Inter-Research
Marine Ecology Progress Series

ABSTRACT: Photosynthesis was measured for the mixotrophic dinoflagellate Fragilidium subglobosum grown with and without prey (Ceratium lineatum), at 5 different irradiances. Photosynthetic rates were measured in phototrophically and mixotrophically grown cultures by use of the single-cell ¹⁴C uptake technique. Photosynthetic rates were reduced by 48 to 69% and cellular chlorophyll a (chl a) content was reduced by 13 to 67% in food-replete mixotrophic cultures as compared with strictly phototrophic cultures grown at the same irradiances. Under the same conditions, chl a-normalized photosynthetic rates were thus 7 to 49% lower in mixotrophic cultures than in strictly phototrophic cultures. It is, therefore, suggested that either the photosynthetic apparatus becomes less efficient when the cells are phagotrophically active or the chl a-normalized photosynthesis is reduced because fed cells contain photosynthetically inactive chl a in their food vacuoles. When food is abundant, the greater part of the gross carbon uptake of F. subglobosum is acquired through phagotrophy even at irradiances saturating for photosynthesis.

KEY WORDS: Mixotrophy · Dinoflagellate · Photosynthesis · Single-cell ¹⁴C technique · Chlorophyll a · Ingestion · C content · N content · C budget

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Published in MEPS Vol. 201 (2000) on August 9
Print ISSN: 0171-8630; Online ISSN: 1616-1599. Copyright © Inter-Research, Oldendorf/Luhe, 2000