![]() Zebra mussels will spit out microcystis into the water and at the same time eat other algae that may be competitors with or help control microcystis. Scientists are also finding a link with zebra mussels and the occurrence of toxic blue-green algal blooms or microcystis. Another invader, the round goby, which predominantly feeds on zebra mussels, may accumulate contaminants in their tissues and may pass those contaminants on to sport fish species which are now consuming them. An example are some duck species such as Lesser and Greater Scaup, which now feed on zebra mussels, have elevated levels of contaminants in their tissues which may influence their survival and/or reproduction success. Although this may sound like a positive thing, organisms that feed on zebra mussels may accumulate these contaminants in their own tissues. When zebra mussels filter the water, they also remove contaminants which become concentrated in their tissues. Changes in weed growth patterns occur and forces some fish, such as walleye that are light sensitive, to find new habitat. This filtering causes the water to become clearer allowing more sunlight to penetrate the water column. Organisms that benefit most from these changes are those that live on the lake bottom such as invertebrates (which include aquatic insects, worms, snails, etc.) and aquatic plants. What they don't eat is combined with mucus as "pseudofeces" and is discharged onto the lake bottom where it accumulates. While each mussel can filter about one litre of lake water per day, not all of what they consume is digested. The feeding activity of zebra mussels results in changes in the normal energy cycle within a water column. 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. The sharp shells can also be a danger to swimmers. Industries that use river water for cooling, like Bruce Power near Tiverton, millions of dollars per year to remove the encrusted mussels clogging intake or outflow pipes and structures. 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. 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. Zebra Mussels can significantly change the nature of the lake bottom, affecting fish habitat and spawning. They infest the exposed clamshell to the extent the clam cannot get enough food to survive. In fact, Zebra Mussels have caused drastic declines in the native Great Lakes mussels commonly called clams. ![]() Overall, the impact is a reduction in the amount of food available to native species. The decline in Diporeia may be linked to declines in numbers and the condition of species such as whitefish, sculpin, smelt and young lake trout from various Great Lakes. Species such as whitefish and other prey fish including alewife, bloater, smelt and sculpin directly depend on Diporeia as a food source. Since zebra mussels invaded in the 1980s, there has been a decline in the numbers of Diporeia which normally make up to 70 percent of the living biomass in a healthy lake bottom. One such species is Diporeia, which is a tiny shrimp-like organism that lives in the bottom mud and who's source of food is settling algae from the water column. Zebra mussels filter out large amounts of phytoplankton, and compete with many species of zooplankton which are an important food source for young fish. Significant changes to aquatic ecosystems have been documented as a result of the introduction of zebra mussels. Researchers are observing some of these effects as they study interactions between zebra mussels and native unionids in the Great Lakes. However, information from Europe tells us that zebra mussels have the potential to severely impact unionids (native mussels) by interfering with their feeding, growth, locomotion, respiration, and reproduction. Most of the biological impacts of zebra mussels in North America are not yet known. Continued attachment of zebra mussel can cause corrosion of steel and concrete affecting its structural integrity. Deterioration of dock pilings has increased when they are encrusted with zebra mussels. Fishing gear can be fouled if left in the water for long periods. Navigational buoys have been sunk under the weight of attached zebra mussels. Small mussels can get into engine cooling systems causing overheating and damage. Navigational and recreational boating can be affected by increased drag due to attached mussels.
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