> EXPLAINER: FLORIDA’S CORAL BLEACHING
FORT LAUDERDALE, FLA.— Corals are turning chalk white and dying on reefs stretching from the Florida Keys to Palm Beach County, in what experts call one of the worst episodes in two decades of coral bleaching.
Under stress from unusually warm water, the corals are expelling the tiny bits of algae that give them their fiery streaks of red, orange or green colour and that provide the coral with nutrition.
Divers have reported tracts of corals that have lost their living tissue, leaving ghostly white skeletons. Bleaching leaves coral vulnerable to diseases that can be fatal, although some corals do regain their colour and survive.
Federal and state officials say the bleaching started this summer, as ocean temperatures peaked. The danger is expected to diminish as cooler weather arrives, but many coral communities, which support a vast range of fish, crabs and other marine life, may not be able to recover.
“It’s significant impact and it’s permanent,” said Margaret Miller, ecologist with the National Marine Fisheries Service Southeast Fisheries Science Center.
“Corals do not grow back very effectively. So that’s a permanent loss to our coral community. It just becomes rock.”
Among the hardest-hit species are pillar corals, maze corals, star corals and staghorn corals.
These include corals off Broward and Miami-Dade counties that had survived 200 or 300 years. Scientists have found that some of these old corals have lost nearly half of their living tissue.
“These corals are very important be- cause they have proven to be quite resilient, withstanding everything over the last couple hundred years,” said Brian Walker, research scientist at Nova Southeastern University’s Halmos College of Natural Sciences and Oceanography. “Understanding how these resilient corals respond to present environmental conditions informs us of how the environment has changed. The fact that they are dying now, after living hundreds of years, may indicate that their surroundings are much more stressful than ever before.”
The corals form the only major reef tract in the continental United States and support fishing, diving and snorkelling. Reporting the bleached and dead corals are scientists from government agencies and universities, as well as volunteer divers, in a system co-ordinated by the Florida Department of Environmental Protection.
The sick corals off the South Florida coast are part of a worldwide bleaching outbreak that includes the coral reefs of Hawaii and other Pacific islands and is projected to reach Indonesia, the Philippines and Australia.
The last global coral bleaching events occurred in1997 and1998, when between 15 per cent and 20 per cent of the world’s coral reefs were lost, DEP said in a statement.
Scientists say it will be difficult for South Florida’s reefs to make up for the loss of coral. Although coral larvae settle out of the water onto rocks and found new colonies, this doesn’t happen to a sufficient extent to make up for the losses, Miller said.
“It’s a bad situation for the corals out there right now,” she said.