We present equations for calculating dry weight from body length for 14 common and widely distributed taxa of crustacean zooplankters; these were generated by regression from weights of individuals chosen from the range of lengths observed for each taxon, usually three replicate weights at each of five lengths. We include regressions for ovigerous and nonovigerous cladocerans, plus nauplii, early copepodites, and adult males and females for the copepods (30 length–weight relationships) and individual weights for given stages of copepods. We calculated the seasonal variation in crustacean biomass for a station in the Bay of Quinte, Lake Ontario, and for each of the three basins of Lake Erie. Biomass was dominated by Cladocera for both lakes, with Copepoda predominant in the spring. Mean individual dry weights varied seasonally for all taxa, confirming previous findings.

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1. Recent increases in phytoplankton biomass and the recurrence of cyanobacterial blooms in western Lake Erie, concomitant with a shift from a community dominated by zebra mussels (Dreissena polymorpha) to one dominated by quagga mussels (D. bugensis), led us to test for differences in ammonia-nitrogen and phosphate-phosphorus excretion rates of these two species of invasive molluscs. 2. We found significant differences in excretion rate both between size classes within a taxon and between taxa, with zebra mussels generally having greater nutrient excretion rates than quagga mussels. Combining measured excretion rates with measurements of mussel soft-tissue dry weight and shell length, we developed nutrient excretion equations allowing estimation of nutrient excretion by dreissenids. 3. Comparing dreissenid ammonia and phosphate excretion with that of the crustacean zooplankton, we demonstrated that the mussels add to nitrogen and phosphorus remineralisation, shortening nitrogen and phosphorus turnover times, and, importantly, modify the nitrogen and phosphorus cycles in Lake Erie. The increased nutrient flux from dreissenids may facilitate phytoplankton growth and cyanobacterial blooms in well-mixed and/or shallow areas of western Lake Erie.

Annual primary production in meromictic Fayetteville Green Lake, N.Y., was estimated to be 290 g C/m2, based on seven measurements by the 14C method. About 83% of this annual production was due to photosynthetic sulfide‐oxidizing bacteria in the chemocline at 18–20‐m depth. Zooplankton densities were higher near the bacterial zone. Bacterial photosynthetic production and concentration of mixolimnetic seston at the chemocline provided adequate food for a relatively large zooplankton population. Evidence for diel migration was observed among the zooplankton.

We used an in situ approach to redefine allometric parameters of consumption and metabolism in a percid bioenergetics model for young‐of‐year (age‐0) walleyes Stizostedion vitreum (0.0021–0.8237 g wet weight; 8–49 mm total length) in ponds across a range of densities (10–50 fish·m–3). Of three methods used to estimate evacuation rates, only the one based on whole‐gut fullness of larvae and stomach fullness of juveniles in food‐free enclosures proved reliable, The intercepts for allometry of maximum consumption and resting metabolism for age‐0 walleyes were higher than the intercepts for adults; however, slopes of age‐0 and adult allometry were similar. Activity costs (ACT = ratio of active metabolism to resting metabolism) for age‐0 walleyes varied across body weights and with fish density; patterns of activity costs at different fish densities reflected patterns of food availability. Activity and p‐values (proportion of maximum consumption realized) were correlated with powers of zooplankton biomass, and they were positively and linearly correlated with each other. The adult walleye bioenergetics model was a poor predictor of growth and consumption by age‐0 walleyes. The age‐0 walleye models with activity linked to prey biomass and with ACT = 3 provided the best fits between predicted and observed values of growth and consumption. We suggest that for active foragers, activity should be modeled as a variable component in bioenergetic models, the variation being a function of prey biomass.