Feeding behaviour of Centropages typicus in calm and turbulent conditions

Feeding of the copepod Centropages typicus on the oligotrich ciliate Strombidium sulcatum was studied in the laboratory under controlled, measured conditions of grid generated small scale turbulence. High levels of turbulence, epsilon (kinetic energy dissipation sate) = 2.9 x 10(-2) to 3 x 10(-1) cm(2) s(-3) increased the clearance rate of C, typicus feeding on S. sulcatum by up to a factor of 4 in comparison to calm water values. At a level of turbulence of 4.4 cm(2) s(-3), we observed a drastic decrease in clearance rates to values equivalent to those in calm water. We suggest an explanation for the observed changes in predation rates with levels of turbulence. Video recorded observations of the behaviour of free swimming C. typicus conducted in calm conditions suggest that the copepod uses a cruising strategy to search and encounter S. sulcatum. In the presence of this ciliate, C. typicus increases the proportion of time spent swimming at a mean velocity of 3.5 mm s(-1): from 49.5 % in filtered seawater without ciliates to 79.5 % in the presence of S. sulcatum (1 cell ml(-1)). Furthermore, a qualitative change of the swimming behaviour is triggered by the presence of the ciliate, resulting in an increased proportion of time spent slow swimming in a 'helical' mode. Our results suggest that high levels of small scale turbulence substantially increase predation rates of cruising copepods.