by Martin Williams
(Appeared in the April/May 1999 issue of Action Asia.)
It's over. The coral bleaching that started off the coast of Australia early last year, then spread like a rash to make 1998 the worst year in history for bleaching worldwide, has at last ebbed and died away. In its wake, there's a chance to reflect on its impacts and possible causes, and to take action that may forestall further such events.
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You may already have seen the kind of data that reflects the severity of the bleaching (which, in essence, involved stressed corals losing their algae and appearing white or translucent; some may have later regained algae, many others simply died): perhaps ten percent of the world's corals were killed, with divers at locations as widespread as the Great Barrier Reef, the Philippines, the Seychelles, Tanzania and Jamaica reporting that 70 percent or more of the corals had bleached; although most affected corals were in shallow waters, bleaching was observed at depths down to 50 metres; some coral colonies that were hundreds of years old bleached and died. As well as the hard corals that typically suffer bleaching, soft corals, anemones, sponges and giant clams were affected. Commented divers after a visit to a site in Palau, "Everything that could bleach was bleaching."
For all that there was a plethora of grim reports, the bleaching was far from uniform. Even in the worst hit areas it was often patchy, with barely affected or unaffected reefs close to others that were devastated; the central Pacific, including Hawaii, was untouched. But the effects are set to be long lasting.
This February - a year after the onset of bleaching - Dr Bette Willis, a marine biologist with Australia's James Cook University, dived over the worst hit area of the Great Barrier Reef. "Staghorn (Acropora) corals had been especially badly affected," she says. "Now, most are covered in algae, and losing their structure. When you swim over, it's like being above an algal mat or an algal thicket rather than a coral reef." Willis has been studying the area for over twenty years, and says this was probably the most severe bleaching event she has seen.
The region that suffered most from the bleaching was the Indian Ocean, where reefs from Sri Lanka to Kenya and the Seychelles whitened and died, and Reef Check surveys revealed an overall decline in live coral cover from 80 percent in 1997 to 64 percent in 1998. In a paper due for publication in Ambio, six authors including Reef Check coordinator Gregor Hodgson and Clive Wilkinson, coordinator of the closely allied Global Coral Reef Monitoring Network, assess the known and likely impacts of the coral mortality. Economic losses loom, as a result of tourism declining, fisheries changing and perhaps dropping considerably, and increased coastal erosion if reefs disintegrate. Though acknowleding there are many uncertainties, the authors have estimated the losses for an "optimistic" scenario, in which the reefs aren't too badly damaged and recover relatively rapidly, and a "pessimistic" one, in which severely damaged reefs recover slowly or not at all. They put the losses over the coming twenty years at around US$700 million in the optimistic case, and over US$8 billion if the pessimistic scenario plays out - but say these figures can't express the potential human suffering.
Even if the reefs do recover, it will be 5 to 10 years before the fast growing, branching and plate corals are of any decent size, while the more massive corals may take 25 to 50 years to recolonize. In the meantime, there will be changes in species compositions, from a current preponderance of massive corals - which are less affected by bleaching - to the mix of branching, plate and massive corals we have been accustomed to. A host of other changes in reef ecology will also happen, though are impossible to predict with any precision. As algae multiply, herbivores will increase. Coral feeders like butterfly fish will be be scarce now, recovering only as the coral does.
But will the reefs recover? No one can say for sure. Corals have proven resilient in geological time, surviving ice ages and other traumas. Today, though, they are assaulted by a barrage of woes resulting from human activities, including over-exploitation and pollution. And, perhaps, global warming.
There is a body of evidence pointing to global warming (resulting from the greenhouse effect) underlying recent bleaching events. Mass bleaching events were not even recorded until 1979, since when they have become almost commonplace, with most linked to water temperatures higher than the warmest the affected locations normally experience. The increase in bleaching is roughly in tandem with the reported increase in the earth's surface temperature which, in turn, roughly follows the build up of greenhouse gases: last year's bleaching event coincided with the highest tropical sea surface temperatures in the modern record. A handful of coral scientists have become so convinced by the evidence that they have announced that bleaching is one of the first massive ecological changes we are seeing as a result of the greenhouse effect: likc canaries in a mine, the reefs are telling us that things are going awry and far worse will happen if we don't take dramatic remedial action.
But the evidence isn't proof; the situation is complex. There hasn't been anything like a steady year-on-year change in the number of bleaching events - which can escalate during El Nino, as happened last year. Then, we don't know if the observed warming is really due to the greenhouse effect, or is just some natural "blip" that the earth experiences from time-to-time, or is even due to the sun heating up. This leaves most coral scientists unwilling to pronounce with any certainty on whether the bleaching events we have seen are linked to global warming. "Most scientists consider me an extremist for even accepting the possibility that global warming might have been partly responsible for last year's bleaching episode," says Gregor Hodgson.
For all the caution, there is widespread consensus that the bleaching event was a harbinger of things to come if predictions of global warming prove correct. An international summit meeting on coral bleaching - held in November last year - concluded with a statement reflecting this,though only recommended further research. Reef Check has proven less circumspect: the program's 1998 summary report calls for reductions in greenhouse gas emissions.
While lowering greenhouse gas emissions is something no one of us can play a major role in, Hodgson is focused on developing the activities of Reef Check, which is heavily dependent on volunteers (if you are interested in helping, check the web page at: http://www.reefcheck.org/participate.html; the program's headquarters is in the Hong Kong University of Science and Technology). "We need to expand from working in around 40 countries now to 140," he says. Since Reef Check is the only monitor of the world's reefs that has a standardised methodology, expansion will enable scientists to far better gauge the state of the world's corals, and how they are changing.
Reef Check is not just about passive monitoring. Hodgson is hoping the program can help boost protection of reefs, by promoting good management techniques that involve local communities. Healthier reefs should in turn help speed recovery from bleaching, by producing more coral larvae.
If monitoring is greatly expanded and good management techniques are implemented, Hodgson and the myriad other people whose lives are interlinked with coral can do little but continue their calls for action to limit greenhouse gas emissions - and, hope and pray that the 1998 bleaching was a one-off event.
To see which areas may be currently threatened by bleaching, visit the National Oceanic and Atmospheric Association web page with a map showing potential coral reef bleaching hotspots at http://psbsgi1.nesdis.noaa.gov:8080/PSB/EPS/SST/climohot.html (evidence to date suggests bleaching in an area is likely when satellite data reveals sea surface temperatures are 1 C or more above the average for that area's warmest month of the year). You can also find archived data here, as well as comments on hotspots and bleaching reports.