Global Warming Could Shrink Fish Populations

Andrea Thompson, LiveScience.com 14 Jan 08;

Certain fish could disappear from restaurant menus and our plates at home by 2100, as global warming changes ocean food webs, a new study suggests.

Climate change has the potential to threaten ecosystems all over the world, and those in the ocean are no exception.

Two marine ecologists led a study of the effects of climate change on the food web of the Bering Sea, which currently provides about half of the fish caught in U.S. waters each year and nearly a third caught worldwide.

"All the fish that ends up in McDonald's, fish sandwiches — that's all Bering Sea fish," said Dave Hutchins of the University of Southern California, whose former student at the University of Delaware, Clinton Hare, led the study.

The Bering Sea has already shown signs of warming, Hutchins says, which could affect the productivity of its ecosystem.

"Its warmer, marine mammals and birds are having massive die-offs, there are invasive species — in general, it’s changing to a more temperate ecosystem that’s not going to be as productive," he said.

Hare and Hutchins studied how climate change affected communities of phytoplankton, which are food for smaller fishes. The Bering Sea is so highly productive because of a large type of phytoplankton found in its waters, known as diatoms.

The researchers collected phytoplankton samples from the sea and incubated them, simulating sea surface temperatures and carbon dioxide concentrations predicted for 2100. Their work is detailed in a recent issue of the journal Marine Ecology Progress Series.

They found that these conditions favored smaller types of phytoplankton at the expense of the diatoms.

As diatoms become more scarce, animals that eat them, including the fish caught in the Bering Sea, will also die off the researchers say.

"The experiments we did up there definitely suggest that the changing ecosystem may support less of what we’re harvesting, things like pollock and hake," Hutchins said.

A decrease in the number of diatoms could also intensify global warming. Because they are bigger than other phytoplankton, diatoms store more carbon when they die and fall to the sea floor. If they disappear, their smaller brethren will leave more carbon dioxide in the atmosphere.

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