Behavioural response of plant-associated Eurycercus lamellatus (O.F. Muller) to different food sources and fish cues

The habitat preference and activity pattern of a large-bodied plant-associated chydorid, Eurycercus lamellatus, were experimentally tested under laboratory conditions using different food sources and fish cues. In the absence of epiphyton, we found significantly higher densities of E. lamellatus on plants when concentrations of phytoplankton were high, while no differences were found for real plants hosting epiphytes. In the absence of predator cues, E. lamellatus preferred plants. Exposure of E. lamellatus to chemical cues released by 0+ roach (Rutilis rutilis) previously fed on E. lamellatus or Ceriodaphnia spp. induced a habitat shift from plants to the bottom of the experimental chambers or to the sediment. However, the activity level of the test animals significantly varied between treatments. Test animals were found to be more agitated (as measured by intensity of crawling and jumping activities) in the presence of cues from E. lamellatus-fed roach then when exposed to Ceriodaphnia spp-fed roach. Most likely, the presence of cues from the conspecific E. lamellatus induced the agitated behaviour of E. lamellatus, which may be an attempt to bury within the sediment to avoid predation. Time series experiments in the presence and absence of sediment showed an almost immediate response of E. lamellatus to the addition of fish cues. The animals, however, returned to the plants during the next 7-24 h, most likely reflecting a rapid degradation of the chemical cues. The results suggest a significant influence of chemical cues on the behaviour of plant-associated microcrustaceans in the littoral zones of lakes.