A laboratory simulation of diel changes affecting cellular composition of the dinoflagellate Ceratium hirundinella

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Abstract
SUMMARY. Changes of cellular composition of a planktonic dinoflageilate, Ceratium hirundinella, were studied over 2–1–48‐h periods in the laboratory on three separate occasions. Samples from a lake population in the stationary phase of the population cycle were incubated at lake temperature under continuous illumination and in a light‐dark (LD) regime of LD 14:10.The magnitudes of diel variability in ratios of carbohydrate:chlorophyll‐a, carbohydrate:carbon. carbon:nitrogen and carotenoids:chlorophyll‐a for samples incubated at LD 14:10, were similar to those observed in situ at a similar phase of the population growth cycle. The ratios involving carbohydrate showed the most diel variation, which was not reduced under continuous illumination.By appearance ‘dark’ and ‘pale’ cells of Ceratium were distinguished in the fixed samples; a persistent periodicity for the interconversion of dark and pale cells is described. The periodicity and amplitude of inter‐conversions were not always in phase with those of chlorophyll‐a synthesis and decomposition. The observed changes were almost certainly independent of the light‐dark cycle: they were apparently induced by nutrient deficiency.