Reefs at Threat, Even When Protected

April 4, 2008 -- The decline of coral reefs bears an unmistakable signature -- human activity. Even efforts to preserve reef habitats through marine protected areas aren't doing anything to help corals.

That is the depressing message of new work by Camilo Mora, now of the University of California, San Diego, appearing in the April 7 issue of Proceedings of the Royal Society B.

Mora gathered more than a decade's worth of data on the status of three major components of reef ecosystems in the Caribbean: fish, corals and macroalgae, which compete with corals for places to settle along the reef. High levels of macroalgae are a sign of poor reef health.

He combined these figures with water temperature measurements, hurricane records and information gathered from satellite images about the extent of agricultural land and human settlement near coastal areas. He also considered the locations of marine protected areas. Mora then used statistical analysis to evaluate the effect of each of these factors on populations of fish, corals and macroalgae.

"What we found is that marine protected areas are good only for fish, but they don't really have any positive effect on coral or on controlling macroalgae," Mora told Discovery News. "Corals are being affected by coastal development, and I think that is mostly because of sewage," he added.

Climate change is contributing, too. Mora found that warmer water temperatures were also correlated with more coral death.

The amount of cultivated land was the dominant factor behind high levels of macroalgae, suggesting that nutrients in the water from agricultural runoff fed algal growth. Algae-eating fish played a secondary role in controlling macroalgae, Mora said.