Characterizing individual, population and community effects of sublethal levels of aquatic toxicants: an experimental case study using Daphnia

Abstract

SUMMARY. 1. The relationship between toxicant‐induced changes in the feeding behaviour of the cladoceran, Daphnia catawba (Coker), and subsequent effects at population and community levels were experimentally addressed.2. We adapted a method for measuring the thoracic appendage beat rate of individuals (termed the TAR and positively correlated with daphnid feeding rate) after exposure to toxicant at known levels, for use as a behavioural bioassay for low levels of aquatic toxicants. The TAR declined significantly with an increase in both sublethal and lethal levels of the surfactant, sodium dodecyl sulphate (SDS).3. We also measured population level effects (i.e. rates of reproduction, survival, and R0), and found that reductions in these values occurred at the same concentrations as the effects on individual behaviour.4. In most cases, the changes in feeding behaviour occurred more rapidly (≤30h) than changes in population parameters (days to weeks).5. We conclude that toxicant‐induced changes in individual feeding behaviour can provide a quicker estimate of effects on individuals and of potential community effects (i.e. effects on their prey populations) than measurements of population parameters. In addition, due to its sensitivity at low levels of toxicants, the behavioural bioassay may be particularly helpful in identifying effects of sublethal levels of aquatic pollutants.