Zebra Mussels in Western Europe and North America

Abstract

The zebra mussel has invaded most freshwaters of Western Europe since the first part of the nineteenth century and important parts of the waterways of Northeastern USA and southern Canada since the 1980s. It's an extremely efficient invader and often, within a few years after having entered a water system, totally dominates the non-photosynthesizing biomass. They will then filter and clear large volumes of water, not seldom a whole lake within days or a week; consume phyto- and microzooplankton; and extract calcium to build their shells. As a result, the pelagic part of the food web is impoverished with a corresponding flourishing of the littoral part. However, other mussel species there may suffer severely from the competition. In many ways, the zebra mussel impacts on the aquatic ecosystem are the opposite of those of eutrophication. Mostly, the period of extreme zebra mussel population density is short, typically a decade or so, after which time the native predators have learned to consume the newcomers and their densities decrease with a factor of 10 or more.