The growth of dinoflagellates in laboratory cultures

SUMMARY The growth rate of Amphidinium carterae Hulburt in axenic culture was unaffected by gentle shaking (100 rpm); in contrast, growth rates of Amphidinium klebsii Kof et Swezy, Scrippsiella trochoidea (Stein) Loeblich III and Gyrodinium aureolum Hulburt were lowered and the latter species was killed by shaking. Amphidinium carterae and Scrippsiella trochoidea grew taster under continuous illumination than under the two light/dark regimes tested. However, growth of Gyrodinium aureolum was much slower under continuous illumination (0·15 divs d-1) than in the photoperiods (0·21–0·36 divs d-1). Growth rates of Amphidinium carterae aerated with elevated CO2 (0·5% v/v) were saturated at a photon flux density of 80μE m-2 s-1. Cells grown at the lowest irradiance used (15 μE m2 s-1) had the highest pigment (chlorophyll a, c and carotenoids) per cell and the highest rate of photosynthesis both on a unit cell and a unit chlorophyll a basis. However, these cells showed no photoinhibition of photosynthesis when rates were measured at photon flux densities up to 150 μE m-2 s-1. Culture filtrates failed to support any further growth of A. carterae, S. trochoidea or O. aureolum when reinoculated with the same dinoflagellate species. However, the growth of A. carterae, but not that of the other two species, resumed when fresh nutrients were added to culture filtrates. Cell yields of A. carterae were increased by over 50% by doubling the nutrient addition to be medium. The nutrient responsible for this increase appears to be nitrate. Nitrate and arginine were also good sole nitrogen sources for the growth of A. carterae. However, ammonium supplied at the same concentration (1 mg atom N NI-1) was toxic; growth was slower, motility was impaired and cells become enlarged and rounded. Lowering the ammonium concentration to 0·2 mg atom N 1-1 restored growth and cellular morphology to normal.