Growth and photosynthetic activity of diatom Thalassiosira weissflogii at decreasing salinity

The relative yield of variable chlorophyll fluorescence (Fv/Fm), rate of photosynthetic carbon fixation (P), growth rate, and production of extracellular photosynthates (Pec) was studied in diatom T. weissflogii in seawater with salinity decreasing from 35 to 15 and 5 per thousand. After incubation at 5 per thousand for 1 day, the diatom abundance (N) decreased as a result of death of a fraction of cells, while viable cells demonstrated decreased Fv/Fm and P, Pec was detectable, and cell division was likely inhibited. After incubation for 2 days, population started to grow, while exponential growth rate and the abundance by day 8 were lower compared to 35 per thousand. After incubation at 15 per thousand for 1 day, P was higher and Fv/Fm was lower compared to 35 per thousand. No cell death was observed and exponential growth rate insignificantly differed from that at 5 per thousand. The value of N by day 8 was lower compared to 35 per thousand but higher compared to 5 per thousand. The dependence of photosynthetic parameters and population dynamics of T. weissflogii on the relative salinity is discussed.