It has effect on the marine life, especially in the anufacture of food.
Yes. It does.
There are different kinds of process that deeply affects the salinity of ocean water. Continental deflections, Coriolis Effect, convection current and also evaporation.
A river flowing into the sea is causing the decrease in salinity
Biomass and temperature, erosion and mineral content.
Arctic ocean
You could increase the salinity of the ocean by adding salt or removing water (ie: by evaporation).
Storms at sea. The evaporated water falls back into the ocean with no net effect on salinity.
salinity
In open ocean evaporation affects the salinity of the oceans, in closed oceans the lack of sunrays cause greater salinity levels.
salinity
The lowest areas of salinity in an ocean are near where fresh water rivers empty into them. This is because the influx of fresh water creates an area of lower salinity compared to the remainder of the ocean.
An increase in ocean salinity can increase density creating a convection current.