CORDIO Status Report 2000

Indian Ocean Islands:
• Coral mortality ranged from 50% to 90% over
extensive areas of shallow reefs in Seychelles,
Comoros, Madagascar and Chagos. In some
areas (around Mahe, Seychelles) the mortality
was almost 100%.
• Algal turf covered coral reefs throughout
much of the region by the end of 1998.
• Monitoring of potentially toxic epiphytic dinoflagellates
showed drastically increased concentrations
in areas where the corals had died.
• By early 1999, much of the dead coral in Chagos
was reported to be eroded to rubble preventing
recolonisation. At Socotra, much of
the coral rubble was washed ashore and could
be found in piles on the beach.
• Preliminary assessments of the reef fish communities
in Chagos indicated that abundance
and diversity was less than 25% of their former
levels.
South Asia:
• Bleaching was reported to depths of 40 m in
Sri Lanka and 30 m in Maldives resulting
from water temperatures of approximately
35° C during the period between April and
June 1998.
• In many areas in Sri Lanka and Maldives, nearly
90% of all corals died. At Hikaduwa and
Bar Reefs in Sri Lanka, close to 100% of corals
died and at the end of 1998, these reefs were
then covered by thick algal turf. In India, surveys
indicated mortality between 50% and
90% on the reefs in the Gulf of Mannar, Andaman
and Lakshadweep Islands.
• Assessments of the reef fish communities showed
drastic reductions in butterfly fish numbers
on Sri Lankan reefs.
Recovery
Recovery of corals and indeed coral reefs is dependent
on re-growth of whole or fragments of surviving colonies
or through settlement and recruitment of planula
larvae from the water column. More than 18 months after
the bleaching event, there is little evidence of recovery
or coral recruitment on the majority of reefs surveyed.
Despite small numbers of recruits being recorded
on a few reefs, recruitment on most reefs surveyed was
generally low. The influx of planula larvae and subsequent
recruitment of corals to reefs degraded by coral
bleaching will depend largely on the spatial distribution
of reproducing adult colonies on less affected reefs
(source reefs).
The following questions arose from the first year of
studies and are the targets of research projects proposed
for 2000:
• Source reefs and their ecology – Where are the reefs
that survived the bleaching event situated? What localised
environmental conditions or physiological
factors enabled the corals on these reefs to survive?
Are these reefs in a position to assist recovery of heavily
impacted reefs through the provision of larvae?
• Recovery versus degradation – How long is recovery
likely to take and what will be the contribution of
re-growth vs. recruitment towards recovery? How is
the rate of bioerosion and other degrading processes
affected by mass mortality of corals? In view of the
widespread destruction of the major contributors to
reef growth, will the rate of reef degradation overwhelm
processes of calcium carbonate (CaCO 3
) accretion?
• Extinction and dispersal – Are particular species of coral
and/or reef associated organisms locally or regionally
extinct? How will widespread mortality of corals
affect rates and taxonomic patterns of recruitment
at local and regional scales?
• Genetic implications – Has there been a decrease in
the genetic diversity of corals as a result of the widespread
mortality? Do different colonies of the same
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