26 mar alien species.jpg
Zebra mussels probably entered the Great Lakes in the mid- to late 70s, when ships arriving from Europe discharged ballast water containing a variety of aquatic organisms, including zebra mussel larvae. The species rapid dispersal throughout the Great Lakes and major river systems was due to its ability to attach to boats navigating these waters, dispersing fertilized larvae as the ships moved about the lakes.
Zebra mussels can grow to a maximum length of about 50 millimeters (1.9 inches) and live 4.5 years. Their common name was inspired by their dark, zebra-like rays. Females generally reproduce in their second year (spawning April-June, and again in August). More than 40,000 eggs can be laid in a reproductive cycle and up to 1 million in a spawning season (for each female...). Each zebra filters about 1.5 ltrs (2.5 pints) of lake water a day, extracting algae as a food and expelling clear, clean water. The Lakes seem to be a perfect host environment.
That's why the Great Lakes are now clear; and why we have no commercial fishing. This is an 18" x 24" section of the bottom of a Montrose Harbor dock support float recently overturned in a spring storm. But marine biologists and divers say that this is what most of the entire lake bottom now looks like.