Escape behavior of planktonic copepods in response to hydrodynamic disturbances: high speed video analysis

Planktonic copepods exhibit rapid escape behavior in response to hydrodynamic disturbances. Small disturbances of brief duration were produced by a piezoelectric transducer moving a small cylinder. The escape responses of free-swimming adult males and females of the copepods Acartia tonsa and A. lilljeborgii were recorded using high-speed video and quantified using computerized motion analysis techniques. Response latency, swimming speed, acceleration and turning rate during escape behavior were measured. Acartia spp. typically respond within 4 ms to a hydrodynamic disturbance with multiple power strokes of the swimming legs. Each stroke and recovery is of ca. 7 ms duration with maximum speeds often exceeding 500 mm s–1 and minimum speeds between strokes rarely falling below 100 mm s–1. Acceleration during initial escape usually exceeds 100 m s–2. Escapes often begin with rapid reorientation away from the source of the disturbance, with maximum turning rates of about 30° ms–1. Significant differences were found between the kinetics of escape responses of adult male and female copepods of each species, with males having greater maximum speeds and accelerations, and females having longer duration jumps. Significant differences were also found between males and females of the 2 species, with A. lilljeborgii exhibiting greater speeds and more rapid acceleration than the smaller A. tonsa.