Swimming and escape behavior in two species of calanoid copepods from nauplius to adult

Abstract

Subject to high predation risk, all developmental stages of copepods depend on evasive behaviors for survival in pelagic environments. Swim and escape behaviors were investigated in copepods from early nauplius to adult using 3D high-speed micro-cinematography. Parvocalanus crassirostris and Eurytemora affinis are two common estuarine species with broad geographic ranges. The early naupliar stages were mostly immobile, whereas the copepodids and adults spent most of the time actively swimming. Escapes and/or behavioral freezes were elicited by a predator mimic, an abrupt hydromechanical stimulus created by the rapid vertical movement of a 3-mm sphere, and video-recorded at 500 frames-per-second. All developmental stages of planktonic copepods responded with evasive behaviors and responses decreased with distance from the sphere. Maximum response distances were greater and response latencies were shorter in copepodids than in nauplii. Maximum escape speeds increased with copepod size, while the duration of the escape response decreased with the developmental stage. Maximum escape speeds scaled to body length as a power function from early nauplius to adult. Species-specific patterns in escape trajectories were apparent at the first nauplius (N1). These results start to differentiate between performance differences that result from size and design constraints, and those that are due to species-specific behavioral patterns.