The Heat Is Online

Small warming disrupts ecosystems

Associated Press, March 26, 1999

A temperature change of just a few degrees may be enough to disrupt a delicate ecological balance in the tidal waters of Oregon, and perhaps elsewhere, according to a study of starfish and mussels.

Eric Sanford of Oregon State University said his study suggests that if a key species in a community of animals is particularly sensitive to temperatures, a slight warming or cooling could start a whole cascade of rapid changes affecting every animal in an ecosystem.

In a study appearing in the March 26, 1999 issue of the journal Science, Sanford said he found that a 5-degree change in temperature is enough to dramatically change the feeding habits of the starfish, a five-armed creature that feeds mainly on mussels, common along the Pacific coast of the United States.

The finding, said Sanford, has important implications for understanding the effects of global warming. "Many people have assumed that the effects of climate change would be gradual," the researcher said in an interview. "But this shows that if an important species in a community is highly sensitive to temperature, then the effects of a small temperature change can happen rapidly."

In his study, Sanford tracked the feeding patterns of starfish kept in the laboratory at different temperatures. He checked his results by manipulating the population of starfish and mussels in two areas along the Oregon coast.

Sanford he found that a temperature drop of 5 degrees caused the starfish to virtually stop feeding on the mussels. This allows the mussels to rapidly expand in population.

Conversely, when the water temperature was increased by 5 degrees, Sanford said starfish went on a feeding binge, quickly reducing the population of mussels.

Either way, he said, there are dramatic changes in the tidal community of animals.

When mussels are not controlled by starfish, said Sanford, their population explodes. The mussels attach themselves to every surface in the near-shore tidal zone, crowding out barnacles, algae and other organisms. "If you take away the sea stars, then you go from an ecosystem with a diverse population of species to a system where there is essentially only one species," Sanford said.

When starfish eat too much, he said, the reef-like mussel communities quickly start falling apart. These reefs, Sanford said, are homes for crab, sea cucumbers and worms, all important parts of the ecosystem.

Temperatures along the Oregon coast are affected by upwelling, cold deep waters surging to the surface. The frequency of upwellings, said Sanford, is determined by winds that, in turn, are affected by global temperatures. If cold upwellings become less frequent, starfish may eat more mussels, said Sanford. Or if the upwellings happen more often, thus cooling the tidal waters, starfish will eat less, allowing the mussel population to suddenly explode.