The Effect of Water Chemistry on Shore Organisms
One of the most striking things about the sea itself is the lack of variation in its properties over the globe. Isolated, or partially isolated bodies, such as The Baltic (and here) and The Mediterranean, do differ, but in the open ocean and on shores exposed to the open ocean, there is not much difference. Even temperatures vary much less than on land.
It is in rock pools that variations in water chemistry can become important on the shore. This can be reflected in major differences in salinity and pH, as well as O2 levels.