Debate Over Future of Coral Reefs

Terry Done tdone at
Mon Jan 17 23:14:47 EST 2000

Dear Jim,

Thanks very much for giving the bleaching debate another airing. Hopefully
all coral-listers who can will make it to Bali for 9ICRS where there should
be a good session on 'Global Climate Change and Coral Reefs'.
(See the homepage at

Seasons greetings to you and all coral-listers.


Terry Done


Debate over future of coral reefs

Planet Ark has produced an attention-grabbing article on coral reefs and
how they may respond to global climate change, in particular, the warming
of the seas.  The article's headline and its bottom line are the same: the
topic is a subject of debate among scientists. On the affirmative side are
the 'government scientists' (Done and Sweatman), who, the article states,
'believe Australia's Great Barrier Reef and other major world coral
formation can adapt to rising ocean temperature'. On the negative side is
the academic Ove Hoegh-Guldberg, who, on the basis of a wide ranging
review, was highly pessimistic: 'there is no evidence coral reefs could
simply adapt to changes in the ocean's temperatures or repopulate with
coral from other reefs' says the Planet Ark journalist.  In fact, I am far
less confident than the "..can adapt
" quote implies, as can be seen in a
careful reading of the direct quotes attributed to me: "
. may not be as
",  "
may give them greater resilience
.". However I
believe it is important that issues of biodiversity and resilience are seen
as part of the climate change and coral reefs debate.

I encourage interested readers of coral-list to dig into this issue as much
as you can, as we are discussing the future of what attracts us all to be
on this list. For starters,  Ove's  review is Hoegh-Guldberg, O. (1999)
"Climate change, coral bleaching and the future of the world's coral
reefs", Mar. Freshwater Res., 1999, 50, 839-966. Another great source is
the output of a four-year SCOR working group 'Coral reefs and environmental
change- adaptation, acclimation or extinction', published as a complete
number in American Zoologist Vol 39. My paper is Done, T.J. (1999) Coral
community adaptability to environmental change at the scales of regions,
reefs and reef zones. American Zoologist, 39, pp. 66-79, and I am happy to
send a reprint.  Another focus for the debate will be the 'Coral Reefs and
Global Climate Change' session at the 9th International Coral Reef
Symposium in Bali, 23-27 October 2000.

Back to the Planet Ark article, where there are two stories mixed together.
 The first is what did happen to reefs in the Great Barrier Reef in the hot
Austral summer of 1997-98. The second is what might happen to this and
other reef systems during the 21st Century if global and regional climates
heat up and otherwise change as we enhance the greenhouse effect by burning
fossil fuels. The first is a report on data: the second is a set of
predictions based on a mixture of knowledge and surmise. 

At AIMS and the Great Barrier Reef Marine park Authority we have some data
for the first story, which shows that compared to other places, we got off
very lightly on the Great Barrier Reef. (The monitoring data and a series
of bleaching items may be viewed on AIMS homepage at  The
results of GBRMPA aerial surveys of over 600 reefs are reported by
Berkelmans and Oliver in Coral Reefs: 18: 55-60.) There were some seriously
bleached reefs in shallow waters within 20 km of the coast between 17 and
19 degrees S,  leading to significant mortality, mainly in faster growing
corals around 5 - 30 years of age. The majority of reefs offshore - those
where most tourism and diving are conducted - suffered negligible bleaching
or death.  The Planet Ark article quotes Ove as saying " To risk industries
like tourism and fishing with unfounded statements
[that the reefs can
adapt].. seems foolhardy."  I agree.  However the immediate risks to the
tourism industry of incorrectly spreading a perception that the Great
Barrier Reef is in generally poor shape when it is in fact good, are of
more immediate concern than the risk of long-term degradation under global

The second story concerns making an assessment about the future.  Contrary
to the impression given by the Planet Ark article, I consider Ove's gloomy
prognostications to have high credibility.  Indeed,  if one accepts the
region by region projections about increased sea temperatures are correct,
and the case that has been made that bleaching thresholds for corals will
increase too little and too slowly, things look bad for coral reefs. 

However I also spend half my waking life thinking of coral reefs as being
interconnected. Their local populations are spatially distributed elements
of metapopulations that are connected by larvae that disperse with the
currents and periodically renew their association with compatible
zooxanthella strains.  In the Great Barrier Reef context (and definitely
not as a generalization to all reefs), I feel hopeful, if not totally
confident, that there will be sufficient transport of more heat-resistant
zooxanthellae and coral larvae from the north, to the now warming seas of
the south.  Temperture differentials along onshore/ofshore axes and between
shallow and deep zones of individual reefs also suggest there may be some
scope for localised adjustment species distributions within reefs. If Ove's
worst case predictions of annual coral bleaching on the Great Barrier Reef
by 2030 are realized, and they  are accompanied by widespread coral
mortality, I am not at all confident that the rate of southward migration
and/or localised redistribution of corals will  prevent a prolonged period
of phase shift to algae.  These are important subjects for
interdisciplinary research.

"We need more research to find the answers
." concludes Ove in the Planet
Ark article.  Yes, and according to my postulate, we also have here yet
another strong case for strategic development of marine protected areas in
a global network.  Sources in already warmer areas to replenish down-stream
reefs depleted by heat-induced bleaching, on top of the other insults we
know so well.

>Date: Thu, 13 Jan 2000 14:49:13 -0500
>From: "Billy Causey" <Billy.Causey at>
>Organization: FKNMS
>X-Mailer: Mozilla 4.7 (Macintosh; U; PPC)
>X-Accept-Language: en
>        coral list <coral-list at>
>Subject: Debate Over Future of Coral Reefs
>Sender: owner-coral-list at
>Reply-To: "Billy Causey" <Billy.Causey at>
>An article for your review:
>PLANET ARK: Debate warms up over future of coral reefs
>BRISBANE, Australia - It's the year 2100 and the once Great Barrier Reef
>is a lifeless skeleton few people visit, a victim of global warming.
>Or maybe not.
>Some scientists see a very different picture and believe Australia's
>Great Barrier Reef and other major world coral formations can adapt to
>rising ocean temperatures.
>Reefs are good barometers of climate change because they are sensitive
>to ocean temperatures. Parts of them can die if the temperature rises
>just a degree or two above normal and scientists are worried because
>such events, called bleachings, are growing in frequency and intensity.
>A report by the Australian Institute of Marine Science (AIMS) says the
>Great Barrier Reef, off Australia's northeast coast, came through severe
>bleaching in 1998 with a net increase in the amount of healthy hard
>coral over the past two years.
>Another report, sponsored by Greenpeace, had said global warming could
>devastate the world's coral reefs by early in the new millennium and
>could eliminate them from most areas of the planet by 2100.
>"The future for the Great Barrier Reef may not be as gloomy as a recent
>report claims," said Terry Done, senior principal scientist with the
>Australian government's AIMS.
>"The biodiversity of coral reefs may give them greater resilience than
>the (Greenpeace) report gives them credit for," he said.
>Bleaching occurs when coral becomes stressed and expels its life-giving
>microscopic plants called zooxanthellae. The plants provide the coral
>with food through photosynthesis.
>AIMS examined 47 reefs which are part of the World Heritage-listed Great
>Barrier Reef system and found that, while inshore reefs had lost up to
>75 percent of corals in the 1998 bleaching, reefs in deeper water were
>largely unaffected.
>"The current state of coral is not as bad as you might be led to
>believe," AIMS project leader Hugh Sweatman told Reuters.
>"In general, the reef is in good shape. The reefs which made up most of
>the world heritage area have shown net increases in hard coral in the
>past two years."
>Sweatman's upbeat assessment contrasts with the Greenpeace-backed report
>in July by Sydney University's Coral Reef Research Institute (CRRI).
>That report predicted the Great Barrier Reef, which comprises 3,000
>individual reefs, faced annual coral bleaching as oceans warm. It said
>the entire reef was at risk of being killed off in 100 years.
>The CRRI report's author, coral reef physiologist Ove Hoegh-Guldberg,
>said there was no evidence coral reefs could simply adapt to changes in
>the ocean's temperatures or repopulate with coral from other reefs.
>"We don't have any experimental data to base that on," Hoegh-Guldberg
>told Reuters.
>"Therefore to make the escape clause that coral bleaching isn't a
>problem because corals will get better at adapting over time is
>unfounded," he said.
>Hoegh-Guldberg, who has studied coral bleaching for the past 15 years,
>said coral reefs would not have time to recover if bleaching became a
>regular event.
>He said corals were now living close to their upper temperature
>tolerance limit and bleaching events will be triggered by even slight
>water temperature rises of one or two degrees Celsius.
>"Corals tend to die in great numbers immediately following coral
>bleaching events, which may stretch across thousands of square
>kilometres (miles) of ocean. Bleaching events in 1998, the worst on
>record, saw the complete loss of live coral from reefs in some parts of
>the world,"
>Hoegh-Guldberg said.
>He said bleachings are likely to occur annually in tropical oceans by
>the end of the next 30 to 50 years, meaning reefs won't have time to
>The result would be bleached skeletons unable to support a fraction of
>the fish species that now depend on them.
>Hoegh-Guldberg also said the loss of the reefs would have dire
>consequences for tourism as well as fisheries.
>His report said A$1.5 billion (US$960 million) was generated annually by
>tourism at the Great Barrier Reef, A$2.5 billion by Floridean reefs and
>about A$140 billion by Caribbean reefs.
>AIMS scientist Done argued that most of the Great Barrier Reef had
>escaped the 1998 bleaching lightly, even though some areas had been
>"Even on the handful of reefs where most of the corals died, hard
>individuals survived the trauma," Done said.
>"This suggests there are genotypes out there that are ready to take over
>as the seas warm. Currents will also tend to transport warm-adapted
>types from the northern Great Barrier Reef to the warming waters in the
>south," he said.
>The AIMS survey measured corals in six separate belts of the Great
>Barrier Reef and included fish counts and videotaping of coral to
>calculate coral cover.
>AIMS scientists said climate changes would likely alter the Great
>Barrier Reef rather than kill it off.
>Hoegh-Guldberg disagreed.
>"We need more research to find the answers," he said.
>"To risk industries like tourism and fishing ... with unfounded
>statements like this seems foolhardy."
>Billy D. Causey, Superintendent
>Florida Keys National Marine Sanctuary
>PO Box 500368
>Marathon, FL 33050
>Phone (305) 743.2437, Fax (305) 743.2357
Dr Terry Done
Leader Sustaining Coral Reefs Project
Australian Institute of Marine Science
PMB #3 Mail Centre,
Townsville Qld          4810

Phone 61 7 47 534 344
Fax   61 7 47 725 852
email: tdone at

WEBSITE for 9th International Coral Reef Symposium

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