A Central Michigan University aquatic ecologist recently served as guest editor of a special-issue academic journal dedicated to recent changes in Lake Michigan's food web. The issue seeks to understand these changes and their impact on the Great Lakes.
CMU biology professor Hunter Carrick joined a team of Great Lakes experts to produce The Journal of Great Lakes Research's special issue titled Complex Interactions in Lake Michigan's Rapidly Changing Ecosystem. The multidisciplinary publication includes 22 papers on the ecosystem of Lake Michigan, including two Carrick authored.
"Lake Michigan is changing rapidly in many ways," Carrick said. "The research in this issue is important as we work to understand and potentially regulate these changes."
The issue includes topics such as the effects on the food web due to the rise in population status of the invasive species quagga mussels. Because the food web is the interconnection of many food chains – a graph of what-eats-what – when changes occur in the food web base, effects ripple through the rest of the web to an array of other consumers. Therefore, changes in even the smallest members of the food chain can have ramifications for large fish. The result, says Carrick, is a change in food quantity and quality at nearly every level of the web.
"There are a number of causes to consider, but the introduction of quagga mussels to the lake is a key factor in these changes," he said. "In 30 years of Great Lakes research, I have never seen anything affect the lakes the way this species has."
Climate change: another culprit
The special issue addresses other aspects of the Great Lakes as a result of the declining food web. Carrick's research in the special issue points to three key factors in the changing outlook: invasive mussels, reduced nutrients and climate change.
"Productivity in Lake Michigan has declined over the last 20-plus years," he said. "Now that we have looked more closely, it's clear that rising temperatures are having an affect."
Carrick uses microorganisms as early-warning indicators to evaluate changes in the ecosystem before larger, more complex living things are affected. Among the most notable differences in his study of Lake Michigan is a large decline in the phytoplankton seasonal bloom, called diatoms. Phytoplankton are microscopic organisms which make up the base of the aquatic food web and are pivotal to sustaining small animals and fish. With this large shift at the base, researchers expect rapid changes in the Great Lakes to continue.
CMU students Emon Butts, Daniella Daniels and Christopher Frazier aided Carrick in the study in addition to Melanie Fehringer, a former student researcher at the CMU Biological Station on Beaver Island. Researchers contributing to the study were Gary Fahnenstiel, Michigan Technological University and University of Michigan, and Steven Pothoven and Henry Vanderploeg, Great Lakes Environmental Research Laboratory, National Oceanic and Atmospheric Administration.
The future of the Great Lakes
Research in the special issue of the journal focused on Lake Michigan but will benefit other lakes with similar ecosystems. Lakes Superior, Huron and Ontario share similar food web structures and challenges of invasive species. Carrick and his fellow CMU researchers are leading efforts to protect and restore the Great Lakes.
"The Great Lakes are tremendously resilient, but the sustainability of their future health remains to be seen," he said. "We are facing unprecedented change in these waters, and our research is a pivotal part of understanding future trends in the species present and the productivity of the ecosystem as a whole."
The special issue of the Journal of Great Lakes Research is available here. Additional guest editors of the issue include Henry Vanderploeg, Great Lakes Environmental Research Laboratory; David Bunnell, Unites States Geological Survey Great Lakes Science Center; and Tomas Hook, Purdue University.