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Scientists look to the Bahamas as a model for coral reef conservation

21.02.2006


One of the greatest challenges facing marine ecologists today is finding innovative ways to reverse the rapid decline of coral reef ecosystems around the world. Ten percent of the planet’s reefs already have been degraded beyond recovery, according to one survey, and another 60 percent could die by 2050, primarily because of human activities, such as pollution, overfishing and climate change.



The situation is particularly acute in the island nations of the Caribbean, which have seen an 80 percent decline in coral cover in recent decades. To address this crisis, an international team of researchers, in consultation with the government of the Bahamas, launched the Bahamas Biocomplexity Project--an interdisciplinary approach to ecosystem management that project leaders say could serve as a model for coral reef conservation worldwide.

"The Bahamas Biocomplexity Project works across various disciplines to understand the intricate scientific and socioeconomic factors contributing to ecosystem changes," said project principal investigator Dan Brumbaugh, senior conservation scientist at the American Museum of Natural History’s Center for Biodiversity and Conservation.


"Under the rubric of ’biocomplexity,’ our approach recognizes that natural and human systems are inextricably linked, and that analyses and solutions must therefore transcend traditional disciplinary boundaries," he added.

On Feb. 20, Brumbaugh and Fiorenza Micheli, assistant professor of biological sciences at Stanford University’s Hopkins Marine Station, moderated a symposium entitled "Coral Reef Ecosystems and People in The Bahamas: Practical Applications of Biocomplexity Science" at the annual meeting of the American Association for the Advancement of Science in St. Louis. Panelists included educators, social scientists and marine biologists, who provided a progress report on how biocomplexity science, still in its infancy, is being applied to the problem of coral reef ecosystem management in the Bahamas.

The Bahamas model

"In 2000, the Bahamas committed to setting up a network of new no-take reserves," said Brumbaugh , who is also a visiting scientist with the National Oceanographic and Atmospheric Administration’s Marine Protected Areas Science Institute. "Starting with the declaration of five new reserves, the country initiated a process that was intended to lead to a system of protected areas covering 20 percent of their marine environment."

He pointed out that in 2002, new marine parks were added to the national park system, which is managed by the Bahamas National Trust, a non-governmental organization.

"This policy setting, along with interest from Bahamian partners in having more scientific input for their decision making, set the stage for researchers to try to look at how to best design a network of marine protected areas," he explained. "Marine protected areas provide promising, though sometimes contentious, tools for the conservation and recovery of coral reef ecosystems. Contributing to the heat of these discussions is the fact that apart from the most direct effects of reserves, we really don’t have a very good understanding for how these complex systems will perform over time."

The Bahamas Biocomplexity Project was designed to address the problem by adopting a holistic approach to marine conservation, he said. In addition to using scientific tools--such as satellite imagery, underwater surveys and population genetics--project members conduct ethnographic and economic surveys to assess local attitudes toward conservation, as well as educational outreach to explain their findings to local stakeholders and decision makers.

"Interdisciplinary collaboration across oceanography, population genetics, community ecology, anthropology and economics is providing new insights into the relevant scales of planning for biodiversity conservation and fisheries sustainability," Brumbaugh said. "Only now are we starting to see some of the emerging lessons."

Predators, prey and seaweed

The project’s most widely publicized finding to date was a study published in the Jan. 6 issue of the journal Science written by Peter Mumbry of the University of Exeter in Britain and a large team of collaborators, including Brumbaugh and Micheli. The study focused on the Exuma Cays Land and Sea Park, which, like other Caribbean coral reefs, was struck by a mysterious disease in 1983 that virtually wiped out a species of sea urchin that feeds on algae. The urchins had played a vital role in the reef ecosystem by controlling the spread of seaweed.

Since coral larvae only grow on rocks or dead corals that are algae-free, too much seaweed can prevent corals from re-establishing damaged reefs in the aftermath of hurricanes and other deadly events.

With the urchins gone, the job of chief seaweed grazer was taken over by a colorful herbivore known as the parrotfish. Parrotfish, in turn, are preyed upon by large carnivores, such as the Nassau grouper, whose numbers had increased in the park since the imposition of a fishing ban in 1986. Today, according to the Science study, Nassau grouper is seven times more abundant inside the park than in three comparable areas elsewhere in the Bahamas.

But did the grouper population explosion occur at the expense of the parrotfish, and therefore to the benefit of algae? For parrotfish, the answer depends on which species. Researchers found that small species were smaller than usual inside the reserve, suggesting that grouper predators were picking off the largest members of their populations inside the park.

In contrast, the number of big parrotfish--species 10 inches or longer, too large for a grouper to swallow--increased inside the park, apparently in response to protection from fish traps. The study concluded that seaweed grazing in Exuma had doubled because of the burgeoning population of big parrotfish, resulting in a fourfold reduction in algal abundance compared to areas outside the park.

"The Science results suggest that parks protecting fishes may also have beneficial effects on corals, by enhancing grazing and thereby contributing to the ability of reefs to bounce back from disturbances." said project co-principal investigator Micheli. These results highlight the inherent complexity of life on reefs, she added.

"There is this idea of redundancy in ecological systems: You lose one species, but another replaces its function," Micheli said. "In the case of grazers, 90 percent of urchins in one system were depleted, but their function was replaced by parrotfishes. Unfortunately, when you look at these small communities in the Bahamas, there may only be a couple of species that have interchangeable functions. Too often the boundaries of reserves are drawn without having all of the necessary details about species and habitats. Right now we’re looking at what combinations of habitats you need to protect to maintain the full set of ecological processes."

Coral villages

In his AAAS presentation, project co-principal investigator Stephen Palumbi discussed the genetics of marine habitats from the point of view of corals--tiny animals closely related to sea anemones that are responsible for building the reef framework. "We’re looking at the organisms that make the reef, because without them, the organisms that use the reef wouldn’t have a home," said Palumbi, professor of biological sciences at Stanford’s Hopkins Marine Station.

He and his colleagues focused on staghorn corals, which used to be common throughout the Caribbean: "We asked, Where do baby corals come from, and from how far away can a healthy reef seed the recovery of a damaged reef?"

To answer these questions, the Palumbi team compared the DNA of staghorn corals collected from nine reefs, some just a few miles apart, others separated by about 600 miles of ocean. "We look for where the genetic barriers are," he said. "That tells us where the larval barriers are. Our results show that genetic family lines can be quite distinct on reefs as close as two kilometers (1.2 miles), so they’re not co-mingling over short distances. All reefs in our study more than 500 kilometers (300 miles) apart were genetically distinct. Coral families thus seem to exist in local villages, with little genetic exchange above the scale of 50-100 kilometers (30-60 miles)."

This finding led Palumbi to raise another question: "If you have a reef damaged by hurricanes, dynamite or sedimentation, how quickly would you expect it to reseed? The answer: perhaps in thousands of years."

Some marine ecologists advocate restoring dying or damaged reefs, but that approach is rarely cost-effective, he argued.

"You can collect sprigs of coral, grow them in an aquarium, then return them to a reef, but transplanted corals are easily killed," Palumbi said. "Maybe 1,000 out of 10,000 sprigs will grow, but with a growth rate of about one centimeter per year, it would take many years to get big. It’s expensive, and not particularly successful. From a management standpoint, the genetics tell us that each island has to husband its own coral garden."

Human dimensions

"Better understandings of the dynamics of coral re-establishment and species interaction are crucial, but these are only parts of the puzzle," said project co-principal investigator Kenny Broad, assistant professor at the University of Miami’s Rosenstiel School of Marine and Atmospheric Sciences.

"How reserves may affect the local human communities that rely on these fishing grounds must also be considered," Broad told the AAAS symposium. "Will fishers shift effort toward other fishing grounds that may then suffer similar environmental consequences? Might they switch to activities and fishing methods even more damaging to the environment once their livelihoods are threatened? Given the lack of enforcement that exists in many parts of the world, how can local groups play a role in developing innovative approaches for managing the resources that they rely upon most directly?"

Such questions are being addressed by social scientists working within the Bahamas Biocomplexity Project, he noted: "Our results in the Bahamas as elsewhere suggest that rigid top-down directives that lack local support will not be effective in protecting or restoring coral reef ecosystems."

Other presenters at the AAAS session were Richard Stoffle of the University Arizona; Alan Hastings of the University of California-Davis; and Karen St. Cyr of the Bahamas Ministry of Education, now on sabbatical at the University of Massachusetts. Stoffle described details of his work with communities in the central Bahamas and their views about marine reserves. Hastings discussed general theoretical guidelines for reserve network design, highlighting some of their intrinsic complexities, and St. Cyr addressed integrating marine research and scientific results into education.

Several presenters highlighted the need for flexibility and special consideration of local context, including history, economics, cultural values and opportunities for advancing ecosystem-based management. For example, public education and involvement--through the formal school system and community workshops, where locals share their ecological knowledge and researchers share their understanding of the sustainability of ecosystem services--may contribute to wider acceptance of ecosystem-based management.

"The parks and marine reserves in the Bahamas are enormously thoughtful and successful, but when you visit there it seems natural, because so much of it is submerged," Palumbi said. "They realize there is a special relationship between the people and the sea. Tourism, which is about 60 percent of the gross national product, is based on environmental protection. But the Bahamas isn’t unique. It’s one of several countries, including St. Lucia, Curacao, Australia and South Africa, which has established the goal of setting aside 20 percent or more of its marine ecosystem. It’s not that these countries are so far ahead, it’s just that the United States is so far behind."

Mark Shwartz | EurekAlert!
Further information:
http://www.stanford.edu

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