Effects of temperature, light and salinity on cyst production and morphology of Tuberculodinium vancampoae (the resting cyst of Pyrophacus steinii)

Cyst forming dinoflagellates are useful in reconstructing past environments. For accuracy it is essential to know how environmental parameters such as salinity, temperature and light influence dinoflagellate cyst production and morphology. Here the effect of variation in these parameters on production and morphology of Tuberculodinium vancampoae (the resting stage of Pyrophacus steinii) is detailed. Encystment of T. vancampoae has been observed in all studied culture-experiments although only a few cysts are being formed at the limits of the temperature and salinity ranges (16.5°C, 34.8 °C and 20, 45 psu) with highest cyst production at 27 °C and 35 psu. Temperature clearly affects cyst morphology; cysts formed in cultures grown at 16.5 °C and 34.8 °C possess small, flattened processes. These cysts are not completely absent in cultures grown at intermediate temperatures but form only a minor part of the association. In previous studies, salinity has been found to influence the cyst morphology of several dinoflagellate species but this seems not to be the case for T. vancampoae. In this study there was no morphological variation related to salinity. High cyst production was observed in cultures grown under moderate to strong illumination but variation in illumination did not lead to morphological change. Our findings correspond to field observations where T. vancampoae has been observed in surface sediments of the sub-tropical to tropical regions characterised by mean sea surface temperatures between 12.7 °C and 29.5 °C, and sea surface salinities between 16.9 and 36.6 psu. In contrast to previous suggestions, T. vancampoae appears to be heterothallic rather than homothallic.