The health of the Bering Sea fisheries off the coast of Alaska depend largely on the plankton blooms that occur as the sea ice retreats in spring. Sunlight causes phytoplankton to bloom, which provides food to copepods and other zooplankton that are fed upon by fish, crabs and other commercial species.
But new research by a large team of scientists suggests that, as the climate warms, the productivity of the fisheries will be increasingly dependent on the survival rate of plankton through the winter months. And warming temperatures may make it difficult for them to survive the season.
Results of the research will be presented this week in Honolulu at the biennial Ocean Sciences Meeting, sponsored by the American Geophysical Union, The Oceanographic Society, and the Association for the Sciences of Limnology and Oceanography.
University of Rhode Island oceanographer Robert Campbell, a member of the Bering Sea Project funded by the North Pacific Research Board and the National Science Foundation, said that changes in the timing of the melting of sea ice in spring was expected to have far-reaching effects on the health of the ecosystem, but the importance of winter plankton survival was unexpected.
"It turns out that when we change the spring ice conditions in our models, we don't see as large an effect on the system's productivity as we expected," said Campbell, a marine scientist at the URI Graduate School of Oceanography. "But overwintering survival changes the productivity of the system. That's very important, and we still don't really understand what happens."
According to Campbell, there is little food available for plankton to eat during the winter months, so they enter a state of dormancy called diapause, when their metabolism slows allowing them to go extended periods without eating. But if water temperatures increase, the plankton may emerge from diapause early, increasing their metabolism and burning through their stored fats before food becomes available.
These findings come from computer models created to study the western Arctic ecosystem, but few direct studies of the ecosystem in winter have been conducted due to the challenging environmental conditions. So Campbell said a great deal is still to be learned about winter plankton survival.
"Maybe they will be able to adapt; maybe they don't raise their metabolism so high. We just don't know," Campbell said.
The one winter study of the region, conducted in 2011 and funded by the National Science Foundation, found that plankton in the Bering Sea may not enter a state of diapause after all.
"Based on the measurements we took, they probably can't survive the winter without lowering their metabolic rates further as the winter season progresses, but they don't appear to go into a hibernation state as we expected," Campbell said.
"Many of the animals we studied were copepods, which usually go down to depth to hibernate. But in the Bering Sea and Chukchi Sea there are expansive continental shelves, so there is no deepwater refuge for them to go to. That makes them more vulnerable to climate change because they have no refuge from the increasing temperatures," he added.
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