THE INFLUENCE OF IRRADIANCE ON GROWTH, PHOTOSYNTHESIS AND RESPIRATION OF GYRODINIUM CF AUREOLUM

The bloom-forming marine dinoflagellate Gyrodinium cf. aureolum was grown in batch cultures over a range of irradiances (35-380 mumol m-2 s-1) and growth. photosynthesis and respiration rates determined. Saturation of growth occurred at irradiances of approximately 100 mumol m-2 s-1. Below this light level, decreases in growth rates and cell size, and a relative increase in carbon specific respiration rates, were observed. On the other hand, photosynthesis-irradiance relationships determined from dissolved oxygen incubations showed that on a cellular and carbon basis. cultures grown at low irradiances had higher rates of light-limited and light-saturated photosynthesis, mainly as a result of large increases in cell chlorophyll content. This adaptation strategy enables low-light-grown organisms to exploit available high irradiance through a relatively high photosynthetic capacity. In cells grown at higher light levels (> 100 mumol m-2 s-1), excess photosynthate may be diverted to storage rather than used for growth,