PREDATION BY JUVENILE FLOUNDER (PLATICHTHYS-FLESUS L.) - A TEST OF PREY VULNERABILITY, PREDATOR PREFERENCE, SWITCHING BEHAVIOR AND FUNCTIONAL-RESPONSE

Predation by juvenile 1 + flounders, Platichthys flesus, (mean total l ength 8.0 cm +/-0.6 cm SD) on juvenile Macoma balthica (mean length 1. 94 mm +/- 0.40 mm SD) and Bathyporeia pilosa (mean length 4.11 mm +/- 0.47 mm SD) was studied in a series of aquarium experiments. Prey vuln erability and consumption, as well as possible switching behaviour by the predator, were studied with varying total and relative prey densit ies. The functional response of the predator was also determined from the experimental results. The consumption and vulnerability of both pr ey species were equal when the prey species were presented separately to the predators (50 ind/aq). In the comparable two-prey-species exper iment, where equal proportions of the prey species were presented to t he predators, total prey consumption was about the same as in the sing le-prey-species experiment. Prey consumption during the night was clea rly lower than grey consumption during the day with the same prey dens ity. In all experiments, juvenile flounder showed a slight preference for Macoma before Bathyporeia independently of the relative or absolut e prey density. No switching behaviour was observed. The consumption o f both Macoma and Bathyporeia increased significantly with increasing total prey density. The functional response of flounder was in both ca ses of the type III. The best fit of the data was achieved with a cont inuous model of the type-III response. (C) 1998 Elsevier Science B.V. All rights reserved.