Ecosystems of hypersaline waters: Structure and trophic relations

N. V. Shadrin^a,# and E. V. Anufriieva^a

^aKovalevsky Institute of Marine Biological Research RAS, 299011 Sevastopol, 2 Nakhimov ave
^#e-mail: snickolai@yandex.ru

Hypersaline waters, with salinity exceeding 35 g/L, are widely distributed on the planet (hypersaline lakes and lagoons, deep-water “lakes”, pore waters of sea ice) and are among the most extreme habitats on Earth. The results of own long-term studies on the hypersaline lake and lagoon ecosystems in the Crimea together with literature data are generalized and analyzed. The analysis showed that these extreme ecosystems are unique according both for the physical and chemical parameters and processes, as well as for the structure and functioning of the biota. In particular, salinity affects the freezing and boiling points of water. As a result, the temperature range in hypersaline waters, in which water remains liquid and life can exist, is wider than in fresh and sea waters; at a salinity of 350 g/L − from minus 35^oС to plus 109^oС. The species diversity of eukaryotic organisms decreases sharply with a salinity increase, while the prokaryotic variety increases somewhat. In freshwater and marine ecosystems, oxygenic photosynthesis is mainly ensures the supply of energy into the ecosystems and, in hypersaline waters, energy input is provided by three phototrophic mechanisms and diversity of chemosynthetic mechanisms. For example, anoxygenic photosynthesis may provide more than 50% of energy (up to 85%) entering into an ecosystem, and its share in the total primary production increases as the salinity increases higher than 100 – 160 g/L. Many hypersaline water bodies, despite the extreme nature of the environment, are highly productive. This paradox can be explained by two points: high concentrations of nutrients in hypersaline waters, and high small-scale spatio-temporal variability of abiotic factors which allows the oppositely directed processes interact to close nutrient cycles within one community. One of the mechanisms of osmoadaptation of primary producers to high salinity and its sharp fluctuations is their release of exo-polysaccharides into the environment, which increases as the salinity increases and may amount to 50–70% of the primary production. This leads to an increase in the role of heterotrophic osmotrophs in food webs. The existing features of ecosystems in hypersaline waters allow considering these ecosystems to be unique; further study of them can expand our understanding of the organization of life in an extreme environment.