Cutting fishing can help reefs bounce back

11 January 2010 by Tom Marshall

Protecting coral reefs from fishing could help them recover from damage more quickly than previously thought possible.

Coral reef

Reefs are some of the planet's richest and most diverse habitats - they host 25 per cent of all known marine species, but take up less that a quarter of one per cent of the ocean's area. But reefs are threatened by climate change, ocean acidification and destructive fishing methods. Because many corals take a long time to grow, there's been pessimism at their chances of recovery; scientists have feared these ecosystems may be doomed.

But researchers have learned that limiting fishing can help restore reefs more quickly than expected. They compared reefs in marine reserves with similar habitats elsewhere, and found that in the reserves, where fishing isn't allowed, the area covered by coral increased much more quickly.

"Coral reefs are the largest living structures on Earth and are home to the highest biodiversity on the planet," says Professor Peter Mumby of the University of Exeter, who led the research. "As a result of climate change, the environment that has enabled coral reefs to thrive for hundreds of thousands of years is changing too quickly for reefs to adapt."

Published in the open-access journal PLOS One, the research describes how Mumby and colleagues monitored ten coral reefs near the Bahamas over two and a half years. Some of these reefs are inside marine reserves, while others aren't. All had been severely damaged by warmer waters, which cause corals to bleach and die, and by Hurricane Frances in 2004.

Coral covered on average seven per cent of these reefs at the start of the period. By its end, this had grown to 19 per cent in reefs within marine reserves, but the other reefs had shown no sign of recovery. The scientists think these increases happened because there were greater numbers of grazing parrotfish at the protected reefs; these fish eat plants which compete with corals for light and nutrients.

"In order to protect reefs in the long term we need radical action to reduce CO2 emissions," Mumby explains. "However, our research shows that local action to reduce the effects of fishing can contribute meaningfully to the fate of reefs. The reserve allowed the number of parrotfishes to increase and because parrotfish eat seaweeds, the corals could grow freely without being swamped by weeds. As a result, reefs inside the park were showing recovery whereas those with more seaweed were not."

He hopes this kind of research may help persuade governments to look at reducing fishing of important herbivores like parrotfish as a way to help reefs recover from damage.

Corals are threatened by warming sea waters, which can cause them to become bleached and die back. Ocean acidification, in which atmospheric CO2 dissolves in the ocean and forms a weak carbonic acid, also puts corals at risk; coral animals make their hard skeletons from calcium carbonate, which is vulnerable to being dissolved by acidic conditions.

The research was funded by the Khalid bin Sultan Living Oceans Foundation and NERC.