Zebra mussels often achieve high densities immediately after colonizing a new habitat. For example, biologists at Detroit Edison reported that zebra mussel densities on an intake screen climbed from 200 individuals/m 2 in 1988 to 700,000 individuals/m2 in 1989. A car submerged for 8 months in Lake Erie was 90-percent covered with mussels at an average density of
45,000 individuals/m2. As many as 10,000 zebra mussels have been counted on a single freshwater mussel. This ability to rapidly achieve high densities makes the zebra mussel a threat to industrial and domestic water supplies.
Within 10 or 20 years of colonization, densities of zebra mussels may decline as natural predators and diseases begin to act as control agents. In much of Europe zebra mussel densities have declined from levels achieved within the first 10 to 15 years of introduction, and are generally lower than those now being reported from the Great Lakes.