Physiological, ultrastructural and growth studies of Prymnesiophyceae coccolithophorid species subjected to continuous light and D:N cycle regimes, and various phosphate concentrations

Thirteen species of marine phytoplankton belonging to the taxonomic division Prymnesiophyceae, eleven of which were coccolithophorids, were tested for their growth, physiological, and morphological responses to continuous light and D:N cycle regimes as well as three phosphate concentrations. The Prymnesiophyceae, Isochrysis qalbana and Chrysochromulina sp. and the non-coccolith forming strain of Coccolithus pelagicus were unable to grow under continuous light. The remaining species showed a trend for lower growth rates under continuous light compared to the D:N cycle. These results suggest that for some species, diel periodicity may be beneficial. The non-coccolith forming coccolithophorids were found to be more sensitive to continuous light than the coccolith-forming strains. No significant differences in pigments, POC, PON, or C:N ratios were observed for species grown under the two light regimes. The coccolith-forming coccolithophorids contained 3-5 times more chl a and chl c than the non-coccolith forming coccolithophorids. These results suggest that the coccosphere reflects light and shades the cell. The cell compensates by producing more chl a. No differences in cell and coccolith dimensions or morphology were observed under either light regime. Four of the five coccolithophorids examined showed no significant differences in growth rates when they were grown under three different phosphate concentrations (13.0, 10.0, and 3.0 or 0.9 µM). The maximum yields were significantly lower at 3.0 and 0.9 µM compared to 13.0 and 10.0 uM phosphate concentrations for all of the coccolithophorids. Phosphate concentration did not affect coccolith formation or morphology. Efforts to induce coccolith formation in noncoccolith forming strains of E. huxleyi under phosphate and nitrate limitation were unsuccessful. Morphological changes were observed in Coccolithus neohelis under the three phosphate concentrations. At 3.0 µM phosphate, 90-100% of cells had flagella and 10-60% had one or more coccoliths, whereas at 13.0 µM phosphate 0-10% of cells had flagella and 100% had coccoliths.Science, Faculty ofBotany, Department ofGraduat