Â鶹ÒùÔº

A study found that invasive zebra mussels significantly alter aquatic ecosystems, and are associated with elevated mercury concentrations in fish. Mercury, a potent neurotoxin, poses a serious threat to both aquatic life and human health.

Recently in Science of the Total Environment, a team of researchers at the University of Minnesota College of Food, Agricultural and Natural Resource Sciences, Minnesota Aquatic Invasive Species Research Center, and the U.S. Geological Survey studied 21 Minnesota walleye lakes to assess the impact of zebra mussels on food webs and fish tissue mercury concentrations.

Researchers compared mercury concentrations of fish collected from lakes with and without zebra mussels and sampled water, zooplankton, invertebrates and fish from both nearshore and open water zones. They analyzed the data to provide critical insights into fish mercury concentrations, diets and habitat use.

The researchers found:

• Walleye exhibited 72% higher mercury concentrations in lakes invaded by zebra mussels compared to uninvaded lakes.
• Average-sized walleye were more than twice as likely to exceed mercury thresholds tied to human health.
• Walleye in zebra mussel-infested lakes reached mercury concentrations exceeding the Minnesota Department of Health threshold of 0.22 parts per million at a significantly smaller size (14 inches vs. 18 inches).
• Yellow perch exhibited 157% higher mercury concentrations in lakes invaded by zebra mussels. Average-sized yellow perch had a 50 times higher risk of exceeding mercury thresholds.
• Zebra mussel invasion led to shifts in fish resource use, with walleye and yellow perch relying more on nearshore feeding habitats.

Increased mercury concentrations in fish add to a growing list of known negative effects of invasive zebra mussels and highlight how ecological stressors can alter contaminant cycling within inland lakes to affect the environment and human health.

"We were surprised to find such a large effect of zebra mussels in fish tissue mercury concentrations, and we are eager to conduct further research to understand exactly the mechanism behind these patterns," said senior author Gretchen Hansen, an associate professor in the Department of Fisheries, Wildlife and Conservation Biology.

Hansen emphasized these results do not mean that fish are unsafe to eat, but rather that they point to a need to assess contaminant loads in fish harvested for consumption in lakes invaded by zebra mussels.

Looking ahead, the research team is committed to further investigating the influence of zebra mussels on mercury levels. Collaborating with state and tribal natural resource agencies, researchers aim to develop predictive models to guide monitoring efforts and mitigate the impact of this aquatic invasive species.