This summer’s extreme heat may seem like a distant memory as winter approaches the United States.
But the summer that broke heat records across the Northern Hemisphere is still being felt below the surface of the Caribbean Sea: 2010 will likely be one of the most deadly years on record for coral reefs.
If diplomats attending the two-week global climate change talks that opened Monday in Cancún, Mexico, want more evidence of the negative and potentially devastating affects of warming temperatures, they need look no further than the blue sea outside their hotels. Researchers say that throughout the Caribbean coral reefs are “bleaching,” a condition that occurs when they are under extreme stress due to warmer-than-normal sea temperatures.
The last major bleaching, in 2005, resulted in the death of 40 percent of corals in parts of eastern Caribbean. When full results are in, this year is likely to be worse, scientists said.
“When we average out the net bleaching events and severity across the Caribbean basin, 2010 (and more than likely 2011) will go down in the record books as having the most severe bleaching and coral mortality in over 20 years,” says Rick MacPherson, conservation programs director of the Coral Reef Alliance (CORAL).
Coral feels heat
Under normal conditions, algae live symbiotically within the coral, giving it color and providing it with a source of food. But under stress, the coral expels the algae, leaving it whitened, or “bleached.” The longer the coral remains bleached, the more likely it is to die, according to marine biologists.
Following a hot summer – the fourth hottest on record for the US, according to the National Oceanic and Atmospheric Administration (NOAA) – nearly the entire Caribbean was at risk for bleaching. While some bleaching occurs every year, this year stands out.
“Temperatures are high in the Caribbean, and we expect this to continue. This season has the potential to be one of the worst bleaching seasons for some reefs,” Mark Eakin, coordinator of NOAA’s Coral Reef Watch, said in a statement in late September.
The phenomenon is not confined to the Caribbean. Coral reefs in Southeast Asia and in the Indian Ocean are experiencing their worst bleaching since 1998. Scientists expect similar results for the Great Barrier Reef off the coast of Australia.
Reefs worth $375 billion a year
The environmental and economic impacts are potentially enormous.
Coral covers less than 1 percent of the ocean floor but provides habitat and supports as much as 25 percent of all marine life. Coral reefs are home to more than 1 million aquatic species. And barrier reefs knock down waves before they reach shore, cutting down on the rate of coastal erosion, according to coral reef conservation groups.
An oft-cited 1998 study, “Reefs at Risk,” found that the food, tourism revenue, coastal protection, and value of new medications provided by coral reefs is worth about $375 billion a year.
Described by some as the tropical rainforests of the sea and others as bustling little cities of marine life, today’s coral reefs are between 5,000 and 10,000 years old. But the past 30 years have been particularly difficult for them. One study suggests that some areas of the Caribbean lost 80 percent of live coral since 1977.
That’s why marine biologists are worried about another massive bleaching like that of 2005. Scientists had hoped that an active hurricane season would stir ocean waters, bringing up colder waters. Coral reefs grow best in temperatures between 70 and 85 degrees F., according to Coral Reef Alliance.
“Some areas of the Caribbean have been experiencing varying levels of bleaching and stress from this year’s unusually warm sea surface temperatures,” Mr. MacPherson says. “Winds have been relatively still throughout the eastern Caribbean and, as a result, little mixing of sea water has been occurring.”
From the coast of Panama to the eastern Caribbean, divers are finding white masses where once brilliantly colored seascapes stood.
Off the coast of Tobago in the southern Caribbean, scientists from Coral Cay, a conservation group, reported bleaching accompanied by an unknown fungal disease covering sponges.
“It’s pretty snowy down there,” says Marie Smedley, lead scientist for Coral Cay’s team in Tobago. “The water temperatures are cooling down now and that’s a good thing. … But we’ve seen extensive bleaching around the island.”
In western Caribbean, divers from the Smithsonian Tropical Research Institute found bleaching and water temperatures that were 7 degrees F. warmer than normal – as warm as 89 degrees.
Off the Caribbean coast of Hispaniola – the second largest island in the region behind Cuba – Dominican marine biologist Ruben Torres found that 5 percent of the coral colonies he checked on a recent SCUBA dive trip had some bleaching.
“Our coast was not affected as [badly] as the southern Caribbean,” near Tobago, he says. “I think we got lucky this year.”