Print PageThe direct effects of invasions by Bythotrephes longimanus in north-temperate lakes have now been reasonably well documented. Reductions in pelagic zooplankton species richness and abundance regularly occur and these changes typically divert resources away from native predators at higher trophic levels. Indirect effects of such invasions, even in the pelagic zone of lakes, have been much more difficult to demonstrate, but some evidence has recently emerged to document such effects on rotifer and phytoplankton communities in these systems. Aquatic ecologists have also recently been investigating the prevalence of benthic-pelagic coupling in lakes because of its potential consequences for influencing nutrient cycling, predator-prey interactions, and food web dynamics. We hypothesize that habitat coupling may result in an extension of the impacts of this invasive predator beyond the pelagic zone and into the littoral. The pre- and post-invasion biology of littoral and pelagic habitats in Harp Lake, Ontario (invaded since 1993) were compared using ordination and time series analysis to investigate the prevalence of both indirect effects and habitat coupling in structuring aquatic communities.
Results/Conclusions
In Harp Lake both pelagic phytoplankton and littoral benthic macroinvertebrate (BMI) communities underwent large changes in community structure following the invasion of Bythotrephes. Similar analyses of BMI community structure in 3 other non-invaded reference lakes also showed substantial shifts in community structure over this same period, potentially confounding the effect of the invader. However, the changes in Harp Lake were orthogonal to and much larger than those observed in the reference systems and were primarily related to increases in large herbivores (Bivalves and Gastropods). Shifts in pelagic communities appear to have induced changes in littoral BMI community structure and these changes seem to be facilitated by the effects of strong habitat-coupling in north-temperate lakes.
