Multi‐steady‐state toxicant fate and effect in laboratory aquatic ecosystems

Abstract

The influence of competition, exploitation and level of energy input on toxicant fate and effect in simple aquatic laboratory ecosystems was studied. Twenty-four systems composed of populations of guppies (Poecilia re/icula/a), snails (family Planorbidae) and various taxa of algae were maintained in 40-liter flow-through glass aquaria. Guppies and snails were competitors for a common food resource. Ecosystems were established in which guppies and snails were sympatric and allopatric. The systems were exposed to three levels of guppy exploitation and received two levels of energy input. System dynamic and near steady-state behavior were documented through monthly measurements of population biomasses. Biomasses of interacting populations were displayed on phase planes. Shifts in system structure followed chronic exposure to a sublethal concentration of dieldrin. System responses to the toxicant ranged from increased population biomass to population extinction and were influenced by level of exploitation, energy input rate and species competition. Toxicant concentrations were determined in adult female fish. Both toxicant effect and fate were influenced by system organization and environment. Quite different conclusions concerning toxicant performance in these systems could have been drawn if observation had been restricted to only one set of organizational and environmental conditions.