Effects of salinity changes on coastal antarctic phytoplankton physiology and assemblage composition

HERNANDO M; SCHLOSS I; MALANGA G; ALMANDOZ GO; FERREYRA G; AGUIAR MB; PUNTARULO S

JOURNAL OF EXPERIMENTAL MARINE BIOLOGY AND ECOLOGY

ELSEVIER SCIENCE BV

Lugar: Amsterdam; Año: 2015 vol. 466 p. 110 - 119

0022-0981

In January 2011, at Potter Cove, Antarctica, the marine plankton community was experimentally exposed to low salinity sea water (30) during 8 days in order to study the adaptation of cells to this changing salinity conditions and the effect of hypoosmotic stress on phytoplankton. Hypoosmotic conditions favour water influx into the cells, which results in increased turgor pressure and increased oxidative stress. This stress is linked to a number of other cellular toxic processes, including damages to proteins, enzyme inactivation and DNA breakage. Inhibition of the instantaneous growth rate started after 48 h exposure to low salinity, but at the end of experiment, growth was significantly higher in the low than in the normal (control) salinity treatment. Hypoosmotic conditions prevented phytoplankton accumulation, as evidenced in reduced Chlorophyll-a concentrations as compared to the control treatment. However, in terms of cell numbers and species composition, we observed a gradual replacement of big centric by small, pennate diatoms, which became dominant by the end of the experiment. In addition, the content of reactive oxygen species (ROS) and 2-thiobarbituric acid-reactive substances (TBARS), which are indicative of oxidative stress were studied. In the low salinity treatments, ROS concentrations were significantly higher than control values on days 4 and 6, decreasing thereafter to close to initial values. TBARS content increased during the first 48 h and then decreased until around day 0 values. This coincided with a significant increased over control values of the antioxidants α-tocopherol and β-carotene in low salinity treatments. These results suggest the existence of protection mechanisms against lipid peroxidation, and lead to the conclusion that the response to stress is species-specific, so that at the community level a change in the relative abundance of phytoplankton taxa appears as a response to hypoosmotic conditions. Big centric diatoms were more sensitive to changing osmotic condition than small pennate diatoms, which tended to dominate the plankton at the end of the experiment. This could have important consequences on the trophic web in areas influenced by fresh water input