Influence of continuous light and L:D cycles on the growth and chemical composition of Prymnesiophyceae including coccolithophores

Abstract

Eleven species of marine phytoplankton belonging to the Prymnesiophyceae, nine of which were coccolithophores, were tested for their growth, physiological, and morphological responses to continuous light and a L:D cycle. Isochrysis galbana (Parke) and Chrysochromulina sp. and the non-coccolith-forming strain of Coccolithus pelagicus (Gaarder et Markali) grew poorly or not at all under continuous light. The response of the nine coccolithophores to continuous light vs. L:D cycle was more variable. Two coccolith-forming species Coccolithus pelagicus COPEL and Coccolithus neohelis (McIntyre and Bé) grew faster under the 14L:10D cycle, while two other coccolith-forming species, Emiliania huxleyi (Lohmann) Hay et Mohler 88E and Cyclococcolithus leptoporus (Murray et Blackman) Kamptner, grew faster under continuous light. The growth rates of the other five coccolithophorids (two coccolith-forming and three non-coccolith-forming species) showed no difference between continuous light and L:D cultures. No significant differences in chlorophyll a (chl a), POC, PON, or C:N ratios were observed for species grown under the two light regimes. The coccolith-forming coccolithophores contained 3–5 times more chl a than the non-coccolith-forming coccolithophores. These results suggest that the coccosphere reflects light and shades the cell, and thus the cell compensates by producing more chl a. No differences in cell and coccolith dimensions or morphology were observed under either light regime.