TRAVERSE CITY, Mich. (AP) -- A newly published scientific paper says crucial nutrients for fish and other organisms are declining in Lakes Huron and Michigan.
The study was conducted by researchers from government agencies and universities.
It says much of the drop-off results from loss of phosphorus, which feeds phytoplankton. They are the tiny plants that form crucial links in food chains.
Invasive mussels have consumed heavy loads of phosphorus since the late 1990s by filtering organic material from the water.
In some places, larger fish have caused downward pressure on food chains by gorging on prey species such as alewives and round gobies.
Study leader David Bunnell of the U.S. Geological Survey said Thursday that the biggest problem seems to be with nutrient supplies at the lower end of food chains.