Perceptive performance and feeding behavior of calanoid copepods

Abstract

The goal of this study was to determine variables associated with calanoid feeding behavior, and thus, to improve our understanding of the basics of calanoid feeding rates. These variables included periods and frequency of appendage motion, rates of cell clearance, distance at which a copepod first reacts to a cell which is eventually captured, and rate of water flow through the area covered by the motions of a copepod's feeding appendages. The effects of these variables on feeding rates were determined for copepodids and adult females of the calanoid copepod Eucalanus pileatus at phytoplankton concentrations covering the range encountered by this species on the south-eastern shelf of the USA. Our results indicate that the distance at which E.pileatus perceives phytoplankton cells increases ˜2-fold as food concentrations decrease from 1.0 to 0.1 mm 3 l −1 . These results lead us to hypothesize that this is due to increased sensitivity of chemosensors on the copepods' feeding appendages. This 2-fold increase in perceptive distance amounts to a near 4-fold increase in perceived volume which is close to the 6-fold increase in volume swept clear (VSC) from 1.0 to 0.1 mm 3 l −1 of Thalassiosira weissflogii . We assume that the increases in VSC by planktonic copepods, when food levels are below satiation, are largely a function of the sensory performance of the individual copepod.