BEHAVIORAL COMPONENTS OF FEEDING SELECTIVITY OF THE HETEROTROPHIC DINOFLAGELLATE PROTOPERIDINIUM-PELLUCIDUM

Protoperidinium pellucidum is a pallium feeding heterotrophic dinoflag ellate that captures phytoplankton cells individually and digests them externally. In laboratory cultures, P, pellucidum feeds on a variety of diatom species and a limited number of dinoflagellate species, and grows more rapidly on diatoms than dinoflagellates. When offered food in mixed assemblages, it feeds selectively on diatoms over dinoflagell ates, and selects between diatom species. Selectivity between differen t diatom species does not appear to be related to size, and size alone does not explain the low selectivity for dinoflagellates. Computerize d motion analysis studies of swimming behavior reveal that P, pellucid um appears to use chemoreception as the major sensory mode to detect a nd locate food. When P. pellucidum passes near a food cell it circles around the cell several times before attaching to the food particle, a pparently using chemoreception to judge the location of the cell. Deta iled behavioral observations reveal that P, pellucidum sometimes loses contact with motile dinoflagellate cells before the capture occurs; s uch losses were not observed with diatoms. In addition, motile dinofla gellate prey often escape after initial capture, their swimming behavi or causing the capture filament to break before the cell can be engulf ed by the pallium of P, pellucidum; loss of a diatom after attachment was extremely rare. Feeding selectivity may be explained in part by th e nature of the chemosensory signals given off by different prey types , and therefore the distance at which P. pellucidum can detect food, a nd in part by the lower capture success of P. pellucidum with motile p rey.