Adaptive abilities of the microscopic red alga Porphyridium purpureum (strain PP-AB11, isolated from the northwestern Japan Sea) are investigated experimentally by its repeated cultivation under various water salinity. Under the salinity of 8 ‰, the growth of P. purpureum was inhibited (0.1 division/day) during the first four days though there were no morphological differences of the cells as compared with those in the control (mean cell size was 6.3±1.2 µm in both cases); the cell density increased to 85 % of the control value after 21 days exposure. Under the salinity of 4 ‰, the lag-phase was also 4 days but size of the cells increased (on average up to 7.8 ± 1.5 µm), the cell morphology changed including the cytoplasm retraction, and contraction and granulation of the chloroplasts; the cell density increased less (to 53 % of the control value) after 21 days exposure. Under the salinity of 2 ‰, changes of the cell morphology and density were the most prominent: density of viable cells decreased to 6 % of the control value after 4-days exposure, size of the cells increased on average up to 8.7 ± 1.6 µm due to hydration, granulation was noticed in the chloroplasts, and the cytoplasm became dense. Under the salinity of 0 ‰, all the cells died after 4 days. Being cultivated repeatedly, the alga was better adapted to low salinity: after 21-days exposure the cell density was 97 % of the control value under salinity of 8 ‰ and 84 % of the control value under salinity of 4 ‰, with the growth rate 0.5 divisions/day and without visible morphological differences of the cells as compared with those in the control. It was adapted even to salinity of 2 ‰: the cells morphology was restored though the growth rate after 21-days exposition was still lower than in the control because of serious deterioration of the cells. The growth rate and cell morphology did not significantly differ from the control after reinoculation of the culture, previously adapted to salinity of 2 ‰, into the medium with salinity of 32 ‰.

Combined effect of cadmium (10, 30, and 50 mg/L) and salinity (32, 24, and 16 ‰) on marine unicellular alga Plagioselmis prolonga (Cryptophyta) is investigated. Such parameters as the cells number dynamics, their size, side scattering (as a characteristic of internal structure of cells), photosynthetic pigments fluorescence (chlorophyll a, phycoerythrin, allophycocyanin, as a measure of the photosynthetic apparatus function), and reactive oxygen species (ROS) content (as an index of the cellular membranes destruction) were registered in experiments using the flow cytometer CytoFLEX (Beckman Coulter). Addition of cadmium in concentration of 10 mg/L to the water with salinity 32 ‰ did not influence on alga growth and its physiological parameters. The higher concentrations of cadmium, as 30 and 50 mg/L, stimulated the cells growth and ROS increased under the concentration of 50 mg/L, but other parameters did not altered. The same contamination with cadmium under salinity 24 ‰ caused the cells size rising and their intensive growth, ROS increasing on 3rd day and decreasing on 7th day of exposition, and phycoerythrin and allophycocyanin fluorescence diminishing, but the side scattering and chlorophyll a fluorescence still did not differ from the control. Any concentration of cadmium in the water with salinity 16 ‰ caused the population growth inhibition, decreasing of side scattering and all photosynthetic pigments fluorescence, and increasing of ROS and cells size. There is concluded that cadmium contamination in conditions of normal (32 ‰) salinity has a stimulation effect on Plagioselmis prolonga growth and no effect on its photosynthetic apparatus, but the same contamination in conditions of lowered salinity has a negative effect on both its growth and photosynthetic functions, whereas the reactive oxygen species content increases and the cells become larger under the cadmium contamination regardless the salinity factor.