Local factors can help coral survive global heat waves.
Christopher Pala Nature 19 Apr 11;
Researchers from East Africa have come up with a model that could help protect coral reefs beset by warming waters. The team has worked out that such factors as winds, currents and light can help reefs survive heat waves.
The study leader, Tim McClanahan, a Kenya-based coral biologist with the Wildlife Conservation Society, headquartered in New York, has been familiar with the problems faced by conservation bureaucrats tasked with protecting coral reefs from overfishing and other human damage: so many reefs, so little money.
So he decided to help them decide where to concentrate their limited resources to maximize the efficiency of conservation.
"There are perhaps 12,000 square kilometres of healthy reefs left in the western Indian Ocean and these officials know they can't protect them all," says McClanahan. "What we've done is help them concentrate their resources on the reefs that are most likely to survive global warming, at least for another century. The model can now be applied anywhere in the world."
The key criteria, pinpointed by McClanahan and other researchers in Global Change Biology1, include winds, currents, UV light and visible light, temperature variability and chlorophyll in the water. They found that even in regions where the water was hot, some reefs survived because these local factors were favorable.
A severe global heat wave in 1998 killed half of the region's shallow corals. The study identifies which will be the most likely to recover from the next spike. "It's not a lot," says McClanahan, who is based in Mombasa, Kenya. "It's about 40 sites that, put together, amount to maybe 1,500 square kilometres."
Coral-reef task forces set up by the Nairobi Convention on coastal environments in the East African states have been struggling to establish which Indian Ocean reefs should be enclosed in Marine Protected Areas (MPA) where fishing would be restricted.
"This study provides the scientific backing we need to lobby for the targeted placement of MPAs in the region," says Nyawira Muthiga, chairman of the Regional Coral Reef Task Force in Mombasa and a co-author of the study.
Mapping survival
An earlier study2 found that satellite surveys of temperatures from the region were not good indicators of which reefs survived the 1998 heat wave, so they added a total of nine variables.
"This model," co-author Joeph Maina of Macquarie University, in Sydney, Australia, says, "was a good predictor of what areas would be bleached in the future. Then we noticed that more than half the MPAs in the western Indian Ocean were in those high-risk areas, which would appear to be unwise." The coral reef task forces used the study to establish guidelines on where to establish MPAs.
"We found that barely 20% of the areas with high biodiversity that would normally be candidates for protection will likely survive the next temperature spike, and those are the ones that should to the top of the list of candidates," adds McClanahan.
Topping the list of regional reefs that should be preserved are Mozambique's Quirimbas Archipelago and Ponta do Ouro, a thriving diving centre sustained by tourists from neighbouring South Africa; and reefs off northeast Madagascar, which has one of the richest diversity of species in the region. In all three, restrictions on fishing are weak or non-existent and need to be increased.
"This paper shows that even if temperatures and acidification will eventually kill most corals, if you can buy a few decades by good local conservation measures, you should fight for it," says Charles Sheppard, a coral biologist at the University of Warwick in Coventry, UK, who predicted in 2003 that most Indian Ocean corals would die by 20503.
References
McClanahan, T. R., Maina, J. M. & Muthiga, N. A. Global Change Biology doi: 10.1111/j.1365-2486.2011.02395.x (2011).
McClanahan, T. R., Ateweberhan, M., Muhando, C., Maina, J. & Mohammed, S. M. Ecological Monographs 77, 503-525 (2007).
Sheppard, C . Nature 425, 294-297 (2003).
