ANN ARBOR, MI, Dec. 19, 2013 -- A recent U.S. Geological Survey (USGS) indicates that a decline in food resources feeding lake organisms are likely causing dramatic changes in the Great Lakes.
According to the research, water clarity has been increasing in a majority of the Great Lakes, while phytoplankton (the microscopic water organisms that feed all other animals), native invertebrates and prey fish have been declining since 1998. These changes fundamentally affect the ecosystem's valuable resources and are likely caused by decreasing levels of lake nutrients and growing numbers of invasive species such as zebra and quagga mussels.
"These findings provide critical information to help decision-makers understand changes that are affecting the Great Lakes fishery that generates about $7 billion for the economy each year," said Suzette Kimball, acting director of the USGS. "The work is the result of a strong public-private collaboration and greatly contributes to managers' ability to deal effectively with the changes occurring in these unique and vast freshwater ecosystems so important to our nation."
The study found that inputs of phosphorus have declined in the Great Lakes since 1972, when the Great Lakes Water Quality Agreement was signed. The growing numbers of invasive species such as zebra and quagga mussels have caused phosphorus levels to decline further over the last decade in some lakes by filtering out nutrients and phytoplankton. Likewise, these decreases have the potential to affect the smallest organisms up to the top predators.
"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."