Marine mammals can go without breathing for as long as thirty minutes while diving. On the other hand, human divers can dive to a maximum of 60 meters while holding their breath for about a minute. Marine mammals have special adaptations which enable them to hold breath for such long periods without damaging vital organs. First, when marine mammals are on the surface of the water they breathe very quickly and then hold their breath for a long duration. The muscles of many marine mammals can go for a long time with minimal or limited oxygen without cramping.
Marine mammals save oxygen by containing blood flow to unnecessary organs. Thus blood goes mainly to the most important organ like the heart and brain. In addition, mammals slow down their heartbeat while diving resulting in lower consumption of oxygen. Some marine mammals can slow down their heart beat rates to almost three beats per minute. With a normal heart beat rate of 100-150 beats per minute, marine mammals may drop this to about 10 beats per minute while diving. These special adaptations are referred to as the marine mammal diving reflex. Scientists are still studying these special adaptations leading to this diving reflex.
Some sea creatures have the ability to go to great depths of water. Of particular interest to note include the bottlenose and the sperm whale. These two marine mammals are known to be exceptional divers, and can last up to two hours under water. They normally reach depths of 1,500- to 3,000-feet; however they have the ability of diving as deep as 6,000 feet. This may have adverse physiological effects resulting in compression of tissues which is mostly evident in spaces in the body that are filled with gases including; the middle ear cavity, air sinuses in the head, and the lungs (Woakes, 1991). Pressure differences, however minimal, that are noticed in the gas-filled hollow and the surrounding tissue may end up causing damage and interference in the tissue. This may result in a condition commonly referred to as the squeeze by human divers (Woakes, 1991).
To prevent this, their middle ear cavity is lined with an extensive venous plexus, which becomes inflamed at great depth thus reducing the air space. In addition, they also have large Eustachian tubes connected to the tympanic cavity of the ear and the large pterygoid sinuses of the head (Stephens, 2007). The air cavities in the cranium contain a large vasculature, which moderates air pressure within these spaces. Furthermore many nautical mammals lack a frontal brain cavity as compared to ordinary mammals.
Deep-diving whales and seals have their non essential airways reinforced enabling the lungs to contract during descent. This pushes oxygen further away from the alveoli, where gas exchange between the lungs and blood occurs (Science Direct, 1991). The collapse of the lungs is important as first the intake of nitrogen is prevented into the blood and this avoids the rise of high levels of nitrogen in the blood. Secondly, it prevents nitrogen bubble formation during ascent which results in decompression sickness. In humans and other land animals air gets trapped in the alveoli as the lungs are compressed, forcing nitrogen into the bloodstream (Stephens, 2007). This may be noted in nitrogen narcosis or the bends, which is a distressing and potentially fatal condition that results from deep seas divers who ascend too fast from lower sea levels.
With the collapse of the lungs, seals and deep-diving whales depend on large quantities of oxygen that are reserved in the muscles and in the blood vessels. This is facilitated by several adaptations. To begin with, these marine mammals have larger quantities of blood that are three or four times in mass as compared to quantities in ordinary mammals. Secondly, the concentration of hemoglobin in their blood is twice that of ordinary mammals. Third, the concentration of myoglobin, the oxygen storage protein in muscle, is very high, with recordings that are almost ten times as those found in the muscles of human beings (Hochachka, 1993).
According to research conducted by scientists at the University of California, Santa Cruz, marine mammals have oxygen-carrying proteins, known as globins, in their brains that aid their diving (Woakes, Grieshaber, & Bridges, 1991). This conclusion was arrived at after the team measured and compared the amount of globins in the cerebral cortex of sixteen differing mammalian species. Such findings suggested several species have gone through the evolution process thus altered the attributes thus are able to prevent their brains from experiencing low oxygen conditions, also known as hypoxia. Marine mammals were discovered to have three to times more neuroprotecting type globins than other mammals (Woakes et al., 1991). However what is not yet clear is whether these marine mammals are born with large quantities of brain globins, or it is their behavior and environment that enhance globins production.
In addition to this, marine mammals have higher capillary density and blood flow that can be shunted especially to the brain (Stephens 2007). In spite of these adaptations, their blood oxygen levels decrease significantly just a few minutes underwater. This calls for some explanation as it is impossible for their vital organs not to get damaged on such low levels of oxygen.
Neuroglobins and cytoglobins which are proteins carrying oxygen residing in tissue in the cranial area may offer an explanation to this phenomenon. Scientists are still conducting research on the natural attributes of globins located in the brain. Their findings so far suggest that cytoglobins act as transporting vessels by moving oxygen out of the blood and into the brain, even when oxygen levels are extremely low(Stephens 2007). Neuroglobins located in the brain on the other hand absorb the reactive oxygen and preventing the formation of destructive free radicals. These two play a vital role in ensuring the proper functioning of the brain as well as offering protection against damage when diving.
In conclusion, the major physiological adaptations for pressure of a deep-diving mammal such as the sperm whale center on air-containing spaces and the prevention of tissue disruption (Stephens, 2007). Venous plexuses which are lined by air cavities which load up on descent, removing oxygen sacs, thus preventing compression effects. Lung contraction and collapse helps the organ avoid rupture while at the same time blocks gas exchange in the lung. The special adaptations of marine mammals also prevent the absorption nitrogen at great water depth thus preventing the development of nitrogen narcosis which may have adverse effects.
Since the lungs do not provide oxygen to the animal’s tissues, marine mammals depend on reservoirs in the muscles and blood that store oxygen. The presence of neuroglobins and cytoglobins in the brain tissue of these mammals also enables them to be deep sea divers. Although research on this area has not been extensive, it is thought that these oxygen regulating proteins may offer an explanation to the special adaptations of these deep sea diving marine mammals.
Stephens, T. (2007). why diving marine mammals resist damage from low oxygen. http://www.bio-medicine.org/biology-news’/>”/> [date accessed 15/11/2008].
Hochachka, W. P., & Lutz, L. P. (1993). Surviving Hypoxia: Mechanisms of Control and Adaptation. CRC Press.
Woakes, A. J, Grieshaber, M.K., & Bridges C. R. (1991). Physiological Strategies for Gas Exchange and Metabolism. Cambridge University Press.
Science Direct. (1991). Deep-sea Research. Pergamon Press.