> **Session No. 5**

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**Course Title: Coastal Hazards Management**

**Session Title: Coral Reefs**

**Author: Professor John J. Bruno, University of North Carolina at
Chapel Hill**

**Time: 1 hour**

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**Objectives**

> 5.1 Understand the basic ecology, global distribution, and structure
> of coral reef communities.

5.2 Outline two other coastal, tropical habitats often associated with
reefs.

5.3 Discuss some of the ecosystem services provided by reefs.

> 5.4 Discuss the main hazards to coral reef communities and some of the
> management strategies designed to protect them.

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**Scope:**

This session introduces students to the ecology of coral reefs, the
services they provide, and the hazards they face. Assuming many of the
students do not have an extensive background in the earth and life
sciences, the material is very basic. The session covers physical and
biological characteristics of tropical coral reefs and the dependence of
both on reef-building corals.

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**Readings:**

*Instructor and Student Reading:*

Knowlton, N. 2001. "The future of coral reefs." *PNAS* 98:5419-5425.

Knowlton, N.K. and J.B.C. Jackson. 2001. "The Ecology of Coral Reefs."
In M.D. Bertness, M.E. Hay, and S.D. Gaines, Eds*. Marine Community
Ecology*. Sinauer: Sunderland, MA, pp. 395-422.

*Additional Background Reading:*

Aronson, R.B. and W.F. Precht. 2001. "Evolutionary Paleoecology of
Caribbean Coral Reefs." In W.D. Allmon and D.J. Bottjer, Eds.
*Evolutionary Paleoecology: The Ecological Context of Macroevolutionary
Change*. New York, NY: Columbia University Press, pp. 171-233.

Edmunds P.J., and R.C. Carpenter. 2001. "Recovery of Diadema reduces
macroalgal cover and increases abundance of juvenile corals on a
Caribbean reef." *Procedures of the National Academy of Science USA*,
98:5067-5071.

Ellison, A.M. and E.J. Farnsworth. 2001. "Mangrove Communities." In M.D,
Bertness, M.E. Hay, and S.D. Gaines, Eds. *Marine Community Ecology*.
Sunderland, MA: Sinauer, pp. 423-442.

Hoegh-Guldberg, O. 1999. "Climate change coral bleaching and the future
of the world's coral reefs." Aust. J. *Freshwater and Marine Biology*
50: 839-866.

Hubbard, D.K. 1997. "Reefs as dynamic systems." In C. Birkeland, Ed.
*Life and Death of Coral Reefs*. New York, NY: Chapman and Hall, pp.
43-67.

Jackson, J.B.C. 2001. "Reefs since Columbus." *Coral Reefs* 16:23-32.

Richardson, L.L. 1998. "Coral diseases: what is really known?" *TREE*
13:438-443.

Szmant, A.M. 2001. "Why are coral reefs world-wide becoming overgrown by
algae?" *Coral Reefs* 19:299-302.

Williams, S.L. and Heck, K.L. "Seagrass Community Ecology." In M.D.
Bertness, M.E. Hay, and S.D. Gaines, Eds. *Marine Community Ecology*.
Sunderland, MA: Sinauer, pp. 317-337.

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**PowerPoint slides:**

**PowerPoint 5.1** Lecture Outline

**PowerPoint 5.2** Global Distribution of Coral Reefs

**PowerPoint 5.3** Coral Biology and Morphology

**PowerPoint 5.4** Coral Morphology

**PowerPoint 5.5** Reef Zonation: the Backreef

**PowerPoint 5.6** Reef Zonation: the Reef Crest

**PowerPoint 5**.**7** Reef Zonation: the Forereef

**PowerPoint 5**.**8** Reef Inhabitants

**PowerPoint 5.9** Seagrass Beds

**PowerPoint 5.10** Mangrove Forests

**PowerPoint 5.11** Some Examples of Ecosystem Services Provided by
Reefs

**PowerPoint 5.12** Some of the Recent Changes in Coral Reefs

**PowerPoint 5.13** Caribbean Reef Decline Case Study

**PowerPoint 5.14** Overfishing on Coral Reefs

**PowerPoint 5.15** Coral Disease Outbreaks

**PowerPoint 5.16** Increasing Ocean Temperatures and Coral Bleaching

**PowerPoint 5.17** Smaller Scale Threats to Coral Reef Health

**PowerPoint 5.18** Managing Coral Reef Ecosystems

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**General Requirements:**

The Instructor should review some of the additional background reading
and prepare handouts for students based on the accompanying PowerPoint
presentation.

The content of this session should be presented as a lecture. Class
discussion can be encouraged in Objectives 5.3 and 5.4. Students could
be asked about their experiences on coral reefs and their awareness of
the threats facing reefs. The Instructor could also lead a discussion on
the many factors (political, geopolitical, scientific, social, economic,
etc.) that have to be considered in mitigating some of these natural and
anthropogenic hazards. Students should read the session readings before
class and use them as resources for further investigation.

> \[**PowerPoint 5.1** Lecture Outline\]

**Supplemental Considerations**:

The material in Objectives 5.1 and 5.2 is fairly straightforward and
well accepted. The ecosystem services provided by coral reefs (Objective
5.3) are generally accepted, but are not as well documented. In
contrast, the relative importance of different threats facing reefs is
controversial and hotly debated among reef ecologists and
conservationists. Some of the threats, widely assumed by scientists and
the public to play an important role (e.g., nutrient pollution) are
actually only marginally supported by rigorous science. It might be
appropriate to emphasize some of these issues and the difficulties
facing scientists trying to untangle the many potentially important
threats (e.g., limited funding and trained scientists, the challenge of
working underwater, the large temporal and spatial scales involved, and
the geographic isolation of most reefs in respect to the home base of
most governmental, non-governmental organization (NGO), and academic
scientists).

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**Objective 5.1 Understand the basic ecology, global distribution, and
structure of coral reef communities**.

**Requirements:**

The content should be presented as lecture, supported by PowerPoint
slides.

**Remarks:**

\[**PowerPoint 5.2** Global Distribution of Coral Reefs\]

\[**Power Point 5.3** Coral Biology and Morphology\]

\[**PowerPoint 5.4** Coral Morphology\]

\[**PowerPoint 5.5** Reef Zonation: the Backreef\]

\[**PowerPoint 5. 6** Reef Zonation: the Reef Crest\]

\[**PowerPoint 5**.**7** Reef Zonation: the Forereef\]

\[**PowerPoint 5**.**8** Reef Inhabitants\]

**Global distribution of tropical, shallow water coral reefs
\[PowerPoint 5.2\]**

Tropical coral reefs are found throughout the world in shallow, warm,
oligotrophic (nutrient-poor) oceans. As a taxonomic group, corals are
hundreds of millions of years old, however, they only form large reefs
under optimal environmental condition. During the last several million
years, this has been during inter-glacial periods. The world's current
living and growing reefs are between 3000 and 7000 years old. Although
corals can be found in most ocean habitats at nearly any depth, the
fast-growing corals that build reefs require clear, warm waters, with
plenty of light and minimal nutrients.

**Biology of corals and their role in generating reefs \[PowerPoint 5.3;
5.4\]**

Coral reefs are generated by the accretion of the calcium carbonate
skeletons of reef-building corals. Corals are Cnidarians, and are
related to sea anemones and jelly fish. Reef-building corals form
colonies of small polyps. The coral tissue is just a thin veneer
covering the skeleton below. Most corals grow quite slowly, but some
branching species can extend 10-15 cm/year.

Corals eat zooplankton and also acquire energy from the symbiotic
zooxanthellae; single-celled organisms that can photosynthesize and live
within the coral tissue. The mutualistic partnership between corals and
zooxanthellae is the key to their success and the presence of tropical
coral reefs.

**Zonation of a typical reef**

Most coral reefs communities can be broken down into three major zones:

**Backreef: \[PowerPoint 5.5\]** This zone is closest to the shore, and
is generally protected from breaking waves by the reef crest. It is
relatively low energy, but experiences greater fluctuations of
temperature and salinity and is often characterized by greater
sedimentation rates. Backreef species are often adapted to coping with
such environmental variability (e.g., many backreef corals can shed
sediments). Back reefs are shallow (usually \< 3 m) and are dominated by
seagrass beds, small patch reefs, and sand and rubble flats. Predatory
grunts and snappers migrate from the forereef to the backreef to hunt
for fish and invertebrates.

**Reef flat and Reef crest: \[PowerPoint 5.6\]** This is the highest
energy zone of the reef. Breaking waves make this a very harsh physical
environment, usually dominated by encrusting algae and very robust coral
species.

**Forereef: \[PowerPoint 5.7\]** The forereef is the optimal habitat for
most coral species. It is dominated by reef-building corals and is the
most diverse zone on the reef. Different species of corals usually
characterize different depths of the forereef. In the Caribbean, the
shallow forereef zone is dominated by elkhorn coral and the deep
forereef is dominated by staghorn and boulder corals. The actively
accreting living reef usually extends down to 30 to 40 m. Below this
depth, light limitation slows coral growth and reef accretion. Sponges
and soft corals are often abundant at this depth.

**Community inhabitants of reefs \[PowerPoint 5.8\]**

Coral reefs are inhabited by thousands of species of invertebrates,
algae, fish, and microorganisms. The exact species diversity on reefs is
unknown, but has been estimated to be about 10,000 to 50,000 species on
a single reef. In general, Pacific reefs are much more diverse than
Atlantic and Caribbean reefs. The species associated with reefs are
dependent on the physical structure generated by corals. When corals
die, this structure slowly erodes and bottom becomes less heterogeneous.

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**Objective 5.2 Outline two other coastal, tropical habitats often
associated with reefs.**

**Requirements:**

The content should be presented as lecture, supported by PowerPoint
slides

**Remarks:**

\[**PowerPoint 5.9** Seagrass Beds\]

\[**PowerPoint 5.10** Mangrove Forests\]

**Seagrass beds \[PowerPoint 5.9\]**

Seagrass beds are a shallow-water habitat usually associated with coral
reefs. Seagrasses are typically found in the shallow, calmer waters of
the backreef zone. When ungrazed by herbivores (e.g., sea turtles, fish,
and urchins), the blades of sea grasses can be 20-30 cm in length.
Predator movements are hindered by this structure, so many prey species
(especially juvenile fish) seek refuge in seagrass beds.

**Mangrove forests \[PowerPoint 5.10\]**

Mangrove forests are a tropical forest community that typically inhabits
the intertidal zone of protected shorelines. Mangrove forests in the
Caribbean are generated by three species of mangroves, a specialized
type of tree that is adapted to living in the waterlogged, highly saline
conditions of this habitat. Mangrove forests also serve as predation
refuge and nursery habitat for fish and provide nesting habitat for
countless birds. Mangroves also play a key role in buffering coastal
shorelines against erosion and can generate new land by the accretion
and stabilization of sediments. The main threats to mangroves are
coastal development and aquiculture (they are often replaced by shrimp
farms).

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**Objective 5.3 Discuss some of the ecosystem goods and services
provided by reefs**.

**Requirements**:

The content should be presented as lecture, supported by PowerPoint
slides

**Remarks**:

\[**PowerPoint 5.11** Some Examples of Ecosystem Services Provided by
Reefs\]

**Storm buffers**

Coral reefs buffer island and mainland shorelines against large waves,
reducing coastal erosion and the impact of hurricanes.

**Tourism**

Healthy coral reefs with intact fish assemblages can be a major tourist
draw. In the Florida Keys alone, this supports a \$1.6 billion/year
industry. In the Caribbean, the recreational income based on coastal
activities (e.g., diving, snorkeling, and fishing) has been estimated to
be \$8.9 billion/year (\>50%of the regional GNP).

**Fishing**

Commercial and recreational fishing industries in coastal tropical
waters are often dependent on healthly coral reefs. Coral reef fisheries
account for:

• 10% of fish harvest in tropical countries

• 25% of fish catch in developing countries

• 90% of protein consumed by people on Pacific islands

**Biodiversity and bioprospecting**

The biodiversity of corals reefs is worth protecting on moral and
ethical grounds, but it also holds great promise for new biomedical
products. For example, some sponges contain active compounds that have
been successful in treating caners in laboratory trials.

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**Objective 5.4 Discuss the main hazards to coral reef communities and
some of the management strategies designed to protect them.**

**Requirements:**

The content should be presented as lecture, supported by PowerPoint
slides.

**Remarks:**

\[**PowerPoint 5.12** Some of the Recent Changes in Coral Reefs\]

\[**PowerPoint 5.13** Caribbean Reef Decline Case Study\]

\[**PowerPoint 5.14**, Overfishing on Coral Reefs\]

\[**PowerPoint 5.15** Coral Disease Outbreaks\]

\[**PowerPoint 5.16** Increasing Ocean Temperatures and Coral
Bleaching\]

\[**PowerPoint 5.17** Smaller Scale Threats to Coral Reef Health\]

\[**PowerPoint 5.18** Managing Coral Reef Ecosystems\]

**Coral reefs \[PowerPoint 5.12\]**

Coral reefs throughout the world have been substantially altered ever
since humans began exploiting their bountiful resources, however, this
change has been especially rapid during the last 20-30 years.

> • Coral cover on most Caribbean reefs has been reduced from about 60%
> to less than 10% over the last 20 years.

• As a result, reef heterogeneity (structural relief) is being lost.

• Macroalgae now dominate most Caribbean reefs and some Pacific reefs.

• Reef fish biomass and diversity has been severely reduced.

• Several species of reef invertebrates are being overexploited.

• Many of these shifts are global, and can be seen on even isolated
central Pacific reefs. \[PowerPoint 5.13\]

**Overfishing \[PowerPoint 5.14\]**

The overfishing of reef fish and invertebrates has reached truly severe
proportions on most of the worlds reefs. Many lack whole functional
groups and large vertebrates (sharks, tuna, sea turtles, manatees, etc.)
are rare in much of the Caribbean. The near removal of hervbivorous fish
on many reefs has caused outbreaks of macro algae, which hinders the
recovery of coral populations after natural and anthropogenic
disturbances.

**Disease outbreaks \[PowerPoint 5.15\]**

In the Caribbean, recent disease outbreaks (called epizootics) have been
the main cause of the loss of coral cover. Populations of all key
reef-building species have declined due primarily to epizootics. In
addition, other important species including the spiny sea urchin, a
keystone herbivore, have been devastated on a regional scale. Ecological
and paleontological monitoring studies indicate that coral epizootics
have become more diverse (affecting more host species), severe (they
have greater effects on host populations), and prevalent. There are
several potential explanations for this:

> • Increased host susceptibility (due to increasing sea surface
> temperature or other stresses)

• Pathogen introductions (due to deforestation, canals, ballast water)

• Increased pathogen virulence (due to temperature increases and
nutrient pollution)

**Global climate change \[PowerPoint 5.16\]**

Increasing sea surface temperatures pose a major threat to short and
long term coral reef health. Corals live very close to their upper
thermal limits. An increase of only 1°C over the usual summertime
temperature can cause corals to "bleach", which is the result of the
death or expulsion of the symbiotic zooxanthellae (corals tissue often
contains very little pigmentation). When the temperature increase is
lengthy or severe enough corals can die. In some cases the result has
been mass coral mortality events. In other cases, most or all bleached
corals can recover. The physiological stress could also make corals more
susceptible to disease. Bleaching is a major factor on Pacific coral
reefs, especially during severe El Niño events.

**Nutrient pollution**

Nutrient enrichment (mainly of nitrogen and phosphorus) is considered to
be a leading cause of coral reef decline. Excess nutrients could in
theory cause algal blooms and exacerbate coral disease epidemics (some
reef disease pathogens are thought to be nutrient limited in tropical
oceans). There are several potential sources of nutrient pollution on
coral reefs including:

> • runoff from terrestrial developments (e.g., garden and golf course
> fertilizers) and agriculture
>
> • deforestation which can release organic matter, sediments, and
> nutrients into watersheds and onto reefs

• untreated or marginally treated sewage

There is little consensus among reef ecologists on the importance of
nutrient pollution. For example, there is very little data that
demonstrates that nutrient concentrations are indeed increasing at large
scales in coastal waters. The relative importance of nutrient pollution
has been questioned by several leading coral reef scientists.

**Hurricanes**

Category 4 and 5 hurricanes can significantly impact reef communities.

Corals can be damaged and killed via sand scour, projectiles, and rapid
changes in temperature and salinity if there is heavy rainfall.

Fish and invertebrates can also be affected. Recovery takes 10-100
years, depending on the extent of the damage and the availability of
sexual propagules from nearby reefs.

Recovery on Pacific reefs is generally faster than on Caribbean reefs
(probably due to greater recruitment of juvenile corals).

Hurricanes are a natural disturbance agent on coral reefs communities,
that can in some cases increase community diversity by preventing
superior competitors from excluding other species.

Many reef species are well adapted to deal with all but the most severe
hurricanes. However, if the frequency or severity of hurricanes
increased (e.g., as a result of global climate change), then the overall
negative impact on reefs could become more significant.

**Other small-scale threats**

There are numerous additional threats that can negatively affect reef
ecosystems, and corals in particular, at local scales. While these
factors are significant and can degrade local reefs, their impacts are
patchy in space and are generally not pervasive. Therefore, they are
rarely significant at regional scales (e.g., throughout the entire
Caribbean).

Some of these threats have been successfully mitigated over the last 10
years by local mangers and NGOs (e.g. reef relief:
<http://www.reefrelief.org/main.html)>. For example, mooring balls have
largely removed damage from small boat anchors to reefs in the Florida
Keys National Marine Sanctuary (http://www.fknms.nos.noaa.gov/).

• Anchors from small boats and cruise ships can damage reefs and kill
corals.

> • Ship groundings can kill corals and other sessile organisms and can
> severely impact the reefs structure, sometimes gouging large rifts in
> reefs. This has been a significant problem in the Florida Keys.

• Divers and snorkelers can harm, break, and kill coral by standing on
or grabbing it.

> • Coastal development can increase runoff and sedimentation on reefs,
> which can kill corals.
>
> • Collecting for home aquaria and commercial trade can harm the
> populations of fish and invertebrates being removed as well as
> reef-building corals that are harmed by some collection techniques
> (e.g., the use of poisons and explosives). This is a major and large
> scale threat in some regions (e.g., the Indo-Pacific)

**Integrated ecosystem management \[PowerPoint 5.18\]**

These and other threats to coral reefs act on different temporal and
spatial scales. Their relative importance and synergistic effects also
appear to vary among regions and oceans. These factors and the sheer
numbers of threats will make it difficult to conserve and manage coral
reefs. Some threats could be effectively managed by local and regional
managers, solutions, and legislation. Others (e.g., global warming) will
have to be addressed at both national and international levels.

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