Which Physicochemical Variables Should Zooplankton Ecologists Measure When They Conduct Field Studies?

Over the last century, a rich literature has developed describing how the physical and chemical environment influences zooplankton communities, but there is little guidance on the suite of limnological variables that should be measured by zooplankton ecologists. We performed a literature review to assess (i) which variables were measured most often by zooplankton ecologists, (ii) which of these variables were consistently related to zooplankton abundance and richness and (iii) whether key variables were overlooked by investigators. Our results show that there is a core group of nine limnological variables that are measured most frequently, including lake surface area, pH, phosphorus, nitrogen, dissolved oxygen, conductivity, chlorophyll-a, maximum depth and temperature. These variables were among those most often associated with variation in zooplankton, but several others, including dissolved organic carbon, alkalinity and nitrate, were sampled infrequently, despite showing promise as important explanatory variables. The selection of variables in past studies did not correlate with how often those variables were significant in the literature, but instead, might have been related to their ease of measurement. Neglecting to measure important variables could have implications for fundamental and applied studies that aim to understand the factors structuring zooplankton communities and their response to environmental change.