EFFECTS OF LARGE NONGRAZABLE PARTICLES ON CLEARANCE AND SWIMMING BEHAVIOR OF ZOOPLANKTON

Latex beads (diameter 45-mu-m) were used to mimic pelagic particle composition dominated by large nongrazable particles and to examine their effect on clearance and swimming behaviour of a tintinnid, Favella ehrenbergii, a rotifer, Brachionus plicatilis, a gastropod veliger, Philine aperta, and copepodites of the neritic copepod Acartia tonsa. Clearance was measured as a function of bead concentration and compared with swimming patterns and grazing behaviour. The ciliates and the rotifers were not sensitive to mechanical obstruction by the polystyrene beads. The gastropod veligers and the copepodites, however, change swimming behaviour by increasing sinking and jumping frequencies accompanied by a significant reduction in clearance. These observations imply that laboratory determined grazing rates may overestimate in situ grazing activity if larger, noningestible particles are present in the water coloumn.