Coral Bleaching Hits Tobago
What is Coral Bleaching?
Every coral species maintains a symbiotic relationship with a microscopic organism (algae) called zooxanthallae.
The zooxanthallae provide the coral with oxygen and some organic compounds they produce through photosynthesis. When stressed, coral expels its zooxanthallae. The polyps of the coral are left without any pigmentation (zooxanthallae give coral its beautiful colours) and appear nearly transparent on the animal's white skeleton. This is what scientists mean when they talk about coral bleaching.
Numerous laboratory studies have shown a direct relationship between bleaching and water temperature. Coral thrives in water temperatures of 28 degrees Celsius. A two or three degree rise in temperature can trigger the bleaching effect.
Corals can recover from bleaching unless high water temperatures persist for too long a period or become too warm to permit recovery. The coral's ability to feed itself in the absence of zooxanthallae seems to be a key to survival, and reestablishing the symbiotic relationship with zooxanthallae could take from two months to a year. When the level of environmental stress is high and sustained however, death of the coral may result. This will go on to effect the rest of the ecosystem in a highly negative way.
Coral bleaching is a global phenomenon. Since the 1980s nearly all of the world’s coral reefs have been effected. Many scientists attribute bleaching to global warming caused by the green house effect. Some experts predict that if a global warming trend continues coral mortality could reach 95%.
Coral Bleaching in Tobago
Coral bleaching has been reported in the reefs around Tobago for the first time this year (1998). The THA Marine Affairs Section has recently conducted a Coral Disease Survey as part of CARICOM’s Caribbean Coastal Marine Production project. Reefs at Buccoo, Speyside and Pigeon Point were studied and bleaching was seen at each location. At one particular area 50% of the coral was affected. Water temperatures as high as 30 degrees C were recorded. Reports of bleaching have been received by Environment TOBAGO at Black Rock and Englishman’s Bay.
Will the coral recover? The Marine Affairs Section will be monitoring the situation in the coming months. If water temperatures return to normal the zooxanthallae may re-establish themselves and the coral will survive and regain its colours.
What Can We Do?
The health of Tobago’s reefs are effected by many other factors besides water temperature. Pollution, siltation, and an increase in fresh water run-off can put stress on coral. An otherwise healthy reef system may be able to withstand and recover from coral bleaching. A reef already under stress from man-made factors will have less chance of recovery. This is why we in Tobago must make every effort to reduce the stress we are placing on our marine environment. We may not be able to stop global warming, but we can stop polluting our coasts. We can plan our development projects in such a way as to reduce siltation (the current flurry of road-building is producing large quantities of silt run-off which is effecting our water supply and our coastal waters). We must realise and take into account how our all our actions effect the environment.
UPDATE (November 1999):
Anecdotal evidence indicates that some of Tobago’s reefs are recovering from last year’s bleaching. An ET member reports that the reef at Englishman’s Bay has almost fully recovered – areas that had turned white are now back to their original colours. Dive operators, however, report that they have noticed little change at dive spots off Speyside and Charlotteville. The fact that no scientific surveys have been conducted to monitor the condition of our reefs since the bleaching began underlines the problem of managing our environment without the hard data needed to inform management strategies.