Bering Sea may not remain productive fishery by 2100 due to ocean warming

The Cheers 12 Jan 08;

Ecologists have predicted that the Bering Sea, which is one of the world's most productive fisheries, would be unsustainable by the year 2100 because of warmer ocean surfaces with increased levels of carbon dioxide.

Experiments done by researchers from University of Southern California (USC) also point towards the fact that the ecosystem in the Bering Sea would change considerably by the next century.

As part of the experiments, the researchers collected the algae samples from the Bering Sea's central basin and the southeastern continental shelf.

"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," said USC marine ecologist Dave Hutchins.

According to Hutchins, while the study must be interpreted cautiously, its implications are harrowing, especially since the Bering Sea is already showing signs of warming.

"It's 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.

The crux of the study was examining how climate change is adversely affecting algal communities of phytoplankton, the heart of marine food webs.

Phytoplankton use sunlight to convert carbon dioxide into carbon-based food. As small fish eat the plankton and bigger fish eat the smaller fish, an entire ecosystem develops, which is the reason why the Bering Sea is highly productive because of the presence of diatoms, a large type of phytoplankton.

But, from the research, the scientists found that greenhouse conditions favored smaller types of phytoplankton over diatoms. Such a shift would ripple up the food chain because as diatoms become scarce, animals that eat diatoms would become scarce, and so forth.

A shift away from diatoms towards smaller phytoplankton could also undermine a key climate regulator called the "biological pump."

When diatoms die, their heavier carbon-based remains sink to the seafloor. This creates a "pump" whereby diatoms transport carbon from the atmosphere into deep-sea storage, where it remains for at least 1,000 years.

"While smaller species often fix more carbon, they end up re-releasing CO2 in the surface ocean rather than storing it for long periods as the diatom-based community can do," Hutchins explained.

This scenario could make the ocean less able to soak up atmospheric carbon dioxide.

"Right now, the ocean biology is sort of on our side," said Hutchins. "About 50 percent of fossil fuel emissions since the industrial revolution is in the ocean, so if we didn't have the ocean, atmospheric CO2 would be roughly twice what it is now," he added. (ANI)