The effect of turbidity and illumination on the reaction distance and search time of the marine planktivore Gobiusculus flavescens

Both reduced illumination and increased turbidity caused a significant reduction in reaction distance of Gobiusculus flavescens. The longest reaction distance, 18.9 cm for larger prey (Calanus finmarchicus), occurred at a light level of 80 mu mol m(-2) s(-1) compared to 12.9 cm for a smaller prey (Acartia clausi) at 8 mu mol m(-2) s(-1). Above a light saturation level of 10 mu mol m(-2) s(-1), additional light had little influence on reaction distance. In the turbidity experiments, the longest reaction distances were measured at turbidity levels of 10-20 JTU. Prey size influenced reaction distance at all tested light levels. Search time was influenced by prey size only at low illumination. With increasing turbidity, reaction distance to a group of prey was longer than to one prey. (C) 1997 The Fisheries Society of the British Isles.