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 expe riments were carried out in 1993 in Gullmarsfjorden (Sweden) to study the interactions between two common species of scyphozoan jellyfish. C yanea capillata was a predator on Aurelia aurita. Gut analyses on 70 s pecimens of C.capillata showed no size dependency in the ability to ca tch sl specimen of A.aurita. However, large medusae of C.capillata cau ght 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 (diamete r = 14-23 cm) in the laboratory was 38 h, but digestion was size depen dent with regard to both prey and predator. Large C.capillata digested A.aurita faster than small specimens, and small medusae of A.aurita w ere digested faster than large ones. Calculations indicate that A.auri ta 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 s wim pulse frequency of A.aurita 30 s after contact increased by 46%. A urelia aurita thereby moved up with an average speed of 0.96 m min(-1) .