In areas closer to the shoreline, this figure will vary because of evaporation and dilution. There is evidence that the salinity of the oceans has changed little since their formation. Through the process of evaporation and freshwater input, the salinity balance stays the same. In addition, much salt returns to land through salt spray or through the salt crystals that form nuclei for raindrops. It then finds its way back to the oceans.
Salinity is vital for animals that live in the ocean.
Most marine organisms in the open ocean have body fluids whose salinity closely approximates that of the water around them. However, problems arise for marine organisms who live in the coastal environment. In the intertidal zones and estuaries, wide fluctuations demand mechanisms that will increase water uptake or remove salt. Some animals protect their internal salinity with shells or scales. Perhaps this adaptation has permitted it to thrive in these stressful habitats.