Mechanisms and feasibility of prey capture in ambush-feeding zooplankton

Abstract

Many marine zooplankters, particularly among copepods, are ''ambush feeders'' that passively wait for their prey and capture them by fast surprise attacks. This strategy must be very demanding in terms of muscle power and sensing capabilities, but the detailed mechanisms of the attacks are unknown. Using high-speed video we describe how copepods perform spectacular attacks by precision maneuvering during a rapid jump. We show that the flow created by the attacking copepod is so small that the prey is not pushed away, and that the attacks are feasible because of their high velocity (Ϸ100 mm⅐s ؊1 ) and short duration (few ms), which leaves the prey no time for escape. Simulations and analytical estimates show that the viscous boundary layer that develops around the attacking copepod is thin at the time of prey capture and that the flow around the prey is small and remains potential flow. Although ambush feeding is highly successful as a feeding strategy in the plankton, we argue that power requirements for acceleration and the hydrodynamic constraints restrict the strategy to larger (> 0.25 mm), muscular forms with well-developed prey perception capabilities. The smallest of the examined species is close to this size limit and, in contrast to the larger species, uses its largest possible jump velocity for such attacks. The special requirements to ambush feeders with such attacks may explain why this strategy has evolved to perfection only a few times among planktonic suspension feeders (few copepod families and chaetognaths).biological fluid dynamics ͉ boundary layer ͉ copepod ͉ potential flow

Turbulence triggers vigorous swimming but hinders motion strategy in planktonic copepods

“…Their success in feeding, reproducing and escaping predation depends on their relative velocity with respect to their prey, their mate and their predator from the time of the detection to the end of the interaction [57]. Copepods race up pheromone trails left by cruising females [18], flee from predators via powerful escape jumps [45] and perform spectacular attacks on their preys [58]. We suggest that copepods may not need to respond to advective transport due to eddies that are much larger than their size because at very large scale, turbulence redistributes preys, mates and small planktonic predators both in time and space, regardless of their swimming strategy.…”

Prey detection in a cruising copepod

“…Small aquatic predators approaching or capturing prey have to 'trick' viscosity in various ways to overcome the boundary layer effect. They do this either: (i) by accelerating out of the viscous regime in the moment of attack as in ambush feeding copepods [7], (ii) by performing asymmetric, 'flicking' movements of feeding limbs as in feeding -current feeding copepods [2], (iii) by creating a suction flow when opening the mouth as they lunge forward towards the prey as in suction feeding larval fish [12], or (iv) by shooting a harpoon-like structure that penetrates the viscous boundary layer, as in some pallium feeding dinoflagellates [13]. All these attack modes require prior detection of the prey.…”

Particle capture mechanisms in suspension-feeding invertebrates

“…Such features are typical at low Reynolds numbers where the viscous length (the ratio of kinematic viscosity to velocity) is large so that a disturbance from a moving object, such as a paddle or appendage, is felt at a considerable distance. Raptorial feeding on motile prey therefore occurs a high Reynolds number leaving little time for the prey to escape the predator as described by the fluid dynamics of attack jumps of ambush feeding copepods by Kiørboe et al (2009).…”