Aug. 24, 1999 BOWLING GREEN, O.—A Bowling Green State University researcher predicts a dramatic drop in the number of zebra mussels in the Great Lakes could occur within five years. But, he warns, if such a drop occurs in Lake Erie, it may affect that lake’s water quality.
Dr. Jeffrey G. Miner, a BGSU fisheries biologist, has been studying the effects of round gobies, an invasive fish from Europe that eat zebra mussels and have now expanded their range to include all of Lake Erie.
Based on research he has been conducting over the past four years, Miner said he believes a dramatic reduction in the zebra mussel population is possible in a relatively short time frame.
Under optimal laboratory conditions, an individual round goby (Neogobius melanostomus) can consume 20-40 small zebra mussels per day. But--as field biologists know--this does not mean that all of the estimated billion round gobies in Lake Erie will be eating this many zebra mussels every day.
To monitor actual consumption, Miner and his students conducted an experiment in Lake Erie at Stone Laboratory on South Bass Island.
They placed enclosures containing round gobies and rocks covered with zebra mussels in 15 feet of water. At the end of one month, rocks introduced to the sites were collected and analyzed for differences in zebra mussel abundance and size distributions of the mussels, as well as for other changes. What did they find? In cages with the greatest density of 4-inch round gobies, more than 2,000 zebra mussels had been consumed, a 66 percent decline.
"These results suggest that the existing densities of round gobies have the potential to regulate the zebra mussel population," Miner says. It may, however, take several years because gobies eat only small zebra mussels (less than half an inch long) and large zebra mussels will have to die from other causes.
Because gobies consume so many small zebra mussels, Miner anticipates that in time few zebra mussels will reach adulthood and the numbers of young will start to decline. If that’s the case, gobies may be able to regulate the amount of algae that zebra mussels filter out of Lake Erie, thus affecting water quality, the BGSU biologist points out.
Zebra mussels, coupled with a decline in phosphorus loading to Lake Erie, have contributed to increased water clarity in Lake Erie. Now, in the middle of summer, boaters can see down 30 feet into Lake Erie’s clean waters.
By consuming large numbers of zebra mussels, round gobies may reduce that cleansing ability in the future," Miner said.
To test these ideas, Miner has teamed up with Dr. Rex Lowe, a professor of biological sciences at Bowling Green and an internationally recognized algologist, a scientist who studies algae.
This summer, the pair are using 10-foot-high, 1,300-gallon tanks to simulate conditions in the lake. They again will introduce zebra mussels and round gobies in the enclosures, but they are interested in learning more about the changes to organisms other than in the zebra mussels.
"By reducing the number of zebra mussels, we predict that more edible algae will be available to small zooplankton floating in the water, and thus they will increase in abundance," Miner said. If so, this could increase the food resources available to prey fish, like shiners, and even young sport fish, like yellow perch.
In addition, the scientists say, the composition of algae may be altered because of changes in the nutrients available for them to grow. Another possible result may be that changes in the density of some algae, such as blue-green algae, can affect the taste of drinking water.
Still, the researchers caution that longer-term experiments are necessary to determine if large zebra mussels will be able to compensate for round gobies feeding on small zebra mussels. They also must determine if round gobies will be kept at low densities by their own predators.
Lowe and Miner have received a $118,000 grant from Ohio Sea Grant to conduct this large-scale, two-year experiment. Their previous research was funded by grants from the Lake Erie Charter Boat Association and the Ohio Division of Wildlife.
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