Zebra mussels boost algae growth
PONTIAC, MICH. -- A study has found the presence of zebra
mussels in inland lakes promotes the growth of a blue-green
algae that produces a toxin harmful to people and animals.
The study, conducted by researchers from Michigan State
University's Department of Fisheries and Wildlife, found
lakes infested with zebra mussels have, on average, levels
of a blue-green algae called Microcystis three times higher
than lakes without the mussels.
The infested lakes also have about twice the level of
microcystins -- poisons produced by the algae.
While the findings may alarm some who live around such
lakes, one of the study's authors cautions against panic.
"I'm not familiar with any instance of people being
poisoned just by swimming," Orlando (Ace) Sarnelle,
an associate professor at MSU, said in a report published
"You have to ingest the water and you have to consume
The toxin can cause liver damage if it is consumed in
large enough amounts.
The study included water samples from about 100 inland
lakes in Michigan.
Sarnelle said the number of blue-green algae blooms has
increased in Michigan's inland lakes and appears to be
linked to the spread of the mussels.
While the zebra mussels eat algae, they tend to steer
clear of the toxic blue-green algae.
Sarnelle said in lakes where nutrient levels are naturally
low, the concentration of the toxins is unlikely to be
high enough to pose a risk to humans and animals.
The study, published in the academic journal Limnology
and Oceanography, found the zebra mussels don't appear
to affect the amount of Microcystis in lakes with high
levels of phosphorus, a nutrient that results from erosion,
fertilizer runoff and human waste.
"In a lot of lakes we've sampled, we're not seeing
levels that are alarming -- they're just higher than they
used to be," he said.
While none of the inland lakes in the study provide drinking
water, blue-green algae blooms have been observed in the
Great Lakes, which provide drinking water for an estimated
40 million people.