The influence of trophic status on the crustacean zooplankton community was investigated in lakes and reservoirs in temperate and subtropical-tropical regions. We tested if there is a consistent relationship between crustacean species richness, assemblages, and abundance and trophic indices such as total phosphorus and chlorophyll a. We also examined if these patterns differ between regions. Cumulative species richness and assemblages varied among regions. The greatest number of crustacean species was found in the temperate oligotrophic region with the largest number of lakes sampled. However, cumulative species richness was similar in temperate and subtropical–tropical regions when comparing subsets with a similar number of lakes and reservoirs. The relationships between species richness and latitude or trophic status were difficult to assess owing to imbalance among regions in number of lakes and reservoirs sampled and to biogeography and fish predation potential influences. Trophic status was associated with changes in abundance of all major crustacean zooplankton groups. Eutrophic ecosystems supported greater crustacean abundances at all latitudes. However, cladocerans and cyclopoids were more abundant in eutrophic lakes and reservoirs, whereas calanoids were more abundant in temperate oligotrophic lakes. Total phosphorus was found to be a better predictor of the biomass of major crustacean groups than chlorophyll a in all regions.

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Abundances and biomass of 38 zooplankton species and accompanying abiotic data from 54 Quebec lakes were subjected to cluster and correlation analysis to determine (1) characteristic zooplankton associations of cooccurring species, (2) relative importance of abiotic variables in lake typology, and (3) relationships between the integrated environmental factors derived from lake morphometry, water quality, and acidification level, and the structure of zooplankton communities. The eight groups of species identified in the cluster analysis may be considered separate "species associations" characterized by distinct patterns of distribution in Quebec lakes. Differences in mean pH and sulphate concentrations can be detected between groups of lakes representing the different species associations. Factor analysis produced seven factor scores which explain 82% of the total variance of the morphological, physical, and chemical variables. The distribution pattern of acidity or alkalinity represents the major feature in water chemistry variation, but lake morphology also account for the observed environmental variability. Each factor represents an integrated environmental property correlated with a set of colinear abiotic variables. These factors are correlated with zooplankton species abundances and biomass. The community structure, whether expressed in size classes or in trophic groups, tends to vary among sets of lakes of different pH.

The body size of zooplankton has substantive effects on the function of aquatic food webs because size affects the ability of zooplankton to: exploit food resources, effectively clear the water of algae, and serve as a food source for fish. A variety of factors may affect size, and earlier studies indicate that water temperature may be a particularly important variable. Here we tested the hypothesis that the body size of cladocerans, calanoids and cyclopoids declines with increasing water temperature, a response documented in an earlier study that considered only cladoceran zooplankton. We tested the hypothesis by comparing body size data that were available from prior studies of lakes ranging from 6 to 74 o latitude and encompassing a temperature range of 2 to 30 o C. Cladoceran body size declined with temperature, however, the trend was just marginally significant (p = 0.01). The decline in size was significant (p = 0.05) for cyclopoids. In both cases, there was considerably more variation around the regression than previously observed suggesting that other variables such as fish predation played an important role in affecting size. Calanoid body size was unrelated to temperature. In contrast with cladocerans and cyclopoids, perhaps calanoid body size is not metabolically constrained by temperature or is differently affected by changes in fish predation occurring with increasing temperature. The unexpected result for calanoids requires further investigation.