Some ocean effects on invertebrates and vertebrates

The exact mechanisms of how the marine environment acts on the invertebrates are more or less known, in that the salinity of the oceans being so similar to that of the body fluids of these invertebrates acts to allow the invertebrates to maintain the proper concentration of the salts in their body fluids "easier" than in the freshwater and/or terrestrial environments. In fresh water, where the body fluids of the invertebrates are considerably "saltier" than the surrounding water, there must be a constant expenditure of energy in the elimination of the excess water that tends to move out of the body (remember osmosis moving from solutions of greater water concentration, or lesser saltier concentrations). This is probably done in general via the kidneys or other excretory organs.
Marine invertebrates are said to be poikilosmotic (a fancy name for that condition where the salinity of a body fluid changes in direct accord with the salinity of the external medium). This occurs "automatically," but only within some narrow limits, so that there must be some kind of a regulatory mechanism that allows for these changes with changes in the environment. However, the ranges in salinity in most parts of the oceans are probably within the limits of tolerance of the invertebrates living there. In being the same "saltiness" as the surrounding sea water, these invertebrates are said to be isotonic (in equal balance); on the other hand, invertebrates living in fresh water are considerably saltier than the surrounding fresh water, and thus said to be hypotonic to the water environment. It is most likely that the same kind of regulatory mechanisms that "control" the response to the ocean waters are effective in fresh water environments as well, only these would have to "be more effective."

What about the situation with vertebrates?
Cartilaginous fishes (sharks,skates, and rays) are said to be "isotonic" with sea water by having a high concentration of uric acid in their blood (perhaps this is what gives shark meat the aroma which used to keep shark meat from being enjoyed for food for a long time), as well as the excretion of dilute urine.
Bony fishes (what most of us call fish) that live in the oceans have the problem of being less salty or hypotonic than their sea environment. Thus, water tends to diffuse out of the body into the surrounding environment. To counteract this osmotic tendency, the fish constantly "pumps salt out of the body" via chloride-secreting glands located at the gills; these fish take in sea water but produces very little urine.
Fish that live in the fresh waters have the reverse problem in that they are hypertonic to their environment; they balance this hypertonicity by the secretion of dilute urine.
In the case of marine reptiles and turtles, since their body fluids are less concentrated than sea water, they have evolved the capacity of being able to drink sea water, while getting rid of the excess salts through special salt glands. In turtles, these salt glands, located near the eyes, produces the turtle's or the crocodile's legendary"salty tears.