The Great Lakes' other mussel menace

By Tammy Grime

ust when industry thought it had come to terms with the zebra mussel, another pest is causing all too familiar problems.

Zoology professor Gerald Mackie has studied the zebra mussel since it was detected in the Great Lakes seven years ago and is now lending his expertise to try to deal with the new nuisance -- the quagga mussel.

Zebra mussels have wreaked havoc in Great Lakes aquatic ecosystems since their arrival via the ballast water from a European vessel. Quagga mussels are believed to have arrived the same way.

The mussels have few natural predators, reproduce rapidly and consume plants that are part of the diet of native aquatic species, leading to the extinction of many -- including 11 species of clams in Lake St. Clair alone. By filtering plankton from the water to feed, they allow light to penetrate deep into aquatic systems, causing bottom-dwelling plants to flourish and push out many organisms. That affects the entire food chain and alters whole ecosystems.

Mussels also clog shoreline industry water-intake pipes -- in the United States, zebra mussels alone have caused an estimated $5 billion in damage. Some industries tried to sidestep the problem by building new intake structures below the depth at which zebra mussels can survive. But the quagga mussel poses all the threats of the zebra mussel and then some -- it can grow and reproduce in deeper, colder waters.

"It is apparent that quagga mussels are adapted to live in a wider range of habitat conditions than zebra mussels, allowing them to infest wider portions of Ontario's lakes," says Mackie.

Industries that use deep intake structures to thwart zebra mussels are now vulnerable to the quagga, as are the intricate food webs of the many organisms that live in deeper waters. The smelt population in Lake Erie alone has decreased by 90 per cent since 1989, and waterfowl populations that feed on zebra and quagga mussels have increased more than tenfold.

Mackie's PhD student Trevor Claxton is investigating the physiological characteristics of the quagga. Specifically, he's trying to establish the threshold temperatures at which quagga can grow and reproduce, to determine the greatest depth the mussel can infest and its potential to spread. If the quagga can thrive in waters colder than 10 C, the number of lakes susceptible to its ravages will greatly increase.

The researcher is also studying differences in growth rates of the zebra and quagga mussels according to water temperature, quality of food available, depth of the lake and distance from shore. He will also examine the substances on which the two mussels prefer to live. This information will help determine the extent to which the mussels can infest inland lakes.

Currently, some industries use chlorine to kill mussels clogging up their pipelines -- not the most environmentally friendly solution because chlorine has been linked by some scientists to serious carcinogenic disorders in animals and humans. If chlorine is also used to control the quagga mussels, the amount of the chemical entering the water may reach hazardous levels.

Mackie's research is supported by the Ontario Ministry of Environment and Energy, the Natural Sciences and Engineering Research Council and the International Joint Commission on the Great Lakes.