Are Zebra Mussels Re-Shaping Great Lakes Shorelines?

Walking along Great Lakes' shorelines, observers will likely see a lot more shells today than in previous years. The masses of shells come from Zebra Mussels and their cousins, the Quagga Mussel, two alien species which have invaded the Great Lakes.

Zebra Mussels arrived in the Great Lakes around 1986 and were first discovered in Lake St. Clair, located between lakes Huron and Erie. They were probably first introduced with the discharge of ballast water from a European freighter. There are now millions of these molluscs living in the Great Lakes system. They have an incredibly rapid reproductive growth and no natural predators in North America. Since the late 1980s the mussels have spread to all the Great Lakes, the Mississippi River system and many inland lakes (see map below).

Problematic Invaders

Zebra Mussels can significantly change the nature of the lake bottom, affecting fish habitat and spawning. In zones near the shore where mussel populations dominate, they appear to be changing the natural process along the shoreline by trapping nutrients and disrupting the normal flow of these nutrients into deeper waters. The mussels also excrete nutrients creating an environment that may be linked to water quality problems, such as algal fouling on rocky shorelines, off-tastes in drinking water and lethal outbreaks of botulism in wildlife, especially during warm water periods.

But these invasive mussels have an impact beyond changing the lake bottom. Mussels eat by filtering algae from the water. This is the same food source for many species of native fish and other organisms. Overall, the impact is a reduction in the amount of food available to native species. In fact, Zebra Mussels have caused drastic declines in the native Great Lakes mussels commonly called clams. They infest the exposed clamshell to the extent the clam cannot get enough food to survive.

Industries that use river water for cooling and other processes spend millions of dollars per year to remove the encrusted mussels clogging intake or outflow pipes and structures. The sharp shells can also be a danger to swimmers. Decay odour along beaches and historical sites like shipwrecks encrusted with mussels are having a negative impact on tourism in many areas around the Great Lakes.

Over the past three years, a group of scientists from the University of Waterloo, the National Water Research Institute of Environment Canada, and the Ontario Ministries of the Environment and Natural Resources have been investigating the effects of mussels on the natural environment in the east end of Lake Erie. The fieldwork will be completed in 2003 and results will be available in the next two years.

Help Prevent the Spread

Zebra Mussels are transported from one lake or river system to another by hitch-hiking on boats, boat trailers, barges, sea planes and other aquatic equipment. Juvenile and adult mussels can attach to boat hulls, engines, anchors, and other submerged equipment, as well as to plant material that may get caught on boats and trailers. In their microscopic juvenile stage, they can also be carried in boat bilge water, live wells, bait buckets, and SCUBA gear.

By taking a few precautionary steps after boating and fishing, people living along or visiting the shoreline can prevent the spread of mussels.

• Inspect boat and trailer carefully for mussels and aquatic vegetation and discard in the trash.
• Drain all water from the boat, including the bilge, live well and engine cooling system.
• Dry the boat and trailer in the sun for at least five days, or if you use your boat sooner, rinse off the boat, trailer, anchor, anchor line, bumpers, and engine with hot water or at a car wash.
• Leave live aquatic bait behind – either give it to someone using the same waterbody, or discard it in the trash.
• Cottagers, homeowners and businesses who draw water directly from a zebra mussel infested waterbody will need to protect their system from infestation.

There are no known methods for eliminating Zebra Mussels from an area once they have become established. Public assistance in preventing the spread of this highly invasive species and reporting new infestations is essential to help reduce their negative impacts on the local environment and economy.