Quantification of flows generated by the hydromedusa Aequorea victoria: a Lagrangian coherent structure analysis

Abstract

Most oblate medusae use flow generated during swimming to capture prey. Quantification of their interactions with surrounding fluid is necessary to understand their feeding mechanics and to develop models to predict their predatory impact. In the present study, we quantified how the hydromedusa Aequorea victoria interacts with both its surrounding fluid and prey. The fluid interactions were examined in the laboratory and in natural field settings using digital particle image velocimetry (DPIV) measurements. The laboratory DPIV data were used to compute finite-time Lyapunov exponent (FTLE) fields, and Lagrangian coherent structures (LCS) were extracted from the FTLE fields. The laboratory LCS analysis demonstrated that swimming A. victoria only encounter discrete packets of fluid originating upstream of the medusan bell. Based on the size of these packets, we estimated that the A. victoria examined have the potential to clear 11.4 l h -1. Used in conjunction with measured prey capture efficiencies, we estimated potential clearance rates on different prey types. These hydrodynamically based clearance rate estimates are consistent with previously measured empirical clearance rate estimates. Velocity vector and shear fields also suggested that the feeding current created by A. victoria may be more suitable for encountering copepods than previously thought. Although still preliminary, in situ DPIV data indicate that natural background flows may alter the encounter process from what is observed in still-water laboratory conditions. KEY WORDS: Lagrangian coherent structures · Medusae · Field measurements · Digital particle image velocimetry · Predator-prey interactions 435: 111-123, 2011 addition to providing thrust, these bell motions transport fluid to prey capture surfaces (i.e. tentacles and manubrium-oral arms), where entrained prey may be retained (Costello & Colin 1995, Colin et al. 2006, Peng & Dabiri 2009). The fluid interactions and patterns of flow around swimming-cruising medusae have been well described qualitatively (Dabiri et al. 2005, Colin et al. 2006. These studies have shown that as the bell expands, fluid adjacent to the bell margin is entrained and drawn through trailing tentacles into a stopping vortex ring (structure created at the end of a swimming cycle) that rotates inside the subumbrellar cavity. As the bell contracts, fluid continues to be entrained adjacent to the bell margin and, along with fluid from the stopping vortex, is drawn into a starting vortex ring (structure created at the start of a swimming cycle) that rotates through the trailing tentacles in the wake of the medusa. Consequently, fluid appears to be continuously entrained throughout the swimming cycle and interacts with capture surfaces (Dabiri et al. 2005). Resale or republication not permitted without written consent of the publisherMar Ecol Prog SerWhile these studies have provided an understanding of the general nature of fluid transport around the bell and in the medusan wake, they have not characterized the...

Ontogenetic propulsive transitions by medusaeSarsia tubulosa

“…kinetic energy and impulse) using planar measurement data (Katija and Dabiri, 2009;Katija et al, 2011). An in-house Matlab code was used to compute the time-varying specific fluid kinetic energy KE(t)/ρ and specific fluid impulse I(t)/ρ in the wake generated by swimming S. tubulosa.…”

Fluid Interactions That Enable Stealth Predation by the Upstream-Foraging Hydromedusa Craspedacusta sowerbyi

“…This is advantageous in drawing prey onto capture surfaces located in this region of maximum flow throughout the entire duration of the pulse (Larson, 1991;Dabiri et al, 2005). Few studies have quantified the fluid dynamics associated with prey capture by these rowing medusae (Katija et al, 2011); however, it has been shown that the generation of a feeding current by rowing medusae is energetically efficient and effective at circulating large volumes through trailing capture surfaces (Dabiri et al, 2005). These traits enable rowing medusae to forage continuously as feeding-current feeders (Colin and Costello, 2002;Colin et al, 2003;Kiørboe, 2011).…”

Bases morfo-funcionais da alimentação e o papel trófico de iLychnorhiza lucerna (Scyphozoa, Rhizostomeae)

“…Esse colágeno da mesogléia umbrelar, na forma de feixes, armazena a energia potencial elástica gerada pela contração e age em ação antagônica à musculatura subumbrelar, para a recuperação da forma inicial da umbrela (Muskatine & Lenhoff, 1974;. Tal propriedade mecânica da umbrela de medusas Rhizostomeae propicia maiores volumes de água transportados contra os braços orais, e assim aumenta o volume filtrado (Acuña et al, 2011;Katija et al 2011).…”

“…and Pelagia noctiluca) (Addad et al 2011). The remarkable hardiness of rhizostome medusae bell allows higher swimming, and potentially feeding performance, since the volume of cleared water depends on the volume of entrained water by bell contractions (Acuña et al 2011;Katija et al 2011). Whereas some semaeostome medusae enhance prey encounter rates by developing long capture structures, such as in C. capillata which bears tentacles up to 10 m long , rhizostomeae medusae have high frequency swimming patterns which allow lager volume of fluids filtered and also higher encounter rates with prey.…”

“…In addition, bell pulsations of rhizostome medusae are stronger than other scyphomedusae, when comparing animals of similar body size . Such differences on swimming behavior can affect: (i) feeding performance, since the volume of cleared water depends on the volume of entrained water by vortex of bell pulsations (Acuña et al 2011;Katija et al 2011); and (ii) prey selectivity, since the strength on feeding currents may affect the types of prey entrained ).…”