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Global Warming: Coral Reefs at Risk

Air Date: Week of

Living On Earth’s Daniel Grossman reports that researchers are finding new diseases attacking coral reefs off the Florida Keys. As they scramble to explain the outbreaks, some scientists say that warmer ocean temperatures could be an important factor.


CURWOOD: This is Living on Earth. I'm Steve Curwood. Researchers studying reefs off the Florida Keys are finding new diseases associated with the dramatic increase in dying coral. Biologists are scrambling to explain the outbreak, and some say the problem may be linked to human-induced global warming. Living on Earth's Daniel Grossman reports.

GROSSMAN: Marine biologists are worried about the health of coral because reefs are the superstructure that support an immensely rich ecosystem of fish, plants, and microorganisms, considered by some to be among the most diverse habitats on earth.

PORTER: Coral reefs are the rainforests of the sea.

GROSSMAN: James Porter is an ecologist at the University of Georgia. He's conducting a study of the health of reefs off the Florida Keys.

PORTER: They build structures which, a biological analogy would be cathedrals, in which the light streams into the environment, with these multicolored fish. The vibrancy is amazing.

GROSSMAN: But recently, Professor Porter has observed something very different.

PORTER: The three-dimensional complexity is not there. The fish life are not there. And it has a sort of mowed-over look.

GROSSMAN: Professor Porter estimates that in the last 20 years about 10% of the world's reefs have been severely damaged. At a recent scientific conference, he reported some even more dramatic statistics about coral reefs in the Florida Keys. Since 1996, the number of reef sites there with diseased coral has quintupled, and the number of coral diseases seen has gone from 4 to 14.

PORTER: One of the reefs that we've been following, in the last 2 years, has lost 62% of all of its living coral. And that's in the space of 2 years. Those kinds of losses are alarming, and clearly they cannot be sustained through time and still have a coral reef left.

GROSSMAN: Researchers believe pathogens are killing the coral, although in most cases the identity of the attacker is unknown. Last year a Florida researcher showed that a previously unknown species of bacterium was responsible for one coral blight, and Drew Harvell of Cornell University says a fungus called Aspergillus sedowiae is killing large numbers of coral sea fans throughout the Caribbean. She says this pathogen is well-known on land, but its appearance in the ocean was a surprise.

HARVELL: It's almost unprecedented that a pathogen could cross the terrestrial-ocean boundary.

GROSSMAN: Professor Harvell, who is conducting a study of sea fans in the Keys, says the big question is: why are these terrestrial microbes suddenly attacking marine life? In the case of the Aspergillus fungus, she thinks she may have an answer.

HARVELL: We do know from laboratory studies that the optimum growth temperature for the Aspergillus is up around 30 degrees, and that's the temperature that was reached at some sites in the Florida Keys last summer.

GROSSMAN: Researchers in the Keys report that in recent years the number of days when water temperatures exceeded 30 degrees Celsius, or 86 degrees Fahrenheit, has increased. Last year water temperatures there were the highest in nearly a decade, probably helped by El Nino. Drew Harvell fears that if climate change causes further warming, that could pose even more serious problems for coral reefs and the life they support. For Living on Earth, this is Daniel Grossman.



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