Study Shows Zebra Mussels Resistant To Deadly Toxin

Brett Smith for – Your Universe Online
Already known as a menace around the Great Lakes, with a “Tribble-like” capacity to reproduce, zebra mussels are unaffected by a deadly toxin that wipes out other freshwater mussels, according to a new study in the Journal of Proteome Research.
When blue-green algae flourish in freshwater, they release a toxin that stresses and weakens most freshwater mussels, but not zebra mussels. Study researchers said the finding is bad news for biodiversity and for water-related industries that consider the prolific species to be a menace.
According to the scientists, zebra mussels’ ambivalence to the toxins allows them to thrive in their watery ecosystem better than other freshwater mussels – to the point where they overrun their competition.
“Zebra mussels live in large colonies in the Great Lakes in the United States, and they are a huge problem,” said Claudia Wiegand, an associate professor of environmental stress physiology and aquatic toxicology at the University of Southern Denmark. “They need something hard to attach themselves to and often they find a suitable surface on the inside of the pipes carrying water from the Great Lakes into factories and other industries along the lake. Often they sit so close that they block the water intake.”
Endeavors to manage the spread of zebra mussels, prevent them from attaching to pipes or ships and remove those already attached have cost several million dollars.
“In European lakes we see that many zebra mussels attach themselves to other mussel species and suffocate them, so they cannot breathe or eat, and therefore die,” Wiegand said.
The researchers also looked at another mussel, the Unio crassus, or Thick-shelled River Mussel, and assessing its ability to combat toxins. Unios were tested for their reactions to the algae toxin in naturally-occurring concentrations.
“Unio is less able to combat toxins from blue-green algae,” Wiegand said. “This may help explain why they are declining in some places in Europe.”
“We saw that the unio’s ability to combat the toxin was inhibited,” she added. “The enzymes that normally help the mussel secrete substances were blocked and thus the mussels could not get the poison out of their body. It became stressed and this may reduce its viability in the long run.  Conversely we have seen that the zebra mussels intensify their detoxification mechanisms and secret (sic) the toxin without being stressed or affected negatively.”
Zebra mussels are originally from Eastern Europe and the Caspian Sea. However, the mollusks have spread to the rest of Europe and North America over the past two centuries. Unios are also native to Europe, but unlike zebra mussels, their numbers have been in decline.
Zebra mussels were first seen in the Great Lakes in 1988 just north of Detroit. Experts have speculated that the mollusks were unintentionally introduced to the lakes by ocean-going ships passing through the St. Lawrence Seaway. Because adult zebra mussels can survive out of water for weeks if the conditions are right, they may have had refuge on a transatlantic vessel, and then they were released when the ship dropped anchor in freshwater ports along the Great Lakes.
The mollusks have become such a pest that they have been targeted by several federal policies, such as the National Invasive Species Act of 1996.

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