Damselfish Study May Help Improve Marine Reserves

John Roach
for National Geographic News

October 13, 2004

In recent years scientific studies have shown that marine environments
made off-limits to fishing fleets are a boon to the fish that swim
there. The question is: What parts of the ocean are the best to close
for the benefit of the fish and those who eat them?

Suzanne Dorsey is an assistant professor of biology at Salem College in Winston-Salem, North Carolina. All too often, she says, politics drive decisions on where to locate marine reserves, which saps them of their full potential.

"We really need science to step up and provide hard quantitative data so we can concentrate our efforts in terms of conservation," she said.

Dorsey is studying the reproductive success of bicolor damselfish (Stegastes partitus) at different habitats in the Caribbean as part of her efforts to provide fisheries managers with the data they need to make marine reserves more effective.

According to Stephen Palumbi, a marine biologist at Stanford University's Hopkins Marine Station in Pacific Grove, California, improved knowledge on where to establish marine reserves may help recover depleted fish stocks outside the reserve boundaries.

For example, "for widespread species, some of the population may be producing offspring and some may be sinks—full of adults that are not able to reproduce. Knowing where the sources and sinks are would be very handy," he said.

Scientists can also lend a hand to fisheries managers by providing data on how species' use of space and information on how all the species in a habitat are connected in marine communities, according to Palumbi. In 2002 Palumbi authored a Pew Oceans Commission report on the design and implementation of marine protected areas.

Current studies show "the numbers of fish and diversity and individual size all go up pretty strongly inside the borders of a reserve," Palumbi said. "What's less clear is how all that bounty inside reserves impacts overall fishing outside the reserves."

Damselfish Studies

Dorsey chose to work with the bicolor damselfish because they are not considered a threatened or endangered species. Thus, they are a reasonable candidate for manipulation by researchers.

Also, the basic damselfish biology is well known, so researchers can begin to ask more complex questions that are relevant to other species living in the coral reef ecosystem, Dorsey said.

"This tiny species that nobody eats or even cares about has a lot to tell us about the health and welfare of this critical ecosystem, an ecosystem that may be playing a crucial role in absorbing greenhouse gases, an ecosystem that certainly is crucial for the economy of a tourism-based nation [such as Barbados or Grenada]," Dorsey said.

Dorsey's study focuses on bicolor damselfish populations and reproductive success at two different kinds of coral reef habitats in the Caribbean—a near-shore fringing reef on Barbados and a deep offshore reef in Grenada.

"These two environments are quite different from the perspective of the fish," she said. For example, there are more predators on the deeper reefs, but the near-shore reefs experience higher wave action and greater pollution.

Preliminary data indicates that the bicolor damselfish are about 60 percent less productive on the deeper outer reefs than on the inshore reefs, which is most likely related to the lower density of predators, though Dorsey said she has yet to directly prove this.

The implication of this finding, Dorsey said, is that even though near-shore reefs visually appear more degraded than the pristine offshore reefs, concentrating efforts to protect them may actually do more to conserve the overall reproductive success of reef fish.

Fisheries Management

Dorsey's damselfish study is ongoing. Each summer she spends three months in the Caribbean. She shares her data with managers at marine reserves in Barbados and Grenada, though she says how the reserve managers "turn around and use that data is limited," because funding for marine reserves is an ongoing battle.

For example, Dorsey said, the marine reserve in Barbados has been opened to recreation and fishing use to pay for its operation.

According to Palumbi, cooperation from scientists, politicians, and social and economic organizations is needed for the marine reserve system to work effectively.

"There's no reason biological, economic, social, and political criteria can't be met in setting up these reserves," he said. "It's a little harder to do that it involves negotiating with and talking and listening to [different] points of view, but in the end this results in setting up a protected area that makes sense."

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