 and 2004, impeding or reversing recovery at many sites.There was an

interesting contrast in the effect of these more recent events on Acropora and Pocillopora

corals, with the latter showing a strong decline in recovery rates while the recovery

trajectory for Acropora (pooled across species) was generally unaffected.

Coral recovery is threatened by overgrazing

At many sites, the distribution and density of grazing sea urchins (Diadema spp. and

Echinometra spp.) appears to have increased in recent years.This is believed to be due to

the reduction in the number of fishes known to prey on these mobile invertebrates. Grazing

of hard substrate by urchins affects recruitment of hard corals because settling larvae are

consumed along with the targeted algae. At locations where grazing is intense, recovery is

limited, or inhibited entirely. Experimental efforts to control sea urchin density proved to be

effective in increasing coral recruitment, with a doubling in the abundance of Acropora and

Pocillopora recruits over a 12-month period in areas where urchins were removed, as

compared to control areas. Consequently, reef managers are considering control of sea

urchin populations to facilitate recovery within MPAs. Priority areas for this management

response are close to coral communities with a demonstrated resilience to bleaching, either

by surviving the bleaching event with minimal mortality, or by rapidly recovering.

Average density of coral recruits in managed areas (urchins removed) and control areas

(urchins not removed)

This graph shows the mean number of acroporid and pocilloporid coral recruits per 1 m2 (0-5 cm size class) in

areas subject to high grazing pressure by black-spined sea urchins (control areas, red line), and areas where sea

urchin densities were maintained at a lower level through active population management (managed areas, blue line). Mean recruits / m2

14

12

10

8

6

4

2

0

Control areas

Managed areas

Nov Jan Dec

2001 2002

Feb Mar May Apr Jul Jun Sep Aug Nov Oct Jan Dec Feb Mar

2003
Some sites were protected by proximity to upwelling

Three reef sites with the fastest rates of recovery–Marianne Island Reef, Aride Island Reef

and Anse Petit Cour Reef at Praslin–suffered minimal coral mortality. This resistance

occurred despite the sites being characterised by a relatively diverse community of hard

coral species, many of which did not survive elsewhere. It is probable that these sites

benefited from cold-water upwelling, and they are likely to be important seed sources for

replenishment of depleted coral communities.These refugia are being considered for special

management measures designed to improve the resilience of the entire system following

impacts from future bleaching events.

Management actions to protect coral refugia

Some of the sites shown to have higher resilience to repeated bleaching events are outside

the boundaries of existing MPAs, indicating that there is value in considering increased

protection of these sites through future incorporation into the MPA network in the

Seychelles.

One site identified as a refuge from bleaching-induced mortality is already protected within

an MPA, but was being threatened by anchor damage associated with heavy tourism use.

Moorings have been installed to minimise anchoring in the area, and ongoing monitoring has

shown that, as a result, the damage to coral has been significantly reduced.

This case study demonstrates the importance of regular monitoring and adaptive

management in responding to emerging threats, such as coral bleaching. The strong

partnerships among government agencies, non-government organisations and stakeholders

and local communities have resulted in a better understanding of the effects of past coral

bleaching events, and identified strategies to support reef resilience.This initiative provides

the foundation for efforts that will help the reefs of the Seychelles to continue recovering

from the mass bleaching event of 1997-98 and maximise the chances that they will survive

future bleaching events.

For more information contact:

Udo Engelhardt

Reefcare International Pty Ltd

reefcare@ozemail.com.au

CASE STUDY 8
BUILDING LONG-TERM REEF RESILIENCE

91

3.4.1 Guiding principles

The following three principles were identified by participants of an international workshop on

'Coral Reefs, Climate Change, and Coral Bleaching' that was hosted by the US government

in 2003. At the workshop, a group of experts was brought together to suggest how mass

coral bleaching could be integrated into broader coral reef management efforts given the

existing limitations in our scientific understanding. Their recommendation was to manage

adaptively for the factors that confer resilience and the cumulative effects of multiple stressors.

Manage for the factors that confer resilience. Broader reef management efforts have a key role

to play in supporting the factors that confer reef resilience (see Section3.1.2). In particular,

efforts to address indirect threats to reefs that degrade coral reef condition can normally not

be achieved through MPAs alone and require integrated, collaborative coastal management.

Examples of indirect threats include degraded water quality that might result from coastal

development or agricultural land use.

Recognise the cumulative effects of multiple stressors. Under the additional threat of mass coral

bleaching, management of localised stressors may need to become more conservative in

order to help maintain ecological condition and services. Managers need to consider how

targets for and expectations of fish abundance, water quality, and physical damage from

recreational use might be revised to reflect the cumulative impacts of global and local

stressors. Ecological modelling can assist managers in this process by identifying the relative

importance of different management goals (Box 3.1).

Manage adaptively. A key issue for implementation of broader measures to build reef

resilience is the limited information available. Current understanding of the factors that

confer resilience is based largely on scientific principles, rather than empirical studies. The

importance of maintaining high coral cover, abundant herbivore populations and good water

quality in promoting resilience is widely acknowledged (see Section 4.2.3).Yet, the complexity

of the ecosystem and the state of scientific knowledge mean that managers must continue

to make pragmatic decisions and implement management actions in an environment of

considerable uncertainty.

The adaptive management approach provides a valuable

framework for active management in the face of

uncertainty40, 78. It may be particularly appropriate in the

context of coral bleaching where there is a strong

imperative to respond to a highly visual event despite the

absence of complete knowledge. Adaptive management

recognises that management actions can be taken in a

hypothesis-driven framework where management is an

iterative learning exercise rather than a 'solution' to a well understood problem. Reflecting on

what has been learned at each stage of the management process provides insights about how

future management actions can be refined or 'adapted'. Adaptive management can also be

helpful in fostering innovation and collaboration in management, attributes that are likely to

accelerate progress in identifying productive approaches to future management in the

context of mass coral bleaching.

Taking an adaptive management

approach to managing reefs in th

context of climate change can he

foster innovation and collaborati

in management that accelerates

progress in identifying productive

future strategies
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

92

Box 3.1 Using models in coral reef management 

The processes driving coral reefs occur on a wide range of spatial and temporal scales.

Given the complexity of such systems, there is an increasing need to use models to answer

some of the questions posed by managers. For example, an empirical study is unlikely to

deliver a prompt answer to the question, 'What level of fishing pressure can be tolerated

given scenarios of increasing sea temperature and cyclone activity?'. However, in

constructing answers, models can be a powerful asset when used in combination with

good empirical data.

Models have two main uses in science. First, they help us understand the relative

importance of single factors in the dynamics of complex systems (sensitivity analysis).The

modeller may create a simplified version of the reef and then test the plausibility of

alternative scientific explanations, or the relative effectiveness of different management

scenarios. For example, managers may use a model to investigate how changing one

condition (for example the abundance of herbivores) can influence the rate of recovery on

a reef impacted by coral bleaching. Moreover, a variety of factors can be modified in

tandem to investigate whether certain combinations affect the reef's recovery more than

others do. These models can identify critical aspects of the ecosystem that

disproportionately influence reef resilience. Managers can then consider how to reduce

stress at these critical parts of the system.

The second use of models is that of prediction. For example, given our present ecological

understanding of scenarios for future climates, what percentage coral cover will be found

on local reefs in 2050? Although models based on ecological data can be used for

prediction, there are many scale issues to consider. For example, it is difficult to reconcile

the impact of a warming climate with the daily foraging of parrotfishes within a single

model.Therefore, different types of models are appropriate for different questions, and an

optimal solution would use a range of inter-connected models at different scales. In

general, predictive models need a firm basis in probability so that the confidence in the

predictions is made abundantly clear.

Modelling the conditions on reefs in relation to coral bleaching and management strategies

is a very active, but relatively new, area of research.Whilst a number of groups are working

on various models, few results have yet been published. The paper by Woodridge et al

(2005)47 illustrates the potential of modelling to support resilience-based management in

the context of coral bleaching. Further information can be found from individual research

groups including AIMS Reef Futures (www.aims.gov.au/reeffutures), the Marine Spatial

Ecology Lab (www.ex.ac.uk/msel) and the National Centre for Caribbean Coral Reef

Research (NCORE, www.ncoremiami.org).
BUILDING LONG-TERM REEF RESILIENCE

93

3.5 Reef restoration strategies

Recent worldwide reports of reef damage due to mass bleaching events, combined with

projections of future warming trends, indicate that reef managers should expect reefs to

continue to deteriorate5, 9. Although the natural resilience of reef ecosystems will facilitate

recolonisation and subsequent recovery of sites that suffer significant coral mortality, full

recovery to pre-disturbance coral cover and diversity can be an extended process, requiring

many years, and usually many decades133,134.The recovery process can be further lengthened,

and even inhibited, if the natural resilience of the reef ecosystem has been eroded through

other pressures, such as excess nutrients or sediments, habitat damage or over-harvesting of

key functional groups88, 93.

In some instances, following severe bleaching-related coral

mortality, reef managers may wish to consider proposals

to assist or accelerate natural recovery processes through

active restoration. Many techniques come under the

banner of reef restoration. Some of these techniques are

only appropriate in very specific circumstances. Care must

be taken to use only those techniques appropriate to the

reef in question and to the nature of the disturbance that

has affected it.

The logistics, costs and effectiveness of restoration activities as well as any legal considerations

should be carefully examined before deciding on a course of action94. Cost-effective

approaches and technologies are still in the early stages of development, and, in most cases, are

currently not viable for implementation on large spatial scales. Given the extreme cost of some

of the techniques, especially coral transplantation, careful consideration is needed when

deciding whether to use available funds for restoration of a small area or for initiatives with

broader influence, such as education and preventative measures.

The diversity and scale of experimental restoration approaches used to date vary widely94.They

cover habitat modification, coral transplantation, species re-introduction and enhancement of

recruitment. Some of these interventions involve large-scale, sub-tidal structures designed to

facilitate natural colonisation of reef-related species95-97, while others use simpler and less costly

approaches that are more readily replicated98-100. The following sections examine restoration

issues in detail.

3.5.1 Considerations for reef restoration strategies

Several overarching considerations are central in deciding whether to pursue restoration

strategies.These include: Is restoration the best use of limited resources? Will restoration

efforts endure in the long-term, given the expected recurrence of bleaching? Will

restoration efforts be effective under the current and expected regime of other stresses?

Is there legal or socioeconomic justification for the undertaking of restoration? This section

examines these issues in more detail with the aim of assisting managers to make decisions

on the use of restoration measures in response to coral bleaching events.

In some instances, following seve

bleaching-related coral mortality

managers may wish to consider

assisting natural recovery throug

active restoration
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

94

Is restoration the best use of resources? Restoration of

coral reefs is an extremely expensive exercise101. For

example, the costs for extensive restoration efforts

following ship groundings have ranged from US$10 000

to an estimated US$6.5 million per hectare102. If there is

no need to repair structural damage, and only coral

transplantations are carried out, the costs can be much lower. However, even in these

situations, it is likely to cost tens of thousand of dollars per hectare just to achieve a realistic

target of 10 per cent coral replacement cover103. Furthermore, these costs are based on

trials in which only a few fast-growing genera, with high aesthetic values and fast growth

rates (such as Acropora and Pocillopora) were used103-105.

In light of the immense costs that are involved in coral transplantation, the ethics and

appropriateness of spending resources for such small-scale projects must also be

considered.The largest coral transplantation projects carried out to date involved an area

of 7.1 hectares, which highlights the limited scale over which transplantation techniques can

be applied. A relatively cost-effective approach using rock piles has been recently

demonstrated in Komodo (Indonesia) over a six hectare area, suggesting potential for

rehabilitation of larger areas106.Yet, these spatial scales are still extremely small compared

with the scale of damage that can result from mass bleaching events. Nevertheless,

restoration strategies may continue to be appropriate for small sites of high value, such as

significant tourist destinations. Even in these circumstances, however, managers will want to

be sure that restoration efforts will result in lasting improvements.

Will restoration efforts endure? Even if funding and technical constraints were to be

overcome, investment in coral reef restoration efforts will be wasted if chronic stresses that

could be exacerbating coral mortality or hindering recovery are not managed. Mass coral

bleaching is expected to be a recurrent phenomenon over coming decades, making it

probable that restored sites will, in the near future, suffer a similar disturbance to that which

motivated the restoration effort.Two approaches can be adopted, both based on current

understandings of restoration and specifically addressing degradation caused by bleaching.

For reefs that have survived past bleaching events, restoration can target the enhancement

of resilience by promoting biodiversity. For reefs with a poor recovery record from

bleaching, restoration should aim at promoting growth of tolerant species and providing

shading against increased solar radiation.

Will restoration efforts be effective? Numerous experiments and case studies of reef

restoration indicate the difficulty in achieving restoration success. Technical and financial

constraints force a bias toward fast-growing coral genera in restoration projects, making it

very unlikely that direct restoration will restore the impacted resource to a level that is

functionally equivalent to pre-disturbance conditions. Furthermore, the survivability of

transplanted corals is variable and subject to many factors beyond human control, leading

to uncertain ecological outcomes.

Before implementing restoration,

managers should evaluate whether

selected strategies will be costeffective, endure in the long-term and

are able to achieve desired results 
BUILDING LONG-TERM REEF RESILIENCE

95

3.5.2 Restoration methods

Direct, site-based restoration efforts that might be contemplated in response to bleachinginduced mortality can be divided into three main categories: coral transplantation, 'seeding'

with coral larvae and reinstatement of herbivores.The potential benefits and limitations of

each of these are discussed below.

Coral transplantation. An examination of case studies demonstrates that most aspects of coral

reef restoration, coral transplantation in particular, are still at an experimental stage. The

limited-scale projects implemented to date demonstrate clearly that coral transplantation is

a very costly exercise, with uncertain ecological outcomes103,104. In fact, coral transplantation

introduces the risk of adverse outcomes, such as shifts in community structure, the transfer

or introduction of diseases, or interference with the natural gene flow, and impacts on the

donor colony or reef105. Harm to existing corals and reefs can be minimised by using in situ

coral mariculture to supply transplantation operations with corals adapted to natural reef

conditions. The viability of in situ nurseries107 has been demonstrated with propagation of

loosely-scattered colonies in a sheltered, lagoon-like reef area108. Yet, even at small spatial

scales, the costs and benefits of coral transplantation require careful consideration before it

is used for reef management purposes. Over spatial scales normally affected by mass coral

bleaching events, coral transplantation is extremely unlikely to be financially viable.

In summary, coral transplantation should be viewed as a strategy of last resort, and should

only be undertaken at small, high value sites where there is strong justification for

accelerating natural recovery processes. If natural recovery is hindered by other stresses,

such as poor water quality or excessive algal growth, management efforts should be

prioritised to address these issues before investment is made in coral transplantation.

Coral 'seeding'. An alternative method to transplanting adult colonies to accelerate recovery

is 'coral seeding'.This technique involves collecting larval slicks from broadcast spawners for

direct transfer to an impoverished site, or 'staging' the slicks in protected habitats to allow

larvae to settle before transferring to the target site109. Coral larvae may also be reared

under laboratory conditions until they are competent to settle, and then released into

eddies associated with target reefs. Larval retention times of 1-3 weeks inside eddies are

believed to promote enhanced local settlement. Although untested, proponents of this

technique have suggested that coral seeding will result in regeneration rates of possibly two

orders of magnitude higher than can be achieved by transplantation efforts109.

Several concerns are relevant to coral seeding as a restoration technique.The method has

not been widely tested, so its effectiveness in different circumstances is not well known.The

practicalities of the method, especially in relation to costs, logistical requirements and

expertise have not been explored for a range of settings. The ability of seeding to assist

recovery to full (pre-disturbance) species diversity is not known, but is likely to be

significantly limited. Furthermore, in most situations, damaged reefs will be supplied with

natural sources of coral larvae from upstream source reefs, particularly when management

schemes promote habitat connectivity. Coral seeding is only likely to be warranted in

situations where a reef is very remote or has only limited connections with upstream

sources of larvae.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

96

In summary, coral seeding techniques are still largely in the developmental stage, and

present many of the concerns and limitations associated with coral transplantation.

However, with further development and in some limited circumstances, they may prove to

be a more cost-effective method for increasing recovery at defined sites109.

Reinstate herbivores. In some situations, natural recovery of reefs following bleachinginduced mortality may be hindered by excessive growth of filamentous or fleshy algae45. On

many reefs, over-harvesting of herbivores, especially fishes, can lead to excessive algal

growth42. This, in turn, results in reduced availability of the bare substrate required for

settlement of coral larvae.

While the effects of reduced herbivory may not be obvious in an intact coral community,

the effects of low recruitment rates resulting from excessive algal growth may be severe

following a major disturbance such as bleaching-induced mortality44. Although the overharvesting of herbivores from a coral reef system should be of concern to reef managers

for a diversity of reasons, the effects of a coral bleaching event can dramatically increase the

urgency of efforts to address this problem11.

Widespread mortality of corals should trigger renewed efforts to prevent further,

unsustainable, removal of herbivores from the system. This could entail greater limits on

fishing activities or increased penalties for non-compliance with fishing restrictions.

However, in situations where herbivore populations are already depressed due to heavy

harvesting, passive management (such as the removal of fishing pressure) may not be

enough to ensure herbivore populations recover. This is particularly relevant in locations

where reef recovery is limited by excessive algal growth caused by chronically depressed

herbivory levels. In these cases, managers may need to consider active reinstatement of

herbivore populations.This might require captive rearing of herbivores, or perhaps methods

of enhancing reproduction and recruitment of key herbivore species. Importantly,

techniques of actively restoring herbivore populations remain to be tested, and the

feasibility of this method requires further investigation.
CORAL BLEACHING –

A REVIEW OF THE CAUSES

AND CONSEQUENCES
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

98

4. CORAL BLEACHING – A REVIEW OF THE

CAUSES AND CONSEQUENCES

The mass coral bleaching events that have occurred throughout the tropics over the last

decade have provided unprecedented opportunity, and motivation, to study this

phenomenon.As a result, knowledge about the causes and consequences of coral bleaching

has increased substantially in recent years. This accumulating body of information is

providing critical advances in our understanding and has generated new insights, which can

assist reef managers to respond to the threat of coral bleaching. This section aims to

provide a summary of recent developments in the science of coral bleaching, highlighting

emerging knowledge and recent insights that are most relevant to reef managers.

4.1 What is coral bleaching?

4.1.1 The coral-algal symbiosis

The great majority of corals live in a symbiotic relationship

with zooxanthellae, a type of single-celled dinoflagellate

algae.These microscopic algae live within the coral's tissues.

Zooxanthellae produce energy-rich compounds through

photosynthesis, providing a food source that is absorbed and

used by the coral. In general, corals are highly dependent on

this symbiotic relationship, receiving up to 90 per cent of

their energy requirements in this way17.

Bleaching is a stress response that results when the coralalgae relationship breaks down. The term 'bleaching'

describes the loss of colour that results when zooxanthellae

are expelled from the coral hosts or when pigments within

the algae are degraded. Because the photosynthetic pigments found in zooxanthellae give

corals most of their colouration, the loss of zooxanthellae renders the tissue largely

transparent.The white of the calcium carbonate skeleton is then clearly visible through the

un-pigmented tissue, making the coral appear bright white or 'bleached'24. Bleaching also

occurs in other animals that are engaged in symbiotic relationships with zooxanthellae, such

as foraminifera, sponges, anemones and giant clams.

In some instances, coral bleaching will result in corals

taking on a pastel shade of blue, yellow or pink rather

than turning bright white. This is due to proteins

produced by some corals, which tint the coral tissue and

become the dominant pigment during bleaching, when

zooxanthellae are absent110, 111.

Bleaching is a stress response that

results when the coral-algae

relationship breaks down

The zooxanthellae can be clearly

seen as golden-coloured dots in

this close-up image of a coral

polyp.The symbiotic relationship

with these tiny dinoflagellates

enables corals to gain energy

from sunlight

© Kirsten Michalek-Wagner
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

99

It isn't only corals that bleach; other organisms that have zooxanthallae, such as this (a) giant clam and (b)

anemone can also bleach in response to thermal stress

a b

4.1.2 The causes of coral bleaching

The primary cause of mass coral bleaching is increased

sea temperatures9,13, 18, 23, 53.At a local scale, many stressors

including disease, sedimentation, cyanide fishing,

pollutants and changes in salinity may cause corals to

bleach. Mass bleaching, however, affects reefs at regional

to global scales and cannot be explained solely by localised stressors operating at small

scales. Rather, a continuously expanding body of scientific evidence indicates that such mass

bleaching events are closely associated with large-scale, anomalously high sea surface

temperatures8, 9, 13.Temperature increases of only 1-2oC can trigger mass bleaching events

because corals already live close to their maximum thermal limits9, 23.

The role of temperature and light. Increased temperatures cause bleaching by reducing the

ability of the photosynthetic system in the zooxanthellae to process light. When

temperatures exceed certain thresholds, incoming light overwhelms the photosynthetic

apparatus, resulting in the production of reactive oxygen species that damage cellular

structures24, 112. Corals cannot tolerate high levels of these toxic molecules, and they must

expel the zooxanthellae to avoid tissue damage. Because of the low tolerance of the

photosynthetic process to high temperatures, even normal levels of sunlight are enough to

damage the photosynthetic system of the zooxanthellae when temperatures exceed

certain levels23, 113. Furthermore, as light levels increase the amount of damage due to

thermal stress increases as well24.

The relationship between temperature and light in

causing coral bleaching helps explain observations of

reduced bleaching on shaded parts of coral colonies or

in shaded reef areas9, 114, 115. It also suggests that the spatial

extent and patterns of bleaching responses may be

influenced by factors that determine the amount of solar radiation to which corals are

exposed. These factors might include cloud cover46, attenuation in the water column116,

stratospheric ozone18 and shading by large landforms such as steep-sided shorelines39.

Mass coral bleaching affects reef

regional to global scales – it is

primarily caused by unusually hig

sea temperatures

Bleaching is reduced in shaded re

areas because light levels influenc

the amount of damage caused by

temperature stress
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

100

Natural variations in turbidity may also play an important role in determining bleaching risk.

A recent study of the patterns in underwater light levels on a coastal coral reef found that

there were periodic intervals of low light levels due to cloud cover and sediment resuspension (high turbidity), which were driven by large-scale pressure systems117. Such

natural variability has strong implications for bleaching risk, and knowledge of these factors

can be used to prioritise management effort to other factors that are amenable to

management intervention.

4.2 Factors that confer resilience to coral bleaching 

Resilience to bleaching is determined by the outcome of three key aspects of the bleaching

process: resistance to bleaching, ability to survive the bleached state (tolerance) and rate of

reef recovery after coral mortality. Understanding the factors that influence each of these

steps is central to our ability to understand, and potentially manage, the factors that confer

resilience to bleaching on corals.

4.2.1 Factors that influence resistance

The variability that characterises bleaching events points

to an important fact: individual corals vary in their

responses to heat and light stress.Variability in bleaching

response has been observed within individual coral

colonies, among colonies of the same species, and

between colonies of different species23,118. These

taxonomic variations are further compounded by

spatial patterns, with corals of the same species often showing different bleaching responses

at different locations18, 19, 79, 118. These patterns have been observed at scales ranging from

metres to thousands of kilometres. Knowledge of the factors, both external and intrinsic to

individual corals, that determine whether corals bleach is an important basis for

management actions in response to the threat of bleaching. Better understanding these

factors is the central aim of an integrated research strategy being taken in the US territory

of American Samoa as a management response to climate change (case study 9).

External factors. Externally, there is considerable variation in the environmental conditions

experienced by coral colonies. This variation creates critical differences in exposure to

heat, light or other stressors, leading to many of the patterns seen in bleaching responses.

Some of this patchiness can be attributed to patterns in sea surface temperatures,

especially at larger spatial scales49. Regional and local differences in weather can also cause

differential heating of the water, while proximity to upwelling of cooler waters, mixing by

currents and other large-scale processes can help keep temperatures below local

bleaching thresholds. At smaller scales, the microenvironment of corals can also vary.

Water currents and flow regimes increase water movement around corals, helping them

to get rid of metabolic waste and toxic molecules74, thereby potentially reducing their

susceptibility to thermal stress.

Understanding the factors that

determine variation in bleaching

response of corals exposed to

temperature stress provides an

important basis for management

actions in responding to the threat of

bleaching
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

101

Box 4.1 Coral taxa and resistance to mass bleaching 

Bleaching resistance is highly variable among corals, as evidenced by the extremely

variable responses of coral species to thermal stress. While some corals will show visible

signs of bleaching after only one or two weeks at temperatures 1.5oC above the normal

maximum, others at the same location will not bleach unless these temperatures persist

for more than four to six weeks.

A strong hierarchy of resistance can be detected in diverse coral assemblages, such as

those in the western Pacific and Indian Oceans80 (Figure 4.1).Typically, fine-structured and

fast-growing corals with thin tissue and good connections between polyps tend to be the

most susceptible to bleaching. Tissue thickness has been shown to correlate with

susceptibility to bleaching123, 124, although the role and relative importance of these various

traits remain to be thoroughly explored.

Common examples of corals with low resistance are the pocilloporids and many

acroporids (especially the branching and tabular growth forms), as well as the hydrocoral

millepora. Species that are more resistant tend to be characterised by solid, massive

skeletons, with thick tissue and slow growth rates, such as porites, faviids, and mussids.

Interestingly, some of the species most often associated with inshore or turbid reef systems

are among the most resistant to bleaching, such as turbinaria125. RESISTANCE

GROWTH FORM

Fine branching

Branching, tabulate,

encrusting/foliose

Acropora

Montipora

CORAL FAMILY EXAMPLES

HIGH

LOW

MEDIUM

Pocilloporidae Seriatopora

Stylophora

Pocillopora

Acroporidae

Massive, brain Favia

Favities

Leptoria

Goniastrea

Platygyra

Faviidae

Massive, boulder Porites

Goniopora

Poritidae

Various Turbinaria

Cyphastrea

Various

Figure 4.1 A generalised hierarchy of coral susceptibility to bleaching

Corals vary in their susceptibility to bleaching. While many factors influence bleaching resistance, the

growth form or family of a coral provides a rough but reliable indication of its susceptibility to heat stress.
An integrated research strategy to assist 

management responses to climate change – American

Samoa

Identifying the need for research

Resource managers increasingly struggle to determine local level responses to climate change.

In the US territory of American Samoa, coral reef managers and scientists have identified climate

change as a key and imminent threat to the health of the islands' fringing reef system. Physical

dangers posed by wave action due to coral loss, increased or decreased rainfall, phase and

community shifts on reefs, and sea level rise are just a few of the things that reef managers and

policy-makers may have to contend with in coming years at this location. Residents of American

Samoa have relied on the reef ecosystem for protection, food, goods and services for millennia.

However, they are likely to face severe disruptions to lifestyle, public health hazards, and a

decreased ability to be self-supportive if projected increases in the frequency and severity of

bleaching eventuate.

In response, local policy-makers are facilitating climate-related research around the islands of

American Samoa. It is hoped that data derived from these projects will give managers options

for site-specific protection measures, such as Marine Protected Areas, targeted reductions in

location-specific land-based sources of pollution, restrictions on use, and even, if appropriate,

artificial propagation of coral.

Ofu Island – a laboratory in the field

The most notable of the recent research

initiatives within American Samoa is being

conducted in the lagoonal system along the

south shore of Ofu Island.This area is the focus

of research aimed at determining whether

some of the coral species residing there have

adapted to bleaching stresses.The hydrography

of the lagoon ensures that there is little, if any,

flushing during low tides. It is during these times

that temperatures and ultraviolet radiation

(UV) around shallow water corals increase

dramatically. The extreme temperature ranges

that corals in Ofu can withstand on a regular basis indicate that this site may be a natural climate

refuge164. The warmer water temperatures projected to accompany climate change are likely to

result in calmer, clear water (due to stratification and the loss of UV blocking compounds in the

water column itself). Knowledge about the characteristics that confer stress resistance to corals

of Ofu lagoon can thus be used to understand the features that will help corals survive future

thermal stress events in more open reef habitats.

Research projects

Four research projects have been developed by American Samoa in conjunction with various

partners. In combination, they will provide valuable insights to guide management efforts aimed

at helping American Samoan reefs survive future coral bleaching events.

CASE STUDY 9

Ofu Island in American Samoa

© Chris Hawkins
Are some corals better prepared for climate change? MMA concentrations in Ofu lagoon corals

(WWF /Emerald Coast Consulting).

This study examines the microsporine-like amino acid (MAA) concentrations in corals in the

lagoons and near-shore (cooler, deeper) reefs of Ofu. Microsporine-like amino acids act as a kind

of sunscreen, protecting corals from damaging UV light. Coral nubs are being collected from a

combination of species found in all lagoons and paired with samples of the same species from

outside of the lagoons, as well as from species only found in some lagoons.These samples will

be compared to determine whether their history has imparted some selective advantage in

terms of their capacity to deal with the thermal stress associated with future climate scenarios.

Nearshore hydrodynamic modeling for Marine Protected Areas (MPAs) in American Samoa

(Eric Treml and Patrick Halpin, Duke University)

This research uses a spatially explicit, hydrodynamic modelling approach to address high-priority

MPA management issues, such as coral bleaching, land-based sources of pollution, and overfishing. The aim is to identify connections among the design of MPAs, long-term monitoring

methods and the local needs of American Samoa. Working closely with the local marine

management community, this research will result in the development of spatial management

strategies and tools for coral reef protection and MPA site development.

Coral disease prevalence on the reefs of American Samoa 

(Greta Aeby, Hawaii Department of Land and Natural Resources)

This study addresses issues related to coral disease, coral bleaching and pollution and works to

examine the relationships between water quality, coral bleaching and the susceptibility of

organisms to disease.The goals of the research are to: (a) conduct a baseline assessment of the

abundance and distribution of bleached and diseased corals and of crustose coralline algae at

sites throughout American Samoa; (b) correlate the incidence of bleached and diseased colonies

with environmental data, and (c) systematically describe gross and microscopic morphology of

lesions in corals and crustose coralline algae. This work will help to develop a standardised

nomenclature for identifying and classifying diseases.This is a particularly important task as the

frequency of disease is expected to increase due to climate change and increases in land-based

sources of pollution in reef areas worldwide27.

Extrinsic and intrinsic factors affecting the resilience of corals to climate change and their use in

designing marine reserve networks (Charles Birkeland, University of Hawaii)

This three-year study aims to determine the intrinsic and extrinsic factors that enhance the

ability of a diverse set of corals (approximately 100 species) to resist environmental stressors,

such as extreme upper temperature limits, temperature fluctuations, and low and high levels of

dissolved oxygen. Intrinsic factors include: zooxanthellae types, microbial community

composition, microsporine-like amino acid levels and genetic traits. Understanding these factors,

and their relevance, will improve knowledge of ecosystem response to environmental factors,

and of how future environmental conditions may affect community structure and functions. Such

information will ultimately inform managers and scientists designing Marine Protected Areas and

similar conservation strategies.

For more information contact:

Chris Hawkins

University of Massachusetts at Amherst

hawkins@frwild.umass.edu
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

104

Other stresses in the external environment of corals can also have an affect on their

susceptibility to thermal stress. Preliminary research indicates that synergies between

temperature and other stressors, such as pollution, turbidity and sedimentation, changes in

salinity or exposure to pathogens, may interact to trigger or exacerbate bleaching41.The role

of pathogens in localised bleaching may also warrant further consideration, as recent

studies have demonstrated the induction of bleaching by bacteria in certain corals from the

Mediterranean and Red Seas119, 120. Further investigation of these issues, and confirmation of

key mechanisms driving synergistic effects involving coral bleaching, have the potential to

reveal opportunities for management interventions that could reduce bleaching impacts.

Internal factors. Intrinsically, both the genetic identity and the history of coral colonies and

their zooxanthellae can contribute to variation in bleaching susceptibility23, 121.This may be

observable in individual colonies, or the effect may be observable in the bleaching

susceptibility of entire reef communities122. At the colony level, species characterised by

branching or tabular growth forms and thin or well-connected tissue, tend to bleach more

than species with massive growth forms and thicker or less-integrated tissues (see Box 4.1).

Thicker tissue may shade zooxanthellae and increase resistance to bleaching9, 123.The ranking

of common coral groups by bleaching susceptibility is remarkably consistent between sites

on opposite sides of the world, suggesting that the properties of the animal host (above

and beyond differences in zooxanthellae type) play an important role in determining the

response of corals to thermal stress80.

The intrinsic characteristics of corals that enable them to

adjust to elevated light levels also play a role in

determining their resistance to bleaching. Coral polyps

that have experienced higher light levels have been

shown to be more resistant to bleaching when exposed

to high water temperatures115, suggesting that corals

acclimatised to high light will be less likely to bleach in

response to thermal stress. This implies that corals that

have experienced (and survived) extreme environmental

conditions in the recent past may be more resistant to

bleaching stress in the future. However, the effects of

historical exposure to light are subtle, and acclimatisation

is unlikely to allow corals to withstand the large

temperature anomalies that have triggered recent mass

bleaching episodes23.

Genetic variation in zooxanthellae is another intrinsic

characteristic that could influence the bleaching

resistance of corals (Box 4.2). Differences in thermal

tolerance among varieties, or clades, of zooxanthellae

suggest that coral hosts that have high densities of heattolerant algae may be less susceptible to coral bleaching126. Shifts toward more heattolerant populations of corals or zooxanthellae can be expected to arise from selective

mortality of more sensitive genotypes during severe bleaching events. However, corals

Genetic variation among individual

zooxanthallae (shown here)

influences the resistance of corals to

heat stress and bleaching. Although

corals may be able to shift the

relative dominance of different

varieties of zooxanthallae within

their tissues in order to increase

their resistance to bleaching, there

are limits to the extent that corals

can use this strategy to acclimatise

to large temperature anomalies

© Ove Hoegh-Guldberg
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

105

may also be capable of forming new symbioses with more tolerant zooxanthellae in

response to changing temperature regimes (the Adaptive Bleaching Hypothesis)127; this

possibility remains the focus of ongoing research and discussion (for example, HoeghGuldberg et al (2002)113).

4.2.2 Factors that influence survival

Bleached corals are still living, and if temperature stress subsides soon enough, most are

capable of surviving the bleaching event and repopulating their tissues with zooxanthellae.

The mechanism by which corals regain their symbiotic algae probably varies among species.

It may occur through uptake of new zooxanthellae from

the water column, although the most likely process is

multiplication of surviving zooxanthellae that remain in

the bleached coral's tissues at very low levels. Even a

coral that appears much bleached to the human eye can

still retain as many as 100-1000 cells per cm2 (normal

densities are 1-2 x 106 per cm2

)

130.

Corals that survive bleaching even

are still likely to suffer sub-lethal

impacts, such as reduced rates o

growth and reproduction and

increased susceptibility to diseas

Box 4.2 Zooxanthellae and resistance to mass bleaching

A characteristic that appears to be important in determining resistance of corals to bleaching

is the type of zooxanthellae hosted.Numerous different types,or clades,of zooxanthellae have

been recognised,and there is some evidence that they have different susceptibilities to thermal

stress128. Many corals have multiple varieties of zooxanthellae within their tissue, and the

relative proportion of the different varieties is variable.A recent experiment has revealed that

some corals can vary the ratio of zooxanthellae clades, with a resulting improvement of their

thermal tolerance129.This feature is akin to acclimatisation as it involves the use of pre-existing

strategies within the coral-zooxanthellae association. If bleaching events increase in both

severity and frequency in the future, this may play a small role in determining bleaching

response patterns on larger spatial scales.As with other examples of acclimatisation, there is

a limit to the extent that corals can use this strategy to shift their thermal tolerance.

Another possible mechanism by which corals could increase their thermal tolerance is to swap

their zooxanthellae for more resistant varieties127.While this idea continues to be debated113,

it seems increasingly likely that changes in zooxanthellae populations are most likely to occur

through shifts in the relative dominance of heat-tolerant varieties already within a coral's

tissues, rather than by taking on new varieties.The potential for corals to adopt new varieties

of zooxanthellae remains an area of active research.

The role of coral pigments in sheltering zooxanthellae from light stress is another area of active

research that could help explain some of the differences in bleaching resistance110, 111.

Fluorescent pigment granules (FPGs) are common in many corals, at least in the western

Pacific. They are positioned within the coral's tissue to optimise the light environment for

zooxanthellae, concentrating light in low-light habitats, and shielding zooxanthellae in high light

conditions. In this way, corals with high concentrations of FPGs may be less vulnerable to

bleaching when water temperatures reach stressful levels.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

106

Corals that survive bleaching events can still suffer significant impacts. Reproduction of

corals that have bleached and recovered, for example, is much lower than that of corals

that have not bleached26, 114, 131. Growth of bleached corals is also reduced, probably due to

the combined effects of the stress and the reduced supply of energy following decreased

zooxanthellae densities25. Bleached corals may also have reduced immunity to pathogens,

making them more susceptible to disease27.

The condition, or health, of individual coral colonies is emerging as a particularly important

factor in determining whether or not a bleached coral survives. Recent and ongoing studies

predict that coral condition (as determined by its energy status or the size of its lipid stores)

will affect mortality risk during and following a bleaching event41. Specifically, large energy

stores are likely to help a coral survive the period of starvation associated with depleted

zooxanthellae populations. With adequate energy stores, a healthy coral will be able to

maintain itself while bleached, until zooxanthellae populations and photosynthesis can be

restored. Similarly, coral species that rely more heavily on heterotrophy (feeding on organic

material from the water column) for their energy supply132, such as those on coastal reefs,

are also more likely to be able to tolerate the loss of zooxanthellae.

Box 4.3 How managers can help corals survive bleaching 

While extreme temperature stress is almost certain to result in widespread coral mortality,

the effects of more moderate temperature anomalies are highly variable. When

temperatures do not greatly exceed bleaching thresholds, the coral loses its zooxanthellae,

but its tissue may not be directly damaged. Whether mortality follows bleaching in these

circumstances is thought to be largely dependent on the coral's ability to endure

starvation, or to supplement its energy requirements from food particles captured from the

water column (heterotrophy).

© Christian Perthen

Without their energy-providing zooxanthallae, bleached corals essentially enter a period of starvation.

The condition of a coral as it enters this state is an important factor determining whether the coral can

survive a bleaching-induced 'famine'. Another factor influencing coral survival during bleaching is the

coral's ability to feed on plankton and other organic matter in the water column by using its feeding

tentacles, as shown here
107

Some corals, especially species adapted to turbid environments, have been shown to rely

heavily on heterotrophy. These corals may be less dependent on the energy provided by

their zooxanthellae and thus less prone to starvation during a bleaching event.While the

importance of heterotrophy to turbid-water corals has been demonstrated132, its role in

helping corals to survive bleaching requires further study. A better understanding of this

issue may help managers identify coral communities that are at reduced risk of mortality

from coral bleaching.

Coral health prior to exposure to heat stress may be the most important factor influencing

colony survivorship during bleaching events. Most corals rely very heavily on the energy

provided by their zooxanthellae, and bleaching effectively robs them of their main energy

source.As a result, corals in the bleached state are beginning to starve, and their ability to

endure this hardship is likely to be important in determining whether they survive. Like

many animals, corals store surplus energy as lipids (fats). Corals in good condition will have

relatively high lipid levels, endowing them with a buffer against periods of low energy

supply. For this reason, it is thought that the condition of a coral at the time it bleaches

may play a key role in determining whether it will be able to survive the period of

starvation that follows. This implies that chronic stresses, such as water pollution or

increased turbidity, which can negatively affect a coral's condition, could increase the risk

of corals dying from the acute stress caused by bleaching. While these ideas have only

recently begun to be examined for corals41, they suggest that coral health should be

considered as a priority focus for reef managers wanting to increase coral survival during

moderate coral bleaching events.

4.2.3 Factors that influence recovery

Significant recovery can occur in only two to three years if mortality is minor (when there

is an abundance of colonies that completely or partially survive the bleaching event).

However, recovery of coral communities following severe mortality is likely to take much

longer5, 133, 134. This is because reef recovery is a complex process influenced by multiple,

interacting factors. On severely damaged reefs, recovery is dependent on the arrival of

suitable coral larvae that have survived the bleaching event elsewhere, and their successful

settlement, survival and growth134. Even assuming conditions favour recruitment, the

recovery process is subject to the vagaries of larval supply and the many risks that confront

the young coral, such as predation, smothering by sediments or algae, overgrowth by other

corals, etc. In combination, these uncertainties mean that recovery of a site to an

abundance, density and diversity of corals comparable to pre-bleaching conditions is a longterm prospect measured in terms of decades133, 134.

A particularly sensitive step in the recovery process is larval recruitment.The production,

settlement and survival of coral larvae is dependent on the availability of 'source' reefs to

provide new larvae, good water quality to promote spawning, fertilisation and larval

development, and suitable substrate for settlement and survival of coral larvae45, 134.

CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

108

Degraded water quality can affect the fertilisation success of corals72, 135, 136, potentially placing

severe limitations on the ability of coral communities to recover after bleaching-induced

mortality. Water quality can also have a negative impact on recovery by encouraging algal

growth, which in turn can reduce larval recruitment44, 45. Coral mortality allows an opening

for frondose (leaf-like) and filamentous macroalgae ('seaweeds') to take on a more

dominant role in reef ecosystems, often at the expense of coral recruitment42, 45, 137. This

window of opportunity for algae following mortality events such as those associated with

severe coral bleaching events means that the influence of nutrients in accelerating growth

is more pronounced.

The abundance of herbivorous fish populations is another

critical factor influencing the success of recovery processes.

In situations where herbivores have been heavily depleted

through a combination of overfishing and disease, recovery

of coral communities following disturbance has been greatly

lengthened, or even stalled, resulting in a persistent shift

from coral-dominated to algal-dominated reef for over a

decade82, 138.

Recovery can be even further compromised on reefs that

are threatened by both degraded water quality and

depleted herbivore populations. Increased nutrient levels

greatly increase the potential for the excessive growth of

algae that can occur when herbivory is reduced. Water

quality and herbivore populations are each important, but

in combination they become critical in determining the

coral-algae balance after a disturbance42, 45.

© Paul Marshall

a b

Recovery of severely damaged

reefs is dependent on 'source'

reefs to provide new larvae, good

water quality, and suitable

substrate.Where these

conditions exist, new corals can

settle and become established

relatively quickly

Reef recovery after severe coral mortality is a complex process influenced by multiple, interacting factors.These

reefs in Palau demonstrate significant differences in their ability to recover. Both were severely affected by mass

bleaching in 1998. Seven years after the event, only (a) minimal recovery is evident in one reef, while the (b)

other has shown dramatic recovery of coral cover

© Paul Marshall
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

109

© Yusri Yusuf

© James Oliver

The importance of local processes highlights the pivotal role that effective management of

local stressors can have in supporting the ability of reefs to recover from mortality

associated with severe coral bleaching. In keeping with the example above, algal growth and

herbivory could be optimised by limiting water pollution and fishing pressure. Furthermore,

recent studies suggest that the 'source' of coral recruits is often from within the same or

nearby reefs.Together, these insights emphasise the importance of managing local stressors

when aiming to support the natural ability of reefs to recover from global stressors like

bleaching events11.

4.3 Can corals adapt to climate change?

The impact of mass coral bleaching on coral reef ecosystems over the long term will

depend on the environmental changes that occur in tropical seas, the extent to which

corals can acclimatise or adapt to changing conditions, and the ways in which repeat

disturbances compound one another to shape coral reef ecosystems.

4.3.1 Future climates

Coral reefs are currently experiencing temperature regimes that exceed any they have

experienced over at least the last 400 000 years28. Projections of temperature increases

suggest that conditions will develop that are vastly different to those in which the majority

of coral reefs have developed over the same time frame11.

Global ocean temperature has increased by an estimated 0.6oC between the mid-1950s

and mid-1990s. Some studies predict future increases in global sea temperatures of 1.4-

5.8oC by 21008, suggesting that mass bleaching events, which may be induced at only 1-2oC

above normal summer temperatures, are likely to be a much more frequent phenomenon

in the future9, 13, 28.

Herbivores, such as grazing fishes, play a key role in

maintaining the conditions that are required for the

recovery of reefs damaged by coral bleaching

Algae can overgrow established corals, or inhibit

recruitment of new corals, when there are excess

nutrients in the system or inadequate levels of herbivory
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

110

Oceanic currents and atmospheric conditions may also

be affected by rising sea temperatures. Changes in the

strength and direction of currents are likely to have a

strong influence on local temperatures, while changes in

atmospheric circulation may influence upwelling,

precipitation patterns and the frequency and intensity of

regional weather extremes8.All of these factors have the

potential to increase the extent and severity of mass coral bleaching events. Importantly

though, while the potential for these very significant changes is recognised, there remains

substantial uncertainty about the direction, magnitude and location of changes in oceanic

circulation due to climate change13.

Potential effects of climate change on coral reefs. Climate change may influence coral reef

ecosystems through processes such as mass coral bleaching, changes in the frequency or

severity of storms8, greater virulence of diseases27, sea level rise139, and reduced calcification

rates in reef-building20 (see Box 4.4). Of these, mass bleaching events are likely to be the

most influential in determining future coral reef condition13, 28. By itself, mass bleaching has

resulted in significant ecological impacts to coral reef areas unaffected by local stressors. For

many other reefs, mass coral bleaching is an additional stress that exacerbates the impacts

of local stressors44.The influence of mass bleaching events on coral reefs and, in particular,

how it interacts with local stressors, will be one of the most important determinants of the

future of coral reef ecosystems over the next 50 years11.

Projections of future sea temperature

increase suggest that conditions will

develop that are vastly different to

those in which the majority of coral

reefs have developed over the last

400 000 years

Box 4.4 Coral reefs and climate change: implications beyond mass bleaching 

Climate change threatens coral reef ecosystems in other ways aside from increasing the

frequency and severity of bleaching impacts. Climate model projections indicate that we

can also expect increases in sea level, greater incidence of coral disease and changes in

ocean chemistry13. While the rates of coral reef growth are likely to keep pace with

projections of sea level rise, shoreline inundation with rising water levels pose other risks.

Among these are an increase in the export of sediments, nutrients and pollutants from

flooded coastal areas. Animals that rely on the low-lying habitat provided by coral reef

islands and cays, such as sea turtles and seabirds, are likely to be significantly affected,

although these potential impacts are just beginning to be explored.

Many coral diseases increase in virulence at higher temperatures, suggesting greater

prevalence of disease outbreaks as average sea temperatures increase. Diseases have

already caused chronic coral mortality in many reef areas, such as the Florida Keys and

the Caribbean, and reports of coral disease are increasing in other regions including the

Great Barrier Reef and other Indo-Pacific locations.
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

111

At a regional or global level, changes in ocean

chemistry will result from changes in the

earth's climate. In particular, dramatic

increases in the levels of carbon dioxide (CO2)

in the earth's atmosphere are leading to a

reduction in the pH of seawater, which in turn

is decreasing the availability of carbonate

ions. Reduced calcium carbonate saturation

states of seawater are expected to

significantly reduce the rates of calcification in

key reef-building organisms such as corals

and coralline algae20, 140. The implications of

this for the ability of coral reefs to withstand

storms and to maintain their role in shoreline

protection are still being examined, but early

indications are that these changes will be

important, even if they manifest themselves

only slowly or subtly. This has particular

significance for the ability of coral reefs to

maintain their roles in protecting shorelines

from oceanic swells and supporting

fisheries–both critical ecosystem functions in

many tropical regions.

The impacts of mass coral bleaching will be

compounded by other climate-related

stressors. In particular, reduced calcification

rates and increases in coral disease (shown

here) are significant concerns.The incidence of

coral disease can be expected to increase

because disease virulence increases at higher

temperatures and because the incidence of

disease has been observed to increase

following mass bleaching events, when corals

are in a weakened condition

© Australian Institute of Marine Science, Long Term Monitoring Program

4.3.2 Can corals keep up?

Comparing projected sea temperature increases with existing coral reef temperature

thresholds indicates that the frequency and severity of mass bleaching events can be

expected to increase significantly. Studies on this issue have concluded that bleaching could

become an annual event in coming decades as conditions that are known to have caused

major mortality events in the past become more frequent9, 28, 29. However, these predictions

assume that bleaching thresholds will not change over time, and do not allow for the effect

of adaptation. The actual impacts on coral reefs will depend strongly on the capacity of

corals to adapt and the rate at which they do so.

Adaptation. There is clear evidence of substantial variation in the resistance and survival of

corals to bleaching, raising the possibility that these variations might be attributable to past

adaptation. For example, corals of the same species may have a bleaching threshold of 28oC

in the Galapagos but be able to tolerate temperatures

over 34oC in the Persian Gulf.While these observations

suggest that corals have historically had sufficient time

and genetic variability to adapt, it is unknown whether

they have the capacity to adapt fast enough to keep

pace with current rates of change.

Studies that have compared futu

climate scenarios with current co

bleaching thresholds predict that 

frequency and severity of mass

bleaching events can be expected 

increase significantly
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

112

Adaptation involves genetic shifts in populations through selection of more resistant

genotypes.This evolutionary process begins as soon as less resistant genotypes are killed.

At that point, genotypes that are more resistant begin to make a greater contribution to

the next generations of corals. However, the rate of adaptation depends on numerous

factors, including the heritability of thermal tolerance, intensity of coral bleaching as a

selective process, and the genetic structure of coral populations11, 23, 28. While there are

differing degrees of optimism among recent studies, there is widespread agreement that

the abundance and composition of reef communities will change substantially over coming

decades, with large-scale degradation and losses of biodiversity possible in the longer term.

Acclimatisation. Acclimatisation refers to the ability of corals to make biochemical or

physiological adjustments that increase their ability to withstand higher sea temperatures23.

This mechanism occurs at the biochemical or cellular level, usually over time frames of

hours or days. Physiological adjustments that give rise to acclimatisation may be highly

ephemeral, lasting only as long as the stress, or they may be persistent, endowing a coral

with the ability to withstand future stress (such as high temperatures during the following

summer). Such adjustments, even short-term ones, usually come with costs, including the

diversion of energy away from other processes (such as reproduction). Additionally, for

acclimatisation to be effective it must outpace the rate of increases in temperature, which

becomes decreasingly likely at the upper level of projected temperature rise.

Incorporation of more heat resistant zooxanthellae within coral tissues is one of the major

mechanisms proposed for acclimatisation; however, the extent to which coral species can

swap algal symbionts remains unclear. This mechanism, called the Adaptive Bleaching

Hypothesis (after Buddemeier and Fautin127), proposes that corals may swap their

zooxanthellae for a more tolerant type following exposure to sub-lethal thermal stress.This

idea is a subject of continuing debate113, 141.

Corals may also acclimatise to warmer conditions by altering the density or positioning of

pigments within their tissue. These pigments, such as fluorescent pigment granules, can

shade the zooxanthellae during thermal stress, reducing damage to the photosynthetic

system and the risk of bleaching43, 111. Enhanced fluorescence seen in some corals that

appear to be more resistant to bleaching may be evidence of the role of pigmentation in

helping corals acclimatise to thermal stress.

Range-shifts in response to increasing sea temperatures. Coral populations may be able to

adjust to increasing temperature regimes through migration of heat-tolerant genotypes.The

large differences in the severity of bleaching suffered by corals exposed to otherwise similar

conditions strongly suggest that corals differ in their inherent ability to resist bleaching. At

least some of the properties that confer thermal tolerance to corals are likely to be

heritable (genetically coded).This leads to the potential for larvae from heat-resistant corals

to travel to reefs formerly dominated by less hardy genotypes, where they may settle and

re-populate areas affected by bleaching-induced mortality. Over time, this could lead to

heat-tolerant species or genotypes shifting their range into habitats previously dominated

by other species.
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

113

The success of this process will depend on the

existence and survival of heat-tolerant genotypes, and

on connectivity among reefs. In addition, the location

and extent of particular thermal realms is not likely to

be static as the climate continues to change.This means

that range-shifts would need to occur at rates that equal

or exceed the rate of movement of thermal realms in

order for this process to compensate for the loss of

corals due to increasing temperatures.

There have also been suggestions that coral reefs may expand into the subtropics as the

temperature warms (see review by Coles and Brown23). However, there is a decrease in

shallow-water areas and an increase in siliceous sediments further from the equator,

creating conditions that are less suitable for reef development.Therefore, although changes

in climate may result in more suitable temperatures for coral growth away from the tropics,

higher latitude marine environments tend to have substrata that are much less suited to

development of carbonate reef structures, resulting in limited potential for reef

communities to move towards the poles.

4.4 Reefs and people in the future

There is now abundant evidence that corals are highly sensitive to increases in sea

temperature5, 9, 11, 13, 80.Their ability to adjust, either through acclimatisation or adaptation, is

limited or widely thought to be too slow to keep pace with even conservative climate

projections23, 28. The implication of these conclusions is that coral reef ecosystems are

destined for further change as sea temperatures continue to warm9, 11, 23. While there

remains great uncertainty about the rate, extent and precise impacts of this deterioration,

the future will almost certainly see degradation of reef systems and consequent losses in

ecosystem services9, 13, 23, 31, 37.

4.4.1 Ecological implications

Effects of mass bleaching on coral cover and biodiversity.The temperature sensitivity of corals,

and the likely limitation in their rate of acclimatisation and adaptation, suggests that coral

reefs are likely to have less live coral cover and lower biodiversity as a result of increases

in the frequency and severity of mass bleaching events11, 23, 28. Among the coral species most

likely to show declines in abundance immediately after a severe bleaching event are those

that tend to be relatively fast growing and visually dominant, such as staghorn and tabular

Acropora19, 80, 115, 118. The loss of these species is likely to have a noticeable impact on the

aesthetics of many reefs, as well as altering the amount of habitat for many reef-dependent

species11.While these species may also be among the quickest to recover by way of larval

recruitment and rapid growth, it remains highly likely that differences in bleaching

susceptibility among corals will result in significant shifts in the community structure of coral

reefs.This change is likely to result in flow-on affects to other organisms, as many species,

including a variety of fish and invertebrates, are dependent on the habitat provided by

branching corals (Box 4.5).

The temperature sensitivity of

corals, and the likely limitation in

their rate of acclimatisation and

adaptation, suggests that coral

reefs are likely to have less live co

cover and lower biodiversity as a

result of a warming climate
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

114

Reefs dominated by corals most sensitive to thermal stress, such as plate and staghorn Acropora, are more likely

to suffer severe impacts from coral bleaching. Loss of these species is likely to have a noticeable impact on the

aesthetics values of reefs as well as the amount of habitat available for many reef-dependent species

© Paul Marshall

Differences in the ability of species to

migrate and to adapt will further

exacerbate changes in community

structure due to differential mortality

from severe bleaching. If bleaching

events become increasingly frequent,

the more susceptible species may have

trouble re-establishing between

bleaching events, leaving abundant

space available for algal growth.

Decreasing time intervals between

bleaching events would also limit

opportunities for resistant species to

establish sustainable populations before

temperatures increase again. While the

exact change to reefs based on

projected increases in the frequency

and severity of mass bleaching are

highly uncertain, recent modelling

studies9, 31, 47 report the possibility of

extensive degradation.

The differential susceptibility of coral species to thermal

stress can result in severe shifts in community composition.

At this site in the Lakshadweep Islands, India, massive corals

such as Porites are now the dominant members of the coral

community. Prior to the 1998 bleaching event, these sites

were dominated by staghorn Acropora

© Rohan Arthur
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

115

Box 4.5 Implications of coral bleaching

for reef biodiversity

Our understanding of the impacts of climate

change on biodiversity is in its infancy. While the

pathway and time course of this change is

undefined, most experts agree that biodiversity

will be affected to some extent by a rapid loss of

reef-building corals resulting from major

disturbances such as coral bleaching events.

Given the strong relationships that characterise

reef ecosystems, many other species are also

vulnerable to the impacts of coral bleaching.

Organisms that depend on corals for food or

shelter and which reproduce via external

fertilisation may be most threatened by

bleaching, with extinction becoming a real risk as

the primary habitat provided by corals becomes

rarer.The kinds of organisms most at risk include

the obligate corallivores: those species that eat only corals. These species are directly

dependent on the presence of coral for their existence and disappear quickly if coral is

removed. The orange-spotted filefish (Oxymonacanthus longirostris) is an example; it

rapidly disappeared from reefs around Okinawa after the 1998 bleaching event142.

The response of the broader coral reef fish community to bleaching-induced losses of corals

has proven more complex. Declines in some species (especially damselfishes that are

strongly associated with branching corals) have been recorded following bleaching63, 64, 143. In

one recent study143, over 75 per cent of reef fish species declined in abundance, and 50

per cent declined to less than half their original numbers, following a devastating decline

in coral cover caused in part by coral bleaching. However, the overall structure of fish

communities in the Seychelles changed very little despite massive (threefold-twentyfold)

decreases in live coral cover after the 1997-98 bleaching event64.Abundances of some fish

have even appeared to increase following the loss of reef-building corals, with an overall

increase in fish abundance observed after the 1998 mass bleaching event on Tanzanian

reef systems63. These increases in fish populations appear to be caused by increases in

herbivorous fishes, which may be responding to the greater availability of algae following

reductions in coral cover.

Other organisms are also likely to respond to changes in coral cover. For example, over 55

species of decapod crustaceans are associated with living colonies of a single coral species,

Pocillopora damicornis144, 145. Nine of these are known to be completely dependant on

living pocilloporid coral colonies. Similarly, branching corals of the genus Acropora have 20

species that depend solely on the habitat they provide.

Coral bleaching also has implications for

biodiversity. For example, the orangespotted filefish rapidly disappeared from

reefs around Okinawa after the 1998

coral bleaching event

© Ove Hoegh-Guldberg
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

116

Prospects for future coral reef condition. Even under

relatively conservative projections, many reefs

previously dominated by a diverse assemblage of hard

corals may give way to low-diversity, low-cover reef

communities. In the extreme, this may lead to algaldominated reefs with low habitat complexity and

limited scope for recovery by hard corals, all within 50

years. Although these projections may sound severe,

they do not rely on catastrophic change. Rather, they

assume, very conservatively, that reefs can recover

between bleaching events as long as there are fewer than three massive mortality events

per decade28, 29.Additionally, these projections do not consider the cumulative or synergistic

effects of other stresses, such as water pollution or destructive fishing practices.

Reef recovery between mass bleaching events may be impeded by several factors (see

Section 4.2.3 for information about factors that support reef recovery). Recovery

processes can be substantially hindered by erosion of reef structures following coral

mortality. The grazing of sea urchins in very high densities has led to erosion of reef

structures in eastern Pacific reefs, such that the degraded state of reefs has persisted for

two decades after the mass bleaching event of 1983146, 147. Projected reductions in the pH

of upper ocean waters are likely to further encourage both biological and chemical erosion

of reefs. Severe erosion can also lead to a shift toward an unstable substrate of coral rubble,

making recovery from bleaching-induced coral mortality difficult106.The evidence from past

mass bleaching events is that, while there are reports of active recovery from some sites,

in general damaged reefs remain degraded compared to their pre-bleaching condition. It

seems likely that the impacts of bleaching-induced mortality are likely to be evident for at

least a decade at many locations.

While coral reefs are unlikely to be eliminated globally because of mass bleaching events,

predicted declines in reef condition have serious implications. Reduced coral cover and

degraded community structures are expected to reduce the suitability of coral reefs as

habitat for many species, impacting the biodiversity and ecosystem services upon which

humans depend. Although knowledge of the inter-dependencies is only beginning to

accumulate, managers are becoming increasingly concerned about the effects of

deterioration in reef condition on the human communities and industries that have come

to rely on healthy ecosystems for their livelihood and lifestyle.

4.4.2 Social and economic implications

Impacts on fisheries. Changes in coral reef ecosystems resulting from bleaching are expected

to translate into shifts in fish species composition and, possibly, reduced fishery catches59, 148-151.

Coral reef ecosystems support fisheries by providing food and habitat for a diversity of

species. Coral mortality from mass bleaching events leads to loss of reef structure and

habitat, as dead coral skeletons erode and break down. This deterioration of the reef

structure is probably not much different in nature from that caused by other disturbances,

such as coral disease or outbreaks of the coral-feeding sea star Acanthaster plancii.

However, the effects of coral bleaching events can extend over hundreds or thousands of

Even under relatively conservative

projections of sea temperature

warming, many reefs previously

dominated by a diverse assemblage

of hard corals may give way to lowdiversity, low-cover reef communities,

reducing the ecosystem services

upon which humans depend
CORAL BLEACHING – A REVIEW OF THE CAUSES AND CONSEQUENCES

117

kilometres152, causing stress or damage

on scales not normally experienced by

coral reef ecosystems. Where

significant coral mortality occurs, coral

bleaching can result in dramatic

decreases in the amount of habitat

available for fish and other mobile reef

species that depend on the structure

provided by healthy coral reefs64, 143.

Strongly coral-dependent fish species

are expected to be the most affected

by bleaching-induced coral mortality.

Several species of fish are reliant on

coral as a primary food source, and

many other species use coral for shelter from predators. Post-bleaching declines in

populations were recorded following the 1997-98 mass bleaching episode for several fish

species that feed exclusively on corals64, 142, 153, as well as for those that rely on coral for habitat,

such as species of damselfishes that are strongly associated with branching corals63, 64.

Coral-dependent fishes are important

prey for larger species, many of which

are targeted in coral reef fisheries.

Bleaching events that result in

widespread loss of physical habitat

would be expected to have 'flow-on'

effects for the higher trophic level

predator fishes often targeted. Yet,

while impacts on fish populations of the

1997-98 mass bleaching event have

been clearly documented in several

locations, evidence of impacts on

fishery yields and income has been

more difficult to document44, 148, 154. This

may indicate that: (1) the expected

relationship between loss of coral

cover and predatory fish abundance is

too simplistic; (2) functional

redundancy at the study sites is, in the

short-term, masking the likely impacts

on higher-level predators in the longterm or (3) the relationship between

fishers and the fishery resources are

more dynamic and complex than

expected (or a combination of these

three factors).

Changes in coral reef ecosystems caused by coral bleaching

are expected to affect fisheries, especially small-scale and

subsistence fisheries 

© Simon Albert

Fish species that are strongly dependant on corals for

habitat or food, such as this damselfish on a reef at Pulau

Pemanggil, Malaysia, are expected to be the most affected

by bleaching-induced coral mortality.These coraldependent fishes are important prey for larger species,

many of which are targeted in coral reef fisheries

© Yusri Yusuf
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

118

Many reef-based fisheries are generalist in

that they target a wide variety of species

and sizes, and are partly subsistencebased. These characteristics make many

reef-based fisheries both adaptable to

changing conditions and able to be

influenced by other external factors.

Consequently, single cause-effect linkages

may be difficult to discern. While the

dynamic and adaptive nature of reefbased fisheries may make them more

resilient to short-term decreases in fish

stocks, they may also obscure indications

of long-term risks to the sustainability of

the fishery (see Section 2.4).

Impacts on tourism. Changes in coral reef ecosystems resulting from bleaching are expected

to translate into economic losses to the tourism industry. The extent of the impact on

tourism businesses varies with the flexibility of individual markets. For example, dive

businesses that are based in population centres are likely to be more capable of responding

to changes in reef quality caused by mass bleaching, because they may be able to shift from

a focus on providing high quality dive sites for experienced divers to new divers expecting

instruction or even to non-divers. By comparison, mass bleaching may significantly affect

businesses based on taking divers to remote locations that are renowned for exceptional

coral reef quality, but where options for business diversification are limited.

Several recent studies have

attempted to quantify losses

resulting from coral bleaching

on reef-based tourism

industries. Estimates of the

welfare loss between 1998-

2001 from the 1997-98 mass

bleaching event in Zanzibar,

Mombasa, and the Seychelles

are US$5.4 million, $6.4 million,

and $9.7 million, respectively37.

A recent study in Australia has

estimated potential losses of

US$95.5 million to US$293.5

million to the tourism industry

by 2020 as a result of predicted

deterioration in reef condition

caused by coral bleaching28.

Coral reef-based fisheries are the major source of food

and income for coastal communities of tropical regions

worldwide

© James Oliver

Reef-based tourism plays a key role in many regional and national

economies. Small-scale reef-oriented businesses, such as this

ecotourism venture in the Philippines are vulnerable to deterioration

in reef condition resulting from coral bleaching.Tourism businesses

based on taking divers to remote locations renowned for exceptional

coral reef quality are more likely to be negatively impacted by mass

bleaching than operators based in population centres that may have

more options for business diversification

© James Oliver
ENABLING MANAGEMENT – 

A POLICY REVIEW
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

120

5. ENABLING MANAGEMENT – A POLICY REVIEW

This guide has aimed to identify and describe actions

that managers can take in response to mass coral

bleaching events. However, in almost all cases,

implementing these ideas will require a mandate from

decision-makers as well as additional resources. Clear

policies that articulate the need for, and value of, managing reefs in the context of an

increased frequency of mass bleaching events will raise the profile of this issue, and so assist

management. Ultimately, management for mass bleaching will require that the demand for

these activities be reflected in national and local policies and resource budgets.

Currently, there are three policy areas of mass bleaching research and discussion: coral

reefs, climate science, and biological diversity. Over the last five years, all three have

demonstrated two trends: (1) recognition of a need for research followed by recognition

of a need for management and (2) a call for international action followed by a call for

national action and, in some cases, local action.These trends are positive signs for managers

wanting support to implement the activities in this guide.This section reviews international

policy related to mass coral bleaching, and provides information on the types of mandates

that currently support management for mass bleaching.

5.1 Coral reefs

Through the International Coral Reef Initiative (ICRI), three important policy statements

have called for international action in relation to mass coral bleaching events and climate

change (www.icriforum.org). Initiated in 1995, ICRI is a partnership among nations and

organisations authorised to implement Chapter 17 of Agenda 21 (adopted at the Earth

Summit, 1992) and other international agreements relevant to the conservation and

management of coral reefs.

In 1995, ICRI issued a 'Call to Action' that identified as one of four key threats to coral reefs

'the potential adverse effects of climate change, including temperature and sea-level

changes, alteration of natural patterns of precipitation, tropical storms and ocean

circulation'.Three years later, recognition of mass bleaching as a major threat to coral reefs

had become much stronger. An ICRI-sponsored event, the International Tropical Marine

Ecosystem Management Symposium (ITMEMS), issued a 'Statement on Coral Bleaching'

that noted the severity of the 1997-98 event, observing that resulting coral mortality

reached as high as 90 per cent in some areas. The statement expressed concern that

projected increases in temperature are likely to lead to an increase in the frequency of coral

bleaching events and associated ecological and socioeconomic consequences. The

statement identified a need for cross-disciplinary research and, specifically, establishment of

'a multi-disciplinary taskforce...to thoroughly inform the IPCC [Intergovernmental Panel on

Climate Change] on coral reef issues prior to their next report due in 2001'.

Implementing management measures

for mass bleaching will require a

mandate from decision-makers as

well as additional resources
ENABLING MANAGEMENT – A POLICY REVIEW

121

By 2003, ITMEMS 2 recognised the need and ability to

manage reefs for mass coral bleaching. The conference

statement concluded that 'coral reefs of the world have

been deteriorating from coral bleaching and mortality due to

warming seas' and that managers can 'address these trends

by adopting a number of risk minimising strategies'. The

statement recommends six strategies, summarised as:

• support resilience by managing threats within

management control

• factor risk of bleaching impacts into representative MPA

networks

• incorporate flexibility to respond to mass bleaching into

coral reef management plans

• influence policy related to climate change

• document and raise awareness about bleaching impacts

• promote documentation and mitigation of other negative

effects of climate change on tropical marine species and

ecosystems, including turtles, seabirds, mangroves, etc.

ICRI policy statements have been effective in catalysing

national and local coral reef management around the world.

In response to recommendations in the 1995 Call to Action,

many countries have developed national coral reef initiatives,

including Indonesia, the Philippines, Thailand, the United

States, Mexico, and Netherlands Antilles. Furthermore, the

International Coral Reef Action Network (ICRAN) was

formed as an action-oriented response and partnership to

ICRI's call. ICRAN continues to work to halt the global

decline in the health of coral reefs.

In the United States, efforts originating from the 1995 ICRI Call to Action have resulted in

national policies calling for management of mass coral bleaching, even at the local level

(www.coralreef.gov). In 2000, the US National Action Plan for Coral Reef Conservation

called for increased research and monitoring to strengthen understanding of and response

to mass bleaching events. Two years later, the US Coral Reef Task Force passed two

resolutions calling for the incorporation of mass bleaching events into management policy.

The first called for a public-private partnership to comprehensively address research into

and management of bleaching-related impacts to reefs.The second called on individual US

states and territories, with their federal partners, to develop local action strategies for

responding to key threats to reefs, including climate change and coral bleaching.While it is

too soon to judge the success of these initiatives, such local level approaches to managing

mass bleaching may be well-suited to other decentralised coral reef management regimes,

such as those of Indonesia and the Philippines.

In 1998, the coral reef

management community, through

ICRI, issued a “Statement on

Coral Bleaching” in its Renewed

Call to Action (shown here) that

raised concern about mass

bleaching and called for research

to evaluate its consequences. By

2003, that call went further by

recognizing both the need and

the ability to manage coral reefs

for mass bleaching, in a

conference statement adopted at

ITMEMS 2. Several policy forums

related to mass bleaching

demonstrate this trend–of

moving from a call for research to

a call for management. They also

move from a call for international

action to a call for national action,

and sometimes, local action.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

122

5.2 Climate science 

Unlike coral reef policy, climate science forums do not issue prescriptive policies. However,

they do aim to be policy relevant, and the technical synthesis documents they produce are

important for establishing the accepted state of knowledge and describing priority

knowledge gaps in existing information. Several important climate science documents have

issued findings that articulate the importance of mass bleaching as a serious threat to coral

reefs, the links between increased sea temperatures and mass bleaching, and the priority

for additional research into coral reef management options in the face of climate change.

In its third assessment (2001), the Intergovernmental Panel on Climate Change (IPCC)

identified coral reefs as one of the natural systems especially vulnerable to climate change.

This suggests that coral reefs are among the ecosystems that, due to their limited adaptive

capacity, may undergo significant and irreversible damage because of climate change. The

assessment considered what type of climate-related impacts will most affect reefs, finding that

increases in the frequency of extreme temperature events and consequent bleaching events,

and changing CO2 levels that reduce the rate of reef calcification will be more significant than

impacts associated with sea-level rise. Quoting several studies, the IPCC Working Group II

technical review noted, 'rising SST [sea surface temperature] will create progressively more

hostile conditions for many reefs.This effect, along with decreased CaCO3 saturation state,

represents two of the most serious threats to reefs in the 21st century'.

The Strategic Plan for the US Climate Change Science Program is similar to the IPCC in

recognising coral reefs as particularly vulnerable, and calling for research to strengthen coral

reef management options.The plan indicates that, while bleaching events prior to the 1980s

were generally attributed to local phenomena, a direct relationship between bleaching events

and elevated ocean temperature has since been found (US Climate Change Science Program,

2003).The plan emphasises that management practices can be used to sustain ecologically

related goods and services. Specifically, it identifies as a priority research question: 'How can

coral reefs be managed for tourism, erosion protection, and biodiversity, considering potential

global changes?'. Research needs listed under this question include assessments of the direct

and indirect ecological effects and economic costs of management practices through regular

monitoring, evaluation, and experimentation–the overarching goal being to enable adaptive

shifts in management.

5.3 Biological diversity

The Convention on Biological Diversity (CBD) has called for management, research,

capacity building and financing of activities that address mass coral bleaching. Additionally,

the CBD has catalysed national efforts to consider climate change-related impacts on

biodiversity. One example of such an effort is Australia's Biodiversity and Climate Change

Action Plan, which includes sections on the mass coral bleaching issue.
ENABLING MANAGEMENT – A POLICY REVIEW

123

In 1998, the CBD formed a Subsidiary Body on Scientific,Technical and Technological Advice

(SBSTTA) for assistance in developing policies on mass coral bleaching. After issuing initial

findings in an Expert's Meeting report, a Specific Work Plan on Coral Bleaching was

developed (www.biodiv.org). Recommended actions in the first work plan included targeted

research, monitoring and assessment, stakeholder engagement, the development of case

studies, technical capacity, and Integrated Coastal Management (ICM) plans.The work plan

also called for increased recognition of coral bleaching in related international conventions

and the mobilisation of financial and technical assistance to address the issue.

At the 2004 CBD Conference of Parties, the Specific Work Plan on Coral Bleaching was

updated, adding a category for 'Management Actions and Strategies'. Recommended

management actions included: (a) identification and management of areas of demonstrated

resilience; (b) assistance for focused management activities; (c) development of pilot projects

for management interventions to increase short- and long-term reef resilience; (d)

integration of resilience principles into MPA design and (e) increased efforts to reduce

localised stressors to promote resilience. Management concepts were also integrated into

the other sections during the 2004 update, including a recommendation to support training

managers in the tools necessary to respond to mass bleaching events.

Countries that are signatories to the CBD are to complete national level assessments of

biological diversity. In Australia, a partnership of federal and state governments has recently

completed a National Biodiversity and Climate Change Action Plan (NBCCAP) that

specifically calls for management efforts to minimise the impacts of coral bleaching events.

This plan calls for the integration of climate change concerns into standard management

operations, and includes research, communication, and management components. The

section on marine and coastal ecosystems recommends:

• building capacity to predict the effects of climate

change on coastal and marine ecosystems in ecological

and socioeconomic terms

• identifying and implementing strategies that minimise

the impacts of climate change on vulnerable coastal

and marine ecosystems and, particularly, for acute

impacts from climate change, such as coral bleaching

• maximising the resilience of coastal and marine

ecosystems to climate change

• considering the impacts of climate change when selecting new Marine Protected Areas.

Summary. Many countries with coral reefs are participants in ICRI, signatories to the CBD,

and involved with the IPCC. Policies and statements issued in these international forums may

help managers develop the political will and acquire the resources to implement their own

plans to respond to mass bleaching events and to build coral reef resilience. As discussed

here, there are already examples of the ways these international policies can and have

influenced the development of policies that incorporate mass coral bleaching into

management at both national and local levels. A Reef Manager's Guide to Coral Bleaching is

intended to provide the knowledge and tools that will enable managers to take the actions

required by these policy initiatives.

International policy forums related 

coral reefs, climate science, and

biological diversity have all recogni

the need for management action t

respond to mass coral bleaching. T

international statements offer su

to managers who want to impleme

the strategies described in this gu
124

A REEF MANAGER’S GUIDE TO CORAL BLEACHING

REFERENCES

1. Moberg F and Folke C (1999). Ecological goods and services of coral reef

ecosystems. Ecological Economics 29:215–233.

2. ICRAN (International Coral Reef Action Network) (2003). Prognosis for the future, last

updated 2003.

http://ww.aims.gov.au/pages/research/coral-reefs/at-the-crossroad.html#prognosis 

(Accessed 16 Mar 2006)

3. Bellwood DR, Hughes TP, Folke C and Nystrom M (2004). Confronting the coral reef

crisis. Nature 429:827–833.

4. CCSP (Climate Change Science Program and the Subcommittee on Global Change

Research) (2003). Vision for the Program and Highlights of the Scientific Strategic Plan,

US Climate Change Science Program,Washington DC.

5. Wilkinson C (2002). Status of coral reefs of the world: 2002, Australian Institute of

Marine Science,Townsville, Australia.

6. ––(2000). Status of coral reefs of the world: 2000,Australian Institute of Marine Science,

Townsville, Australia.

7. ––(2004). Status of coral reefs of the world: 2004,Vol. 1, Australian Institute of Marine

Science,Townsville, Australia.

8. IPCC (Intergovernmental Panel on Climate Change) (2001). Climate Change 2001:

Synthesis Report. A Contribution of Working Groups I, II and III to the Third

Assessment Report of the Intergovernmental Panel on Climate Change. In: Watson

RT (ed.), IPCC 3rd Assessment Report, Cambridge University Press, Cambridge, United

Kingdom, and New York, USA.

9. Hoegh-Guldberg O (1999). Climate change, coral bleaching and the future of the

world's coral reefs. Marine and Freshwater Research 50:839–866.

10. Smith SV and Buddemeier RW (1992). Global change and coral reef ecosystems.

Annual Review of Ecology and Systematics 23:89–118.

11. Hughes TP, Baird AH, Bellwood DR, Card M, Connolly SR, Folke C, Grosberg R,

Hoegh-Guldberg O, Jackson JBC, Kleypas J, Lough JM, Marshall P, Nystroem M,

Palumbi SR, Pandolfi JM, Rosen B and Roughgarden J (2003). Climate Change, Human

Impacts, and the Resilience of Coral Reefs. Science 301:929–933.

12. Westmacott S,Teleki K,Wells S and West J (2000). Management of bleached and severely

damaged coral reefs, IUCN,The World Conservation Union,Washington DC, USA.

13. Buddemeier RW, Kleypas JA and Aronson R (2004). Coral Reefs and Global Climate

Change: Potential Contributions of Climate Change to Stresses on Coral Reef Ecosystems.

Prepared for the Pew Center on Global Climate Change.

14. ISRS (International Society for Reef Studies) (1998). ISRS Statement on Global Coral

Bleaching in 1997–1998, last updated 1998.

http//www.fit.edu/isrs/council/bleaching.htm (Accessed May 2006).

15. Wilkinson C (1998). Status of Coral Reefs of the World: 1998, Australian Institute of

Marine Science,Townsville, Australia.

16. Spalding MD, Ravilious C and Green EP (2001). World Atlas of Coral Reefs, Prepared

at the UNEP World Conservation Monitoring Centre, University of California Press,

Berkeley, USA.
REFERENCES

125

17. Muscatine L (1990).The role of symbiotic algae in carbon and energy flux in coral

reefs. Coral Reefs 25:75–87.

18. Brown BE (1997). Coral bleaching: causes and consequences. Coral Reefs

16:S129–S138.

19. Glynn PW (1993). Coral reef bleaching: Ecological perspectives. Coral Reefs 12:1–17.

20. Kleypas JA, Buddemeier RW, Archer D, Gattuso JP, Langdon C and Opdyke BN

(1999). Geochemical consequences of increased atmospheric carbon dioxide on

coral reefs. Science 284:118–120.

21. Knowlton N (2001).The future of coral reefs. Proceedings of the National Academy of

Sciences of the USA 98:5419–5425.

22. Harvell CD, Mitchell CE,Ward JR, Altizer S, Dobson AP, Ostfeld RS and Samuel MD

(2002). Climate warming and disease risks for terrestrial and marine biota. Science

296:2158–2162.

23. Coles SL and Brown BE (2003). Coral bleaching––capacity for acclimatization and

adaptation. Advances in Marine Biology 46:183–223.

24. Jones RJ, Hoegh-Guldberg O, Larkum AWD and Schreiber U (1998).Temperatureinduced bleaching of corals begins with impairment of the CO2 fixation mechanism

in zooxanthellae. Plant, Cell and Environment 21:1219–1230.

25. Goreau TJ and Macfarlane AH (1990). Reduced growth rate of Montastrea annularis

following the 1987–1988 coral bleaching event. Coral Reefs 8:211–215.

26. Ward S, Harrison P and Hoegh-Guldberg O (2000). Coral bleaching reduces

reproduction of scleractinian corals and increases susceptibility to future stress. In:

Moosa MK, Soemodihardjo S, Soegiarto A, Romimohtarto K, Nontji A, Soekarno and

Suharsono (eds), Proceedings of the Ninth International Coral Reef Symposium, Bali

2:1123–1128.

27. Harvell CD, Kim K, Burkholder JM, Colwell RR, Epstein PR, Grimes DJ, Hofmann EE,

Lipp EK, Osterhaus ADME, Overstreet RM, Porter JW, Smith GW and Vasta GR

(1999). Emerging marine diseases––climate links and anthropogenic factors. Science

285:1505–1510.

28. WWF (2004). The Implications of Climate Change for Australia's Great Barrier Reef,

World Wildlife Fund, Sydney.

29. Hoegh-Guldberg O (2000). The future of coral reefs: Integrating climate model

projections and the recent behaviour of corals and their dinoflagellates. Proceedings

of the Ninth International Coral Reef Symposium, Bali 2:1105–1110.

30. Strong AE, Kearns E and Gjovig KK (2000). Sea surface temperature signals from

satellites––an update. Geophysical Research Letters 27:1667–1670.

31. Done TJ, Whetton P, Jones R, Berkelmans R, Lough J, Skirving W and Wooldridge S

(2003). Global Climate Change and Coral Bleaching on the Great Barrier Reef. Final

report to the State of Queensland Geenhouse Taskforce. Department of Natural

Resources and Mining,Townsville, Australia.

32. Westmacott S, Cesar H, Soede LP and Lindén O (2001). Assessing the

socioeconomic impacts of the coral bleaching event in the Indian Ocean. In:

Schuttenberg HZ (ed.), Coral Bleaching: Causes, Consequences and Response. Selected

papers presented at the Ninth International Coral Reef Symposium on Coral

Bleaching: Assessing and linking ecological and socioeconomic impacts, future trends

and mitigation planning. Coastal Management Report 2230, Coastal Resources

Center, University of Rhode Island, Narragansett 31–39.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

126

33. Bunce L and Pomeroy B (2003). Socioeconomic Monitoring Guidelines for Coastal

Managers in Southeast Asia: SOCMON SEA. World Commission on Protected Areas,

Australian Institute of Marine Science,Townsville, Australia.

34. Cesar HLP (2000). Coral Reefs: their functions, threats and economic value. In: Cesar

HSJ (ed.), Collected Essays on the Economics of Coral Reefs, CORDIO, University of

Kalmar, Sweden, 14–39.

35. Hodgson G and Dixon JA (2000). El Niño Revisited: ecotourism, logging and fisheries.

In: Cesar HSJ (ed.), Collected Essays on the Economics of Coral Reefs, CORDIO,

University of Kalmar, Sweden, 55–68.

36. White AT, Vogt HP and Arin T (2000). Philippine coral reefs under threat: the

economic losses caused by reef destruction. Marine Pollution Bulletin 40:598–605.

37. Cesar H, Pet-Soede L,Westmacott S, Mangi S and Aish A (2002). Economic Analysis

of Coral Bleaching in the Indian Ocean–Phase II. In: Linden O, Souter D,Wilhelmsson

D and Obura D (eds), Coral degradation in the Indian Ocean: Status Report 2002.

CORDIO, Department of Biology and Environmental Science, University of Kalmar,

Kalmar, Sweden, 251–262.

38. Cesar H, Burke L and Pet-Soede L (2002). The Economics of Worldwide Coral Reef

Degradation, Cesar Environmental Economics Consulting, Arnhem,The Netherlands.

39. The Nature Conservancy and Partners (2004). R2

-Reef resilience: building resilience into

coral reef conservation; additional tools for managers: Volume 2.0. CD ROM Toolkit, last

updated 2004. http://www.reefresilience.org (Accessed 19 June 2006).

40. West JM, and Salm RV (2003). Resistance and resilience to coral bleaching:

implications for coral reef conservation and management. Conservation Biology

17:956–967.

41. Anthony KRN, Connolly SR and Hoegh-Guldberg O (in press). Bleaching, energetics

and coral mortality risk: effects of temperature, light and sediment regime. Limnology

and Oceanography.

42. McClanahan TR (2002). The near future of coral reefs. Environmental Conservation

29:460–483.

43. Hoegh-Guldberg O and Jones RJ (1999). Photoinhibition and photoprotection in

symbiotic dinoflagellates from reef-building corals. Marine Ecology Progress Series

183:73–86.

44. McClanahan T, Polunin N and Done T (2002). Ecological states and the resilience of

coral reefs. Conservation Ecology 6(2):18.

45. McCook LJ (1999). Macroalgae, nutrients and phase shifts on coral reefs: scientific

issues and management consequences for the Great Barrier Reef. Coral Reefs

18:357–367.

46. Mumby PJ, Chisholm JRM, Edwards AJ, Andrefouet S, and Jaubert J (2002). Cloudy

weather may have saved Society Island reef corals during the 1998 ENSO event.

Marine Ecology Progress Series 222:209–216.

47. Wooldrige S, Done T, Berkelmans R, Jones R and Marshall P (2005). Precursors for

resilience in coral communities in a warming climate: a belief network approach.

Marine Ecology Progress Series 295:157–169.

48. Philander SGH (1990). El Niño, La Niña, and the southern oscillation, Academic Press,

San Diego, USA.
REFERENCES

127

49. Skirving WJ and Guinotte J (2001).The sea surface temperature story on the Great

Barrier Reef during the coral bleaching event of 1998. In: Wolanski E (ed.),

Oceanographic Processes of Coral Reefs: Physical and Biological Links in the Great Barrier

Reef, CRC Press, Boca Raton, Florida.

50. Liu G, Strong AE, and Skirving W (2003). Remote sensing of sea surface temperatures

during 2002 Barrier Reef coral bleaching. EOS 84:137–144.

51. Sheppard CRC (2003). Predicted recurrences of mass coral mortality in the Indian

Ocean. Nature 425:294–296.

52. Berkelmans R (2002).Time-integrated thermal bleaching thresholds of reefs and their

variation on the Great Barrier Reef. Marine Ecology Progress Series 229:73–82.

53. Coles SL and Jokiel PL (1978). Synergistic effects of temperature, salinity and light on

the hermatypic coral Montipora verrucosa. Marine Biology 49:187–195.

54. English S,Wilkinson C and Baker V (1997). Survey Manual for Tropical Marine Resources,

2nd edition, ASEAN, Australia Marine Science Project, Living Coastal Resources,

Australian Institute of Marine Science,Townsville, Australia.

55. Oliver J, Marshal P, Setiasih N and Hansen L (2004). A Global Protocol for Assessment

and Monitoring of Coral Bleaching,World Wildlife Fund, Bali.

56. McClanahan TR, Muthiga NA and Mangi S (2001). Coral and algal changes after the

1998 coral bleaching: interaction with reef management and herbivores on Kenyan

reefs. Coral Reefs 19:380–391.

57. Brown EK, Cox E, Jokiel PL, Rodgers SK, Smith WR,Tissot BN, Coles SL and Hultquist

J (2004). Development of benthic sampling methods for the Coral Reef Assessment

and Monitoring Program (CRAMP) in Hawaii. Pacific Science 58:145–158.

58. Cesar H (2000). Coral Reefs:Their Functions,Threats and Economic Value. In: Cesar

H (ed.), Collected Essays on the Economics of Coral Reefs, CORDIO, University of

Kalmar, Sweden.

59. Cesar H, Pet-Soede L, Quibilan MCC,Aliño PM,Arceo HO, Bacudo IV and Francisco

H (2001). First evaluation of the impacts of the 1998 coral bleaching event to

fisheries and tourism in the Philippines. In: Schuttenberg HZ (ed.), Coral bleaching:

Causes, consequences, and response, Selected papers presented at the Ninth

International Coral Reef Symposium on Coral Bleaching: Assessing and linking

ecological and socioeconomic impacts, future trends and mitigation planning. Coastal

Management Report 2230, Coastal Resources Center, University of Rhode Island,

Narragansett, 41–58.

60. Cesar H (2000). Coral Bleaching Event on Tourism in El Nido, Philippines. Report to

Coastal Resources Centre, University of Rhode Island, USA.

61. Graham T, Idechong N and Sherwood K (2001).The Value of Dive-Tourism and the

Impacts of Coral Bleaching on Diving in Palau. In: Schuttenberg HZ (ed.), Coral

Bleaching: Causes, Consequences and Response. Selected papers presented at the

Ninth International Coral Reef Symposium on Coral Bleaching: Assessing and linking

ecological and socioeconomic impacts, future trends and mitigation planning. Coastal

Management Report 2230, Coastal Resources Center, University of Rhode Island,

Narragansett, USA, 59–72.

62. MPA News (International news and analysis on Marine Protected Areas) (2001).

How Climate Change Could Affect MPAs: what practitioners need to know, last

updated 2001. http://depts.washington.edu/mpanews/MPA21.htm#climate

(Accessed 1 March 2006).
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

128

63. Lindahl U, Ohman MC and Schelten CK (2001).The 1997–1998 mass mortality of

corals: effects on fish communities on a Tanzanian coral reef. Marine Pollution Bulletin

42:127–131.

64. Spalding MD and Jarvis GE (2002).The impact of the 1998 coral mortality on reef

fish communities in the Seychelles. Marine Pollution Bulletin 44:309–321.

65. Fenton DM and Marshall NA (2001). A Guide to the Fishers of Queensland. Part A:TRCAnalysis and Social Profiles of Queensland's Commercial Fishing Industry. Technical

Report No. 36, CRC Reef Research Centre,Townsville, Australia.

66. Folke C, Colding J and Berkes F (2003). Synthesis: Building resilience and adaptive

capacity in social-ecological systems. In: Berkes F, Colding J and Folke C (eds),

Navigating Social-Ecological Systems: Building Resilience for Complexity and Change,

Cambridge University Press, Cambridge, UK, 352–387.

67. Slootweg R, Vanclay F and van Schooten M (2001). Function evaluation as a

framework for the integration of social and environmental impact assessment. Impact

Assessment and Project Appraisal 19:19–28.

68. Bunce L,Townsley P, Pomeroy R and Pollnac R (2000). Socioeconomic manual for coral

reef management, Global Coral Reef Monitoring Network, Australian Institute of

Marine Science,Townsville, Australia.

69. Westmacott S, Cesar H, Pet-Soede L and Lindén O (2000). Coral bleaching in the

Indian Ocean: Socio-economic assessment of effects. In: Cesar H (ed.), Collected essays

on the economics of coral reefs, CORDIO, University of Kalmar, Sweden, 94–106.

70. Jones RJ (1997). Zooxanthellae loss as a bioassay for assessing stress in corals. Marine

Ecology Progress Series 149:1–3.

71. Meesters EH and Bak RPM (1993). Effects of coral bleaching on tissue regeneration

potential and colony survival. Marine Ecology Progress Series 96:189–198.

72. Harrison PL and Ward S (2001). Elevated levels of nitrogen and phosphorus reduce

fertilization success of gametes from scleractinian reef corals. Marine Biology

139:1057–1068.

73. Lesser MP, Stochaj WR, Tapley DW and Shick JM (1990). Bleaching in coral reef

anthozoans: effects of irradiance, ultraviolet radiation, and temperature on the

activities of protective enzymes against active oxygen. Coral Reefs 8:225–232.

74. Nakamura T and Van Woesik R (2001).Water-flow rates and passive diffusion partially

explain differential survival of corals during the 1998 bleaching event. Marine Ecology

Progress Series 212:301–304.

75. Hansen LJ, Biringer JL and Hoffmann JR (2003). BUYING TIME: A User's Manual for

Building Resistance and Resilience to Climate Change in Natural Systems, WWF,

Washington DC.

76. Nyström M and Folke C (2001). Spatial resilience of coral reefs. Ecosystems

4:406–417.

77. Holling CS, Schindler DW,Walker BW and Roughgarden J (1995). Biodiversity in the

functioning of ecosystems: an ecological synthesis. In: Perrings CA, Maler K-G, Folke

C, Holling CS, and Jansson B-O (eds), Biodiversity loss, ecological and economical issues,

Cambridge University Press, Cambridge, UK.

78. Gunderson LH (2000). Resilience in theory and practice. Annual Review of Ecology

and Systematics 31:425–439.
REFERENCES

129

79. Baker AC (2004). Diversity, distribution and ecology of Symbiodinium on coral reefs

and its relationship to bleaching resistance and resilience. In: Rosenberg E (ed.), Coral

Health and Disease. Springer-Verlag, Heidelberg, Berlin.

80. McClanahan TR, Baird AH, Marshall PA and Toscano MA (2004). Comparing bleaching

and mortality responses of hard corals between southern Kenya and the Great

Barrier Reef, Australia. Marine Pollution Bulletin 48:327–335.

81. Bellwood DR, Hoey AS and Choat JH (2003). Limited functional redundancy in high

diversity systems: resilience and ecosystem function on coral reefs. Ecology Letters

6:281–285.

82. Hughes TP (1994). Catastrophes, phase shifts, and large-scale degradation of a

Caribbean coral reef. Science 265:1547–1551.

83. Cappo M and Kelley R (2001). Connectivity in the Great Barrier Reef World Heritage

Area –– An Overview of Pathways and Processes. In Wolanski E (ed.), Oceanographic

Processes of Coral Reefs: Physical and Biological Links in the Great Barrier Reef, CRC

Press, Boca Raton, Florida, 161–185.

84. DeVantier L, De'Ath G, Klaus R, Al-Moghrabi S, Abdal-Aziz M, Reinicke GB, Cheung

C (in press). Reef-building corals and coral communities of the Socotra Archipelago,

Yemen: A zoogeographic 'crossroads' in the Arabian Sea. Fauna of Arabia 20.

85. Done T (2001). Scientific Principles for Establishing MPAs to Alleviate Coral Bleaching

and Promote Recovery. In: Salm RV, Coles SL (eds), Coral Bleaching and Marine

Protected Areas. Proceedings of the Workshop on Mitigating Coral Bleaching Impact

Through MPA Design, Bishop Museum. Asia Pacific Coastal Marine Program Report

# 0102,The Nature Conservancy, Honolulu, Hawaii, USA, Honolulu, Hawaii, 53–59.

86. Salm RV, Clark J and Siirila E (2000). Marine and coastal protected areas.A guideline for

planners and managers, IUCN, Gland, Switzerland.

87. Yohe G and Neumann J (1997). Planning for sea level rise and shore protection

under climate uncertainty. Climate Change 37:243–270.

88. Obura DO (2005). Resilience and climate change: lessons from coral reefs and

bleaching in the Western Indian Ocean. Estuarine, Coastal and Shelf Science: Science for

management in the western Indian Ocean 63:353–372.

89. Salm T and Coles SL (2001). Coral Bleaching and Marine Protected Areas In: Salm R

and Coles SL (eds), Coral Bleaching and Marine Protected Areas. Proceedings of the

Workshop on Mitigating Coral Bleaching Impact Through MPA Design. Asia Pacific

Coastal Marine Program Report 0102, Bishop Museum, Honolulu, Hawaii, USA,

118–122.

90. West JM (2001). Environmental Determinants of Resistance to Coral Bleaching:

Implications For Management Of Marine Protected Areas. In: Salm R, Coles SL (eds),

Coral Bleaching and Marine Protected Areas. Proceedings of the Workshop on

Mitigating Coral Bleaching Impact Through MPA Design. Asia Pacific Coastal Marine

Program Report 0102, Bishop Museum, Honolulu, Hawaii, USA, 40–52.

91. Salm R, Smith S and Llewellyn G (2001). Mitigating the impact of coral bleaching through

marine protected area design. In: Schuttenberg HZ (ed.), Coral Bleaching: Causes,

Consequences and Response. Selected papers presented at the Ninth International Coral

Reef Symposium on Coral Bleaching:Assessing and linking ecological and socioeconomic

impacts, future trends and mitigation planning. Coastal Management Report 2230,

Coastal Resources Center, University of Rhode Island, Narragansett, 81–88.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

130

92. Done TJ (1982). Patterns in the distribution of coral communities across the central

Great Barrier Reef. Coral Reefs 1:95–107.

93. Nyström M, Folke C and Moberg F (2000). Coral-reef disturbance and resilience in

a human-dominated environment. Trends in Ecology and Evolution 15:413–417.

94. Jaap WC and Hudson JH (2001). Coral reef restoration following anthropogenic

disturbances. Bulletin of Marine Sciences 69(2):33.

95. Jensen AC (1997). European artificial reef research. Proceedings of the 1st EARRN

conference, Ancona, Italy, March 1996, Technical Report No. 0904175286,

Southampton Oceanography Centre, Southhampton, UK.

96. Pickering H, Whitmarsh D and Jensen A (1998). Artificial reefs as a tool to aid

rehabilitation of coastal ecosystems: investigating the potential. Marine Pollution Bulletin

37:8-12.

97. Van Treeck P and Schumacher H (1999). Artificial reefs created by electrolysis and

coral transplantation: an approach ensuring the compatibility of environmental

protection and diving tourism. Estuarine, Coastal and Shelf Science 49:7581.

98. Bowden-Kerby A (2001). Low-tech coral reef restoration methods modelled after

natural fragmentation processes. Bulletin of Marine Science 69:915931.

99. Franklin H, Muhando C and Lindahl U (1998). Coral culturing and temporal

recruitment patterns in Zanzibar,Tanzania. Ambio 27:651–655.

100. Rinkevich B (2000). Steps towards the evaluation of coral reef restoration by using

small branch fragments. Marine Biology 136:807–812.

101. Spurgeon JPG and Lindahl U (2000). Economics of Coral Reef Restoration. In: Cesar

HSJ (ed.), Collected Essays on the Economics of Coral Reefs. Coral Reef Degradation in

the Indian Ocean (CORDIO), University of Kalmar, Sweden, 125–136.

102. Spurgeon J (1998). The socio-economic costs and benefits of coastal habitat

rehabilitation and creation. Marine Pollution Bulletin 37:373–382.

103. Kaly UL (1995). Experimental test of the effects of methods of attachment and handling

on the rapid transplantation of corals, CRC Reef Research Centre Ltd Technical Report

No. 1, CRC Reef Research Centre,Townsville, Australia.

104. Harriot VJ and Fisk DA (1988). Coral transplantation as a reef management option.

In: Choat JH, Barnes D, Borowitzka MA, Coll JC, Davies PJ, Flood P, Hatcher BG,

Hopley D, Hutchings PA, Kinsey D, Orme GR, Pichon M, Sale PF, Sammarco P, Wallace

CC,Wilkinson C and Bellwood O (eds), Proceedings of the 6th International Coral Reef

Symposium. 6th ICRS Executive Committee,Townsville, Australia, 375–379.

105. Edwards AJ and Clark S (1998). Coral Transplantation:A Useful Management Tool or

Misguided Meddling? Marine Pollution Bulletin 37:8–12.

106. Fox, HE, Mous PJ, Muljadi A, Purwanto and Pet JS (2003). Enhancing Reef Recovery in

Komodo National Park, Indonesia Coral Reef Rehabilitation at Ecologically Significant

Scales. Report from The Nature Conservancy, Southeast Asia Center for Marine

Protected Areas in collaboration with Komodo National Park Authority, Bali.

107. Rinkevich B (1995). Restoration strategies for coral reefs damaged by recreational

activities: the use of sexual and asexual recruits. Restoration Ecology 3:241–251.

108. Bowden-Kerby A (1997). Coral transplantation in sheltered habitats using unattached

fragments and cultured colonies. Proceedings of the 8th International Coral Reef

Symposium, Panama, 2:2063–2068.
REFERENCES

131

109. Heyward AJ, Smith LD, Rees M and Field SN (2002). Enhancement of coral

recruitment by in situ mass culture of coral larvae. Marine Ecology Progress Series,

230:113–118.

110. Dove SG, Hoegh-Guldberg O and Ranganathan S (2001). Major colour patterns of

reef-building corals are due to a family of GFP-like proteins. Coral Reefs 19:197–204.

111. Salih A, Larkum A, Cox G, Kuehl M and Hoegh-Guldberg O (2000). Fluorescent

pigments in corals are photoprotective. Nature 408:850–853.

112. Takahashi S, Nakamura T, Sakamizu M, van Woesik R and Yamasaki H (2004). Repair

machinery of symbiotic photosynthesis as the primary target of heat stress for reefbuilding corals. Plant and Cell Physiology 45:251–255.

113. Hoegh-Guldberg O, Jones RJ, Ward S and Loh WK (2002). Is coral bleaching really

adaptive? Nature 415:601–602.

114. Baird AH and Marshall PA (2002). Mortality, growth and reproduction in scleractinian

corals following bleaching on the Great Barrier Reef. Marine Ecology Progress Series

237:133–141.

115. Brown BE, Dunne RP, Goodson MS and Douglas AE (2000). Bleaching patterns in reef

corals. Nature 404:142–143.

116. Kirk JTO (1994). Light and Photosynthesis in Aquatic Ecosystems, 2nd edition,

Cambridge University Press, Cambridge, UK.

117. Anthony KRN, Ridd PV, Orpin A, Larcombe P and Lough JM (2004). Temporal

variation in light availability in coastal benthic habitats: effects of clouds, turbidity and

tides. Limnology and Oceanography 49:2201–2211.

118. Marshall PA and Baird AH (2000). Bleaching of corals on the Great Barrier Reef:

differential susceptibilities among taxa. Coral Reefs 19:155–163.

119. Kushmaro A, Loya Y, Fine M and Rosenberg M (1996). Bacterial infection and coral

bleaching. Nature 380:396.

120. Ben-Haim Y and Rosenberg E (2002). A novel Vibrio sp. pathogen of the coral

Pocillopora damicornis. Marine Biology 141:47–55.

121. Edmunds PJ (1994). Evidence that reef-wide patterns of coral bleaching may be the

result of the distribution of bleaching-susceptible clones. Marine Biology 121:137–142.

122. Brown BE, Dunne RP, Goodson MS and Douglas AE (2002). Experience shapes the

susceptibility of a reef coral to bleaching. Coral Reefs 21:119–126.

123. LaJeunesse TC, Loh WK, van Woesik R, Hoegh-Guldberg O, Schmidt GW and Fitt WK

(2003). Low symbiotic dinoflagellate diversity in Great Barrier Reef corals relative to

those of the Caribbean. Limnology and Oceanography 48:2046–2054.

124. Fitt WK, McFarland FK, Warner ME and Chilcoat GC (2000). Seasonal patterns of

tissue biomass and densities of symbiotic dinoflagellates in reef corals and relation to

coral bleaching. Limnology and Oceanography 45:677–685.

125. Loya Y, Sakai K,Yamazato K, Nakano Y, Sambali H and Van Woesik R (2001). Coral

bleaching: the winners and the losers. Ecology Letters. 4:122–131.

126. Baker AC (2003). Flexibility and specificity in coral-algal symbiosis: diversity, ecology,

and biogeography of Symbiodinium.Annual Review of Ecology, Evolution and Systematics

34:661–689.

127. Buddemeier RW and Fautin DG (1993). Coral bleaching as an adaptive mechanism.

Bioscience 43:320–326.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

132

128. Rowan R (1998). Diversity and ecology of zooxanthellae on coral reefs. Journal of

Phycology 34:407–417.

129. Ulstrup KE, Berkelmans R, Ralph PJ and van Oppen MJH (2006).Variation in bleaching

sensitivity of two coral species across a latitudinal gradient on the Great Barrier Reef:

The role of zooxanthellae. Marine Ecology Progress Series 314:135–148.

130. Hoegh-Guldberg O, McCloskey LR and Muscatine L (1987). Expulsion of

zooxanthellae by symbiotic cnidarians from the Red Sea. Coral Reefs 5:201–204.

131. Michalek-Wagner K and Willis BL (2001a). Impacts of bleaching on the soft coral

Lobophytum compactum. I. Fecundity, fertilization and offspring viability. Coral Reefs

19:231–239.

132. Anthony KRN and Fabricius KE (2000). Shifting roles of heterotrophy and autotrophy

in coral energetics under varying turbidity. Journal of Experimental Marine Biology and

Ecology 252:221–253.

133. Connell JH, Hughes TP and Wallace CC (1997). A 30-year study of coral abundance,

recruitment, and disturbance at several scales in space and time. Ecological Monographs

67:461–488.

134. Karlson RH (1999). Dynamics of Coral Communities, Kluwer Academic Publishers,

Dordrecht, Netherlands.

135. Gilmour J (1999). Experimental investigation into the effects of suspended sediment

on fertilisation, larval survival and settlement in a scleractinian coral. Marine Biology

135:451–462.

136. Negri AP and Heyward AJ (2000). Inhibition of fertilization and larval metamorphosis

of the coral Acropora millepora (Ehrenberg, 1834) by petroleum products. Marine

Pollution Bulletin 41:7–12.

137. Done TJ (1999). Coral community adaptability to environmental change at the scales

of regions, reefs and reef zones. American Zoologist 39:66–79.

138. McManus JW, Menez LA, Kesner-Reyes KN,Vergara SG and Ablan SM (2000). Coral

reef fishing and coral-algal phase shifts: implications for global reef status. ICES Journal

of Marine Science 57:572–578.

139. Church J, White NJ, Coleman R, Lambeck K and Mitrovica J (2004). Estimates of the

regional distribution of sea level rise over the 1950–2000 period. Journal of Climate

17:2609–2625.

140. Gattuso JP, Frankignoulle M, Bourge I, Romaine S and Buddemeier RW (1998). Effect

of calcium carbonate saturation of seawater on coral calcification. Global Planetary

Change 18:37–47.

141. Baker A (2002). Is coral bleaching really adaptive? Nature 415:601–602.

142. Kokita T and Nakazono A (2001). Rapid response of an obligately corallivorous filefish

Oxymonacanthus longirostris (Monacanthidae) to mass coral bleaching event. Coral

Reefs 20:155–158.

143. Jones GP, McCormick MI, Srinivasan M and Eagle JV (2004). Coral decline threatens

fish biodiversity in marine reserves. Proceedings of the National Academy of Sciences

101:8251–8253.

144. Abele L and Patton WK (1976).The size of coral heads and the community biology

of associated decapod crustaceans. Journal of Biogeography 3:35–48.

145. Black R and Prince J (1983). Fauna associated with the coral Pocillopora damicornis at the

southern limit of its distribution in Western Australia. Journal of Biogeography

10:135–152.
REFERENCES

133

146. Glynn PW (1988). El Niño warming, coral mortality and reef framework destruction

by echinoid bioerosion in the eastern Pacific. Galaxea 7:129–160.

147. Eakin CM (2001).A tale of two ENSO events: carbonate budgets and the influence of

two warming disturbances and intervening variability, Uva Island, Panama. Bulletin of

Marine Science 69:171–186.

148. Grandcourt EM and Cesar HSJ (2002). The bio-economic impact of mass coral

mortality on the coastal reef fisheries of the Seychelles. Fisheries Research 60:539–550.

149. McManus JW (1996). Social and economic aspects of reef fisheries and their

managemen. In: Polunin NVC and Roberts CM (eds), Coral Reef Fisheries. Chapman and

Hall, London, UK, 249–281.

150. McClanahan T, Maina J and Pet-Soede L (2002). Effects of the 1998 coral morality event

on Kenyan coral reefs and fisheries. Ambio 31:543–550.

151. Schuttenberg HZ (ed.) (2001). Coral Bleaching: Causes, Consequences, and Response.

Selected papers presented at the Ninth International Coral Reef Symposium on Coral

Bleaching: Assessing and linking ecological and socioeconomic impacts, future trends

and mitigation planning. Coastal Management Report 2230, Coastal Resources Center,

University of Rhode Island, Narragansett.

152. Berkelmans R and Oliver JK (1999).Large-scale bleaching of corals on the Great Barrier

Reef. Coral Reefs 18:55–60.

153. Sano M (2004). Short-term effects of a mass coral bleaching event on a reef fish

assemblage at Iriomote Island, Japan. Fisheries Science 70:41–46.

154. Muhando CA and Mohammed MS (2002). Coral reef benthos and fisheries in Tanzania

before and after the 1998 bleaching and mortality event. Journal of Marine Science 1:43–52.

155. McField MD (1999). Coral Response during and after mass bleaching in Belize. Bulletin

of Marine Science 64:155–172.

156. ––(2002). Influence of Disturbance on coral reef community structure in Belize.

Proceedings of the 9th International Coral Reef Symposium, 63–68.

157. Aronson RB, Precht WF, MacIntyre IG and Murdoch TJT (2000). Coral bleach-out in

Belize. Nature 405:36.

158. FAO (Food and Agriculture Organisation) (2000). Conservation and Sustainable use of

the Meso-American Barrier Reef System in Mexico, Belize, Guatemala and Honduras:Threat

and Root Cause Analysis. Mesoamerican Barrier Reef Systems Project.Technical Report

No. 00/008 CP-CAM.

159. Kramer PA and Kramer PR (2002). Ecoregional Conservation Planning for the

Mesoamerican Caribbean Reef. McField M (ed.),WWF,Washington DC, USA.

160. Rowan R, Knowlton N, Baker A and Jara J (1997). Landscape ecology of algal symbionts

creates variation in episodes of coral bleaching. Nature 388:265–269.

161. Toller WW, Rowan R and Knowlton N (2001). Zooxanthellae of the Montastrea

annularis species complex: patterns of distribution of four taxa of Symbiodinium on

different reefs and across depths. Biological Bulletin 201:348–359.

162. Toller WW, Rowan R and Knowlton N (2001). Repopulation of zooxanthellae in the

Caribbean corals Montastrea annularis and M. faveolata following experimental and

disease-associated bleaching. Biological Bulletin 201:360–373.

163. Baker AC (2001). Reef corals bleach to survive change. Nature 411:765–766.

164. Craig P and Basch L (2001). Paper presented at the Workshop report prepared as a

result of the Vital Signs Workshop, National Park of American Samoa, Pago, Pago,

American Samoa, 2001.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

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GLOSSARY OF TERMS

Note that many of these definitions are in a coral bleaching or climate change context, and that

more general definitions may apply in other fields.

Biodiversity The numbers and relative abundances of different genes (genetic diversity),

species, and ecosystems (biological communities) in a particular area.

Climate Climate in a narrow sense is usually defined as the 'average weather,' or more

rigorously, as the statistical description in terms of the mean and variability of relevant

quantities over a period of time ranging from months to thousands of years.The classical

period is 30 years, as defined by the World Meteorological Organisation (WMO). These

quantities are most often surface variables such as temperature, precipitation, and wind.

Climate in a wider sense is the state, including a statistical description, of the climate system.

Climate change Climate change refers to any change in climate over time, whether due to

natural variability or as a result of human activity.This usage differs from that in the United

Nations Framework Convention on Climate Change (UNFCCC), which defines 'climate

change' as: 'a change of climate which is attributed directly or indirectly to human activity

that alters the composition of the global atmosphere and which is in addition to natural

climate variability observed over comparable time periods'. See also climate variability.

Climate variability Climate variability refers to variations in the mean state and other

statistics (such as standard deviations, the occurrence of extremes, etc.) of the climate on

all temporal and spatial scales beyond that of individual weather events.Variability may be

due to natural internal processes within the climate system (internal variability), or to

variations in natural or anthropogenic external forcing (external variability). See also climate

change.

Coral bleaching The paling of corals resulting from a loss of symbiotic algae. Bleaching

occurs in response to physiological shock in response to abrupt changes in temperatures,

salinity and turbidity (also see Mass coral bleaching).

Coral reef A marine ridge or mound that has been built up over thousands of years from

limestone (calcium carbonate) deposited in the skeletons of coral polyps.The term coral

reef is often used to refer to the entire ecosystem: the coral, the substrate built by the coral

and the organisms that live in, on and around the reef.The geographical shape of a reef can

also be part of the definition: fringing reefs, barrier reefs and atolls.

Diurnal temperature range This is the difference between the daily maximum and

minimum temperatures, which has been observed to be decreasing globally, especially in

Australia.
GLOSSARY OF TERMS

135

ENSO El Niño Southern Oscillation (ENSO) refers to widespread 2-7 year oscillations in

atmospheric pressure, ocean temperatures and rainfall associated with El Niño (the

warming of the oceans in the equatorial eastern and central Pacific) and its opposite, La

Niña. Over much of Australia, La Niña brings above average rain, and El Niño brings

drought.A common measure of ENSO is the Southern Oscillation Index (SOI) which is the

normalised mean sea level pressure difference between Tahiti and Darwin. The SOI is

positive during La Niña events and negative during El Niño events.

Eutrophication The increase in dissolved nutrients and decrease in dissolved oxygen in a

(usually shallow) body of water, caused by either natural processes or pollution.

Global temperature Usually referring to the surface temperature, this is an area-weighted

average of temperatures recorded at ground- and sea-surface-based observation sites around

the globe, supplemented by satellite-based or modelbased records in remote regions.

Global warming An increase in global average surface temperature due to natural or

anthropogenic climate change.

Integrated coastal management (ICM) A continuous and dynamic process by which

decisions are made for the sustainable use, development, and protection of coastal and

marine areas and resources. The process is designed to overcome the fragmentation

inherent in both the sectoral management approach and splits in jurisdiction among levels

of government at the land-water interface.This is done by ensuring that the decisions of all

sectors and all levels of government are harmonized and consistent with the coastal policies

of the nation in question. A key part of ICM is the design of institutional processes to

accomplish this harmonization in a politically acceptable manner. See 'Integrated Coastal

and Ocean Management: Concepts and Practices' by B. Cicin-Sain and R. Knecht (1998).

IPCC The Intergovernmental Panel on Climate Change, set up in 1988 by the World

Meteorological Organisation and the United Nations Environment Program to advise

governments on the latest science of climate change, its impacts and possible adaptation

and mitigation. It involves panels of climate and other relevant experts who write relevant

reviews, which are then critically reviewed by many other researchers and governments

from member countries around the world. Summaries for Policymakers are adopted in a

plenary session of government delegates, typically from over 100 member countries

including developed and developing countries. See www.unep.ch/ipcc.

Marine Protected Area Any area of the intertidal or subtidal terrain, together with its

overlying water and associated flora, fauna, historical and cultural features, which has been

reserved by law or other effective means to protect part or all of the enclosed

environment.

Mass coral bleaching Coral bleaching extending over large distances (often affecting reef systems

spanning tens to hundreds of kilometres) as a result of anomalously high water temperatures.
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Mitigation Mitigation of climate change refers to those response strategies that reduce the

sources of greenhouse gases or enhance their sinks, to subsequently reduce the probability

of reaching a given level of climate change. Mitigation reduces the likelihood of exceeding

the adaptive capacity of natural systems and human societies.

Photosynthesis The production of chemical compounds in the chlorophyll containing

tissues of plants, in particular the formation of carbohydrates from the carbon in carbon

dioxide and the hydrogen in water with the aid of sunlight, releasing oxygen in the process.

Predictions A prediction is a statement that something will happen in the future, based on

known conditions at the time the prediction is made, and assumptions as to the physical or

other processes that will lead to change. Because present conditions are often not known

precisely, and the processes affecting the future are not perfectly understood, such

predictions are seldom certain, and are often best expressed as probabilities. Daily weather

forecasts are 'predictions' in this sense: they are predictions of what the weather will be

like, but have uncertainties due to inexact observations and weather models.They are often

expressed in probabilistic terms.

Projection Projections are sets of future conditions, or consequences, derived on the basis

of explicit assumptions, such as scenarios. Even for a given scenario or set of assumptions,

projections introduce further uncertainties due to the use of inexact rules or 'models'

connecting the scenario conditions to the projected outcomes.

Protected Area An area of land and/or sea especially dedicated to the protection of

biological diversity, and of natural and associated cultural resources, and managed through

legal or other effective means.

Risk Risk is the probability that a situation will produce harm under specified conditions. It

is a combination of two factors: the probability that an adverse event will occur; and the

consequences of the adverse event. Risk encompasses impacts on human and natural

systems, and arises from exposure and hazard. Hazard is determined by whether a

particular situation or event has the potential to cause harmful effects.

Scenario A climate scenario is a coherent, internally consistent and plausible description of

a possible future state of the climate. Similarly, an emissions scenario is a possible storyline

regarding future emissions of greenhouse gases. Scenarios are used to investigate the

potential impacts of climate change: emissions scenarios serve as input to climate models;

climate scenarios serve as input to impact assessments.

Sensitivity The degree to which a system is affected, either adversely or beneficially, by

climate related stimuli, including mean (average) climate characteristics, climate variability

and the frequency and magnitude of extremes.

Sustainability Sustainable activities meet the needs of the present without having a negative

impact on future generations. A concept associated with sustainability is triple bottom line

accounting, taking into account environmental and social costs as well as economic costs.
GLOSSARY OF TERMS

137

Threshold Any level of a property of a natural or socioeconomic system beyond which a

defined or marked change occurs. Gradual climate change may force a system beyond such

a threshold. Biophysical thresholds represent a distinct change in conditions, such as the

drying of a wetland, floods, or breeding events. Climatic thresholds include frost, snow and

monsoon onset. Ecological thresholds include breeding events, local to global extinction or

the removal of specific conditions for survival. Socioeconomic thresholds are set by

benchmarking a level of performance. Exceeding a socioeconomic threshold results in a

change of legal, regulatory, economic, or cultural behaviour. Examples of agricultural

thresholds include the yield per unit area of a crop in weight, volume or gross income. See

also critical thresholds.

Uncertainty The degree to which a value is unknown, expressed quantitatively (for

example, a range of temperatures calculated by different models) or qualitatively (for

example, the judgement by a team of experts on the likelihood of a collapse of the West

Antarctic Ice Sheet. Uncertainty in climate projections is primarily introduced by the range

of projections of human behaviour which determine emissions of greenhouse gases, and

the range of results from climate models for any given greenhouse gas.

VulnerabilityThe extent to which a natural system or human society is unable to cope with

the negative impacts of climate change, variability and extremes. It depends on changes in

climate as well as the sensitivity and adaptive capacity of the system or society.

Zooxanthellae Microscopic single-celled algae (usually dinoflagellates) that form symbiotic

relationships with corals, sea anemones, molluscs and several other types of marine

invertebrates.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

138

ACRONYM LIST

AIMS Australian Institute of Marine Science

CBD Convention on Biological Diversity

CDOM coloured dissolved organic matter

CORDIO Coral Reef Degradation in the Indian Ocean

COTS crown-of-thorns starfish

CRW Coral Reef Watch

CSIRO Commonwealth Scientific and Industrial Research Organisation 

(Australia)

DHW degree heating weeks

ENSO El Niño-Southern Oscillation

FKNMS Florida Keys National Marine Sanctuary

GBR Great Barrier Reef

GBRMPA Great Barrier Reef Marine Park Authority

GCRMN Global Coral Reef Monitoring Network

ICLARM International Centre for Living Aquatic Resources Management (now 

WorldFish Centre)

ICM integrated coastal management

ICRAN International Coral Reef Action Network

ICRI International Coral Reef Initiative

IPCC Intergovernmental Panel on Climate Change

ITMEMS International Tropical Marine Ecosystem Management Symposium

IUCN IUCN - The World Conservation Union

KEYS Keep your Eyes on the Reef program

KMR Kiunga Marine Reserve

KWS Kenya Wildlife Service

LIT line intercept transects

MAA microsporine-like amino acid

MPA Marine Protected Area

NBCCAP National Biodiversity and Climate Change Action Plan

NGO non-governmental organisation

NOAA US National Oceanographic and Atmospheric Administration

SBSTTA Subsidiary Body on Scientific,Technical and Technological Advice

SEYMEMP Seychelles Marine Ecosystem Management Project

SST sea surface temperature

TNC The Nature Conservancy

WCS Wildlife Conservation Society

WTP willingness to pay

WWF World Wildlife Fund
GREAT BARRIER REEF

CORAL BLEACHING

RESPONSE PLAN
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

140

INTRODUCTION

Large-scale coral bleaching events, driven by unusually warm sea temperatures, have now

affected every major coral reef ecosystem on the planet (Wilkinson 2004). The effects of

coral bleaching are pervasive and potentially devastating to ecosystems and the people and

industries that depend upon them. The frequency and severity of these large-scale

disturbances is predicted to increase as temperatures continue to warm under a global

regime of climate change. Climate change, in combination with the multitude of other

stressors resulting from human activities is leading to unprecedented pressure on coral reefs.

Understanding the effects and implications of coral bleaching and identifying strategies to

reduce stress and mitigate impacts are urgent challenges for the conservation and

management of coral reefs worldwide.

The Great Barrier Reef Marine Park has experienced two major coral bleaching events in

recent years: 1998 and 2002.The spatial extent of these events, combined with the high level

of mortality seen at severely affected sites, has lead to widespread concern about the future

of the Great Barrier Reef in the face of global climate change.The Great Barrier Reef Marine

Park Authority's (GBRMPA) Coral Bleaching Response Plan has been developed to provide

an early warning system for conditions that are conducive to coral bleaching, and to

document the extent and severity of coral bleaching events using broad-scale synoptic

surveys and ecological surveys.The information collected under this Response Plan can be

used to compare and analyse the frequency and patterns of bleaching events and to develop

forecasting tools.

1. Plan Overview

This document describes a Coral Bleaching Response Plan for the Great Barrier Reef (GBR).

This will enable GBRMPA to:

• develop a system to forecast coral bleaching events;

• provide early warnings of a major coral bleaching event;

• measure the spatial extent and severity of mass coral bleaching events;

• assess the ecological impacts of mass coral bleaching events;

• involve the community in monitoring the health of the GBR;

• communicate and raise awareness about coral bleaching and climate change impacts on the

GBR; and

• provide information to evaluate the implications of coral bleaching events for management

policy and strategies.

The Great Barrier Reef Coral Bleaching Response Plan (the Response Plan) has been

developed in conjunction with 'A Global Protocol for Assessment and Monitoring of Coral

Bleaching' (WWF, FishBase and GBRMPA), and 'A Reef Manager's Guide to Coral Bleaching'

(an international collaborative effort led by the US Coral Reef Task Force and GBRMPA).
APPENDIX

141

It aims to maximise comparability and

consistency with bleaching response

plans in other regions.The Response Plan

also links in with GBR tourism industrybased monitoring programs such as 'Eye

on the Reef'.

The GBR Coral Bleaching Response

Plan has the following three main

components (Figure 1):

• Early Warning System

• Bleaching Assessment and Monitoring 

• Communication Programme

The following sections detail the

rationale, strategies and methods for

each of the components. The final

section of the Response Plan includes

a detailed description of the

implementation plan.

1.1 Selecting Appropriate Coral Bleaching Monitoring for the GBR

A Global Protocol for Assessment and Monitoring of Coral Bleaching outlines a range of

monitoring activities that can be conducted to address the objectives of a coral bleaching

monitoring plan.The broad objectives of the GBR Coral Bleaching Response Plan are to

document and assess:

1.The extent and severity of coral bleaching (if an event occurs)

2.The duration of a coral bleaching event

3.The ecological impacts of a coral bleaching event

a. Does bleaching result in changes to species diversity and/or coral cover?

b. Does bleaching result in changes to relative abundance and dominance of

different species?

c. Does bleaching result in changes to reef structure and habitat complexity,

for example are there impacts on other species?

d. Does bleaching result in changes to the ability of reefs to recover after an

impact?

4. Other anthropogenic stresses that may affect the severity of coral bleaching and recovery

The GBR Coral Bleaching Response Plan also expects to provide a foundation to develop

an understanding of the social and economic impacts of coral bleaching.

Table 1 from the Global Protocol provides a guide to the types and frequency of monitoring that

should be considered for different resource scenarios and for different objectives.The GBRMPA

Climate Change Response Team reviewed the needs of the Response Plan and designed the

monitoring plan using the following selected methods based on the available resources.

Communication Programme

GBRMPA Coral Bleaching Response Plan

Coral Bleaching

Early Warning System

Bleaching Assessment

and

Monitoring Programme

Climate Monitoring Broad-scale synoptic

surveys

Sea Temperature

Monitoring Bleaching surveys

BleachWatch

Figure 1. Schematic overview of

GBR Coral Bleaching Response

Plan elements
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

142

Question

Table 1. Monitoring activities of the GBR Coral Bleaching Response Plan

Resource scenarios

A.

What is the general

extent and severity of

the current bleaching

event?

B.

Is the bleaching

associated with specific

environmental factors

such as temperature,

solar radiation, water

circulation?

C.

How long will it last

and is it a recurring

event?

D.

What are the

ecological impacts on

the reef system?

E.

Are adjacent human

impacts causing or

exacerbating the

bleaching?

A1

• Circulate questionnaires

(BleachWatch) amongst

local divers and other

reef users.

• Submit information to

ReefBase.

B1

• Ask other reef users to

collect similar data.

C1

• Ask local reef users for

details on bleaching

events and record these

on BleachWatch

questionnaires.

D1

• Conduct before and after

bleaching observations

including

mortality/recovery.

E1

• Note location, timing

(onset, duration, cessation)

and severity of local human

impacts.

• Ask other reef users to give

you similar information.

A2

• Identify major species

affected (take photos or

video footage).

B2

• Get local weather data

from meteorological office

on air temperature, sun

hours, and wind.

• Consult with

oceanographers regarding

the circulation patterns,

water exchange and any

upwelling features in the

area.

• Compare bleaching

records with hotspots and

degree heating weeks on

NOAA's website.

C2

D2

• Measured estimates of

benthic cover through

time (transects/quadrats).

E2

• Collect information on

key environmental

variables at impact sites

(turbidity, sedimentation,

gross pollution

indicators).

A3

• Conduct detailed surveys of

representative sites using

transects and a precise

measure of percentage of

coral affected (line transect,

video-transect).

• Use remote sensing to obtain

synoptic estimates over wider

geographic area.

B3

• Install recording temperature

loggers at main bleaching

sites.

• Install remote weather

stations to record

temperatures, wind and solar

radiation.

• Measure currents and tidal

flow at key sites.

• Acquire and analyse remote

sensing data to correlate

bleaching records with

thermal anomalies and

degree heating weeks.

C3

• Repeat detailed observations

in A3.

• Repeat same observations

for any subsequent bleaching

events.

D3

• Measured estimates of

benthic cover through time at

higher taxonomic resolution

(transects/quadrats).

• Transects include other

macro-invertebrates.

• Fish abundance and diversity

surveys.

E3

• Detailed surveys at control

and impact sites.

• Collate existing data on

human impacts such as water

quality, chronic disturbance

from destructive fishing.

1. Low 2. Medium 3. High
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143

2. Early Warning System

Mass coral bleaching is preceded by a series of stages. Beginning with the build-up of

climatic conditions that warm sea temperatures, above-average water temperatures follow,

which in turn can lead to patchy bleaching or bleaching of more vulnerable coral species. If

stressful conditions persist, widespread bleaching of a range of coral species can ensue,

resulting in a mass bleaching event. The onset of each of these stages can be used to

provide an early warning of a mass bleaching event.

The GBRMPA Early Warning System consists of three elements designed to detect the

onset of each of the three stages that lead to a mass coral bleaching event:

1. Climate Monitoring. Development of weather conditions that are conducive to elevated

sea temperatures.

2. Sea Temperature Monitoring. Persistence of increased sea temperatures to levels known

to cause stress to corals.

3. BleachWatch. Early signs of bleaching on reefs and the spatial extent and severity of any

bleaching.

2.1 Climate Monitoring 

Above-average sea temperatures are associated with El Niño conditions in many reef

regions around the world. While the El Niño Southern Oscillation is an important

influence on weather patterns over eastern Australia, other factors are also known to

result in high sea temperatures in the GBR region. In particular, delayed or weak

development of the monsoonal trough over northern Australia during summer appears

to be a strong precursor to the anomalously warm conditions that cause stress to corals.

Based on an emerging understanding of the relationship between weather and sea

temperatures for the GBR, current and forecast weather conditions can provide a useful

indicator of pending warming of waters in the GBR, and thus serve as early warnings of

potential stress.

Seasonal climate predictions will be reviewed in the early stages of summer to monitor

the development of regional weather patterns that may lead to anomalous sea

temperatures.These will be complemented with long- to mid-range weather forecasts as

the summer progresses.

Objectives:

Strategies:

Triggers:

Monitor climate and weather conditions in the lead up to summer to assess risk of elevated sea

temperatures.

• Monitor long-range climate predictions and weather forecasts.

• Obtain 4-Day forecasts and weather summaries from the Bureau of Meteorology.

• Explore the value of long-range forecasts for predicting potential warming conditions.

Forecasts of calm, clear conditions, above average summer temperatures, or below average rainfall

will trigger logistic preparations for the Bleaching Assessment and Monitoring component.
144

2.2 Sea Temperature Monitoring 

Sea temperatures on the GBR are an indicator of actual stress on corals, and thus serve

as an early warning of potential bleaching on the GBR.The NOAA HotSpots programme

provides regional-scale near real-time measurements of sea surface temperature (SST)

anomalies above the maximum expected summertime temperature. HotSpots and

Accumulated Heat Index products from the NOAA web site provide reliable indicators

of levels of heat stress in reef regions, and coral bleaching events have been noted in areas

where the HotSpots are greater than 1oC anomalous. Over the last year, the GBRMPA has

been developing ReefTemp, an improved sea temperature monitoring product for the

GBR region with the Bureau of Meteorology (BoM) and the Commonwealth Scientific and

Industrial Research Organisation (CSIRO). ReefTemp improves the GBRMPA's ability to

monitor thermal stress, and allows for the now-casting of bleaching risk at the scale of an

individual reef (~2 km resolution). Images of the (a) SST anomaly (above the long-term

average temperature for that month); (b) number of degree heating days and (c) Rate of

Heat Stress Accumulation are updated on the ReefTemp website daily.

Excessive and persistent SST anomalies indicate sea temperatures are approaching levels

that are known to be stressful to corals, and therefore provide an early warning of coral

bleaching. The development of conditions likely to induce bleaching will be monitored

using ReefTemp and the accumulated stress indices therein as indicators of local thermal

stress during the summer.

In addition, in situ measurements of local sea temperatures are available from a network

of weather stations on the GBR.These weather stations record water temperature at the

surface and 6 m depth, providing important information about any depth-related

variability in water temperatures, while also providing a mechanism to ground-truth

ReefTemp predictions.

A network of temperature loggers is also maintained in collaboration with the Australian

Institute of Marine Science (AIMS) and the CRC Reef.The lengthy retrieval times required

for these loggers preclude them from contributing to an early warning system. However,

the data that they provide has proven invaluable in retrospective analyses of the links

between sea temperatures and coral bleaching, enabling AIMS scientists to develop

bleaching thresholds for key locations throughout the Great Barrier Reef.

Objectives:

Strategies:

Triggers:

Obtain early warnings of temperature stress and conditions that could lead to bleaching on the

GBR over summer.

• Actively monitor ReefTemp.

• Evaluate sea temperature from weather station data to validate the remotely sensed sea

temperatures used in ReefTemp.

• Actively monitor NOAA HotSpots.

The onset of stressful conditions will trigger increased vigilant monitoring of coral condition

through BleachWatch and site inspections (Table 2). Stressful conditions (event triggers) are

defined in Table 4.

A REEF MANAGER’S GUIDE TO CORAL BLEACHING
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145

2.3 BleachWatch 

The initial onset of mass coral bleaching can range from gradual and patchy to rapid and

uniform, and can occur with varying synchrony over hundreds or thousands of square

kilometres. Detecting the early signs of a mass bleaching event requires a wide network

of observers providing regular reports of conditions throughout the region. BleachWatch

is a community monitoring initiative that has been designed to provide reliable reports of

reef condition from a wide range of reef sites throughout the GBR. BleachWatch is built

on a network of regular reef users, including tourism professionals, scientists, conservation

groups, fishers and community members who voluntarily monitor and report on

conditions at reefs that they visit regularly.

BleachWatch was initially established at the start of 2002, during the major bleaching event

that occurred that summer on the GBR. Participants visiting reefs between Port Douglas

in the north and Bundaberg in the south have been enlisted to provide regular reports

on the appearance and health of the sites they visit during summer. The number of

participants and geographic coverage of BleachWatch has continued to grow, with

currently more than 100 participants.

BleachWatch participants are provided with a BleachWatch kit and asked to complete

purpose-designed monitoring forms on a weekly basis. Participants are asked to provide

general observer information, as well as details about their site, type of habitat and specific

weather conditions that are known to influence risk of bleaching (such as water

temperature, cloud cover, air temperature, and wind speed). Detailed information about

reef condition and bleaching observations is also collected (a copy of the form is given in

Appendix A). Once the observer has submitted the first site report to the GBRMPA, they

need only fill out sections 1 and 2 and tick 'no change' unless coral bleaching is observed

or there has been a change in conditions at the reef site. It is estimated that completion

of the form takes approximately 10 minutes per week for each participant. The data

submitted by BleachWatch observers will be compiled and synthesised into summary

reports during the summer season; these will be sent to participants for their information

and for display to their clientele on board tourism vessels.The data collected is reviewed

weekly to identify where coral bleaching has been sighted, whether it is spatially or locally

significant and whether the Assessment and Monitoring component of the Response Plan

should be implemented.

Less regular or one-off reef visitors can also submit observations on reef status and coral

bleaching to a central database on the GBRMPA website. Reports will be compiled onto

maps every 1-2 months during the summer season, and published on the website.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

146

Objectives:

Strategies:

Triggers:

To detect the early stages of coral bleaching events over a wide geographic area.

To involve the community in reef monitoring, reef education and reef conservation relating to

coral bleaching and climate change.

• Develop and maintain a network of regular reef users who will provide reports of coral

bleaching conditions at reefs that they regularly visit.

• Provide operators with a BleachWatch kit that assists them in reporting on reef conditions and

detecting coral bleaching.The BleachWatch kit includes:

- Interpretive material on coral bleaching and climate change

- Examples of coral growth forms

- Examples of bleaching severity

- Monitoring forms

- Instructions for the monitoring form

- In-water identification wrist band

• Regularly enter and evaluate data received to determine the composition of each reef to assist

with evaluations of bleaching susceptibility.

• Provide regular feedback in the form of summary site reports to all participants.

• Develop and maintain a website providing information on BleachWatch, including a

downloadable version of the datasheet, on-line reporting form and copies of the site reports

for each participant.

• Provide regular feedback in the form of reports, web updates and informal communications to

all participants.

Reports of spatially extensive or severe local bleaching will trigger the Bleaching Assessment and

Monitoring component.

2.4 BleachWatch (Aerial)

BleachWatch (Aerial) is the product of broad-scale aerial surveys conducted in previous

years. BleachWatch (Aerial) is a partnership between the GBRMPA and Coastwatch and

benefits from the active involvement of Coastwatch pilots and crew who visit an extensive

number of reef sites regularly throughout summer. Pilots and crew are trained in

identifying possible bleaching from the air and asked to take geo-referenced photographs

for later analysis. The information collected by BleachWatch (Aerial) helps GBRMPA

detect the onset of bleaching and helps assess the full spatial extent and distribution of a

bleaching event.

Objectives:

Strategies:

Triggers:

Assess the spatial extent and distribution of coral bleaching for the entire GBR.

• Implement a partnership with Coastwatch to incorporate bleaching observations and

photography into routine surveillance flights covering reefs spanning the full length and breadth

of the GBR.

Confirmation of conditions conducive to bleaching from the climate and sea temperature

monitoring will trigger the broad-scale synoptic surveys.
APPENDIX

147

3. Bleaching Assessment and Monitoring Component 

The objective of the Bleaching Assessment and Monitoring component is to assess the

spatial extent and severity of coral bleaching events and determine the ecological

implications (for example coral mortality and shifts in community structure) resulting from

coral bleaching.

Timing is critical for the implementation of bleaching surveys. A bleaching event can

progress quite quickly once visible signs of stress are prevalent, with only four to six weeks

required for bleached corals to either recover or die. On the Great Barrier Reef, the peak

of previous bleaching events has occurred around March-April. If assessments are delayed

beyond this time, they are likely to provide an underestimate of the amount of bleaching

that has occurred as many corals may have died or recovered, making it difficult to

confidently attribute any coral mortality to bleaching-related stress.

A tiered approach using two methods will be used to provide the best possible

combination of spatial coverage and detailed information. The Bleaching Assessment and

Monitoring component is comprised of broad-scale synoptic surveys and in-water

bleaching surveys. The broad-scale synoptic surveys will use both MERIS and Quickbird

satellite imagery to access different spatial resolution data. CSIRO will provide the MERIS

mapping and the Centre for Remote Sensing and Spatial Information Science at the

University of Queensland will provide the Quickbird high resolution and field mapping.The

bleaching surveys will collect detailed ecological information from a set of established reef

sites that represent cross-shelf as well as latitudinal reefs.This tiered approach is the most

effective for obtaining a synoptic overview of where bleaching is occurring from a GBRwide perspective.

3.1 Broad-scale Synoptic Surveys 

The correlation between sea surface temperatures and bleaching risk is an area of active

research, and early results are indicating that sea surface temperatures are reliable

indicators of regional-scale stress, but not an accurate predictor of bleaching at individual

reefs. Broad-scale synoptic surveys are the most effective method for obtaining an

overview of the extent of bleaching over spatial scales that are relevant to management

on the GBR (ie hundreds to thousands of kilometres). As well as being important for

temporal comparisons of the extent of future bleaching events, broad-scale synoptic

surveys help to identify the reefs or regions worst affected by thermal stress.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

148

During the 2005/2006 summer, a pilot project trialed MERIS remote sensing mapping to

detect coral bleaching at 300 m resolution. The pilot project included field validation of

MERIS and Quickbird satellite images to provide a high level of detail on the health of

corals during a localised bleaching event. Due to the high level of resolution, the pilot

project was limited in spatial coverage to only inshore reefs around the Keppel Islands.The

MERIS data was also captured for other reefs in the GBR where bleaching did not occur,

to test the mapping algorithm developed at CSIRO, for both inshore and offshore reefs.

As there was a localised bleaching event, Quickbird (2.4 m pixels) image data was

captured over the Keppel Island sites where bleaching surveys were conducted. These

images covered 10 km x 10 km sections and were used to map bleached versus nonbleached coral areas.

3.2 Bleaching Surveys

Although the phenomenon of bleaching has received much attention, the ecological

significance of mass bleaching is still poorly understood. Severe bleaching events have the

potential to kill large areas of living coral, and consequently cause major disturbance to

coral reef ecosystems. However, the fate of bleached corals cannot readily be predicted

from observations of the severity or extent of bleaching.Widespread bleaching does not

necessarily equate to widespread coral mortality. To better understand the long-term

implications of these events, information on the extent and patterns of coral mortality that

result from bleaching need to be measured.

In-water bleaching surveys will provide more precise information about the percentage

and types of corals that bleach, and then subsequently die or survive. Over longer time

frames, the bleaching surveys will also enable the direction and rate of community

recovery to be evaluated. The quantitative data provided by the bleaching surveys will

enable the testing of hypotheses about differences or trends between sites or through

time. Differences in coral community structure that may occur because of bleaching and

mortality will be detected, and information on whether certain community types are more

susceptible to bleaching than others can be obtained.

Bleaching surveys will use a combination of rapid visual assessment and more detailed

video transects to provide information about the bleaching event and its ecological

impacts.The rapid assessment and video transects will be done simultaneously at all sites.

The two techniques are designed to be complimentary: the rapid assessment provides

Objectives:

Strategies:

Assess the spatial extent and distribution of coral bleaching for select locations along the GBR.

• Utilise satellite imagery (at a spatially relevant scale) to document coral cover and extent of

bleaching at target reefs.

• Build a hierarchical system using satellite imagery, and in-water data to get a complete picture,

and possibly predictive capacity for the extent of bleaching.
APPENDIX

149

basic information about the severity of the bleaching event in near real-time, while the

video transects provide more detailed information, but require intensive analysis that

normally takes weeks to months to complete. Details on site selection, integration with

the AIMS LTMP and survey methods are outlined in the following section..

3.2.1 Spatial and Temporal Scale of surveys

The Coral Bleaching Response Plan will build on existing programmes, in particular the

AIMS Long Term Monitoring Programme (LTMP), which has a suite of core sites that are

surveyed annually for benthic cover and diversity, fish diversity and abundance and other

stressors (eg COTS). By surveying the AIMS LTMP sites during a bleaching event,

important baseline and recovery data can be incorporated in any assessments.

Additionally, the AIMS targeted bleaching surveys will complement the GBRMPA surveys.

The dynamic nature of coral bleaching requires multiple temporal and spatial surveys in

order to characterise the extent and severity of bleaching that occurs, and the ecological

implications (ie the amount of mortality that occurs).This ideally requires three temporal

surveys:

Baseline. The first survey is used to document reef status (coral cover and composition)

prior to any changes caused by bleaching. This is best conducted before the onset of

bleaching. The Response Plan will utilise the AIMS LTMP data from the previous survey

period.

Event monitoring. The second survey will be timed to coincide with the peak of the

bleaching event, and is used to document the spatial and taxonomic patterns of bleaching.

This information is necessary to report on the extent and severity of bleaching, and to

interpret the causes and significance of changes in reef condition.

Recovery. The third survey should be done shortly after the bleaching event, but not until

all corals have either recovered or died.This survey determines the ecological impacts of

the bleaching by assessing changes in coral cover or composition attributable to the

bleaching event. The AIMS LTMP data set from the next survey period will be used to

determine reef status after the bleaching event.

Structured survey sites will be monitored from Lizard Island in the north to One Tree

Island in the south and have been selected to match the AIMS Long Term Monitoring

Programme (LTMP) sites (see Section 3.2.2).

Objectives:

Strategies:

Assess the percentage of coral bleaching, affected species and mortality for select reefs along the GBR.

• Rapid visual assessments to document coral cover, community composition, and severity of bleaching

at target reefs.

• Video transects to quantify coral cover, community composition, and extent and pattern of bleaching

at target reefs.

• Ground truth aerial data using in-water fine scale surveys.
150

Transect Region

Far Northern 

(Cooktown to

Lizard I.)

Northern

(Cairns)

Central

(Townsville)

Southern

(Whitsundays)

Far Southern

(Capricorn

Bunkers and

Swains South)

Reef Name

Martin Reef (I)

Linnet Reef (I)

Decapolis Reef (I)

MacGillivray Reef (M)

Nth Direction I. (M)

Lizard I. lagoon (M)

Yonge Reef (O)

Carter Reef (O)

No Name Reef (O)

Green I. (I)

Low Isles (I)

Fitzroy I. (I)

Mackay Reef (M)

Michaelmas Cay (M)

Hastings Reef (M)

St Crispin Reef (O)

Opal Reef (O)

Agincourt No.1 Reef (O)

Pandora Reef (I)

Havannah I. (I)

Middle Reef (I)

Davies Reef (M)

Rib Reef (M)

John Brewer Reef (M)

Chicken Reef (O)

Dip Reef (O)

Myrmidon Reef (O)

Hayman I. (I)

Border I. (I)

Langford and Bird I. (I)

Reef 19131S (M)

Reef 19138S (M)

Reef 20104S (M)

Slate Reef (O)

Hyde Reef (O)

Rebe Reef (O)

Nth Keppel I. (I)

Pelican I. (I)

Humpy I. (I)

Gannet Cay (M)

Chinaman Reef (M)

Reef 21529S (M)

Turner Cay (O)

Wreck I. (O)

One Tree I. (O)

Table 2. Location of sites for

fine scale ecological impact

assessments

(I), inner-shelf reef; (M), mid-shelf reef;

(O), outer shelf reef.

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151

3.2.2 Survey Sites

Each survey will assess the condition and composition of the benthic community along five

cross-shelf transects (Table 2) lists the reef sites for each of these transects).These will be

located at latitudes centred on Lizard Island, Cairns,Townsville,Whitsunday Islands and the

Capricorn Bunker Group.

Forty five sites have been selected based on existing AIMS LTMP site locations, to provide

for a long-term data set on coral cover and community composition at the sites. Three

inshore, three mid-shelf and three outer shelf reefs have been selected for each transect.

Sites were selected from the AIMS LTMP database based on the existence of previous

coral bleaching survey data (1998 and 2002), accessibility under predominant weather

conditions and location of Reef Water Quality Protection Plan survey sites.

The benefit of this approach is that baseline and recovery data for the deep transects can

be obtained from the AIMS LTMP routine surveys and thus reduce the need for multiple

GBRMPA survey trips and duplication with existing programmes. However, the LTMP only

surveys the coral community on the lower reef slope (6-9 m) while the GBRMPA

Response Plan also surveys the community on the upper slope (3-4 m), as this is the area

most affected by coral bleaching. It is necessary to obtain a quantitative baseline

assessment of the upper slope community at all of the survey sites to enable us to

evaluate the long-term ecological impacts of coral bleaching on the Great Barrier Reef.

Some remote locations along the GBR have been omitted from the standard sites

selected, such as the northern Swains and Pompey Complex. These locations are rarely

visited and do not have long-term datasets as they are not AIMS LTMP survey sites. If a

significant bleaching event occurs, these sites will be surveyed if logistics allow.

Additional sites may be surveyed using manta tow or rapid assessment techniques in a

bleaching event.These sites would be selected to match those surveyed in the 1998 and

2002 bleaching events, reefs surveyed under the Reef Plan monitoring programme (for

example Daydream I., Dent I. and Double Cone I.), and other sites of interest.They will be

surveyed as time and resources permit

3.2.3 Survey Design

Three shelf positions will be surveyed in each transect: inshore, mid-shelf and outer shelf.

Three replicate reefs will be surveyed at each shelf position. Sites will be those established

by the AIMS LTMP and will be divided into two depth zones: shallow and deep. The

shallow station includes the reef crest and upper slope from about 1- 4 m in depth.The

deep station includes the mid to lower reef slope from 5-10 m. Actual depths at each

station vary according to the reef morphology and coral community type and distribution.

At more turbid stations, or areas with poorer reef development, these depths may be

shallower, while at stations that are generally characterised by clear conditions they are

deeper. In the few stations with very restricted reef development, only the shallow depth

zone is present.These depth zones, once established, will be fixed for each station.

APPENDIX
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152

Three random transects will be surveyed at each depth at each station. Random transects

will be used rather than fixed transects to reduce the time required for establishment and

survey, avoid unsightly markers on the reef and ensure independence among consecutive

surveys. Each transect will be surveyed simultaneously by two independent methods: a

rapid visual assessment and video transects.

Two divers will swim along a 50 m belt transect, one recording information on the Rapid

Assessment Survey data sheet and the other recording the same substratum area with an

underwater video camera. The rapid assessment survey will record observations on the

condition of corals and other benthos within a band 5 m wide along the length of the

transect.Three sets of information will be recorded: station information; general coral and

bleaching observations; and detailed information for selected coral groups. All data will be

entered directly onto the specially designed Rapid Assessment Survey data sheets. The

categories for estimating per cent cover and progress of bleaching have been standardised

on the survey sheet to enable consistent surveying methods by different observers. A

table showing schematic representations of per cent cover will be utilised to maximise

consistency in estimates made underwater.

Video transects will be recorded at a distance of 40 cm above the substrate at a speed

of 10 metres per minute (in accordance with the standard protocol used by AIMS).

3.2.4 Data Analysis and Management

Video transect data will be analysed by an appropriately skilled and experienced analyst,

and stored in a database maintained by GBRMPA and shared with AIMS. Data from video

transects will be used to quantify coral cover, community composition, and extent and

pattern of bleaching at target reefs. Data collected using the Rapid Visual Assessment

surveys will be stored in a database maintained by GBRMPA. Data will be used to

document coral cover, community composition, and severity of bleaching at target reefs.

3.2.5 Complementary Studies

AIMS Climate Change Programme: temperature loggers

AIMS coordinate the Sea Temperature Monitoring Programme, which includes the

deployment and collection of in situ data loggers, and the maintenance of a network of

weather stations. Data loggers have been placed on the reef flat, at or near Lowest

Astronomical Tide, and on the reef slope at ~50 locations spanning the extent of the GBR.

At some locations, loggers have been placed on the upper reef slope (~5-9 m), or on the

deep reef slope (~20 m). Following the 1998 and 2002 bleaching events, data from these

loggers allowed for a better understanding of the link between temperature and the

severity of bleaching responses. Bleaching 'thresholds' developed from this research can

currently be monitored at the weather station sites on the Reef Futures website, and are

an important component of the Early Warning System in the Response Plan. Additionally,

AIMS targeted bleaching surveys will complement the GBRMPA surveys.
APPENDIX

153

AIMS LTMP

The AIMS Long-term Monitoring Programme has been tracking the condition of the

Great Barrier Reef for more than a decade, by surveying fish, corals, crown-of-thorns

starfish, and coral disease. The AIMS monitoring team is the one of the premier bodies

focussing on the condition of coral reef ecosystems in the Great Barrier Reef World

Heritage Area.The GBR Response Plan utilises the information collected under the LTMP

to obtain baseline and recovery data.

Reef Water Quality Protection Plan

In addition to the fine-scale ecological surveys, water quality data collected for the Reef

Water Quality Protection Plan (Reef Plan) marine monitoring will be utilised to assess the

influence of water quality stressors on susceptibility to bleaching and recovery postbleaching.The Reef Plan monitoring programme will collect information on temperature,

salinity, turbidity, chlorophyll a, sediment and nutrients loads, flood events (pollutant loads,

salinity and flow), pesticide concentrations and reef health at a number of inshore

locations. Many of these sites overlap with proposed fine scale ecological impact

assessment sites of the GBR Response Plan and there is the opportunity to correlate

these sites further for broad-scale synoptic surveys and bleaching surveys during a

bleaching event.

4. Communication Strategy 

Coral bleaching and global climate change are issues that attract strong interest from the

public, the media and senior decision-makers. It is important to proactively release accurate

information about coral bleaching events to all stakeholders as it becomes available in order

to raise awareness and ensure discussions and debate are well informed.The GBR Coral

Bleaching Response Plan will be the main source of timely and credible information on

coral bleaching on the GBR, and on the ecological implications for the reef ecosystem.

Information will be delivered directly to stakeholder groups via public meetings, existing

formal and informal networks (including GBRMPA initiatives such as Eye on the Reef,

Tourism and Recreation Newsletter and LMACs) and email. Information will also be

distributed more widely through the GBRMPA website and via media outlets. The

Communication Strategy aims to increase awareness of the implications of climate change

for the GBR, and the occurrence and consequences of coral bleaching events through a

variety of strategies. Information about coral bleaching will be communicated using the

following methods:

• In the months prior to the period of high bleaching risk, beginning in November, the

website will be reviewed to present the most current information on predicted climate

and local weather conditions and the estimated potential for coral bleaching.

• Information about bleaching issues and notification of web updates will be circulated via

industry newsletters, meetings, and email lists.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

154

• During summer (December to April), the GBRMPA will post regular web reports (every

2-4 weeks) on bleaching conditions on the GBR.

• Reports will also be sent directly to stakeholder groups (tourism operators, Marine Parks

staff, scientists, etc.) via email on a semi-regular basis (every 2-4 weeks).

• Media statements will be prepared and released if/when:

- conditions develop that indicate a high risk of coral bleaching;

- a bleaching event occurs (describing spatial extent and general severity); and

- the bleaching event has concluded (describing coral mortality and ecological

impacts).

5. Implementation

The sequence of events and decision points for implementation of the GBR Coral

Bleaching Response Plan are shown in the Schedule below (Figure 2). Climate and weather

conditions will be monitored from mid-November, approximately three months prior to

the period of greatest bleaching risk. Sea temperature monitoring and BleachWatch will be

implemented from December each summer. If the onset of high bleaching risk conditions

are confirmed, or if there are any reports of significant coral bleaching, the Bleaching

Assessment and Monitoring component will be implemented (Figure 2).

Figure 2 Schedule for the GBR Coral Bleaching Response Plan

Targeted 

Aerial 

Surveys

Ecological 

Impact 

Asse ssment

Communication Program

Bleaching Asse ssment and 

Monitoring Program

Coral Bleaching 

Early Warning System

Climate Monitoring

Sea Temp 

Monitoring

Bleach 

Watch

Have bleaching predictive 

triggers been reached?

NO YES

Review Response 

Program

Establish web/email 

reporting system

Establish BleachWatch 

network

Confirm ve ssel 

availability 

Plan aerial surveys 

and charters 

November December January February March

Coral Bleaching Assessment and Monitoring

Elements

dependent on

contingenc y

funding 

Prepare for Implementation

of Response Plan 
155

5.1 Response Schedule

The GBR Coral Bleaching Response Plan consists of a combination of routine tasks and

responsive tasks that are triggered by thresholds.

Routine tasks are designed to provide basic information to help determine if and when a

bleaching event is occurring, and to ensure the Climate Change Response Team is

prepared for the responsive tasks. Responsive tasks are implemented if it appears that a

major bleaching event is imminent, and are designed to provide a more detailed picture

of bleaching conditions and their ecological significance. An outline of these tasks is

provided below, with a detailed breakdown of tasks provided in Table 3.

5.1.1 Routine Tasks

• Prepare for implementation of responsive tasks.

• Initial assessment of probability of stressful conditions to corals based on long term

climate predictions for summer (ie ENSO conditions; development of monsoonal

trough).

• Establish bleaching reporting system, including email updates and website.

• Establish BleachWatch networks.

• Monitor weather conditions and sea temperatures and compare against thresholds.

• Update assessment of conditions and predicted levels of stress to corals.

• Solicit and coordinate information about early signs of bleaching through BleachWatch.

• Advise Senior Management and Minister of any increase in bleaching risk or bleaching

reports.

5.1.2 Responsive Tasks

• Confirm bleaching reports (site inspections).

• Advise Senior Management, Minister, stakeholder groups and the community of onset of

coral bleaching.

• Implement broad-scale synoptic surveys to assess bleaching extent.

• Deploy bleaching survey team to measure extent and severity of bleaching.

• Monitor ecological impacts of bleaching.

APPENDIX
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

156

Trigger type

Routine: weekly

Routine:

weekly/fortnightly

Routine:

weekly/fortnightly

Routine:

weekly/fortnightly

Event-based

Event-based

Timing

Monday

Tuesday

Wednesday

Constant

Substantial increase in

environmental stress1

Moderate bleaching event

detected1

Table 3. Coral Bleaching Response Plan:Task Schedule

Information 

Check GBRMPA ReefTemp and NOAA HotSpot maps

on web.

Receive updated GBR sea temperature graphs from

AIMS (operational).

Receive high resolution sea temperature maps for GBR

(2 km resolution) from BoM.

Obtain weather summary for week, eg air

temperatures, cloud cover and wind (BoM).

Review bleaching reports received via BleachWatch

and update maps.

Review bleaching reports and images received via

BleachWatch (Aerial) surveys and update maps.

Print out ReefTemp and NOAA HotSpot maps for

STIG Director to brief SMT.

Summarise weather, sea and coral conditions and draft

updated Bleaching Risk Current Conditions Report for

website. Include any recent images that may be

available.

Have updated Current Conditions Report reviewed,

approved and published on external web.

Send brief update to all-staff and other lists (ACRS,

DDM, AIMS, CRC Reef, Coral-List and BleachWatch

participants).

Monitor extent of bleaching using existing information

channels and evaluate for trends (ie is the bleaching

situation worsening/improving).

Advise Senior Management and Minister if dramatic

worsening of conditions is evident.

Actively seek and solicit confirmatory bleaching reports

from reliable sources, including BleachWatch

participants, DDM Field officers, AIMS, other

researchers, etc.

Alert relevant project coordinators and managers.

Brief Senior Management.

Brief Executive and Minister.

Prepare media position, draft statement and consult

with Media Coordinator and Executive.

Brief all staff and stakeholders.

Brief collaborators (especially AIMS, NOAA, DDM).

Release media statement.

Actively promote and solicit submissions to online

bleaching reports to provide wide spatial coverage.

Implement Bleaching Assessment and Monitoring

component.

1

see Section 5.2 for description of thresholds for event-based tasks.
APPENDIX

157

5.2 Definition of Event Triggers for Implementation Plan

The triggers for monitoring tasks and briefings outlined in the Implementation Plan (Table

5) are defined in Table 4 below.

Trigger

High bleaching risk

Low bleaching

level

Moderate

bleaching level

Severe bleaching

level

Definition

• Persistence of strong hotspots (anomaly > 1.5 °C) for 2 weeks or very strong

hotspots

(anomaly > 2 °C) for 1 week over majority of GBR region;

• degree heating days index is greater than 21 at multiple sites;

• bleaching thresholds exceeded at inshore and offshore sites; or

• there are anecdotal reports of bleaching from multiple sites.

• Reliable reports of low coral bleaching (1–10 % of colonies completely white) from

multiple sites from multiple locations spanning at least two GBRMP sectors; or

• reliable reports of mild bleaching (10–50%) from a few sites only, scattered

throughout the GBRMP or concentrated in only one sector.

• Reliable reports of moderate coral bleaching (10–50% of colonies completely

white) from multiple sites from multiple locations spanning at least two GBRMP

sectors; or

• reliable reports of severe bleaching (>50%) from a few sites only, scattered

throughout the GBRMP or concentrated in only one sector.

• Reliable reports of severe to extreme coral bleaching (>50% of colonies

completely white) from multiple sites spanning multiple GBR sectors.

Table 4. Definition of event triggers for Implementation Plan
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158

Summer approaching; bleaching risk period; GBRMPAis preparedTemperature trends for December; plans forChristmas breakTemperatures unusually high; coral bleaching eventprobableHigh temperatures recorded; moderate bleachingobserved; areas worst affected Very high temperatures recorded; severe bleachingobserved; areas worst affected; mortality likelyTemperature trends for first half of summer;summary of reports of coral bleachingSummer concluding; bleaching risk period over; nosignificant bleaching observedHigh water temperatures recorded during summer;bleaching observed; preliminary assessment of extentand severity; detailed surveys underwaySummary of full extent and severity of bleaching;implications for GBRMPUpdates on temperature trends and coral condition;also publish to web and email to all staff etc.

Monitoring Briefings

ACTIONS

Site

inspections

Broad scale

synoptic

Bleaching

surveys

Brief Senior

Management

Brief Minister Press release Message

TRIGGER1

1 December20 DecemberHigh bleaching riskModerate bleaching Severe bleaching215 February331 March (if no significant bleaching observed)31 March (if moderate or severe bleachingreported)31 April (if moderate or severe bleachingreported)Monthly4

✓✓✓

✓✓

✓✓

✓✓✓✓✓✓✓✓✓✓

✓✓✓✓✓✓✓

✓✓✓✓✓✓

1 Event-based triggers are defined in Table 3 of the GBR Coral Bleaching Response Plan2 Aerial surveys, site inspections and bleaching surveys are likely to already have been triggered by moderate bleaching levels3 This briefing will not be necessary if a moderate or severe bleaching event has already been declared4 Th

d

t

t

b

d

t

i

thl

if 

diti

h

i

idl

Table 5. Implementation Plan for Summer Period 2005-2006
APPENDIX

159

6. References

English S,Wilkinson C and Baker V (1997). Survey Manual for Tropical Marine Resources. 2nd

edition., ASEAN, Australia Marine Science Project, Living Coastal Resources, Australian

Institute of Marine Science,Townsville, Australia.

Wilkinson C (2004). Status of Coral Reefs of the World: 2004 Summary. Australian Institute

of Marine Science,Townsville, Australia.
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

160

Appendix A. BleachWatch reporting form
APPENDIX

161

Appendix B. Rapid Assessment Survey data sheet
A REEF MANAGER’S GUIDE TO CORAL BLEACHING

162

Appendix C. Code tables for key variables

No bleaching

Low level bleaching

Moderate level bleaching

Severe bleaching

Extreme bleaching

No bleaching observed, or only very occasional, scattered

bleached colonies (one or two per dive)

Bleached colonies seen occasionally and are conspicuous, but

vast majority of colonies not bleached

Bleached colonies frequent but less than half of all colonies

Bleaching very frequent and conspicuous, most corals

bleached

Bleaching dominates the landscape, unbleached colonies not

common.The whole reef looks white

Site bleaching category table

<1

1-10

10-50

50-90

>90

0

1

2

3

4

Index % Description Visual Assessment

Colony bleaching table (for use in Line Intercept or Video Transect surveys)

No bleaching evident

Partially bleached (surface/tips);

or pale but not white

White

Bleached + partly dead

Recently dead

0

1

2

3

4

Category Description
APPENDIX

163

Appendix D. Schematic representations of 

per cent cover

(Adapted from English et al 1997; after Dahl 1981. Category 0 added.)
NOTES
NOTES
Dr Paul Marshall leads the Climate Change Response Program for

the Great Barrier Reef Marine Park Authority. His work with a range

of scientific, government and non-government organisations has

focussed on improving knowledge about the implications of climate

change for coral reef ecosystems. He plays a key role in national and

international initiatives to adapt coral reef management in the face of

climate change. He has published numerous scientific papers, book

contributions and reports on coral bleaching and climate change

impacts on tropical marine ecosystems.

Heidi Schuttenberg specialises in coral reef management and policy,

focussing on Southeast Asia and the U.S. She previously worked for

NOAA leading a series of initiatives to strengthen management for

key threats to U.S. reefs, with special emphasis on options for

responding to climate change and mass coral bleaching. She is active

in international policy forums related to reef management and has

worked on both local and regional projects to support coral reef

management in Southeast Asia. She was awarded a Fulbright

scholarship to Thailand and is currently completing her PhD at James

Cook University in Australia.

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