Salt, Water, and pH Balance in the Sea Turtle
Sea turtles live in a medium that is almost three times more concentrated than their body fluids, some ions having even greater plasma/sea water gradients. Like most marine vertebrates, therefore, sea turtles must continuously combat the problems of water loss and salt gain. While respiration can be a major source of water loss for terrestrial air-breathing vertebrates, this route is probably minimal for sea turtles since the relative humidity of the ocean surface air that they inspire will be about 100% and the expiratory gas will have a similar water content. Ingestion is probably the major source for salt loading. The diet of marine turtles consists mainly of marine invertebrates or, in the case of C. mydas, various marine grasses and algae. With the apparent exception of the marine mammals, the kidneys of marine vertebrates are insufficient to handle their salt influx and all have extrarenal mechanisms for excreting salt.