Whole-lake effects of invasive crayfish (Orconectes spp.) and the potential for restoration

Abstract

Effects of invasive species are often extrapolated to whole systems based on small-scale, short-term, and (or) single-system studies. For example, previous laboratory studies and in-lake cage experiments suggest that invasive crayfish Orconectes rusticus and O. propinquus reduce macrophyte and snail abundance in north temperate lakes, and snapshot lake surveys provide supporting evidence. Still, these impacts have not been demonstrated in multiple whole lakes over time. Thus, in summer of 2003, we resurveyed benthic invertebrates and macrophytes in lakes originally surveyed by the Michigan Department of Natural Resources in the late 1930s. Our multilake survey supports the macrophyte results from small-scale and comparative studies: macrophyte species richness and abundance declined significantly in invaded lakes relative to uninvaded lakes. We next conducted a laboratory seed-bank study to examine the potential for macrophyte restoration in a lake occupied by rusty crayfish for at least 15 years. Only two macrophyte species (Najas flexilis and Chara spp.) germinated from sediments from the invaded lake compared with eight species from reference sediments. This suggests that invaded lakes may have depauperate seed banks and that restoration of invaded macrophyte communities may require manual planting, even if crayfish could be removed.