Swan Song for Corals?

By Phil Berardelli
ScienceNOW Daily News
10 July 2008

The first comprehensive survey of reef-building coral species suggests that one-third of them are in danger of extinction, a sevenfold increase in just the past decade. If current trends continue, the authors predict a mass die-off among the engineers of some of the world's most important and diverse ecosystems.

Coral reefs may be tough enough to rip through the hulls of large ships, but the soft-bodied animals that lay down the minerals that make up the reefs are surprisingly fragile and sensitive to changes in their environment. Those changes include nutrient overloads caused by agricultural runoff, predation by invasive species, and ocean acidification--a byproduct of carbon dioxide buildup in the atmosphere (ScienceNOW, 9 June). Surveys of reef destruction and shrinking habitats over the past decade have been worrisome, but up to now they have concentrated mainly on the condition of the hard reef structures rather than on the individual coral species themselves.

In the new study, a team led by marine biologist Kent Carpenter of Old Dominion University in Norfolk, Virginia, censused 704 reef-building coral species and rated them according to International Union for Conservation of Nature (IUCN) standards of extinction risk. One-third of those species fall into the threatened or near-threatened categories, which are considered at increased risk for extinction, the researchers report online today in Science. The highest concentration of jeopardized species lives in the Caribbean Sea and in the "Coral Triangle" of the western Pacific, an archipelago spanning parts of Indonesia, Malaysia, the Philippines, and nearby areas. Using current figures and extrapolations from historical data, the researchers estimated that in the 1990s less than 5% of the 704 species would have been placed in the threatened or near-threatened IUCN categories.

Time is of the essence, says paleontologist and co-author Richard Aronson of the Dauphin Island Sea Lab in Alabama: "We can still pull back from an incipient mass extinction of corals if we take action on both local and global levels." Global carbon control is the most important step, he says. Local actions such as limiting commercial fishing--which can damage the reef structure--and reducing nutrient levels in agricultural runoff would also "buy time for the coral species and ecosystems they inhabit." In addition, Aronson says, there should be similar studies of the plants and animals that inhabit the reefs "to formulate a clear picture of what we stand to lose and what we should do about it."

The study "brings home the shocking news that we are about to lose a lot of colors in the ocean's Van Gogh," says marine ecologist Joan Kleypas of the National Center for Atmospheric Research in Boulder, Colorado. Marine biologist John Bruno of the University of North Carolina, Chapel Hill, calls the work a "real milestone of marine conservation." But he says conservationists shouldn't be satisfied with just saving coral species from extinction. "Simply trying to maintain viable coral populations is setting the bar far too low. We need to restore corals to their historical abundances so that we can reclaim the services people derive from healthy reefs."