Read more: Extreme survival: The toughest life forms on Earth
Just a few hundred metres below the ocean surface, proteins get bent out of shape. So how come the deepest waters are buzzing with life?
Dip beneath the ocean and the pressure starts to rise, causing problems for anything adapted to living at the surface, like us.
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The most obvious difficulty is that rising pressure puts the squeeze on the lungs and any other air spaces in the body. To combat the effects, diving mammals that reach depths of over 1000 metres, such as elephant seals and sperm whales, allow their ribcage and lungs to collapse, squeezing the air out. So they can go longer without breathing, they have higher levels of oxygen-binding haemoglobin in their blood, plus more of a similar molecule called myoglobin in their muscles.
Still, at only a few hundred metres down, where pressure reaches a few tens of atmospheres, a whole host of other problems kick in. Nerves and heart muscle start to struggle as vital communication channels in the cell membranes are squeezed, and many proteins cannot fold into their correct three-dimensional shape properly, becoming physically deformed.
Yet the deep sea is full of life. Even the deepest parts of the ocean – with pressures up to 1000 times that at the surface – are buzzing with shrimp-like creatures called amphipods, as well as sea cucumbers, nematodes and other worms, and bacteria. Fish make it as far as 8730 metres down, just a couple of thousand metres shy of the deepest part of the ocean, although no one knows why they don’t get any further.
To survive, these creatures have a number of clever cellular adaptations. Deep-sea organisms, from bacteria to fish, tend to have more flexible cell membranes, having replaced saturated fats with unsaturated versions. They use a compound called trimethylamine oxide to help proteins fold properly.
Once adapted, deep-sea creatures are as committed to a life in the depths as we are at the surface. Deep-sea crabs and amphipods suffer the same kinds of tremors and movement problems on the surface as we would under pressure, as their cell membranes become too flimsy for atmospheric pressure. Gas-filled spaces, such as fish swim bladders, will swell and burst as pressure is released on the way up. When it comes to pressure, the best plan is to stick to what you know.
