PREY SELECTION BY THE SCYPHOMEDUSAN PREDATOR AURELIA-AURITA

We describe feeding behavior of Aurelia aurita (Linnaeus) using gut co ntent analyses of field-collected specimens and a mesocosm experiment. The field studies were conducted in Narragansett Bay, Rhode Island, U SA from March to April 1988, and the mesocosm studies were done at the Marine Ecosystems Research Laboratory at the University of Rhode Isla nd. Patterns of prey selection changed with medusa diameter. Smaller m edusae (< 12 mm diameter) consumed mostly hydromedusan prey whereas la rger medusae (up to 30 mm diameter) ingested greater numbers of copepo d prey. While larger medusae did feed on copepods, their diet also con tained more barnacle nauplii and hydromedusae than expected from the r elative abundances of these prey types in plankton samples. A marginal flow mechanism of feeding by A. aurita provided an explanation for th e patterns of prey selection we observed in medusae of different sizes and among widely divergent prey types. Our data indicated that large prey, with escape speeds slower than the marginal flow velocities arou nd the bell margins of A. aurita, made up a substantial fraction of th e daily ration when they were available. Such prey species may be more important to nutrition than the more abundant copepods and microzoopl ankton. Successful development of young medusae may depend upon an ade quate supply of slowly escaping prey.