INFLUENCE OF CONTINUOUS LIGHT AND L-D CYCLES ON THE GROWTH AND CHEMICAL-COMPOSITION OF PRYMNESIOPHYCEAE INCLUDING COCCOLITHOPHORES

Eleven species of marine phytoplankton belonging to the Prymnesiophyce ae, 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 Chsysochromulina sp. and the non-coccolith-forming strain of Coccolithus pelagicus (Gaarder et Mar kali) grew poorly or not at all under continuous light. The response o f the nine coccolithophores to continuous light vs. L,D cycle was more variable. Two coccolith-forming species Coccolithus pelagicus COPEL a nd Coccolithus neohelis (McIntyre and BC) grew faster under the 14L:10 D 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 ra tes of the other five coccolithophorids (two coccolith-forming and thr ee non-coccolith-forming species) showed no difference between continu ous light and L:D cultures, No significant differences in chlorophyll a (chi a), POC, PON, or C:N ratios were observed for species grown und er the two light regimes. The coccolith-forming coccolithophores conta ined 3-5 times more chi a than the non-coccolith-forming coccolithopho res. These results suggest that the coccosphere reflects light and sha des the cell, and thus the cell compensates by producing more chi a, N o differences in cell and coccolith dimensions or morphology were obse rved under either light regime. (C) 1998 Elsevier Science B.V.