Chlorophyll a and c in Cultures of Marine Algae

Abstract

Gymnodinium, Nitzschia closterium, and Skeletonema costatum were grown in the presence of bacteria, and N. closterium in the absence of bacteria, for 7 weeks. Each week samples were analysed by the Richards-Thompson method for chlorophyll a and c. Maximum cell numbers were reached in 1-3 weeks. Gymnodinium grew better at 680 f.c. than at 420 f.c. but the reverse was true of Nitzschia and Skeletonema. The chlorophyll content of the Gymnodinium cultures was similar at each light intensity but Nitzschia gave more chlorophyll at 420 f.c. With Skeletonema there was no consistent effect of light. During the initial growth phase, Gymnodinium contained 0.33-0.87 µg chlorophyll a and 0.56-1.88 pg chlorophyll c per million cells. The corresponding figures for Skeletonema were 0.03-0.06 and 0.03-0.08, and for Nitzschia 0.13-1.08 and 0.11-0.87. The ratio of c to a varied from 1.30 to 1.84 for Gymnodinium, 0.69 to 1 .61 for Skeletonema, and 0.44 to 2.21 for Nitzschia. These ratios are all less than the maximum (3.3) found for natural populations of phytoplankton from the Coral and Tasman Seas. There was no evidence in the culture experiments that chlorophyll c breaks down more slowly than a and thus accumulates in old populations.