EFFECTS OF SMALL-SCALE TURBULENCE ON PHOTOSYNTHESIS, PIGMENTATION, CELL-DIVISION, AND CELL-SIZE IN THE MARINE DINOFLAGELLATE GONYAULAX-POLYEDRA (DINOPHYCEAE)

Several experiments were conducted to understand better the physiologi cal mechanisms underlying growth inhibition of the dinoflagellate Gony aulax polyedra Stein due to small-scale turbulence shear. To measure p hotosynthetic C-14 uptake, a ''phytoplankton wheel'' device for rotati ng cultures in closed bottles was used. Turbulence was quantified biol ogically in the bottles by comparing growth inhibition with that in cu ltures with constant shear between a fixed cylinder and an outer conce ntric rotating cylinder (a stable Couette flow). At saturating irradia nces, particulate photosynthesis (P-sat) or photosynthesis per unit ch lorophyll (P-sat(B)) were not inhibited completely at the highest turb ulence level (26.6 rad(.)s(-1)), and photosynthesis was less sensitive than growth. Photosynthesis per cell (P-sat(C)) was increased by turb ulence. In three experiments on the effects of turbulence on photosynt hesis versus irradiance curves, the slope of the curve, alpha, for par ticulate photosynthesis at limiting irradiances did not change. Photos ynthesis per unit chlorophyll per unit irradiance (alpha(B)) decreased at high (but not intermediate) turbulence levels. Photosynthesis per cell per unit irradiance, alpha(C), increased with turbulence, suggest ing an increase in photosynthetic efficiency in turbulent cultures. In two of the three experiments, respiration rates increased with turbul ence, and in one experiment excretion of photosynthetically fixed C-14 was not affected by motion. Ratios of accessory pigments to chlorophy ll alpha did not change with turbulence, but pigments per cell and per dry weight increased with turbulence These findings suggest little or no disruption of the photosynthetic apparatus. When turbulence was ap plied for 1 week, beta-carotene increased while peridinin and diadinox anthin decreased, suggesting inhibition of synthesis of these latter p igments by prolonged turbulence. Since cell numbers did not increase o r decreased during turbulent 72-h incubations, cell division was inhib ited and also the cells were very much enlarged. Increases in alpha(C) per cell suggest that, in the sea, photosynthetic metabolism can pers ist efficiently without cell division during turbulent episodes. After turbulence ceases or reaches low levels again, cells can then divide and blooms may form. Thus, blooms can come or go fairly, rapidly in th e ocean depending on the degree of wave- and wind-induced turbulence.