Prey resource use by coexistent hydromedusae from Friday Harbor, Washington

Prey selection patterns were quantified for a sympatric group of hydromedusae from Friday Harbor, WA. Selection patterns varied between species, but were largely replicable between sample dates and resembled dietary patterns found in similar studies from neighboring regions. Ambush-foraging medusae (Aglantha digitale, Sarsia tubulosa, and Proboscidactyla flavicirrata) fed primarily on crustacean and ciliated prey but the dietary niches of these hydromedusan species centered on different fractions of the available plankton. Consequently. little dietary overlap occurred between the ambush foraging hydromedusae. In contrast, the dietary niches of cruising predators (Aequoroa victoria, Mitrocoma cellularia, and Phialidium gregarium) overlapped substantially because those species all fed on similar soft-bodied prey such as eggs and appendicularians. These results have two important implications for trophic patterns involving medusae. First, different mechanisms of prey eucounter and capture used by hydromedusae (ambush vs. cruising patterns) result in important interspecific dietary differences and, hence. trophic roles of the medusae. Second, whereas cruising, medusae may consume similar prey and hence form a feeding guild, ambush-foraging medusae may experience substantially less prey overlap and. for the community examined here, do not experience potentially strong feeding competition from other medusan species.