How can crabs, shrimp etc. live in deep sea when we barley have machinery that can handle it?

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I’m sorry in advance for poor format and english, I recently peaked an interest in the deep sea, and learnt how there are shrimp and crabs that are lower in depth than what we can send machinery, which is made of metal, and if i stand on a shrimp it crushes, but they can live at a depth where the pressure is 3000* my weight.

In: Biology

Animals that live in high pressure environments have adaptations that allow them to such as an internal pressure that keeps them from being crushed. Our machines lack this kind of internal pressure regulation.

Our machines and people can’t stand high pressure because we have air sacs, our lungs.

Deep sea animals don’t have air sacs so they don’t have this problem

Air, like all gases, is *compressible*. This means that pressure affects their volume. Most non-gases, including what machines and crabs and shrimps are made of, do not have this property. So any creature or machine (like a submarine) that is a mixture of solids and gases has a really hard time dealing with pressure change – the gas bubble wants to expand/contract, the rest of the animal does not. This causes gas sacs and membranes and other vulnerable material to rupture or get crushed in horrific ways, an effect known as [barotrauma](https://en.wikipedia.org/wiki/Barotrauma).

You can try getting around this by maintaining a low-pressure bubble inside a high-pressure region, but this requires very strong walls to resist the inwards pressure and redirect it into the structural frame. That’s hard, but by no means impossible – multiple humans have gone down to the deepest parts of the ocean inside such low-pressure bubbles (bathyspheres and submarines).

Another way to try getting around it is by trying to increase the pressure of the gas inside your body, but since gas is compressible, higher pressure air also has a higher *concentration* of molecules. So as you effectively end up adding more and more air into your lungs, you also end up increasing the concentration of everything in your bloodstream. Our bodies and metabolic systems are pretty complicated, and having an excess of even inert gas like nitrogen or helium in your bloodstream is generally a bad idea. So in general, you’d also need to gradually change the *composition* of the air you’re breathing, to keep things like the oxygen content unchanged, and at some point we just run out of ideas for what gases to add – even helium is toxic at high enough pressures (below 1000 m).

Conversely, sending a robot down to those depths is actually really easy – it doesn’t have the same issue at all, so it can effectively function just like a crab would. The main hurdles there are engineering hurdles related to the *robot* part, not the *deep sea* part – though, in particular, *communication* between a human at the surface and a robot at ocean’s floor is non-trivial.

It’s the same as us living at the bottom of our atmosphere, which is like an ocean of air. We are at roughly the same pressure internally as the atmosphere around us, which means you can’t survive in the low pressures of the upper atmosphere. Life deep in the ocean have an internal pressure roughly equal to the water around them.