CHLOROPHYLL CONTENTS AND PHOTOSYNTHETIC RATES OF THE FRESH-WATER MIXOTROPHIC CILIATE STROMBIDIUM-VIRIDE (CILIOPHORA, OLIGOTRICHIDA)

The photosynthetic rates and chlorophyll-a contents of Strombidium vir ide, a chloroplast-retaining mixotrophic ciliate, are reported for ind ividuals collected from Lake Carter, a small productive pond located i n northwest England. This species fixed C-14 (added as bicarbonate) at rates between 18 and 54 pgC cell-1 h-1, according to the light intens ity used in each incubation. The mean chlorophyll-a content of S. viri de was estimated to be 160 pg. The mean cell volume of S. viride indiv iduals was 57.5 mum3. Measurements of the C-14-uptake rates of whole w ater samples suggested that the contribution of this species to commun ity primary production in Lake Carter was 0.5 % at the time of samplin g. The possible advantages and disadvantages of chloroplast-retention to freshwater ciliates are discussed. It is suggested that the augment ing of phagotrophy with photosynthesis becomes a requirement for many strombidiids living in low nutrient environments in order to meet the high metabolic cost associated with maintaining high swimming speeds.