Another event specific to the Caribbean was the sudden die-off of the sea urchin Diadema antillarum in 1983. This urchin ate algae, so when it diedfor reasons that to this day remain unknown, noted McManusthe algae took over the reefs.
McManus said that the greatest worry is that coral reefs worldwide seem to be losing their ecological resilience. They no longer bounce back like they did for hundreds of thousands of years from periodic hurricanes, typhoons, floods, and tidal waves.
"In the last decade or two we've seen many, many cases where coral reefs have been damaged and instead of coming back as coral-dominated systems, they develop a heavy cover of seaweed," he said.
The rates of decline appear to be slowing in Florida, the Virgin Islands, Jamaica, and south Central America, but Côté and colleagues say that the slowing is likely because the most susceptible coral species were lost in the 1980s. What remains are hardier species.
"In all of the places where the rates of decline have slowed there is no good evidence of recovery, therefore the coral cover through the '90s has remained largely unchanged at very low levels," said Côté.
In addition, the composition of coral species has changed over the past 25 years. Many of the new coral growth comes from species known as non-framework builders that do not contribute to the growth of reef structure.
"If this is a widespread phenomenon, then there is serious concern about the capacity of Caribbean reefs to cope with rising sea levels," said Côté. Many scientists believe that sea levels will rise in the Caribbean as a result of global warming.
To reverse the trend of coral decline in the Caribbean, Côté and colleagues said that the known human causes for decline must be addressed through legislation and strict enforcement.
Specific measures the researchers suggest include strengthening the network of marine protected areas via enforcement of laws and the creation of more protected areas. As well, the researchers recommend pollution-control measures such as mandatory treatment of sewage water and strict controls on coastal development.
"They are all realistic propositions and there are already many new and promising initiatives in this direction," said Côté.
McManus said that what the coral reefs need more than anything is solid, long-term management that takes into account the socio-economic impact of reef conservation measures as well as the reef ecology.
"Funding mechanisms have to be established for really serious, long-term, high-interdisciplinary projects where we compare coral reefs around the world," he said.
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