Influence of food supply and a potential predator ( Crangon crangon) on settling behaviour of plaice ( Pleuronectes platessa)

Abstract

For many benthic fish species, initial settlement patterns are dependent on the supply of larvae to nursery grounds, and recent work on flatfish population dynamics indicates that larval supply may influence recruitment. After the larvae arrive on the nursery grounds, selection of an appropriate substratum is necessary to maximize their subsequent growth and survival. This paper describes the results of experiments undertaken to determine the behavioural responses of settling plaice, Pleuronectes platessa, to the presence of food and predators. Reared plaice larvae were starved for 24 h, transferred to aquaria and the proportion of time spent on the sediment was recorded in four treatments: no food, benthic food, pelagic food, and benthic + pelagic food. The food supply consisted of newly hatched Artemia as pelagic food and meiofauna extracted from natural sediment as benthic food. Settling behaviour was evident for late stage 3b larvae but there was no effect of food supply on time spent on the sediment. Stage 4b and early stage 5 larvae spent significantly more time on the bottom in the food treatments than in the no-food treatment. No differences could be established between food treatments. In another experiment, with the potential predator Crangon crangon as stimulus, stage 4b and early stage 5 larvae spent significantly more time on the bottom when predators were absent than when predators were present. Behavioural preferences were also studied to establish if benthic food and potential predators, C. crangon, influenced habitat selection. Newly metamorphosed plaice (mean TL 13 mm) were given a choice of sediment with and without food and in a separate experiment, a choice of sediment with and without predators. Plaice spent significantly more time on a sediment with benthic food than on one without food and on a sediment devoid of predators than on one with predators. The habitat selection experiments showed that food supply and predators can influence distribution patterns on a small spatial scale.