8th International Nannoplankton Association Conference


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Dorothea Janofske:
Calcification in dinoflagellates as survival strategy in the open ocean

Dinoflagellates capable of producing calcareous cysts are a group of marine phototrophic algae. The life-cycle with vegetative reproduction and the production of calcareous cysts takes place in the photic zone of the oceans. In neritic taxa, the motile stage, with two different flagellae, is the dominant stage during the life-cycle; the non-motile calcareous cyst is a resting stage produced during the sexual reproduction phase (S. trochoidea, C. operosum). In oceanic taxa, the production of cysts is not related to a sexual reproduction phase; the calcareous cysts may form 50% or more of the living specimens of a culture (C. albatrosianum) or are even the dominant stage during the life-cycle (P. tuberosa, L. granifera, T. heimii).

In field studies, calcareous dinoflagellates were found to inhabit the mixed layer at the top of the water-column. They can be regarded as a mixing, less migrating organism group sensu Cullen & MacIntyre (1998), since maximum amounts of living specimens are found from surface-waters to 175m water-depth. The morphological features of the calcareous skeleton, such as size, shape, porosity and rigidity, as well as the ultrastructure of the cell contribute to buoyancy strategies which are used by the coccolithophorids and diatoms in this environment as well. The control of crystal growth, with specific crystallographic orientation of the calcite crystals, is discussed to be of benefit with the highly variable light conditions.

Fossil calcareous dinocysts with such 'oceanic' morphological features are known from the K/T boundary to Recent strata. The Cenozoic evolution of the calcareous dinoflagellates is discussed with regard to the adaptation to open-ocean conditions.


Cullen, J.J. & MacIntyre, J.G. 1998. Behaviour, physiology and the niche of depth-regulating phytoplankton. NATO ASI, Ser. G, 41: 559-579.


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