General Features of Dinoflagellate Material Collected by the “Anton Bruun” during the International Indian Ocean Expedition
Dinoflagellates are a nutritionally diverse group and cannot be totally included with the diatoms, coccolithophorids and blue-green algae as primary producers. Many are photosynthetic autotrophs, although typically these have strong requirements for organic micro-nutrients such as vitamin B12 (auxotrophs), a characteristic they share with many planktonic diatoms. Secondly, some of the autotrophs are also capable of ingesting other cells (Biecheler, 1936), presumably as a supplement to their photosynthetic nutrition (myxotrophs). This phenomenon appears to be relatively rare although the large ventral opening in the thecae of the marine ceratia may be an adaptation for this phenomenon (Norris, 1969) in addition to rarely observed sexual conjugation (Von Stosch, 1964). Whether or not this phenomenon is ecologically significant on a large scale has not been accurately evaluated. Thirdly, a large number of dinoflagellates lack any photosynthetic ability and it is assumed that these are phagotrophic grazers. Although the largest of these colourless dinoflagellates may regularly be observed to contain ingested cells (e.g. Noctiluca scintillans), many of the dinoflagellates below 40 or 50 μ in size, such as many neritic species of Peridinium, cannot be seen to contain ingested cells. Two large, specialized vacuoles termed “pusules” are usually present in these smaller non-pigmented forms (and also in some pigmented species), typically one being much larger than the other and sometimes occupying a great part of the epicone. The content of these pusules is a fluid which is sometimes distinctly pinkish or violet in colour. The function of the pusules is unknown at present but it is tempting to assign a nutritional role to them.
KeywordsIndian Ocean North Equatorial Current South Equatorial Current Dorsal Process Agulhas Current
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