Salinity is a measure of the quantity of dissolved salts in water. Salinity is measured in terms of the electrical conductivity of a salt solution.
To some extent, ocean salinity is influenced by the geologic formations underlying the sea. Salinity is lower in areas underlain by igneous formations and higher in areas underlain by sedimentary formations.
Higher salinity is more likely in arid regions where evaporation rates are high. Evaporation leaves the same amount of salt in less water, which increases the salinity.
But does extreme high level of salt in seawater kill animals like fishes, birds ? Answer is yes,
Many marine organisms are highly affected by changes in salinity. This is because of a process called osmosis which is the ability of water to move in and out of living cells, in response to a concentration of a dissolved material, until an equilibrium is reached. In general the dissolved material does not easily cross the cell membrane so the water flows by osmosis to form an equilibrium. Marine organisms respond to this as either being osmotic conformers (also called poikilosmotic) or osmotic regulators (or homeosmotic).
Marine fishes usually survive in an environment that is more concentrated in salt than them. Without any regulation the high salt concentration of the ocean would draw all the water out of them. To prevent dehydration, marine osmoregulators drink salt water and actively transport salts to the environment with chloride cells on its gills. Salts are also excreted in the urine.
