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Study Uncovers a Predictable Sequence Toward Coral Reef Collapse

Posted by Lindy on October 2, 2011


ScienceDaily (Sep. 29, 2011) — Coral reefs that have lots of corals and appear healthy may, in fact, be heading toward collapse, according to a study published by the Wildlife Conservation Society and other groups.

Research has identified how overfishing creates a series of at least eight big changes on reefs that precipitate a final collapse. This information can help managers gauge the health of a reef and tell them when to restrict fishing in order to avoid a collapse of the ecosystem and fishery.

The authors say these changes are like a series of light switches, each of which make the reef more degraded and dims the chances of sustained fishery production and recovery.

1. The study shows that in well-protected areas, there are typically 1000-1500 kilograms of reef fish of various species per hectare of coral reef.

2. As the volume is fished down below 1000 kilograms, the early warning signs — like increased seaweed growth and urchin activity — begin to appear.

3. The researchers found that between 300-600 kilograms per hectare, there appeared to be a “window” of what is known as maximum sustainable yield, but when the fish stock drops below 300 kilograms per hectare, the reef is in real trouble, they said.

4. “Below 300 kilograms per hectare we see a series of dramatic changes on reefs. This is where you get on a real slippery slope,” McClanahan noted. “Strangely, the metric used by most managers to gauge the health of reef systems — coral cover — is the last threshold before ecosystem failure. Overfished reefs can appear healthy and then shift to algae dominated seascapes.”

The authors recommend measuring the biomass of fish instead of coral cover to identify the early warning rather than the final sign of reef collapse. Then where possible to restrict fishing using certain types of equipment or reduce the fishing times rather than try to stop it all together. Coral fisheries are too important to the local people to stop all fishing.

http://www.sciencedaily.com/releases/2011/09/110928152100.htm

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