Ecology: Biology of Interaction. V-21. (Supplement) Pressure at Depth: Withstanding and Overcoming

V-21. (addendum) Pressure at Depth: Endurance and Overcoming Sometimes environmental influences are so severe that they are practically impossible to resist. This is the case, for example, with water pressure at great depths. We live under a thick layer of atmosphere and are accustomed to ignoring its pressure, which is about 1 kg per cm 2 of surface area (approximately 10 m of water column). But as you descend, the pressure increases rapidly. At a depth of 10 m, it is already 2 atmospheres (one is the pressure of air, the other is the pressure of a ten-meter water column). The greatest ocean depth exceeds 11 km, and the World Ocean is inhabited by animals, including fish, crustaceans, mollusks, and echinoderms, down to its greatest depths. As you can calculate, at this depth, the pressure exceeds 1100 atmospheres, amounting to over 11 tons per square centimeter of body surface. Can a living organism withstand such pressure? Imagine lowering an empty (i.e., air-filled) tin can to a great depth. The external pressure of 1100 atmospheres will inevitably crush this can, reducing its volume 1100 times. Building bathyscaphes (deep-sea vehicles) that can withstand such pressure is an exceptional engineering challenge and requires significant thickness of walls and portholes. What happens if the same can is lowered to the same depth, but open or at least with a hole? Nothing special! Water under pressure will fill the can without changing its shape, as the external pressure on its walls will be balanced by the internal pressure. Deep-sea organisms withstand pressure due to the same mechanism as open cans – by not resisting its action. The tissues of organisms inhabiting our planet have a water base. Water under pressure is practically incompressible. The external pressure on the tissues of deep-sea organisms is balanced by the internal pressure, so they do not feel it. Can it be considered that in this case, being at great depth and at the surface are equivalent? No. At high pressure, chemical reactions accelerate, and the solubility of gases in water increases. "Boiling" (formation of gas bubbles) when pressure decreases is responsible not only for the "fizz" of carbonated water in a bottle but also for the bloating of deep-sea fish brought to the surface in nets and for the bends experienced by scuba divers. Terrestrial quadrupeds (including humans) may encounter difficulties when diving due to the presence of air in their lungs. After all, before diving, we take a deep breath. Lungs filled with air give the body positive buoyancy, which must be overcome during descent. But as soon as you dive deeper by working your limbs intensely, the situation changes. Given that the pressure of ten meters of water column roughly corresponds to a pressure of one atmosphere, at this depth, the external pressure doubles, and the lung volume halves. The body's buoyancy becomes negative, and it is pulled further down – and here you need to ascend, overcoming this effect. Is it possible to withstand the terrible pressure at depth? Surprisingly, to some extent, yes. And the sperm whale, the largest toothed whale, adapted to hunting deep-sea squid, is capable of this (Fig. V-21.1). The most striking feature of the sperm whale's appearance is its huge head. It occupies up to a third of the sperm whale's body length and appears rectangular from the side due to a cavity filled with a waxy substance – spermaceti – located above the upper jaw. The name of this substance is associated with the fact that in ancient times it was considered whale sperm (and it was assumed that the sperm whale stored a huge supply of it in its head!). By the way, sperm whales were hunted extensively precisely for spermaceti – it is an exceptionally good base for perfumery, providing fixation (longevity) for the scents of expensive perfumes. Its true purpose has only recently become clear. Fig. V-21.1. Body contour and skeleton of a sperm whale, as well as an artistic depiction of its hunt for a giant squid. The sperm whale systematically dives to depths of over a kilometer (recorded record is 2,200 m, and there is no certainty that this is the limit of its capabilities) to hunt giant squid there. Naturally, this requires a rib cage that can withstand more than a two-hundredfold reduction in volume (with significantly less compression, human ribs would break, or the lungs would detach from their membranes). But even with such a "complex" rib cage, the sperm whale would have to dive and ascend, overcoming forces related to unfavorable buoyancy. It would have to, if it didn't use the spermaceti cavity. This substance transitions to a liquid state at body temperature and solidifies, significantly increasing its volume, with a slight decrease in temperature. Before diving, the sperm whale increases blood supply to the spermaceti cavity. The spermaceti melts, the whale's head decreases in volume, and it begins to be pulled down. The sperm whale dives. When it's time to ascend, it cools the spermaceti (either by reducing blood flow or by taking "sea" water into its nostrils). The spermaceti expands and increases the volume of the head, overcoming the terrible external pressure. Headfirst, the sperm whale shoots to the surface, holding the weakened squid in its jaws. For bathyscaphes and submarines, changes in buoyancy are associated with the consumption of certain substances – dropping ballast, releasing fuel from auxiliary tanks, expending air to blow out tanks. A scuba diver wears an excessively heavy weight belt (which can be dropped if necessary) and balances their buoyancy using a compensator – a tank into which they can either add air from breathing cylinders or "release" it. The sperm whale, by changing its buoyancy, expends only the energy obtained from oxidizing food caught at depth with oxygen from the air it took at the surface. Can one not admire the perfection of this device?