Effects of small-scale turbulence on interactions between the heterotrophic dinoflagellate Oxyrrhis marina and its prey, Isochrysis sp.

The effects of small-scale turbulence on interactions between the heterotrophic dinoflagellate Oxyrrhis marina Dujardin and its prey, the haptophyte Isochrysis sp. Parke, were investigated. Under food-limited conditions growth of Oxyrrhis marina decreased with decreasing prey density. At a given prey density, however, the growth of O. marina was significantly lower at high turbulence (epsilon = 1 cm(2) s(-3)) than at low turbulence (epsilon = 0.0001 cm(2) s(-3)), whereas ingestion and clearance were not affected by small-scale turbulence. In food-saturated conditions a significant negative effect of small-scale turbulence on growth was found at epsilon = 1 cm(2) s(-3), but not at 0.05 cm(2) s(3) and lower turbulent dissipation rates. Although the growth of O. marina was reduced by approximately 20% at the highest turbulence level, it was still 0.64 d(-1), which is higher than the reported maximum growth of several other heterotrophic dinoflagellates. Ingestion and cell volume were unaffected and the decreased growth was caused by an increased mortality when O. marina was exposed to the highest turbulence level (epsilon = 1 cm(2) s(-3)). Small-scale turbulence had no significant effect on the growth of the prey, Isochrysis sp..