SEXUALITY AND CYST FORMATION IN THE DINOFLAGELLATEGONYAULAX TAMARENSIS:CYST YIELD IN BATCH CULTURES1

ABSTRACT Encystment of the toxic dinoflagellateGonyaulax tamarensisLebour (var.excavata) was monitored in batch cultures exposed to a variety of nutritional and environmental treatments. Limitation by nitrogen (as ammonium or nitrate) or phosphorus (as phosphate) resulted in cyst formation. When the initial concentration of limiting nutrient was varied, total cyst yield (mL−1) was directly proportional to the cell yield at all but the highest nutrient concentrations (where encystment was minimal). Encystment efficiency was relatively constant (0.1–0.2 cysts · cell−1) over a 5‐fold range of cell densities, indicating that 20 to 40% of the vegetative populations successfully encysted. Cyst formation was negligible in nutrient‐replete medium, even with a significant reduction in growth rate due to non‐optimal light, temperature, or to high batch culture cell densities. Low light levels did decrease cyst yield once encystment was initiated by nutrient limitation, but this was probably linked to smaller motile cell yield and not to a specific inhibition of encystment. In contrast, encystment was more sensitive to temperature than was growth rate: optimal cyst production occurred over a relatively narrow temperature range and no cysts were formed at [Page missing]