Modulation of ecdysal cyst and toxin dynamics of two <i>Alexandrium</i> (Dinophyceae) species under small-scale turbulence

Abstract

Abstract. In some dinoflagellate species, physiological processes appear to be altered by exposure to certain turbulent conditions. Here we investigated how two levels of turbulent kinetic energy dissipation rates (ε = 0.4 and 27 cm2 s−3) affected the toxin and ecdysal cyst dynamics of two bloom forming species, Alexandrium minutum and A. catenella. The most striking responses were observed at the high ε generated by an orbital shaker. In A. catenella, lower cellular toxin content was measured in cultures shaken for more than 4 days. The same trend was observed in A. minutum, although variability masked statistical significance. For the two species, inhibition of ecdysal cyst production occurred immediately and during the period of exposure of the cultures to stirring (4 or more days) at any time during their growth curve. Recovery of cyst abundances was always observed when turbulence stopped. When turbulence persisted for more than 4 days the net growth rate significantly decreased and the final biomass yield was lower than in the unshaken cultures. This study suggests that high levels of small-scale turbulence would contribute to the modulation of the harmful bloom dynamics through the interaction at the level of toxin and encystment processes.