Populations of Caribbean reef fish have plummeted between 32% and 72% over the past decade in response to widespread disappearance of coral, according to a new study. If the trend continues, it could worsen the already unprecedented deterioration of reef habitats and disrupt Caribbean countries that rely on the fish as a source of food and income.
Scientists became increasingly concerned about Caribbean reef fish after a 2003 paper reported an 80% reduction in the sea's hard coral--the main part of the reef that provides a foundation for other types of coral--between 1975 and 2000. Coral reefs provide refuge from predators and a rich food source, so researchers assumed that the deterioration in the reefs, which resulted primarily from coral diseases, storm damage, pollution, and sedimentation from soil erosion, would mean bad news for fish. Several studies had previously reported that fish populations were falling in specific parts of the Caribbean, but no one knew whether that was true for the whole sea.
Ecologist Michelle Paddack, a postdoctoral student at Simon Fraser University in Burnaby, Canada, teamed up with an international group of scientists to find out. They analyzed data from 48 studies, including peer-reviewed papers, government and university research reports, and unpublished data sets, that covered trends on 318 Caribbean coral reefs and 273 species of reef fish over a 53-year period. Today in Current Biology, the team reports that reef fish populations were relatively constant from 1955 through 1995 but then plunged by about 3% to 6% each year through 2007. The declines occurred in three of six dietary groups, including those that fed primarily on algae, invertebrates, or a combination of fish and invertebrates. The loss of algae-eating fish, such as parrotfish and surgeonfish, is worrying, says Paddack, because they help the reefs thrive by clearing away algae.
The declines don't appear to be caused by overfishing, because the losses were similar for fished and nonfished species. Paddack says that doesn't mean fishing doesn't have an impact but that something even bigger is influencing the entire sea. The researchers suggest that the culprit is unprecedented loss of coral reefs over the past 3 decades. Even though the reduction in fish populations lags nearly 20 years behind the coral loss, the consistency in fish declines across a wide range of species points to the loss of coral as the cause, they say.
"We've known that corals are declining and fish are declining, but boy, I think it's powerful just to see the patterns at the regional scale," says marine ecologist John Bruno of the University of North Carolina, Chapel Hill. Biologist Richard Aronson of the Florida Institute of Technology in Melbourne says that the suggestion that coral reef loss is behind the declines in reef fish is intriguing. But to nail down the link, he's hoping to see studies that relate fish declines to the time it takes for the reefs to structurally deteriorate after they die. "I liked this paper a lot; it got me excited [about coral reefs] all over again," he says.