DEVELOPMENT AND USE OF ZOOPLANKTON LENGTH—FILTRATION RATE RELATIONSHIPS FOR ESTIMATING PHYTOPLANKTON GRAZING LOSSES

Abstract

Water quality is impaired by high chlorophyll concentrations. Limitation of algal stocks by high zooplankton grazing is an important component in many lake ecosystems and models. Measurement of grazing rates is labour intensive, expensive and requires specialized skills. This paper examines relationships that allow use of easy-to-obtain data on zooplankton to calculate clearance rates and thus estimate phytoplank-ton grazing losses in eutrophic and hypertrophic lakes dominated by blue-green algae. A positive correlation exists between zooplankton body-length and filtration rate regardless of species. Pooled data from in situ experiments on five species of cladocerans fed Chlorella shows that 70% of variance in filtration rate is explained by body-length. Temperature has little influence. Feeding rates on Microcystis colonies can also be predicted from zooplankton body-length; decreasing intercept with increasing slope showing marked size limitation to colony ingestion by small cladocerans as colony size increases. Application of this suite of relationships is of value to estimation of grazing loss in simple ecosystem models.