A comment on Reddit reminded me of a question I received on multiple occasions. The question is always a good one because it is a matter of knowledge and deductive reasoning. This question requires knowing that one of the most extreme environmental gradients is the increase in pressure with increasing depth, at the surface being 1 atmosphere and reaching well over 1000 atmospheres in the deepest parts. deep in the ocean. The question? How do organisms survive this great pressure and what happens to the organisms when you bring them to the surface?
I really never tire of answering this question. In short: the pressure, or the lack of a moment when you bring them to the surface, usually does not kill deep-sea organisms. Several studies indicate that deep-sea organisms can withstand a wide range of pressures. We frequently capture organisms at depth and bring them back alive to the surface, as long as we can keep them cool. They either live in an aquarium in the laboratory, or even shipped alive across the country. I have personally kept or seen deep water snails, echinoderms, crabs, giant isopods and cephalopods in aquariums. Some pelagic organisms also have amazing vertical migrations over the course of 24 hours that can encompass thousands of feet and many pressure levels. Basically, putting a low-pressure-adapted animal into high pressures will often kill it, but deep-sea animals often seem immune to the release of pressure. * Understanding how deep-sea animals are pressure-adapted will help you understand Why.
Now a few more specific details.
- Cell membranes: As you may remember from high school or college biology, a cell membrane is made up of a lipid bilayer. The structure is fully maintained by the interaction of charges (or absence of) between water and phospholipids. This makes the membrane semi-permeable much like a layer of oil on water. Extreme pressure results in tighter packing of the phospholipids, which reduces the permeability of the membrane. An adaptation by deep-water animals is to increase cell permeability and increase the percentage of unsaturated fatty acids. In a saturated fatty acid, all the carbons in the chain are backed by a single covalent bond. As you remember, a carbon can take four chemical bonds. If all of these bonds are covalent (single), then one carbon could potentially attach to 4 other atoms. Thus the saturated comes from the fact that the carbon chain is loaded with hydrogens. If one carbon forms a double bond with another atom, then the carbon will have to bond with one less hydrogen. Thus, an unsaturated fatty acid is an acid with double bonds and not “saturated” with hydrogen. The covalent double bond between adjacent carbons in an unsaturated fatty acid results in a “fold” in the tails of the molecule. Thus, increasing their concentration in the membrane leads to looser packing.
- Enzyme Form: At the baseline level, pressures would also select different enzymes. Changes in the structure of proteins can influence their cellular function. Thus, selection for stiffness is necessary to counteract the pressure and resulting warpage of proteins. Proteins contain hydrogen and disulfide bonds between different subunits and parts of the amino acid chain which both dictate structure. Selection of proteins with increased binding would minimize shape changes to pressure.
- Urea: As Al Dove noted previously, âPressure can even make molecules more (or less) toxic. Urea is a good example: it becomes much more toxic as the pressure increases. Thus, deep-sea sharks, which like all sharks have a lot of urea in their blood, also have a lot more of the protective chemical TMAO to offset this effect than their shallow-water cousins.
- Air-filled bags: Basically it’s bad for a pressurized animal, so most deep-sea animals avoid having them. Deep-sea fish do not have a swim bladder. Other deep-diving animals like whales and seals have bendable lungs to deal with extreme pressure (without forgetting a host of other adaptations)! The penguins have practically closed all their organs except their heart and brain during deep dives.
Basically, releasing the pressure doesn’t stop any of these adaptations or the animals from stopping functioning. In a simple and perhaps silly analogy, if I wear a hat on the outside to prevent my bald head from scorching in the sun, the hat is not causing me any problems indoors where there is no Sun.
* All that being said, I have tried several times to harvest a particularly gelatinous red sea cucumber. Each time on the surface, when I remove the collection cartridge from the ROV, the cartridge is filled with a thick red Kool-Aid, which I guess is the remnants of said red sea cucumber.