The effect of temperature and salinity on Margalefidinium polykrikoides group III VA, USA strain growth.

Margalefidinium polykrikoides is a cosmopolitan dinoflagellate that blooms in coastal waters. Despite genomic evidence that it belongs to Group III and so closely related to isolates from Puerto Rico, Malaysia, North America, and Central America, M. polykrikoides blooms in the Chesapeake Bay at warmer temperatures and lower salinities than in coastal ecosystems occupied by its closest relatives. In this study, the effect of temperature and salinity on the growth rate and total cell yield of an M. polykrikoides VA culture isolate were examined and compared with environmental observations made during M. polykrikoides blooms in the Chesapeake Bay. M. polykrikoides group III VA strain grew at 18-32 ̊C and 15-30 salinity. M. polykrikoides group III VA strain grew better at warmer temperatures and lower salinities than other M. polykrikoides strains from related groups, but did not grow at 16 or 34 ̊C or at a salinity of 10. Low salinity and excessively warm temperatures interacted to inhibit M. polykrikoides group III VA strain growth at 32 ̊C and 15 salinity. Temperature and salinity likely interact in estuarine waters to inhibit or promote M. polykrikoides bloom initiation and development. The range of water temperatures observed during M. polykrikoides blooms in the Chesapeake Bay was narrower than what was observed for most of the other dinoflagellate species that bloom there, but the range of salinity was the broadest. M. polykrikoides bloomed at warmer temperatures and higher salinities than most of the other bloom-forming dinoflagellate species in the Bay.