Behavioral responses of the marine tintinnid Favella sp. to phytoplankton: influence of chemical, mechanical and photic stimuli

Abstract

Computerized motion analysis was used to experimentally investigate the locomotory responses of a tintinnid, Favella sp., to phytoplankton and to chemosensory and mechanosensory stimuli associated with the presence of phytoplankton. When exposed to increased concentrations of the dinoflagellate Heterocapsa triquetra (strain HT984), Favella show transient change in behavior which result in a decrease in swimming speed, increase in turning rate and a decrease in net to gross displacement ratio; this should result in the aggregation of Favella in patches of the dinoflagellate. Similar behavioral responses are elicited by exposure to exudates of H. triquetra and to plastic beads of approximately the same size as the alga. When Favella was exposed to other phytoflagellates or their exudates, the behavioral responses were less pronounced or absent. Favella do not respond to beads < 6 μm; for larger beads, the response appears to depend on the concentration of beads. Favella do not exhibit a phototaxis or photokinesis but they do have diel behavior patterns that may be entrained by the light cycle. These diel changes in locomotory behavior may increase the probability of encounter with food patches.