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

CAROLINA TROCHINE,; E BALSEIRO,; BEATRIZ ESTELA MODENUTTI O BEATRIZ MODENUTTI O B. MODENUTTI

Figueiras da Foz

Congreso; Plankton Symposium; 2005

PS

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