title: Ontogenetic propulsive transitions by Sarsia tubulosa medusae.
abstract: While swimming in their natural environment, marine organisms must successfully forage, escape from predation, and search for mates to reproduce. In the process, planktonic organisms interact with their fluid environment, generating fluid signatures around their body and in their downstream wake through ontogeny. In the early stages of their life cycle, marine organisms operate in environments where viscous effects dominate and govern physical processes. Ontogenetic propulsive transitions in swimming organisms often involve dramatic changes in morphology and swimming behavior. However, for organisms that do not undergo significant changes in morphology, swimming behavior or propulsive mode, how is their swimming performance affected? We investigated the ontogenetic propulsive transitions of the hydromedusa Sarsia tubulosa, which utilizes jet propulsion and possesses a similar bell morphology throughout its life cycle. We used digital particle image velocimetry and high-speed imaging to measure the body kinematics, velocity fields and wake structures induced by swimming S. tubulosa with bell exit diameters from 1 to 10 mm. Our experimental observations revealed three distinct classes of hydrodynamic wakes: elongated vortex rings for 10<Re<30 (1-2 mm bell exit diameter), classical elliptical vortex rings for Re>30 (larger than 2 mm bell exit diameter) and elliptical vortex rings (or leading vortex rings) followed by trailing jets for most instances where Re>100 (larger than 4 or 5 mm bell exit diameter). The relative travel distance and propulsive efficiency remained unchanged throughout ontogeny, and the swimming proficiency and hydrodynamic cost of transport decreased non-linearly.
authors.affiliation: Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA kakani@mbari.org.
authors.forename: Kakani
authors.initials: K
authors.lastname: Katija
authors.affiliation: Environmental Sciences, Roger Williams University, Bristol, RI 02809, USA Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA.
authors.forename: Sean P
authors.initials: SP
authors.lastname: Colin
authors.affiliation: Whitman Center, Marine Biological Laboratory, Woods Hole, MA 02543, USA Biology Department, Providence College, Providence, RI 02819, USA.
authors.forename: John H
authors.initials: JH
authors.lastname: Costello
authors.affiliation: Applied Ocean Physics and Engineering, Woods Hole Oceanographic Institution, Woods Hole, MA 02543, USA.
authors.forename: Houshuo
authors.initials: H
authors.lastname: Jiang
mesh_terms: D000818:Animals; D001696:Biomechanical Phenomena; D057446:Hydrodynamics; D037402:Hydrozoa / Q000254:growth & development* / Q000502:physiology; D012212:Rheology; D013550:Swimming / Q000502:physiology
keywords: Jet propulsion; Medusan swimming; Ontogeny