Eco-fingerprinting of the dinoflagellate Borghiella dodgei: experimental evidence of a specific environmental niche

In Lake Tovel, an oligotrophic and weakly stratified lake, the dinoflagellate Borghiella dodgei Moestrup, Hansen et Daugbjerg, showed a peculiar spatial-temporal pattern with highest abundances in the bottom of the shallow side bay (4 m) along with remarkable abundance variations from year to year. We investigated B. dodgei's growth in laboratory cultures and related results to their implication for bloom formation. B. dodgei was cultivated under different temperature, nutrient and light conditions. Growth rates, cell biovolume, cyst formation and pigment and mycosporine-like amino acids (MAAs) concentrations were determined. Experiments showed that this alga (i) had higher growth rates at low temperatures (< 7A degrees C) and high irradiance levels (similar to 250 mu mol m(-2) s(-1)), (ii) produced higher yields with organic supplements such as peptone, (iii) did not grow in the dark even with organic supplements, (iv) survived for long periods without a light source, (v) synthesised MAAs, (vi) showed an increase in cell volume with nutrient shortage and increasing temperatures (> 7A degrees C) and (vii) had high encystment rates with temperatures > 7A degrees C. These laboratory fingerprints allowed us to construct a theoretical model defining the species' niche. Borghiella needed a mixture of low temperatures, high irradiance levels and sufficient quantities of dissolved organic nitrogen to form blooms. Such a strict combination was probably a transient situation and occurred in oligotrophic Lake Tovel only in early summers followed by heavy spring rains.