THE GOOD NEWS ON

CORAL REEFSPeter Ridd

The Global Warming Policy Foundation
Note 33

The Good News on Coral Reefs
Peter Ridd
Note 33, The Global Warming Policy Foundation© Copyright 2022, The Global Warming Policy Foundation

Contents
About the author	iiiIntroduction	

1What is coral cover? 	

1

AIMS and the reef surveys	1

Why coral is not 100% on a coral reef	2Coral cover in the reef as a whole	

2

Reconstructing the missing averages	

3Final comment	

4Note	

5

About the Global Warming Policy Foundation	

6

About the authorPeter Ridd is a physicist. He has researched the Great Barrier Reef since 1984, and has publishedover 100 scientific publications. A former head of the Marine Geophysical Laboratory at James
Cook University, Townsville, Australia, he was fired in 2018 for pointing out quality assurance deficiencies in reef-science institutions.

iii

Introduction
Up to 2016/2017, the Australian Institute of Marine Science (AIMS) published aggregate datafor coral cover on the Great Barrier Reef (GBR).
Since then, only disaggregated data has been
made available. This paper examines AIMS’ explanation for this decision, and recreates theaggregate figure for recent years, showing thatAIMS has effectively hidden the good news oncoral cover.

What is coral cover?
Coral cover is a measure of abundance; it is thepercentage of the seabed that is covered withcoral. The measure reduces after major cyclones,
when coral-eating starfish numbers increase,and after some bleaching events. Coral cover at
a given location usually takes five to ten years torecover from these events. Coral cover on an individual reef can drop to just a few percent after
a major mortality event. It fluctuates naturallywith time.

AIMS and the reef surveys
Since 1986, the Australian Institute of Marine
Science (AIMS) has surveyed roughly 100 of the3000 coral reefs of the Great Barrier Reef (GBR).
The data is published on its website.1
The data is broken into three regions: Northern, Central and Southern. These regions arebroken down further into ‘sectors’, with 3, 5 and3 sectors in the Northern, Central and Southern
regions respectively. For each of the 11 sectors,
there are roughly 5–10 individual coral reefs surveyed each year. The survey for each reef is performed by towing a diver around the perimeterof each reef. The diver observes coral cover overa 140-m distance and estimates the percentage
cover. The perimeter of each reef is many miles
long, so there could be 50–100 sample transects
for each reef.
The coral cover for each reef is an aggregate of the figures of all the 140-m-long sample
points. The cover for each sector is an aggregateof all sampled reefs in the sector. The cover forthe three regions can be calculated by aggregating the data from the contributing sectors.
The sector data for 2022, as found on the
AIMS website, is shown in Table 1.
1

Table 1: Great Barrier Reef
coral cover by sector.
Uncertainty estimates vary, but
are typically between 5 and 10%
according to the AIMS graphs for anindividual sector.

SectorCape GrenvillePrincess Charlotte Bay
Cooktown/Lizard Island
CairnsInnisfailTownsville
Cape Upstart
Whitsunday
PompeySwainsCapricorn Bunkers
Average (unweighted)

2022 cover (%)
47.0
41.0
25.3
29.5
15.6
34.7
30.0
37.4
31.8
21.8
58.6
33.9

Why coral is not 100% on a coral reef
Coral cover is the percentage of the seafloor covered with coral.
It is often assumed that coral cover should be 100% on a healthy
coral reef. However, a reef is made of many different ecosystems.
These include coral sand made from broken down coral, ancientdead coral ‘rock’, soft corals, algal beds, and the hard crustosecoralline algae that help cement together the dead coral on areef. Dead coral is like concrete – it does not rot like wood. Coral grows on the dead bodies of their ancestors, and in doing sobuild ‘reefs”. Most of the reefs of the GBR have built up 50 to 100
meters above the surrounding seafloor in the last million years.

Coral cover in the reef as a whole
Up to 2017, AIMS published the average for the Great Barrier Reef.
The relevant graph, taken from the report for 2016/17 is shownin Figure 1. However, ever since, it has only issued disaggregatedfigures.
Its explanation, although never stated formally, is that it
does not regard a single figure (the average) as representative of
Figure 1: Aggregate GBR
coral cover 1986–2017.
As published on the AIMS website.
This was the last year it publishedaggregate data.

2

the full diversity of the conditions on the reef. That is correct, but
the average is nevertheless an interesting statistic, and the region, sector, reef and 140-m transect data is available for anyone
wanting a more detailed discussion.
AIMS is also being inconsistent. It aggregates transect data
to produce a single number for each surveyed reef. It aggregates
reef data to produce a single number average for each sector. It
aggregates reef/sector data to produce a single number averagefor each region. So why does it not aggregate reef/sector/region
data to produce a single number average for the entire GBR?
Nevertheless, AIMS should be congratulated. Over the last
30 years, it has now towed divers a distance roughly equivalent
to the circumference of the world. The result is a remarkabledataset.

Reconstructing the missing averages
With the sector data freely available, it remains straightforward
to prepare an average coral cover figure for the whole GBR, for1986 to 2022. This is shown in Figure 2. The average as at 2022
is found to be 33.9%, with an uncertainty of about 4 percentage
points. This assumes equal weighting of each sector. This is thehighest level on record.
Figure 2 makes it clear that AIMS has effectively hidden thevery good news about the reef between 2016 and 2022 by not
publishing the GBR average data since 2017. It is very unusual for
all three major regions, and almost every sector, to be well above
average at any moment in time. For example, the waves caused
by a large cyclone will often kill large amounts of coral over avast region, so some sectors are often recovering from such an
event and have low coral cover. Only by seeing all the data ag-

Figure 2: Aggregate GBR
coral cover 1986–2022.

30
Percentage coverPrepared by the author. AIMS
averages are used for 1986–2017,with the figures for subsequent years
prepared from the sector data in
Table 2.

40

20

10

0

1990

1995

3

2000

2005

2010

2015

2020

gregated as an average for the entire reef can the exceptional state of
the coral cover be appreciated. AIMS shows graphs for all three regions,and all have very high coral cover – but none are record-breaking highs.
Because there is roughly a 1-in-3 chance that a region has very high coral
cover, there is only a 1-in-27 chance that all three are high simultaneously,
as is the case in 2022.
It is surprising that AIMS no longer provides an average coral coverfor the entre GBR, because they have previously made far reaching claims
about its poor state based on reef-wide average data. For example, when
the coral cover hit a low point of around 10% in 2011, after major cyclones destroyed large amounts of coral, AIMS authors De’ath et al. (2012)
wrote in a very high-profile paper, that was widely quoted in the world
media, the following:
Without significant changes to the rates of disturbance and coral growth,coral cover in the central and southern regions of the GBR is likely to decline to 5–10% by 2022. The future of the GBR therefore depends on decisive
action. Although world governments continue to debate the need to cap
greenhouse gas emissions, reducing the local and regional pressures is one
way to strengthen the natural resilience of ecosystems.

This prediction of 5–10% for 2022 has clearly turned out to be incorrect; as we have seen, the average coral cover for all the regions is now
over 30%. By no longer publishing the GBR average, AIMS has obscured
the good news for 2022, and drawn a veil over their inaccurate predictionof a decade ago.

Final comment
The latest data on the GBR indicates it is in good shape. It happens tohave a great deal of coral in 2022 because there have been few major
mortality events over the last five to ten years. The three or four bleaching
events since 2016, which have been widely reported in the media, could
not have killed much coral, otherwise the 2022 statistics would not be sogood.
The data since 1986 shows that every region, every sector and mostreefs have had occasionally had periods of very low coral cover for one
reason or another. This is entirely natural. The media makes much of occasional setbacks to coral cover, but a measure of the health of an ecosystem is the ability to recover from a major stress. Frail systems will not recover, robust systems recover well, just as healthy people recover quickly
from disease.
The GBR has proven to be a vibrant and healthy ecosystem. Thisshould not be a surprise; there are few human pressures on the reef, and
it is well protected. It is also unreasonable to expect that the small temperature rise over the last century (1°C) will have caused much impact, especially as it is well known that most corals grow faster in warmer water.
The data collected by AIMS shows that the GBR is a robust systemwith rapidly fluctuating coral cover. We must expect that, sometime in
the future, a sequence of events will cause the coral cover to fall sharply,
as it did in 2011. We must then remember that this is almost certainly
natural, and not allow the merchants of doom to depress the children.
4

Table 2: Coral cover by sector and region, 2017/18–2021/22
Sectors
Cape Grenville
PCB (Princess Charlotte Bay)
Cooktown/Lizard Island
CairnsInnisfailTownsville
Cape Upstart
Whitsunday
PompeySwainsCapricorn Bunkers
GBR averageassuming equal weight by sector

2017/18 2018/19 2019/20 2020/21 2021/22
23.8
26.4
29.2
34.6
47.0
20.4
20.5
16.3
26.9
41.0
9.0
10.2
12.8
21.4
25.3
14.6
13.1
13.5
22.9
29.5
10.4
12.3
10.2
13.3
15.6
19.4
18.8
19.6
26.6
34.7
24.2
24.2
24.2
25.8
30.0
29.6
24.4
24.4
29.3
37.4
20.2
18.5
25.1
33.4
31.8
29.7
20.4
24.2
25.4
21.8
39.4
49.1
44.5
52.6
58.6
21.9

21.6

22.2

28.4

33.9

17.7

19.0

19.4

27.6

37.8

19.6

18.6

18.4

23.6

29.4

29.8

29.3

31.3

37.1

37.4

Regions
Northern Region
Grenville, PCB, Cooktown/Lizard Island
Central Region
Cairns to Whitsunday
Southern Region
Pompey, Swains, Capricorn Bunkers

Source: AIMS data. Shaded entries indicate sectors not surveyed. The results of the previous survey have been used instead.

Note

1. https://www.aims.gov.au/docs/research/monitoring/reef/latest-surveys.html

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