MEPS 167:105-117 (1998)  -  doi:10.3354/meps167105

Swimming orientation in autotrophic marine dinoflagellates often follows a pattern attributed to positive phototaxis during the day and positive geotaxis at night. Exceptions that occur in field and laboratory observations most often describe ascents or descents that anticipate sunrise or sunset. These exceptions may originate in biochemical synthesis patterns that use sequential photosynthate (carbohydrate and lipid) production and dissolved nitrogen absorption for subsequent cell growth (RNA and protein) and division (DNA). Instantaneous biochemical state may influence orientation either through mechanical ballasting or through growth optimization that influences sensory-mediated responses to environmental cues. In the present mesocosm (150 cm length x 44 cm diameter) study, samples from a quantized (all cells divide together at approximately 3 d intervals) population of Gymnodinium breve Davis collected at the surface and mid-column support comparisons of diel orientation preferences and cellular biochemical states over a 3 d period. Up to 50% of the column population aggregates at the surface during the day, but this percentage decreases with time since cell division. Within a given day, G. breve exhibits continuous negative geotaxis associated with surface aggregation when the taxis is stronger and with dispersion through the water column when the taxis is weaker. Positive phototaxis helps maintain surface aggregation during the afternoon as negative geotaxis weakens. The surface cells exhibit only slightly lower concentrations of DNA and RNA, somewhat lower concentrations of protein and carbohydrate, and significantly lower concentrations of chlorophyll a and lipid, compared to the cells sampled from mid-column. The strength of the negative geotaxis of the mid-column cells negatively correlates with lipid concentration. These results support the case for a biochemical influence on orientation but require more experimental data to establish cause and effect.

Dinoflagellate · Behavior · Biochemistry