BBP in Brief, Issue 8, Spring 2007

Marine Reserves and Coral Recovery:
BBP Publications Demonstrate How Reserves Can Facilitate Reef Recovery
Kate Holmes, Dan Brumbaugh (AMNH-CBC), and Steve Vollmer (Northeastern University)

Two recent research articles by BBP researchers have revealed important information about how marine protected areas (MPAs) can contribute to the recovery of Caribbean corals.

The first paper, published in the Journal of Heredity in January 2007, addresses the maximum spacing among reefs that would allow for reef recovery via an adequate supply of coral recruits (coral larvae that disperse, settle, and grow to become small new coral colonies). That is, how close should damaged reefs be to healthy reefs for them to be able to benefit from a supply of new corals? This information is particularly needed in the Caribbean where the two once-dominant shallow water corals, staghorn coral (Acropora cervicornis) and elkhorn coral (A. palmata), have suffered unprecedented declines due to white-band disease and other factors. In many locations, losses of these corals have been greater than 95 percent, and both species have been listed as threatened under the U.S. Endangered Species Act.

The researchers, Steve Vollmer and Steve Palumbi, show that larval dispersal in staghorn corals is generally quite limited over moderate to long distances (greater than 500 km). In addition, dispersal can sometimes be limited at local scales, to the point where even adjacent reefs can be genetically different. Their review of coral population genetic studies also found that limited gene flow over 500-km distances is common in a variety of Caribbean and Pacific reef corals. The study’s results imply that damaged Caribbean staghorn corals require local source populations for their recovery, and need targeted conservation efforts over spatial scales much smaller than the hundreds to thousands of kilometers often proposed for marine reserves.

The second paper, published in the Proceedings of the National Academy of Sciences in May 2007, demonstrates how The Bahamas’ Exuma Cays Land and Sea Park (ECLSP) facilitates coral recruitment through the protection of grazing parrotfishes. The results build on a earlier paper published in Science in January 2006 (discussed in BBP in Brief, Issue 6, May 2006) that showed how the ECLSP, in addition to protecting large numbers of Nassau grouper, also enhanced some parrotfish populations, and the grazing function that these fish have on reefs. In turn, this grazing reduced the amount of seaweed growing in the park, thereby freeing up space for corals to settle and grow. The new paper, led by Peter Mumby, shows how grazing pressure correlates with coral recruitment: sites within the park, with twice as much grazing, also had twice as many coral recruits as sites outside the park. After comparing a suite of alternative hypotheses, Mumby and collaborators concluded that the grazing itself, rather than other potentially confounding factors, best explain the enhanced coral recruitment. “This is the first evidence we have that marine reserves benefit coral,” said Mumby. “Coral reefs are unique ecosystems that have supported thousands of fish and other marine species for millions of years. We estimate that humans have already destroyed around 30 percent of the world’s coral reefs and climate change is now causing further damage to coral. These findings illustrate the need to maintain high levels of parrotfish on reefs in order to give corals a fighting chance of recovering.”

Taken as a whole, this research from the ECLSP shows that in addition to protecting an economically important but threatened fish species (the Nassau grouper), the reserve also nurtures the growth of corals, which are the long-term foundation of many other ecosystem processes and services in The Bahamas. The studies also demonstrate how reserves, as outposts of less disturbed, more natural marine ecosystems, can serve as important scientific “controls” for understanding human impacts in surrounding waters. By teasing apart the ecological effects of protected places such as the ECLSP, one of the largest and best enforced marine reserves in the Caribbean, researchers are also able to address what ecological functions are missing from surrounding, less protected waters.

These articles, and others produced by the BBP, are available via the BBP website’s publication page.