How do deep-sea creatures survive pressures that would crush a submarine?

The answer

Deep-sea organisms survive extreme pressure through remarkable biochemical adaptations. Their cell membranes contain higher proportions of unsaturated fatty acids, keeping them fluid under crushing pressures. A key molecule called trimethylamine N-oxide (TMAO) stabilizes proteins that would otherwise be deformed by pressure. Concentrations of TMAO increase linearly with depth - a snailfish at 8,000 meters has five times more than shallow-water relatives. In 2014, the hadal snailfish (Pseudoliparis swirei) was discovered at 8,178 meters in the Mariana Trench. These fish lack swim bladders and have incompletely ossified skeletons. Their skulls have gaps between bones, allowing pressure equalization. Deep-sea organisms essentially equalize internal and external pressures, eliminating the crushing differential.