Clearance potential of jellyfish Aurelia aurita, and predation impact on zooplankton in a shallow cove

Abstract

Population clearance potential was calculated from laboratory clearance rates and from measurements of medusae size and abundance during 1991 and 1992 in the shallow cover Kertinge Nor, Denmark. Clearance rate increased with increasing medusae diamater when rotifers Brachionus plicatilis were used as prey. For Medusae >5mm clearance on copepods Acartica tonsa and B. plicatilis was similar. Water tmperature had marked effect on clearance. In spring, when medusa were small, the population in Kertinge Nor could potentially have cleared the volume of water in the cove less than 0.1 times each day. This value was 3.5 times each day in late summer when biomass was high. High predation pressure by medusae appears to control zooplankton in the shallow cove, at least during summer and early fall, and A. aurita may thus be considered as a keystone species in the control of the trophic structure in Kertinge Nor. -from Author