BERKELEY, CALIFORNIA--The most important species of coral in the Caribbean have been dying since the 1970s at tremendous rates, and the once majestic reefs are overgrown with algae. The main suspects include human activities, such as overfishing and pollution. Now, a paleontologist has bolstered the evidence that humans are to blame, by showing that Caribbean reefs have always been inhabited by the same species during the last 220,000 years--but have only recently started changing drastically.
To identify past trends in coral reef ecology, John Pandolfi of the Smithsonian Institution's National Museum of Natural History in Washington, D.C., examined ancient reefs in the Caribbean that were left high and dry when sea level dropped during the ice ages and the islands rose. He made numerous 40-meter-long surveys of fossil reefs on San Andres, Curaçao, and Barbados, counting every coral species.
The communities had the same composition of coral species at the four time intervals--220,000, 190,000, 125,000, and 104,000 years ago respectively--that Pandolfi described here on 29 June at the North American Paleontological Convention. Elkhorn coral (Acropora palmata), made up about 80% of all the coral. Since 1973, however, this species has become exceedingly rare in the Caribbean. Another 15% of the coral community was comprised of five other species--always the same ones--in every survey. Another 24 rare species that made up the remaining 5% also showed up every time too. "I almost fell off my chair when that came out," Pandolfi says. The reefs didn't always exist during those 220,000 years, but when they reappeared, they had the same community structure each time. That means that the argument that reef ecology may change all the time doesn't fly, says Pandolfi: "People can't say we don't know what's normal."
The baseline provided by the fossil record reveals "a profound change that's unprecedented in recent geologic history," says John Ogden, a marine ecologist at the University of South Florida in St. Petersburg. "It's difficult to lay that at the feet of any cause other than humans."