Role of chloroplast retention in a marine dinoflagellate

Abstract

The dinoflagellate Gymnodinium 'gracilentum' feeds on the cryptophyte Rhodomonas salina and retains the chloroplasts of the prey as functional kleptochloroplasts. Using kleptochloropldsts, G. 'gracilentum' becomes a mixotroph, acquiring a proportion of its organic carbon demand through photosynthesis, but the kleptochloroplasts and their photosynthetic activity are lost within a few days. Photosynthesis seems, primarily, to be an important means of nutrition for G. 'gracilentum' during food depletion, thereby enhancing the survival of the species during food limitation and starvation. However, light has a positive effect on growth kinetics of G. 'gracilentum' in food replete cultures: growth and ingestion rates are higher at a high light intensity than at a low light intensity. This effect may be due to other factors than photosynthetic activity of kleptochloroplasts, since a control experiment with a supposed strictly heterotrophic dinoflagellate, Gymnodinium sp., also showed a dependence of growth kinetics on light intensity.