Lakes With Zebra Mussels Have
Higher Levels Of Toxins, MSU Research Finds
EAST LANSING, Mich. - Inland lakes in Michigan that have
been invaded by zebra mussels, an exotic species that
has plagued bodies of water in several states since the
1980s, have higher levels of algae that produce a toxin
that can be harmful to humans and animals, according to
a Michigan State University researcher.
In a paper published in the recent issue of Limnology
and Oceanography, Orlando "Ace" Sarnelle, an
associate professor in MSU's Department of Fisheries and
Wildlife, and colleagues report that lakes that are home
to zebra mussels have, on average, three times higher
levels of a species of blue-green algae known as Microcystis.
Those same lakes also have about two times higher levels
of microcystins, a toxin produced by the algae.
"If these blooms of blue-green algae are a common
side effect of zebra mussel invasion, then hard-fought
gains in the restoration of water quality may be undone,"
Sarnelle said. "Right now, it appears that the numbers
of blooms in Michigan have been increasing and appear
to be correlated with the spread of zebra mussels."
Initially, water samples were taken from nearly 100 inland
lakes in Michigan's Lower Peninsula, ranging from Benzie
County in the northwest to Oakland County in the southeast,
that had established zebra mussel populations.
Follow-up experiments by Sarnelle and colleagues in west
Michigan's Gull Lake showed that zebra mussels are indeed
the cause of the increase in toxic algae.
There have been documented cases in which animals, including
cattle and dogs, died after drinking water with high levels
of microcystins. The toxin is also believed to be responsible
for liver damage in humans.
Surprisingly, zebra mussels seem to have no effect on
the amount of blue-green algae in lakes with high levels
of phosphorus, a nutrient that builds up in lakes and
other bodies of water as a result of erosion, farm run-off
and human waste.
In contrast, zebra mussels cause an increase in toxic
Microcystis in lakes with low to moderate levels of phosphorus,
anywhere between 10 and 25 micrograms per liter. Such
lakes are not normally expected to have very many blue-green
algae, Sarnelle said.
"Our data suggest that zebra mussels promote Microcystis
at low to medium phosphorous levels - not at very low
or very high phosphorous levels," he said. "However,
we're still not sure why this happens."
Zebra mussels have been causing problems in the Great
Lakes since the late 1980s. For example, in Lake Erie,
Sarnelle said, increased incidence of blue-green algae
blooms have been reported since the establishment of zebra
"Similarly, data from the Bay of Quinte in Lake
Ontario show a dramatic increase in the biomass of Microcystis
after zebra mussel establishment," he said. "In
addition, toxic algal blooms in Saginaw Bay and Lake Erie
are disturbing because they come after many years of expensive
reductions in nutrient loading to improve water quality."
Zebra mussels, which are native to the Caspian Sea region
of Asia, were first discovered in Lake St. Clair in 1988.
It's believed they were transported to the Great Lakes
via ballast water from a transoceanic vessel.
Since then, they have spread to all of the Great Lakes,
as well as many other U.S. and Canadian inland lakes and
Sarnelle's co-authors on the paper are Alan Wilson of
the Georgia Institute of Technology, and David Raikow
and Stephen Hamilton of the MSU Department of Zoology
and Kellogg Biological Station.