Omnivory by the small cosmopolitan hydromedusa Aglaura hemistoma

We investigated the feeding of the small hydromedusa, Aglaura hemistoma (bell diameter, 4 mm), to determine if it occupies a trophic position similar to that of large medusae. Feeding was examined using gut-content analysis of preserved and unpreserved medusae and by analyzing prey-capture events using microvideographic techniques. Analysis of gut contents and prey-capture events revealed that A. hemistoma fed heavily on protistan prey and that it possessed a prey-capture mechanism, specifically a feeding current, that is effective at entraining and capturing protists with low motility. We suggest that many species of small hydromedusae possess prey-capture mechanisms adapted to capture small protistan prey and that many of these small hydromedusae feed omnivorously on micro-planktonic prey. The trophic roles of small hydromedusae in different systems are not understood and more studies are needed. However, based on their often high abundances and the cosmopolitan nature, if small hydromedusae are primarily omnivores, they need to be considered when estimating the impact of zooplankton on primary pro-duction and, more generally, protistan community dynamics. Large medusae are widely recognized as important pred-ators of crustacean zooplankton, fish eggs, and fish larvae and for their ability to structure marine coastal ecosystem