Declines of the food resources that feed lake organisms are likely causing dramatic changes in the Great Lakes, according to a new U.S. Geological Survey (USGS) study.
The study, published in the journal BioScience, found that water clarity has been increasing and phytoplankton (the microscopic water organisms that feed all other animals), native invertebrates, and prey fish have been declining in at least 3 of the 5 Great Lakes since 1998.
These food web changes fundamentally affect the ecosystem’s valuable resources and are likely caused by decreasing levels of lake nutrients, and by growing numbers of invasive species, such as zebra and quagga mussels.
These decreases in nutrients have the potential to affect the smallest organisms up to the top predators. In Lake Huron, for example, plankton and fish appear to be controlled by declining nutrients or food.
“Our study provides a comprehensive ecological report card that highlights existing gaps in scientific understanding and monitoring of the complex Great Lakes ecosystems,” said David “Bo” Bunnell, USGS scientist and lead author of the study. “Ideally, it will spur future research to more rigorously test some of the predictions born from our relatively simple analyses.”