Title

Prey Capture by the Cosmopolitan Hydromedusae, Obelia Spp., in the Viscous Regime

Document Type

Article

Publication Date

2016

Digital Object Identifier (DOI)

https://doi.org/10.1002/lno.10390

Abstract

Obelia spp. are cnidarian hydromedusae with a cosmopolitan distribution but very little is known about their feeding. The small size of Obelia (bell diameter ∼ 1 mm, tentacle width ∼ 0.05 mm) suggests that feeding occurs in a viscous regime characterized by thick boundary layers. During feeding observations with a natural prey assemblage the majority of prey were captured at the tentacle tips during the contraction phase. Swimming kinematics from high speed videography confirmed that swimming was a low Re number process (Re < 50) and showed that maximum tentacle velocities occurred at the tentacle tips midway through a bell contraction. Flow visualizations from particle image velocimetry demonstrated that fluid motion between the tentacles was limited and that velocities were highest at the tentacle tips, leading to a thinning of boundary layer in this region. The highest nematocyst densities were observed in this same region of the tentacle tips. Taken together, the body kinematics, flow visualizations and nematocyst distributions of Obelia explain how these predators are able to shed viscous boundary layers to effectively capture microplanktonic prey. Our findings help explain how other small feeding-current medusae whose feeding interactions are governed by viscosity are able to successfully forage.

Was this content written or created while at USF?

Yes

Citation / Publisher Attribution

Limnology and Oceanography, v. 61, issue 6, p. 2309-2317

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