Predator avoidance by nauplii

Abstract

We examined anti-predation strategies in relation to motility patterns for early and late nauplii of 6 species of copepods (Calanus helgolandicus, Centropages typicus, Eurytemora affinis, Euterpina acutifrons, Acartia tonsa and Temora longicornis). Remote detection and escape abilities were quantified in siphon flows. Nauplii respond with distinct escape jumps at species- and stage-specific average fluid deformation rates between 0.5 and 4.2 s-1, and escape with average velocities corresponding to ∼60 to 130 body lengths s-1. Most of the species and stages orient their escape jumps upwards and also away from the flow, and are thus able to assess direction of flow. Sensitivity to hydrodynamic signals is tightly linked to the general motility pattern. Hydrodynamically conspicuous nauplii that move in a jump-sink pattern are more effective at remotely detecting predators than are continuous swimmers of similar size. We assessed the effects of different motility strategies in terms of detectability and volume encounter with copepod predators by means of simple hydrodynamic models. While jump-sink type nauplii may be at an advantage over swimmers in interactions with sinking and attacking ambush predators, models suggest no immediate relative benefit in terms of escaping flows of filtering copepods. We discuss these predictions in relation to copepod feeding rates.