Storms Threaten Coral Diversity

Hurricanes and tropical storms can be destructive to coral reefs, and are known to wipe out whole areas of delicate branching corals and the marine life that they support. But data from the Earthwatch-supported Jamaica's Coral Reefs project show that such storms have far-reaching effects on stouter, non-branching corals as well, by stifling their "recruitment" of future generations: the settling out of coral larvae that starts new colonies and supports local biodiversity.

In an article in the latest Bulletin of Marine Science, Dr. James Crabbe (University of Reading, U.K.) and his coauthors used a mathematical model of coral colony growth to calculate the recruitment dates of 438 non-branching corals from 11 species. They found a significant negative correlation between storm severity recorded over the last 60 years and recruitment of non-branching coral. In years with severe storms, recruitment dropped.

"This is surprising, particularly in respect of the fact that it takes some years to recover recruitment levels," said Crabbe, principal investigator of Jamaica's Coral Reefs. His findings contrast with earlier studies suggesting that Hurricane Allen cleared the reef surface in 1980, making it especially favorable for coral recruitment.

Crabbe found that there was considerable variation in recruitment, with some years represented by only one colony recruited. The three years when the most severe storms hit the area, 1944, 1951, and Hurricane Allen in 1980, correlated with the lowest recruitment. Recruitment took one or two years to return to levels found before hurricanes.

Data on coral surface areas were collected by Earthwatch volunteers using scuba at five sites in Discovery Bay, Jamaica. The bay's coral reef ecosystem has experienced major change in the last two decades, including a general decline in biodiversity. Crabbe's finding shows that severe storms, which may be exacerbated by global climate change, play a role in this loss of diversity.

"The protective effects of the reef, both with regard to marine life and to the human populations that live in the coastal areas, may become compromised and under threat in future years," said Crabbe. "There will be fewer massive corals around to help break up waves, and act as retreats for marine life."

The estimation of a coral colony's recruitment date, i.e. when it settled and began to grow, was made possible by the polynomial function model for coral colony growth developed by Crabbe and his colleagues. It allows a more accurate fit of observed growth than other kinds of models used previously, and can be modified to reflect differences between non-branching, plate, and branching corals.

Last year, Earthwatch team members measured more than 1,200 corals, which will allow more detailed analysis of coral growth rates and the effects of climate, pollution, and other environmental changes. Crabbe looks forward to expanding his research to other areas in the Caribbean and Indo-Pacific Oceans.

For information on volunteering on Jamaica's Coral Reefs , click here.

Earthwatch Institute is an international nonprofit organization which supports scientific field research worldwide by offering members of the public unique opportunities to work alongside leading field scientists and researchers. The Institute's mission is to engage people worldwide in scientific field research and education to promote the understanding and action necessary for a sustainable environment.