Laboratory experiments on trophic relationships and remote detection between two ciliates and Cyclops vicinus vicinus

Abstract

Laboratory experiments were performed to study the feeding behavior of Cyclops vicinus (Copepoda, Cyclopoida), fed two ciliates (Cyclidium sp. and Tetrahymena corlissi) chosen for their different size and swimming behavior. All grazing experiments were conducted with predators starved for 24 hr. Cyclidium sp. was fixed with Glutaraldehyde and Tetrahymena corlissi with mercuric chlorid in order to reduce counting errors. The Incipient Limit Level (ILL) for Tetrahymena corlissi was reached at the initial concentration of 76 000 cell 1-1 and corresponded to an ingestion rate of 340 cell ind-1 h-1; that for Cyclidium sp. was reached at 12 000 cell 1-1 with an ingestion rate of 54 cell ind-1 h-1. The detection experiments were based on visual observations of Cyclops movements in experimental chambers with prey concentrations corresponding to the ILL. Both ciliates were used to evaluate the mechanisms involved in the detection of prey by Cyclops vicinus. Direct observations showed that Tetrahymena corlissi had a significant attractive effect on C. vicinus. Such behavior suggests that mechanoreception may be the overriding mechanism of remote detection. In contrast, C. vicinus does not react to the presence of Cyclidium sp. (at low concentration). These small prey, which swim actively in comparison with T. corlissi, are preyed on haphazardly. Ciliates can be a significant part of the diet of Cyclops vicinus, confirming their importance as mediators for energy transfer from the microbial loop to higher trophic levels; the mechanism of detection Of such motile prey by Cyclops vicinus varies with prey swimming behavior.