Differences in the photoacclimation and photoprotection exhibited by two species of the ciguatera causing dinoflagellate genus, Gambierdiscus.

In culture, Gambierdiscus spp. have been shown to prefer irradiances that are relatively low (≤250μmol photonsm-2 s-1 ) versus those to which they are frequently exposed to in their natural environment (>500μmol photonsm-2 s-1 ). Although several behavioral strategies for coping with such irradiances have been suggested, it is unclear as to how these dinoflagellates do so on a physiological level. More specifically, how do long term exposures (30days) affect cell size and cellular chlorophyll content, and what is the photosynthetic response to short term, high irradiance exposures (up to 1464μmol photonsm-2 s-1 )? The results of this study reveal that cell size and chlorophyll content exhibited by G. carolinianus increased with acclimation to increasing photon flux density. Additionally, both G. carolinianus and G. silvae exhibited reduced photosynthetic efficiency when acclimated to increased photon flux density. Photosynthetic yield exhibited by G. silvae was greater than that for G. carolinianus across all acclimation irradiances. Although such differences were evident, both G. carolinianus and G. silvae appear to have adequate biochemical mechanisms to withstand exposure to irradiances exceeding 250μmol photonsm-2 s-1 for at least short periods of time following acclimation to irradiances of up to 150μmol photonsm-2 s-1 .