Marine Ecosystems Collapse When Predators Removed

CORVALLIS, Oregon, August 21, 2002 (ENS) - The preservation of biodiversity is an absolute necessity to keep marine ecosystems healthy and prevent local or regional extinction of multiple species, say marine zoologists at Oregon State University.

Their newly published study was done on coral reefs in the Bahamas, where the scientists were able to isolate some reefs and selectively remove certain fish, and their competitors or predators, to observe the effect.

They found that overfishing of any one species, especially predator species, can have ripple effects that destabilize the whole fishery.


Dr. Mark Hixon (Photo courtesy Oregon State University)
"The research showed that all fish species within a food web are connected with one another, and the removal of any one species can cause whole populations to break down," said Dr. Mark Hixon, Oregon State University professor of zoology, the study's lead author.

"This is especially true when you take away the predatory species, which are a key to the natural balance and health of marine ecosystems, said Hixon, a marine ecologist and conservation biologist specializing in coastal fishes.

The study is relevant to the global problems now being experienced in many commercial fisheries, Hixon said, because many of the fish species most commonly targeted by fisheries are marine predators.

The study, published this week in a professional journal, the "Proceedings of the National Academy of Sciences," was funded by a four year, $400,000 grant from the National Science Foundation, and also by the National Undersea Research Program of the U.S. National Oceanic and Atmospheric Administration (NOAA).

"We found that the removal of any one species can have ramifications for the whole ecosystem," Hixon said. "Without predation, a fish species can increase its population to an unsupportable size. Lacking food, fish become vulnerable to disease, changes in water conditions and ultimate collapse of that species or the whole fishery. Everything is connected to everything else."


Lingcod (Photo by V. O'Connell courtesy Alaska Department of Fish and Game)
In the Pacific Northwest, some of the key predatory species are lingcod, some larger rockfish and other groundfish.

The findings may help explain why some fish populations undergo such dramatic changes either naturally or when pressured by external forces such as fishing, Hixon said.

Fish populations within a certain species and location may vary by as much as 10 to 100 times. There is much less risk of population collapse or regional extinction when there's a proper and natural balance between a species, its competitors and its predators, Hixon said,

In future research, Oregon State University scientists hope to study these processes in marine reserves. They want to learn whether or not maintenance of balanced, healthy fish populations in reserves can have a positive influence on the availability of the same species elsewhere, and will focus on species sought in commercial or recreational fisheries outside the reserves.


In the Caribbean Sea, a Nassau grouper eyes its next meal. (Photo courtesy National Undersea Research Program)
Dr. Hixon is a member of the Marine Protected Area Federal Advisory Committee, created by executive order of President Bill Clinton and retained by President George W. Bush. The advisory committee is mandated to provide expert advice and recommendations to the Secretaries of Commerce and the Interior on the development of a national system of marine protected areas.

Marine protected areas may be established by federal, state and local governments to protect marine habitats and natural and cultural resources from overexploitation, destructive uses, or other threats, and they may also be created to conserve species, habitats, or biological diversity.