Din flagellates are primarily unicellular aquatic organisms that typically occur as biflagellate motile cells. At ascertain stage of their life cycle, several marine din flagellates produce non-motile cells surrounded by calcareous wall. Calcareous din flagellates constitute an important group of the marine calcareous phytoplankton and their cysts are subject to an increasing number of palaeoenvironmental studies. However, fundamental biological and ecological characteristics of these organisms are yet unknown.Neritic and oceanic habitats are characterised by different species. Neurotic species produce calcareous resting cysts, within the sexual reproduction cycle. In cultures, the motile stage is the dominant phase and resting cystproduction occurs only when the conditions for vegetative growth are unfavourable. By contrast, in the most abundant oceanic species (Thoracosphaera hemi) the calcareous stage is dominant and is formed during the vegetative cycle. Apart from T. hemi, approximately 10 other extant oceanic species exist. There are strong indications that these species also calcify in their vegetative stage, as they show a constant production of calcareous non-motile cells that make up more than 50 % of all specimens within a culture under normalconditions.DINO-CULT will test the hypothesis of a shift in the life cycle of oceanic calcareous din flagellates, through which the calcareous stage became dominant. Policy investigations on motile and non-motile stages of cultures will reveal when in the life cycle calcareous tests are produced. The effect of environmental parameters (e.g. light, temperature, nutrients) on cyst production will be investigated in experiments under controlled laboratory conditions and the results will be applied in a palaeoenvironmental case study on the S1 saprobe of the Mediterranean Sea.
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