Feeding mechanism, prey specificity and growth in light and dark of the plastidic dinoflagellate Karlodinium armiger

The food uptake mechanism and prey specificity of the most recently described member of the ichthyotoxic photosynthetic dinoflagellate genus Karlodinium (K. armiger) was studied. K. armiger extracts the contents of prey through an inconspicuous feeding tube (peduncle), but may also ingest whole prey cells. This species is omnivorous, ingesting prey from all major groups of marine protists. K armiger displays a searching pre-capture behavior with attraction to prey cells and formation of feeding aggregates. In batch cultures, growth rates in the light without food were low (0.01 to 0.10 d(-1)), but when the culture medium was enriched with soil extract, initial growth rate increased (0.19 d(-1)); it further increased (0.60 d(-1)) when fed the cryptophyte Rhodomonas marina in the light (170 mu mol photons m(2) s(-1)). R. marina was also ingested in the dark, but did not support positive growth rates and survival. Thus, K armiger is an omnivorous obligate phototrophic mixotroph which seems to obtain a growth-essential substance or growth factor through phagotrophy.