Swimming and escape behavior of copepod nauplii: Implications for predator-prey interactions among copepods

Abstract

This study focuses on how prey behavior may affect predation risk through encounter rates and the escape success of the prey given an encounter. Temora longicornis nauplii require stronger hydrodynamic signals to elicit escape than Acartia tonsa nauplii (critical fluid deformation rates, Δ* of 2.8 to 4.0 and 1.2 to 2.5 s-1, respectively) suggesting that T. longicornis may be more susceptible to predation. Quantification of naupliar motility behavior and subsequent estimation of the hydrodynamic signals which the nauplii generate suggest that an adult female Centropages typicus may detect an A. tonsa nauplius at a greater distance than a similarly sized T. Iongicornis nauplius. Observations of attacks of free swimming C. typicus and the naupliar prey confirmed that T. longicornis is poorer at detecting predators than A. tonsa, and that the same predator detects A. tonsa at a greater distance than it detects T. longicornis nauplii (2.37 ± 1.46 and 0.34 ± 0.18 mm, respectively). The combined effect of prey motility and escape behavior was tested by offering C. typicus females the 2 prey species alone and in mixtures. Clearance rates on T. longicornis (442 ± 125 ml ♀-1 d-1) were ca 3-fold that on A. tonsa nauplii (146 ± 35 ml ♀-1 d-1) in both single species and mixed treatments. While the low profile motility behavior of T. longicornis appears to reduce encounter rates, its post encounter (i.e., escape) behavior is less effective. In contrast, the behavior of A. tonsa acts predominantly at the post-encounter stage where its sensitivity to hydrodynamic signals (i.e., low Δ*) effectively compensates for the high predator encounter rate generated by its motility.