Status of Coral Reefs of the World 2000

Status of Coral Reefs of the World: 2000
equal or even greater threat to coral reefs than direct anthropogenic impacts. Coral
bleaching and mortality due to elevated sea surface temperatures is one of several major
climate-related threats to coral reefs. Possibly the most alarming is evidence that increasing
concentrations of CO2 in seawater will reduce the rate of coral calcification, thus slowing
growth and increasing their fragility and capacity to build reefs. A major concern is that the
location and timing of the next bleaching event is unpredictable, and climate induced
bleaching can devastate pristine coral reefs as well as reefs which are effectively managed.
Thus, the agenda for coral reef conservation changed radically after the 1997-98 coral
mortality events. Until then, the major action to conserve coral reefs was to reduce direct
human impacts of land-based pollution and sediment releases, and over-exploitation, by
establishing Marine Protected Areas (MPAs). Now the fight has shifted to two fronts: the
need to increase management to abate direct anthropogenic impacts at all scales; and
action to study the impacts of global climate change on coral reefs and reduce global
emissions of greenhouse gases.
CORAL BLEACHING AND MORTALITY IN 1997-98
There is both encouraging and dismal news in the following summary reports on the coral
bleaching event of 1997-98 (and early 2000). The mortality after the bleaching was varied in
scope and scale with large parts of the Indian Ocean, Southeast Asia and the far western
Pacific being the most dramatically affected. In the wider Caribbean and parts of the Great
Barrier Reef, mortality was minimal even after extensive bleaching, as many severely
bleached reefs recovered almost fully. Over vast areas of the Pacific, there was no
bleaching (summarised in Chapter 1).
There are now encouraging reports of new recruitment on coral reefs in Eastern Africa, the
Seychelles, the Maldives and Palau indicating that sufficient parent corals survived to
provide some larvae, if not for the 1999 season, then for the 2000 spawning season.
However the down side is that many of the major reef building corals, such as Acropora
and Pocillopora are either recruiting in very low numbers or not at all. This will mean that
many of the affected reefs will be dominated by slow growing massive species that provide
poor habitat for fishes and are less attractive for diving tourists. Many reefs that were
dominated by large table and branching corals, now have a smaller, low profile corals.
It may be several years before we can state that the reefs will recover, or whether there will
be local losses of species, including the extinction of rare endemic species. Reef recovery is
dependent on few or no repeats of the extreme event of 1997-98, at least not within the
next 20 to 50 years which will be the time required for many of the reefs to recover to
structures resembling those before the bleaching. Recovery, in many cases, will also depend
on the reduction of human pressures through the application of sound management.
8