|Coral reef degradation in the Indian Ocean: status reports and project presentations 1999|
(1999). Coral reef degradation in the Indian Ocean: status reports and project presentations 1999. CORDIO/SAREC Marine Science Program: Stockholm, Sweden. ISBN 91-630-8329-9.
The reports in this volume summarize the extent of damage to the coral reefs of the Indian Ocean caused by the elevated temperatures in 1998. Most of the reports also contain information on the status of reefs 6 to 12 months after the events of 1998, thus describing the fate of dead corals, the first signs of recovery in some areas, and the secondary damage to other organisms dependent on the reef, such as fish. A brief summary of the results is given here. EAST AFRICA • Several areas suffered very high coral mortality. For example, surveys in Kiunga and Malindi (Kenya), Misali and Mafia (Tanzania), and Pemba and Inhacca (Mozambique) showed that 90–100% of the corals died after exposure to water temperatures that exceeded 32?C, mainly in March and April 1998. The mortality of corals culminated around mid- May. In some areas, however, corals continued to die until October. • Following the event in 1998, coral cover appears to have been reduced to between 10 to 50% of previous levels in most areas along the coast of Kenya, Tanzania and northern Mozambique. In some areas the reduction is greater, i.e. up to or above 90%. • Initial investigations indicate that fish communities associated with coral reefs were affected by the coral mortality and that, in general, herbivorous species increased while corallivorous species decreased. • In most affected areas, the cover of algal turf on bleached and dead reefs increased significantly. On Kenyan reefs, for example, algal cover in many areas increased up to 200% as a result of the newly available substrate. INDIAN OCEAN ISLANDS • Coral mortality ranged from 50–90% over extensive areas of shallow reefs in Seychelles, Comoros, Madagascar and Chagos. In some areas (around Mahe, Seychelles), mortality was close to 100%. • By the end of 1998, algal turf covered coral reefs throughout much of the region. • Monitoring of potentially toxic, epiphytic dinoflagellates has shown drastically increased concentrations in areas with dead corals. • By early 1999, much of the dead coral in Chagos was reported to be eroded to rubble, preventing recolonisation. In Socotra Archipelago, coral rubble has been washed ashore and can be found in piles on the beach. • Preliminary assessments of the reef fish communities in Chagos indicate that abundance and diversity have decreased to less than 25% of their former levels. SOUTH ASIA REGION • Bleaching was reported down to a depth of 40 m in Sri Lanka and 30 m in Maldives, as a result of water temperatures of approximately 35?C during the period April to June, 1998. • In Sri Lanka and Maldives, nearly 90% of the corals died in many areas. In the Hikkaduwa and Bar reefs of Sri Lanka, close to 100% of the corals died, and by the end of 1998, these reefs were covered by thick algal turf. In May 1999, large areas of reefs in Maldives showed few signs of recovery. • In India, surveys indicated mortality between 50 and 90% in the reefs in Gulf of Mannar, Andaman Islands and Lakshadweep. • Assessments of the reef fish communities showed drastic reductions in butterfly fish numbers in Sri Lankan reefs.