Growth and photosynthetic activity of diatom Thalassiosira weissflogii at decreasing salinity

The relative yield of variable chlorophyll fluorescence (F (v)/F (m)), rate of photosynthetic carbon fixation (P), growth rate, and production of extracellular photosynthates (P (ec)) was studied in diatom T. weissflogii in seawater with salinity decreasing from 35 to 15 and 5 parts per thousand. After incubation at 5 parts 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 F (v)/F (m) and P, P (ec) 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 parts per thousand. After incubation at 15 parts per thousand for 1 day, P was higher and F (v)/F (m) was lower compared to 35 parts per thousand. No cell death was observed and exponential growth rate insignificantly differed from that at 5 parts per thousand. The value of N by day 8 was lower compared to 35 parts per thousand but higher compared to 5 parts per thousand. The dependence of photosynthetic parameters and population dynamics of T. weissflogii on the relative salinity is discussed.