An overview of hybrid marine and lacustrine seas and saline lakes of the world

Water salinity is one of the major environmental factors influencing hydrobionts. Based on the concept of relativity and plurality of barrier salinity zones, barrier salinities are related to the development of the osmoregulatory capacities of hydrobionts and to the chemical composition of the water they inhabit. These zones are not of equal importance. The entire hydrosphere might be divided into freshwater, brackish water, marine and hyperhaline salinity zones and transitional zones between them. Approximate boundaries and corresponding barrier salinities are defined for all these zones. Revealing barrier salinity zones requires studying the osmoregulatory capacities of hydrobionts and the distribution of their salinity boundaries. We distinguish between four barrier salinities or horohalinicums for marine and continental waters: α (5–8‰), β (22–26‰), γ (45–50‰) and ™ (0.5–2‰). In metamorphized continental waters, barrier salinities are shifted to higher concentrations. Salinity barrier values can change the subsequent evolution of salinity adaptations and osmoregulation capacities. Maracaibo Lake is characterized by freshwater and freshwater–brackish water zones. Deepening of the lake shipping lane increased the salt flux, with the appearance of a brackish‐water zone. This study proposes to distinguish hybrid lentic waterbodies that include the Baltic Sea, Black Sea, Sea of Azov and Maracaibo Lake, which have lost their lacustrine characteristics and are now characterized by intermixing marine (saline) and continental (fresh) waters.