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.
Hurricanes did not show a significant effect on fish, corals or macroalgae.
Fish can benefit from well-managed marine protected areas (MPAs) because it is possible to prevent fishing inside the boundaries. But for other problems, these zones appear to be inadequate.
"Climate doesn't respect the boundary of an MPA," Mora said. "Pollution doesn't know where an MPA is."
The work helps identify the relative importance of various factors on reef ecology, a subject of debate among reef scientists, said Peter Sale, a coral reef ecologist at the International Network on Water, Environment and Health of the United Nations University, in Hamilton, Ontario, who was not involved in the study.
But "the main message of this paper is that reefs are deteriorating and it's because of us," he said. "We are the elephant in the room."
"What we need is regional-scale coastal management," he added. "There is far too much complacency around the degree to which our current activities are sufficient."
"MPAs are just not going to be enough to protect coral reefs," Mora agreed. The combined pressures from human activities in coastal areas and climate change may be more than the reefs can handle, both researchers noted.
"It's like lighting the candle at both ends," Mora said. "That is exactly what is happening with coral reefs."
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