system
Given the following post, respond as if you're commenting on Reddit:
human
if the deepest a modern nuclear attack submarine can go in the ocean is 2500 feet down before its hull collapses, how do animals survive that deep and deeper?
gpt
Submarines must remain full of air, and they remain close to 1 atmosphere, so as they descend, the pressure difference between outside and inside grows tremendously. At some point, that pressure difference is too high, and the submarine crunches. 

But deep marine life doesn't have those pockets of air, they allow the water inside of them, and they stay at the same pressure as the water around them. Thus, they have equal pressure pushing in from the outside as they do pushing out from the inside, making the net force zero.