Scientists struggle to measure impact of invasive species

ALEXANDRIA, Minn. (AP) — Scientists still don’t have a clear answer on whether invasive species are destroying Minnesota’s lakes more than 20 years after they started spreading in the state’s waters.
Researchers are struggling to understand the impact that species like zebra mussels have on the underwater ecosystem, Minnesota Public Radio News reported. Zebra mussels are now found in more than 330 lakes and rivers statewide.
Some lakes with invasive species will have low-level populations, while others will see massive impacts to their ecosystem, said Nick Phelps, who runs the Minnesota Aquatic Invasive Species Research Center.
Scientists and anglers worry when invasive species enter a lake because they start a chain reaction by eating microscopic algae called phytoplankton. Less phytoplankton means less food for tiny animals like zooplankton. Some baby fish depend on zooplankton to survive just after they’ve hatched, while others eat zooplankton their whole lives.
Lake Carlos is one of 25 lakes that are studied regularly because they represent lakes across Minnesota’s various ecosystems. The monitoring program started on Lake Carlos in 2008, a year before zebra mussels were first found in the lake, which has given researchers a good set of “before” data.
Despite the dramatic loss of zooplankton in Lake Carlos, the lake’s fish populations appear to be surviving.
There’s even been an increase in smallmouth bass, something that often happens after zebra mussels infest a lake, said Casey Schoenebeck, who coordinates monitoring of Minnesota’s sentinel lakes for the Department of Natural Resources.
Other key gamefish species, like walleye, are still doing well, but the DNR continues to stock walleye in the lake to supplement natural populations. Fish habits are changing in Lake Carlos, as they adapt to the lake’s ecosystem.
“For the most part, our growth rates are unchanged,” Schoenebeck said. “But their location has changed. As the water clarity increases, they’re moving deeper. Some of the light-sensitive species, like walleye, are deeper in the lakes now.”
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Information from: Minnesota Public Radio News, http://www.mprnews.org

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