How do organisms at great depths live under such crushing pressures and do they have special enzymes?
Generally the deep sea organisms have internal pressure as same as the pressure of the waters surrounding them. But in adverse condition like less light, oxygen, food, etc.they have to adapt themselves in different ways.
Organisms follow many adaptations to survive in the deep sea and manage the pressure. For example, Whales have a large lung to manage the air pressure. Animals dive and swim to protect themselves from the air and water pressure.
Some organisms use chemosynthesis to attract prey or to attract a mate. Some can float and swim and get solar energy. Some have shells to protect themselves from the water and air pressure.
The red algae is successful to live in deep water, because the presence of red pigment, phycoerythrin, which can absorb the blue green region of the spectrum reaching the greatest depth in water.