Woods Hole Oceanographic Institution
Jet or die: Ontogeny and swimming by ambush-feeding medusae
Wednesday— July 24, 2013
Pacific Forum — 3:00 p.m.
As organisms swim in their natural environment, they are constantly striving to successfully forage, escape from predation, and search for mates to reproduce. Marine organisms are accomplishing these tasks while interacting with their fluid environment, generating hydrodynamic signatures in their wake and around their bodies. The resulting hydrodynamic signatures are detected by predators and prey, and are also indicative of the energetics and proficiency of a swimming organism. Changes in hydrodynamic signatures as an organism grows and develops provide useful insight into its ecology. A widespread swimming strategy employed by squid, salps, and medusae is jet propulsion. Although jet propulsion in medusae has been shown to be energetically costly, organisms remain motionless most of the time and forage as ambush predators. In this study, we examined swimming by hydromedusae Sarsia tubulosa over ontogeny (one millimeter to one centimeter bell diameters) using high-speed video recordings and digital particle image velocimetry. Using this data, we evaluated biomechanical metrics (proficiency and Froude efficiency) that allow for accurate comparison of swimming ability through ontogeny. Our results show that jet propulsion becomes less proficient and less efficient with increasing bell diameter, which has important implications for larger organisms utilizing jet propulsion.