INFLUENCES OF TEMPERATURE, SALINITY AND IRRADIANCE ON GROWTH OF PROROCENTRUM-MINIMUM (DINOPHYCEAE) FROM THE MEDITERRANEAN-SEA

A Mediterranean clone of the red-tide forming dinoflagellate Prorocent rum minimum was studied in vitro for its capacities to adapt to salini ty, temperature and light. This clone is euryhaline and shows optimal growth between 15 and 35 parts per thousand. After adaptation, slow gr owth was observed at salinities as low as 5 parts per thousand. An app aratus generating crossed gradients of temperature and light allowed 1 00 combined experimental conditions to be studied. Variations in light ing between 30 and 500 mu mol photons m(-2) s(-1) had little effect on growth, and no photoinhibition occurred. The clone can grow between 8 and 31 degrees C, but is thermophilic with an optimal growth between 18 and 26.5 degrees C As a result of large variations in temperature f rom 18 degrees C down to 10 degrees C and maintained at 10 degrees C, small spherical structures (8-10 mu m) were observed; they are describ ed as temporary cysts. These results were compared to those obtained b y different authors in vitro and in situ, notably in the Mediterranean region.