Comparative study of selenium requirements of three phytoplankton species: Gymnodinium catenatum, Alexandrium minutum (Dinophyta) and Chaetoceros cf. tenuissimus (Bacillariophyta)

This study investigated the selenium (SE) requirements of threephytoplankton species which commonly bloom in southern Australianestuaries. The present study showed that the toxic dinoflagellateGymnodinium catenatum Graham had an obligaterequirement for Se (IV) in culture. After two transfers (4 weeks =7 generations) in Se-deficient seawater medium, this phytoplankton speciesexhibited a decline in growth rate (25%) and biomass yield (90%), whilecomplete cessation of cell division occurred under prolonged (8 weeks = 12generations) Se starvation. Addition of10^-9-10^-7 M H2SeO3 tonutrient-enriched seawater medium resulted in increasedG.catenatum growth and biomass yields in directproportion to the Se concentrations offered. In contrast toG.catenatum, Se limitation was observed in thedinoflagellate Alexandrium minutum Halim after fourtransfers (5 weeks = 20 generations) in Se-deficient medium. Exponentialgrowth rates of A.minutum decreased slightly (5-10%)when Se was not supplied, but biomass yields decreased as much as 80-90%.The diatom Chaetoceros cf.tenuissimus Meunier showed no evidence of Selimitation even after eight transfers (8 weeks; >60 generations) inSe-deficient medium. Variations in growth rates and biomass yields betweentransfers provide valuable information about the relative potential for Selimitation in the three species studied. In addition, differences in Serequirement between these bloom-forming phytoplankton species suggest thatthis micronutrient may play a role in structuring phytoplankton communitiesin southern Australian waters.