Losing Species
The worldwide decline in coral cover has serious implications for the health of coral reefs. But what is the future of reef fish assemblages? Marine reserves can protect fish from exploitation, but do they protect fish biodiversity in degrading environments? The answer appears to be no, as indicated by our 8-year study in Papua New Guinea. A devastating decline in coral cover caused a parallel decline in fish biodiversity, both in marine reserves and in areas open to fishing. Over 75% of reef fish species declined in abundance, and 50% declined to less than half of their original numbers. The greater the dependence species have on living coral as juvenile recruitment sites, the greater the observed decline in abundance. Several rare coral-specialists became locally extinct. We suggest that fish biodiversity is threatened wherever permanent reef degradation occurs and warn that marine reserves will not always be sufficient to ensure their survival.
Organisms Affected
Animals that help filter and clarify the water on a reef include sea squirts and salps (“tunicates”), and giant clams (mollusks), which sieve and eat phytoplankton. And even primitive animals like sea sponges are important to reef health, providing habitat for crustaceans, marine worms, and young fish in their intricate aquiferous canals, and for barnacles and tiny mollusks in their complex surfaces. They are also “recyclers”—taking in nutrients they filter from the water and producing waste products that feed lots of other reef species. Sponges themselves become food for nudibranchs, sea stars, turtles, and fish. And they are valuable to humans as well, producing diverse chemical compounds that are being explored for human medicines.
