Fluid and predator-prey interactions of Scyphomedusae fed calanoid copepods

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.