Marine Ecosystems Collapse When Predators Removed
CORVALLIS, Oregon, August 21, 2002
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.
"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."
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.