An 18-year study of Kenya's coral reefs by the Wildlife Conservation Society and the University of California at Santa Cruz has found that overfished reef systems have more sea urchinsorganisms that in turn eat coral algae that build tropical reef systems.
By contrast, reef systems closed to fishing have fewer sea urchinsthe result of predatory fish keeping urchins under controland higher coral growth rates and more structure.
The paper appears in the December 2010 issue of the scientific journal Ecology. The authors include Jennifer O'Leary of the University of California at Santa Cruz and Tim McClanahan of the Wildlife Conservation Society.
The authors found that reefs with large numbers of grazing sea urchins reduced the abundance of crustose coralline algae, a species of algae that produce calcium carbonate. Coralline algae contribute to reef growth, specifically the kind of massive flat reefs that fringe most of the tropical reef systems of the world.
The study focused on two areasone a fishery closure near the coastal city of Mombasa and another site with fished reefs. The researchers found that sea urchins were the dominant grazer in the fished reefs, where the predators of sea urchinstriggerfish and wrasseswere largely absent. The absence of predators caused the sea urchins to proliferate and coralline algae to become rare.
"These under-appreciated coralline algae are known to bind and stabilize reef skeletons and sand as well as enhance the recruitment of small corals by providing a place for their larvae to settle," said Dr. Tim McClanahan, WCS Senior Conservationist and head of the society's coral reef research and conservation program. "This study illustrates the cascading effects of predator loss on a reef system and the importance of maintaining fish populations for coral health."
The study also focused on the effects of herbivorous fishsurgeonfish and parrotfishon coral reefs. W
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Wildlife Conservation Society