'Fishy herbivores' help to save the reef

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Scientists in America have discovered that certain fish may be able to help save Pacific coral reefs from dying and even help them recover from cyclones and predators.

The researchers from UC Santa Barbara have discovered that the health of the coral l reefs in the South Pacific island of Moorea, in French Polynesia, may be due to protection by parrotfish and surgeonfish. These fish eat the algae that can damage coral.

In many cases, especially in the case of severely damaged reefs in the Caribbean, coral reefs that suffer large losses of live coral often become overgrown with algae and never return to a living state. In contrast, the reefs surrounding Moorea have experienced a number of large losses of live coral including in the 1980s and each time have returned to be healthy, live corals.

The research wanted to investigate what was different around Moorea. They found that the number of herbivores on the reef increased dramatically following the loss of live coral with significantly more parrotfish and surgeonfish being found on the reef. They also found that fringing reefs – reefs that grow against island – were protected from the predatory crown of thorns sea star and cyclones by the fish

"We discovered that these fringing reefs act as a nursery ground for baby fishes, most notably herbivorous fishes," said co-author Andrew Brooks. "With more food available in the form of algae, the survivorship of these baby parrotfish and surgeonfish increased, providing more individuals to help control the algae on the fore reef. In effect, the large numbers of parrotfish and surgeonfish are acting like thousands of fishy lawnmowers, keeping the algae cropped down to levels low enough that there is still space for new baby corals to settle onto the reef and begin to grow."

The study suggests that one of the main reasons for the inability to recover of the Caribbean reefs is the fact that they do not have healthy populations of fish such as parrotfish and surgeonfish due to overfishing.

Adam added. "Without these species to help crop the algae down, these reefs quickly become overgrown with algae, a situation that makes it very hard for corals to re-establish themselves," he said.

He went on to add that any managers of MPAs should also protect fringing reefs that act as nursery grounds: "Without these nursery grounds, populations of parrotfishes and surgeonfishes can't respond to increasing amounts of algae on the reefs by outputting more baby herbivores."

For more information see the paper: Thomas C. Adam, Russell J. Schmitt, Sally J. Holbrook, Andrew J. Brooks, Peter J. Edmunds, Robert C. Carpenter, Giacomo Bernardi. Herbivory, Connectivity, and Ecosystem Resilience: Response of a Coral Reef to a Large-Scale Perturbation. PLoS ONE, 2011; 6 (8): e23717 DOI:

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