Aquatic mammals, such as seals and dolphins, are able to stay submerged in water for long periods of time because of the mammalian diving reflex. when submerged in cold water, and while the mammal is holding its breath, receptors in the nasal cavity and other areas of the face relay a message to the brain that causes blood to only circulate between the heart and the brain. this allows oxygen to be conserved and increases the time aquatic mammals can stay underwater between breaths.