Hydrostatic pressure is the most generally applicable factor with a constant increase of 10 atm per 100 m depth. Beginning with a depth of ca. 6000 m a change in faunal composition can be observed that is possibly related to pressure.
The deepest creatures
Decapod crustaceans, anemones and sea urchins (echinoids) decrease and sea cucumbers (Holothuroidea) and Polchaetes increase in relative abundance. The maximum depth at which fishes have been discovered so far is 8370 m (Abyssobrotula galatheae, Ophidiidae – cuskeels).
Fish in the deep
The influence of pressure on the biology of deep-sea animals is less marked than was assumed earlier. Recent experiments have shown that even trout and goldfish survive a pressure of more than 200 atm (approx. 2000m). Some changes in behaviour, central nervous system and metabolism were observed however, that appeared to be reversible after decompression. Only pressure of more than 500 atm (approx 5000m) proved to be lethal for surface-living fishes.
Interestingly, the littoral bivalve Mytilus edulis survives even a pressure of more than 800 atm (approx 8000m)!
Salinity and low temperatures increase pressure tolerance. The muscles of deep-sea fishes have low protein and lipid content that possibly further improve their resistance to pressure.
Read more about the physical challenges of the deep-sea
By Franz Uiblein, a MAR-ECO scientist