Can Marine Mammals Suffer From Decompression Sickness?
Marine mammals are able to suffer from decompression sickness, which is a condition that occurs when sudden decompression causes nitrogen bubbles to form in the blood and tissues of the body. The lifestyles of marine mammals makes them susceptible to this condition, however, they have adapted to overcome this obstacle. Many marine mammals are capable of storing gas in their trachea during dives. The trachea is reinforced by cartilage, which supports its structure during dives where the lungs collapse under pressure. This prevents the gas from being forced into the bloodstream, also preventing nitrogen from entering the blood. Increased myoglobin concentrations, increased blood volume, and decreased lung size relative to body size are also adaptations seen in diving mammals (Hooker et al., 2011). Lung collapse, which occurs with increasing pressure and depth during a dive, limits the absorption of nitrogen and decreases the probability of decompression sickness in these organisms. The lack of gas exchange during a dive reduces the amount of nitrogen the blood absorbs (McDonald and Ponganis, 2012). Surfactants are also produced in the lungs to keep them from adhering together and allows the organism to refill its lungs at the surface (Miller et al., 2004).
Decompression sickness is unusual in diving mammals, but may occur under specific circumstances, including an uncharacteristically rapid ascent to the surface. Rapid ascents such as these may be the result of predation, stress, or even due to sonar signals from sources such as military operations. Marine mammals such as beaked whales have been found stranded on coasts with gas bubble associated lesions on vessels and in vital organs. This is thought to be the result of intense sound that may destabilize the gas nuclei, leading to nitrogen bubble growth in tissues that have been supersaturated during a dive (Jepson et al., 2003). Decompression sickness due to sonar from naval and military operations seems to arise from repetitive shallow dives instead of long, deep dives, facilitating higher tissue supersaturation levels (Tyack et al., 2006).
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