A global analysis of more than 8000 coral cover surveys from 1969-2006 has compared annual changes in coral cover inside MPAs to unprotected areas. The study, published in the journal PLoS ONE, found that marine protected areas halted the loss of coral cover over time while coral cover on unprotected reefs continued to decline. In the most recent complete year in the study (2004-2005), for example, coral cover within MPAs increased 0.05% in the Caribbean and 0.08% in the Pacific and Indian Oceans. In contrast, unprotected reefs in that same year declined 0.27% in the Caribbean and 0.41% in the Indo-Pacific.
The loss of coral cover does not immediately reverse upon MPA designation, perhaps due in part to the slow growth rates of many reef-building species, according to the study's authors. "The benefits of MPAs appear to increase with the number of years since MPA establishment," wrote Elizabeth Selig, currently of Conservation International, and John Bruno of the University of North Carolina (US).
There were regional differences in the time it took to see a benefit from MPAs to coral cover. In the Caribbean, coral cover continued to decline (albeit more slowly) for approximately 14 years on average after protection began; then it stopped declining and began increasing. In the Indo-Pacific, coral cover in MPAs continued to decline for five years on average before rebounding.
Selig speculates the regional differences may have to do with differences in fishing pressure and other local factors. "High-level exploitation of fisheries and the loss of top predators has been well-documented in the Caribbean, so it may take more time there to restore the natural dynamics that could lead to indirect benefits to corals," she says.
Notably, the authors included MPAs in their study that still allow fishing or have poor enforcement of regulations. So the study's findings may represent an underestimate of the benefits that could come from well-enforced, no-take protection, they write. The article "A Global Analysis of the Effectiveness of Marine Protected Areas in Preventing Coral Loss" is downloadable for free at www.plosone.org/article/info:doi/10.1371/journal.pone.0009278.
For more information:
Elizabeth Selig, Center for Applied Biodiversity Science, Conservation International, Arlington, Virginia, US. E-mail: e.selig [at] conservation.org