"The day after tomorrow": anatomy of an ‘r’ strategist aquatic invasion

Abstract

Invasive alien species, following an arrival, undergo different colonization stages. The full pattern of an invasion is seldom tracked as many studies on invasive processes only take place over a few years. In this study the invasion of the zebra mussel, Dreissena polymorpha (Pallas, 1771), was followed for more than a ten-year period. It developed an expansion stage with peak abundance (outbreak) four to six years following arrival. Thereafter the population entered an accommodation stage at a lower level of abundance and biomass. This pattern was repeated for two separate lakes on the Shannon River in Ireland. In concert with the biomass at each invasion stage there were changes to the transparency and chlorophyll a levels of lake water. Based on the results of the current study, revision of the terminology of invasion stages is suggested. Providing some additional insight into the invasion process, it can be accorded with existing frameworks and bioinvasion impact assessment approaches. The sequence of invasion stages with corresponding direct (semi-quantitative) and indirect (qualitative) features as well as examples of empirical evidence is presented in this account.