AUTECOLOGY OF THE TOXIC DINOFLAGELLATE ALEXANDRIUM-OSTENFELDII - LIFE-HISTORY AND GROWTH AT DIFFERENT TEMPERATURES AND SALINITIES

Batch culture experiments were conducted with Alexandrium ostenfeldii, a toxic, marine dinoflagellate common in Danish waters. Growth occurr ed at 11.3-23.7 degrees C and from 10 to 40 psu. Maximum division rate s of more than 0.3 divisions d(-1) took place at 20 degrees C and 15-2 0 psu. Growth phase variations resulted in mean cell sizes from 12 x 1 0(3) to 20 x 10(3) mu m(3). Variations in cell size were observed at d ifferent temperatures and salinities, and mean cell size was closely c orrelated with division rate for all temperatures investigated (11.3-2 3.7 degrees C) and for salinities between 10 and 30 psu. Sexual stages , fusing gametes and planozygotes were observed in nutrient deficient cultures of A. ostenfeldii from New Zealand, but mixing of two Danish nutrient-deficient, clonal cultures did not result in mating. Sexual f usion did not lead to the formation of resting cysts, which are presen tly known only from nature. Temporary cysts were very common in ageing cultures and in unfavourable environmental conditions that did not pe rmit growth. These cysts showed a high degree of morphological variabi lity. When stained with calcofluor, the cysts revealed a surface patte rn. Germination of temporary cysts caused the release of a naked, bifl agellate stage. At germination, the transverse flagellum was located o utside the cingulum, next to the longitudinal flagellum. The transvers e flagellum became positioned in the cingulum only after the cell was clear of the cyst wall.