ABSTRACT
Hydrostatic pressure affects all organisms as barometric pressure in air and hydrostatic pressure in water. It is normally close to 1 atmosphere (atm) on land with a reduction for height e.g. around 50 kPa at a height of 5800m. As hydrostatic pressure in water, it is the natural proxy for depth and in simple terms changes by around 100 kPa or 1 atm for every 10m of descent down through the water. The marine environment has a considerable vertical component with average depths roughly 4000 m and maximum depths down to over 10000 m in the ocean trenches. Shallow seas and inshore areas have much smaller depth ranges down to several hundred meters. Diving animals have long been observed descending hundreds and even thousands of meters. Furthermore many animals are known to feed at the depths implying that animals are routinely using this sort of range.
