Under pressure

This chapter questions how marine mammals cope with the huge pressures they face at depth. For some species, these can be pressures of over 200 atm at 2000 m depths. It examines the gas laws relating to pressure and particularly the inverse relationship between pressure and volume. Marine mammals have adaptations to help counter the decreasing volume of air spaces as they dive, such as expanding veins to fill empty space in the middle ear and a compressible ribcage to more easily allow the lungs to collapse. The uptake of pressurized gas can cause further problems, particularly with the depressurization of these gases during the ascent and return to the surface. Experimental physiological research to examine this is difficult, particularly for species which never come ashore, and we still do not fully understand how marine mammals cope with repeated exposure to high pressure. Microelectronic time-depth recorders have allowed great insights into diving behavior, and advances in wearable medical technology are poised to greatly improve our understanding of lung structure, blood flow and blood gas dynamics during diving.