Something has been eating Charlie Kerfoot's doughnut, and all fingers point to a European mollusk about the size of a fat lima bean.
No one knew about the doughnut in southern Lake Michigan, much less the mollusk, until Michigan Technological University biologist W. Charles Kerfoot and his research team first saw it in 1998. That's because scientists have always been wary of launching their research vessels on any of the shipwreck-studded Great Lakes in winter. But NASA's new Sea-viewing Wide Field-of-view Sensor (SeaWiFS) Project was giving scientists a safer way to look at the lakes in bad weather. SeaWiFS satellite data showed Kerfoot's team a roughly circular river of phytoplanktonalgae and other tiny plantsthat was drifting counterclockwise around the southern end of Lake Michigan, creating a doughnut.
The group determined that the doughnut was formed when big winter storms kicked up sediments along the southeastern shore of the lake. There, Michigan's biggest rivers drain a watershed rich in phosphorus and other nutrients from cities and farms. Those nutrients settle in the lake's sediments until storms stir them up. Then, suspended in the water column, they begin circulating in a slow-moving gyre that flows from Grand Haven in the north to Chicago in the south. That gyre creates a Thanksgiving feast for phytoplankton. "We saw that with each storm, you get a ring, and it can persist for weeks or even months," says Kerfoot.
"We were floating in the clouds, saying 'Hey, we discovered a new phenomenon,'" he remembers. Samples of lake water taken from research vessels verified the satellite data. Plus, they found that zooplankton, the tiny animals that feed on phytoplankton, were much more abundant in the doughnut. For them, the seasonal bloom was an all-you-can-eat salad bar, an important part of their strategy to survive winter. Those zooplankton were eaten in turn by small fish, which were eaten by large fish, which f
|Contact: Marcia Goodrich|
Michigan Technological University