“It is certainly the worst coral die-off we have seen since 1998. It may prove to be the worst such event known to science,” says Dr. Andrew Baird, an Australian coral reef specialist in an interview by Underwatertimes.com published on 18 October, 2010.
Dr. Baird estimates that approximately 80% of Acropora coral colonies and 50% of colonies by other species have died during the past six months on the bleached coral reefs in the Indian and Pacific Oceans.
The reefs are numerous: the mass bleaching affects an area which extends from the Seychelles to Sulawesi and the Philippines. Included are reefs in Sri Lanka, Burma, Thailand, Malaysia, Singapore, and Indonesia. The most diverse reefs of the world are found in the so-called “Coral Triangle” which is within the affected area.
In the Underwatertimes article Dr Baird comments the seriousness of the situation by stating that the live percentage coral cover on the reefs could drop from 50% to about 10% (these are average values). The recovery, if it ever occurs, will take years. Fisheries and tourism in the affected coastal and island nations will suffer: the livelihoods of millions of people are likely to be hampered.
The bleaching is being caused by elevated mean seawater temperatures which result in the loss of symbiotic microalgae from the coral tissues. As the pigments are in the algae, the coral colony turns white. When the seawater temperature stays higher than normal for weeks, the bleached coral colonies often die – for nutrition the coral depends on the algae.
The warming of seawater to levels which are higher than normal is related to the planet-wide effects of the periodic El Niño and La Niña weather disturbances, which in turn seem to be getting more extreme with global climate change.
In non-scientific terms the recent events in South-East Asia could perhaps be summarised by stating that “the rainforests of the sea are dying”. People who have seen a healthy coral reef might also use the expression “a very sad and serious ecological disaster is taking place”.