ZOOPLANKTON SIZE AND ITS RELATIONSHIP TO TROPHIC STATUS IN DEEP ONTARIO LAKES

We found the size distribution of crustacean zooplankton in deep (>20 m) oligotrophic to mesotrophic lakes in southern Ontario to be highly variable. Mean lengths varied from 0.48 to 1.12 mm. This difference is not strongly correlated to community composition at the genus to fami ly level but is related to the presence of planktivores, cisco (Corego nus artedii) and Mysis relicta. Empirical analysis of our data demonst rates that mean zooplankton length is correlated to the residuals of t he chlorophyll - summer total phosphorous relationship and also to the decline in total phosphorus from spring to summer. Our analysis sugge sts that zooplankton size distribution plays a significant role in det ermining the trophic status of these lakes, and we speculate that huma n alteration of fish communities may affect zooplankton size distribut ion and trophic status.