PARENT SESSION
Oral Session #56: Aquatic Ecology: Plankton. Presiding: N. Hairston.
Wednesday, August 8, 2001. 1:00 PM to 5:00 PM. Hall of Ideas I.
Comparing the impacts of bass and Bythotrephes introductions on the zooplankton of Canadian Shield lakes.
Yan, Norman1,2, Ramcharan, Charles3, McQueen, Donald1, Sprules, Gary4, 1 2 3 4
ABSTRACT- It is commonly assumed that zooplankton communities are more sensitive to introductions of fish than invertebrate predators; however this assumption has not been tested at a whole-lake scale. An opportunity for such a test developed when the invading spiny water flea (Bythotrephes) appeared in Harp Lake, Ontario, in 1993, the same year we experimentally introduced large- and small-mouth bass to the nearby Mouse Lake. Using Levene's tests, we compared the inter-annual variability of four univariate (richness, biomass, abundance, mean Cladoceran size) and two multivariate (two axes of a correspondence analysis, CA) zooplankton metrics in Mouse and Harp Lakes and two reference lakes. Most community metrics did change after introduction of either predator. However, inter-annual variability in richness, cladoceran size, and the first CA axis could not be distinguished in Mouse and Harp lakes, and the compositional information represented by the second ordination axis was actually more variable in Harp Lake. Total biomass and abundance were more variable in Mouse Lake than in Harp Lake; however, these two metrics were just as variable in the two reference lakes as in Mouse and Harp lakes. This implies that some factor other than predator additions was regulating total zooplankton standing stock in the lakes. Our comparison does not support the assumption that the addition of bass exerts larger impacts on freshwater zooplankton than the addition of at least one invertebrate predator, Bythotrephes.
KEY WORDS: Bythotrephes, zooplankton, inter-annual variability, predation