How do undersea organisms manage it?

April 16, 2005 10:04 PM

So I was watching BBC's Blue Planet documentary, a chapter of which covered deep sea life...

If the underwater vessel capturing all the film footage needs to be pressurized to keep from being squashed from the external water pressure, what physiological differences allow organisms that live that deep to survive without also being "squished"?

posted by Rothko to science & nature (7 answers total)

A gross oversimplification (and probably wrong in many ways), but:

Gases (i.e. the atmosphere) is compressible. Fluids (i.e. the ocean) and solids (the bits of sea life that aren't liquid) aren't.

You only need to worry about pressure if you have bits that contain gases (lungs, ear canals, sinuses, etc.) or don't like being wet and thus must be contained in gases (like expensive electronic cameras).
posted by nmiell at 10:13 PM on April 16, 2005

Pressure differential plays a huge part. When standing at sea level, your body is bearing the weight of the atmosphere above you, 14.7 pounds per square inch or thereabouts. Over the entire surface area of your body that comes to a staggering amount of pressure, but you don't get crushed because the gases inside your body cavities are also at 14.7psi or thereabouts. Because the pressure is equalized you don't even notice all that weight of atmosphere bearing down on you.

Similarly, a deep-sea creature's insides are equalized with the pressure of the water outside its body, and so it goes about its business neither knowing nor caring about the immense pressure at the depths where it lives.

But when you have a submersible maintaining something resembling normal atmospheric pressure, and suddenly it gets punctured, the submersible undergoes a crushing equalization of internal and external pressure. This is exactly the reverse of the explosive decompression you would experience if you opened the cabin door of an airliner at cruising altitude; where in the airliner you have air inside rushing out with tremendous force to equalize pressure, in the submersible you have water outside rushing in with tremendous force to equalize pressure.

This is also the reason for the bends: when you dive, the pressure of the water compresses the gases, particularly nitrogen, inside your body. If you come back up too quickly, the gases inside you likewise expand too quickly, wreaking havoc on your body; the effect is the same as compressed carbon dioxide gas expanding when you open a bottle of soda.
posted by ubernostrum at 1:17 AM on April 17, 2005

nmiell: A small nit. Gases are also considered fluids.
posted by grouse at 2:09 AM on April 17, 2005

Good explanation, ubernostrum.
posted by weapons-grade pandemonium at 6:59 AM on April 17, 2005

In summary, the primary anatomical adaptations for pressure of a deep-diving mammal such as the sperm whale center on air-containing spaces and the prevention of tissue barotrauma. Air cavities, when present, are lined with venous plexuses, which are thought to fill at depth, obliterate the air space, and prevent "the squeeze." The lungs collapse, which prevents lung rupture and (important with regard to physiology) blocks gas exchange in the lung. Lack of nitrogen absorption at depth prevents the development of nitrogen narcosis and decompression sickness. In addition, because the lungs do not serve as a source of oxygen at depth, deep divers rely on enhanced oxygen stores in their blood and muscle.

The main adaptation to the pressure is the reduction or loss of the swim bladder. Many fish have also developed swim bladders filled with lipids instead of gas. The lipids are relatively incompressible when compared to gases.

In passing I noted that one of the adaptations that allow the enhanced oxy stores as above are an increased amount of hemoglobin and myoglobin. Proteinous enzymes are also different such that they can still catalyze reactions without getting squished.
I think other creatures (like the jelly's and similar) have a great water content - which isn't subject to pressurization. Also, most creatures have less dense (or no) bones and (I think) this means that their body shape is squishable without being breakable....well that's the gist I got.

[Uncanny as it seems, deepsea creatures are able to speak with posh accents and are known to be fond of fish and chips when on documentary film sets]

on preview....dang.....you removed the tags!
posted by peacay at 7:54 AM on April 17, 2005

oh ok....can't see tags on prev.
posted by peacay at 7:55 AM on April 17, 2005

As an interesting aside, sperm whales apparently aren't impervious to decompression illness. Examinations of whale bones have uncovered the exact kind of decompression damage that humans suffer.
posted by gentle at 8:34 PM on April 17, 2005