Capture and digestion of the scyphozoan jellyfish Aurelia aurita by Cyanea capillata and prey response to predator contact

Laboratory experiments, field observations and manipulative field experiments were carried out in 1993 in Gullmarsfjorden (Sweden) to study the interactions between two common species of scyphozoan jellyfish. Cyanea capillata was a predator on Aurelia aurita. Gut analyses on 70 specimens of C.capillata showed no size dependency in the ability to catch ≥1 specimen of A.aurita. However, large medusae of C.capillata caught a higher number of A.aurita than small ones. The average time for C.capillata diameter=11–20 cm) to fully digest one A.aurita (diameter=14–23 cm) in the laboratory was 38 h, but digestion was size dependent with regard to both prey and predator. Large C.capillata digested A.aurita faster than small specimens, and small medusae of A.aurita were digested faster than large ones. Calculations indicate that A.aurita may be an important source of carbon for C.capillata. After contact with C.capillata, the marginal tentacles of A.aurita contracted, the medusae directed themselves with the exumbrella upwards and the mean swim pulse frequency of A.aurita 30 s after contact increased by 46%. Aurelia aurita thereby moved up with an average speed of 0.96 m min−1.