Stanford Report, Mar. 10, 2004
Marine scientists study Bahamas reef ecosystems to save them
BY JOY KU
The Bahamas conjures up images of intense blue waters and sun-drenched beaches for most of us. But it means much more than that for Stanford marine scientists Stephen Palumbi and Fiorenza Micheli and visiting scholar James Sanchirico from Resources for the Future, a Washington, D.C.-based think tank. These researchers are key participants in a project called the Bahamas Biocomplexity Project (BBP). This collaborative study aims to provide a multidisciplinary view of the Bahamas ecosystem for use in designing marine policies for the region.
"This is the first time a group of people has gone in and simultaneously studied the physical side of the system, the connectivity side, the ecological and habitat side and the socioeconomic side all together," says Palumbi, a professor of biological sciences at Stanford's Hopkins Marine Station. Researchers hope that policies based upon this systems perspective will produce more viable and sustainable marine environments.
The three scientists provided a progress report on the project during a talk sponsored by the Stanford Institute for International Studies on Feb. 26 titled "Coupled Natural and Human Dynamics in Coral Reef Ecosystems of the Bahamas."
The BBP is a five-year project funded primarily by the National Science Foundation and headed by Dan Brumbaugh of the American Museum of Natural History. Participating researchers come from disciplines as varied as anthropology, biology, physics, economics and applied mathematics.
The focus of the BBP is on marine reserve networks. These are collections of many small marine protected areas, or MPAs -- regions that are entirely closed off to fishing and exploitation. The BBP researchers think marine reserve networks may be preferable to one large marine reserve.
Micheli, an assistant professor at Hopkins Marine Station, remarks that these marine reserve networks are important because they spread risks. In a reserve network, a hurricane or other disaster, natural or man-made, could ruin one MPA without causing the entire system to stop functioning.
Palumbi's research on the staghorn coral population in the Caribbean supports this idea of a marine reserve network. He generated a family tree of the DNA sequences for each staghorn coral population. By comparing these DNA family trees, Palumbi concluded that most populations of staghorn corals through the Caribbean are genetically distinct. This implies that staghorn coral do not easily propagate from one region to another.
In the Bahamas alone, Palumbi has identified at least four genetically distinct regions based on coral data. "The replenishment of corals in the Bahamas is going to have to be a fairly local thing," he concludes. "One can't imagine that coral in San Salvador are going to be rescued by larval production elsewhere in this archipelago."
His colleagues, project leader Brumbaugh and biodiversity specialist Kate Holmes of the American Museum of Natural History, are also beginning to see similar regional distinctions based on DNA family trees for lobsters in the Bahamas. What emerges from both the coral and the lobster studies is the suggestion of an east-west division of the Bahamas. The coral and lobsters on the east side of the islands are genetically different from those on the west side. Palumbi excitedly notes that this pattern correlates with oceanography data describing how particles travel in the Caribbean.
While Palumbi's work provides guidelines about how big the reserve network should be, Micheli focuses on what to preserve. According to Sanchirico, a visiting scholar at Stanford's Center for Environmental Science and Policy, more than 60 percent of the coral reefs are estimated to disappear over the next 30 years.
"[The coral reefs] are sort of the quarterback of habitats," says Sanchirico. But other habitats are necessary for the Bahamas ecosystem to function. It's not enough to protect just the coral reefs, Sanchirico says. There needs to be what he calls "a portfolio of habitat types." Biologist Micheli and other BBP team members have identified at least three essential habitat types in the Bahamas -- coral reefs, seagrass beds and mangroves.
BBP colleague Peter Mumby of the University of Exeter published a study in the Feb. 5 issue of Nature suggesting that these three habitats need to be located near one another to maintain biodiversity and sustain populations important for fisheries in the region. The study specifically looked at striped parrotfish, bluestriped grunt, yellowtail snappers and schoolmaster snappers. These fish all live in the Caribbean reefs as adults, and all of them increased in size and/or abundance if mangrove habitats were nearby.
The results suggest mangroves may be an intermediate habitat that allows juvenile fish more time to grow before they move to their more dangerous adult habitat, the coral reef. Mangrove deforestation will have "significant deleterious consequences for the functioning, fisheries, biodiversity and resilience of Caribbean coral reefs," Mumby says.
Micheli also worked with the BBP team to map out the marine habitats in the region. By combining satellite imagery with direct observations, the team was able to identify approximately 19 different habitat categories. Habitat maps like these will be valuable when selecting the sites for the MPAs.
The BBP is also investigating the socioeconomic impact of marine reserve networks. Will closing an area force fishermen into another trade? Or will they just begin fishing in another area? The research of Sanchirico and his social science colleagues in the BBP addresses these questions. The answers are critical in determining when and where a marine reserve will improve the biological "health" of the ecosystem at the lowest cost to users of that marine environment, Sanchirico says.
And how does the BBP's work impact the design of marine policies in other regions of the world? Palumbi describes a few similarities between ecosystems in the Bahamas and other locations. But he emphasizes that it is the methodology, the BBP's multidisciplinary approach, that will be most helpful in designing marine policies in other regions.
Joy Ku is a postdoctoral researcher in the Pediatric Cardiology and Mechanical Engineering departments at Stanford University.
Courtesy: OAR/National Undersea Research Program