Horizontal distribution of <i>Daphnia pulex</i> in response to toxic and non-toxic algal extracts

Abstract

We studied the horizontal distribution of Daphnia pulex as a response to gradients of toxic extracts of two cyanobacteria, Microcystis aeruginosa and Oscillatoria agardhii and non-toxic extracts of the green alga Scenedesmus obtusiusculus. The experiment was performed in the dark using a flow through system with five chambers. Daphnia pulex aggregated at the inlet of Scenedesmus extract, but showed similar responses to extracts of toxic cyanobactena and food-free medium. Chemical cues seem to affect food search, but do not effect Daphnia pulex's avoidance of toxic algae.