UW student addresses international ocean scientists

The world’s ocean scientists can learn a lot from the humble lakes of the Midwest, and a UW–Madison student has been asked to teach them.

Chris Harvey, a doctoral limnology student, has been selected to represent the Great Lakes region at an international ocean science conference Nov. 21 in Gilleleje, Denmark. He will give two presentations at the Young Scientists Conference on Marine Ecosystems Perspectives, organized by the International Council for Exploration of the Sea (ICES).

Harvey

With support from the UW–Madison Sea Grant Institute, Harvey has studied the diets of lean and siscowet lake trout in Lake Superior. Understanding how their diets overlap, he says, is important for learning how each of these top-level predators affects the other-and how they both affect other levels of the food web in Lake Superior.

Harvey says the Great Lakes and small lakes in Wisconsin and Michigan offer opportunities to learn things about food webs that are hard to study in the ocean: “The oceans are enormous systems. You have all these things happening across all kinds of scales of time and space. When one thing changes, you don’t know what effect it has because so many other things are changing, too.”

In small lakes, however, scientists can change something — by adding or removing predators, for example — and see what happens to the rest of the system. Harvey will talk about what scientists call top-down effects on food webs — the idea that changes in the population of high-level predator fish can alter numbers of other species far below them on the food web.

Ocean scientists have most often studied things in the other direction, Harvey says. They have often assumed that the bottom levels of food webs-like how much algae is available-determine what happens at the higher levels.

But Harvey says research in the Midwest has shown very strong top-down effects.

“For example, when lots of walleye were put into Lake Mendota, they ate the small fish that eat zooplankton,” Harvey says. “So there were more zooplankton then, and zooplankton eat algae. So the zooplankton ate the algae, and the water cleared up. That showed that large predators can reduce algae.”

The conference in Denmark “is intended to give young scientists an opportunity to participate in an international forum and to contribute to the international scientific work that forms the basis for managing the marine environment,” according to ICES.