Abstract
The feeding current of scyphomedusae entrains and transports surrounding fluids and prey through trailing tentacles to initiate encounters with prey. After contact, most prey are retained for ingestion. However, the probability that a contact will occur depends on several factors including capture surface morphology, prey size and behavior. We examined how hydrodynamics, capture surface morphology and prey behavior affect the capture probability of copepods. To do this, we documented medusa-copepod interactions of four species of scyphomedusae (two semeostomes and two rhizostomes) possessing different capture surface morphologies. We tracked the movement and behavior of entrained copepods throughout the feeding process to quantify prey behavior effects upon capture efficiency (# captures/# encounters). The feeding currents generated by all the medusan species generated fluid shear deformation rates well above the detection limits of copepods. Despite strong hydrodynamic signals, copepod behavior was highly variable and only 58% of the copepods reacted to entrainment within feeding currents. Furthermore, copepod behavior (categorized as no reaction, escape jump or adjustment jump) did not significantly affect the capture efficiency. The scale and complexity of the feeding current generated by scyphomedusae may help explain the poor ability of copepods to avoid capture.
Highlights
Scyphomedusae are influential predators within marine ecosystems, capable of consuming a high abundance and a diverse array of prey items [1,2]
The capture efficiency of copepods by medusae was quantified throughout the swimming cycle
Shear rates were greater during bell contraction but were above the detection threshold of A. tonsa within 5 mm from the bell margin throughout the swimming cycle
Summary
Scyphomedusae are influential predators within marine ecosystems, capable of consuming a high abundance and a diverse array of prey items [1,2]. Zooplankton within the entrained fluid are drawn into the tentacles or oral arms and, once physically contacted, are unlikely to escape [3]. While physical contact between these predators and their prey usually leads to prey capture, there is no guarantee that entrained prey will contact a capture surface. Pre-contact interactions between medusae and prey may influence capture probability but are poorly understood. This contrasts sharply with the fluid mechanics of propulsion by swimming medusae, which are well described [5,6,7,8]. The response patterns of prey to the fluid flows generated by medusae require quantification in order to understand how these responses affect the likelihood of prey capture
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