The red-tide dinoflagellate Protoceratium reticulatum is shown to be protected against turbulence-associated damage by the use of the additives Pluronic F68 (PF68) and carboxymethyl cellulose (CMC) in the culture medium. Relative to agitated controls, these additives had a dose-dependent protective effect at concentrations of up to 0.4 and 0.5 g L(-1) for CMC and F68, respectively. In static cultures, these additives inhibited growth directly or indirectly at a concentration of >0.5 g L(-1). Compared to CMC, PF68 was a better protectant overall. Cell-specific production of yessotoxins was enhanced under elevated shear stress regimens so long as the turbulence intensity was insufficient to damage the cells outright. Shear-induced production of reactive oxygen species and direct effects of turbulence on the cell cycle contributed to the observed shear effects.