CAN WE USE LABORATORY-REARED COPEPODS FOR EXPERIMENTS - A COMPARISON OF FEEDING-BEHAVIOR AND REPRODUCTION BETWEEN A FIELD AND A LABORATORY POPULATION OF ACARTIA-TONSA

Motility patterns and egg production were investigated in two populati ons of Acartia tonsa, field animals from the Oresund and laboratory an imals from a 12-year-old (approximate to 120 generations) culture. Whe n observed in aquaria with a layer of Thalassiosira weissflogii in the middle, laboratory animals displayed weak aggregation behaviour, whil e field animals did not aggregate at all. Both populations made longer and more frequent feeding bouts inside the patch. Egg production meas urements were in accordance with the behaviour of the laboratory popul ation if no diel feeding rhythm was assumed. The held population produ ced fewer eggs than predicted from activity measurements, probably due to a diel feeding rhythm. It is concluded that laboratory reared A. t onsa can be used for experiments involving behaviour, but that the pos sible loss of diel rhythms should be a concern. Both populations diffe red considerably from held-caught A. tonsa from the eastern United Sta tes, where both behaviour and egg production changed consistently and in accordance with a strong aggregation in food patches. (C) 1995 Inte rnational Council for the Exploration of the Sea