| Zusammenfassung: | ABSTRACT: The morphology, swimming kinematics and prey selection of hydromedusae have been shown to be closely related to hydromedusan foraging mode. In order to confirm this link, we examined thein situforaging behavior of hydromedusae by video-recording and quantifying thein situswimming activity and tentacle-extension behavior of 8 co-occurring hydromedusae from the waters surrounding Friday Harbor, Washington. The cruising-predatory medusaeAequorea victoria,Mitrocoma cellularia,Phialidium gregarium, andEutonina indicansspent a greater proportion of their time swimming (on average from 74.1 to 92.1%) than the ambush-predatory medusaeAglantha digitale,Sarsiasp.,Leuckartiarasp., andStomotoca atra(on average from 19.5 to 47.0%). In addition, the cruising-predatory medusae were observed with their tentacles extended almost continuously, regardless of whether they were swimming or drifting. In contrast, the ambush-predatory medusae drifted with their tentacles extended but contracted their tentacles when swimming. These patterns indicate that cruising-predatory medusae can feed while either swimming or drifting, whereas the ambush-predatory medusae feed while drifting but not while swimming. Thus, swimming plays a distinctly different role within the behavioral repertoire of each of these medusan foraging modes. Furthermore, the swimming activity and tentacle-extension behavior we observed were consistent with strategies that optimized feeding by each of the predator types.
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