Influence of spatial heterogeneity on the predation of Mesostoma ehrenbergii on calanoid and cyclopoid copepods.

TROCHINE, C.; BALSEIRO, E.G; MODENUTTI, BE

Figueiras da Foz

Congreso; III Plankton Symposium; 2005

Spatial heterogeneity plays an important role in nature and in a predator-prey relationship it mayinfluence the probability and frequency of encounters. Zooplankton of Patagonian shallow lakesis mostly dominated by copepods and the predaceous turbellaria Mesostoma ehrenbergii is alsoa commom inhabitant of these lakes eating planktonic prey. Besides, these systems arecolonized by aquatic vegetation that provides a marked spatial heterogeneity. The present studyaimed to examine the ability of M. ehrenbergii to consume copepods, Boeckella gracilis(Calanoida, Centropagidae) and Acanthocyclops robustus (Cyclopoida, Cyclopidae) undervariable spatial heterogeneity. We conducted a series of laboratory experiments in 200 mlvessels in which different prey abundances were exposed to the predator. A full factorial designwas carried out with four treatments with five replicates each: vessels without and with spatialheterogeneity (cylindrical sticks placed in three different vertical arrangements) and 5 preyabundances. Experiments were carried out in a temperature-light controlled incubator. Resultsindicate that M. ehrenbergii predation depends upon prey abundance and that calanoids werepreferred in the highest abundances tested. Since both copepods were approximately of thesame size, differences in swimming behavior and escape responses may be related with thepredation rates observed. Besides, the higher predation rates were obtained in the higherheterogeneity tested for both copepods. Probably, M. ehrenbergii displays a more effective useof its mucus trapping in highly heterogeneous environments.