pressure and depth?

[dots]

Here is something that I often think about and haven't seen anything on....

There is a lot of talk to light intensity and proper water parameters. But what about water pressure and the depths that corals have adapted to survive, and how is the health changed when that coral is placed in lower pressures. Home aquariums for instance? I wonder if that would have anything to do with gas exchange rates of certain species or food production for the coral to sustain itself. Has anyone ran across any material on this subject?

[jbrody1214]

I believe 1 BAR (14.7 psi) is at 32 feet of sea water. Someone correct me ifI'm wrong

[ChemE]

Actually, at 33.054 feet of depth (in salt water) the pressure is 2 bars or 2 atmospheres. People tend to forget that the pressure at sea level is 1 atmoshphere not 0.

[ConsultantERP]

Pressure acts in all directions not just straight down, so it seems that pressure would not cause any extra flow across or through a coral, but if you add flow with that pressure then it is possible you are getting more fluid through the coral at greater pressure. Seems to me that a sponge could benefit from this but an SPS might be not be porous enough to make any difference. It would be interesting to know the answer, but how would you simulate the extra pressure without haveing a 33.054 deep aquarium ( I wish).

[ChemE]

Oh, I think I see where this is going. The compressibility of water is frequently assumed to be zero and it turns out this is a very good assumption. Water compresses exceedingly little even at tremendous pressures; 2 atm is nothing and you haven't changes the pressure of water at all.

[Freed]

I have always been under the assumption that you CANNOT compress water at all.

[ChemE]

Water, just like every other substance, is compressible. Some compress more readily than others. Water is relatively incompressible in that 1 psi reduces a given volume of water by 0.00034%.

The only thing that we know of that is truly incompressible is nuetron star (commonly called a black hole) but now we are moving way outside the realm of reefkeeping.

[Qcks]

just as an aside.

there are many species of jelly fish, that are kept in national aquariums, that can not live at surface pressures.

Since jelly fish and coral are in the same family (Cnidaria) i would assume (which is where i can be mistaken), that the same is true for some coral.

As for the fish.

Wild caught fish that live in deep water have to be slowlybrought up to the surface, much like a human going through decompression, other wise they can die.

some fish die any way. (from the stress of decompressing.)

[G_cuvier]

Decompressing a fish is not the same as decompressing a diver. A fish needs either decompressing or have their swim bladder punctured to allow the increasing pressure to vent or the fish will die.

Disregarding the decompression of a swim bladder, decompression on marine animals is utterly unrelated to decompression sickness, aka the bends, in humans. Decompression sickness is due to the additonal intake of nitrogen into the bloodstream due to the fact that divers breathe compressed air which is 75%+ nitrogen. Marine animals do not have the nitrogen issue because they extract their oxygen from water which has very little dissolved nitrogen. When a diver rises too quickly from depth the nitrogen that was so readily passed from the lungs to the bloodstream does not make the return journey so readily. But, unfortunately for divers, the reduction in ambient pressure does allow the nitrogen to "drop out of solution".... Since it doesn't pass well back out through the lungs it causes it to collect in other tissues and possibly, (if the ascent is too rapid and the exposure to high pressure gas too long), to cause bubbles in the blood/tissues that create a deadly situation. This is a long and complicated issue that depends upon the gas breathed, the pressure at which it is breathed, the physical health of the diver, the partial pressures of the gasses in the body etc. etc. etc.

Suffice it to say... Marine creatures do not suffer decompression in the same way a human diver would. There are some issues with fish because of their physiology but it is unrelated to traditional decompression issues humans face after time at depth.

[photobarry]

Originally posted by G_cuvier
Suffice it to say... Marine creatures do not suffer decompression in the same way a human diver would. There are some issues with fish because of their physiology but it is unrelated to traditional decompression issues humans face after time at depth.

That's for sure! My last job involved research on hydrothermal vent animals and we would routinely decompress them from 4000psi to ambient pressure and animals like crabs would still be able to crawl around although they would lose quite a bit of coordination. In any case, any photosynthetic coral will not be found at great enough depth for pressure (or lack of it) to have any effect on it. And even if it did, you could simulate the pressure by dropping temperature. (We kept organisms found at 500 meters alive at ambient pressure just by keeping them cold.)

[Freed]

?But how long did they live at sea level pressure compared to what they could have lived if you could have kept them at deep sea pressure on the ship or in the lab?

[photobarry]

Originally posted by Freed
?But how long did they live at sea level pressure compared to what they could have lived if you could have kept them at deep sea pressure on the ship or in the lab?

We have had mussels live for about a year and the lab that we got them from has kept shrimp indefinitely. (I believe they have reproducing populations of them.) If an organism is going to die from a lack of pressure it will happen within a week. (a month at the longest) Pressure affects membrane permeability and they simply subsitute different lipids and carbohydrates. They have to do the same thing to acclimate to differing temps on the bottom. It's pretty amazing what they can adjust to.

[BeanAnimal]

I watched an old eposide of jacque cousteau where they were pulling baskets of stuff off of the bottom of the Mariana Trench. They were looking for giant squid. Two thing stand out in my memory.

1) Giant jellyfish liek creatures the size of a football field, and a diver swimming among them

2) the basket from the bottom contained a totally clear shrimp and fish. Both were alive and well after the 7 mile journey to the surface.

If anybody knows the name of this episode or has a copy of it...

Bean

[BeanAnimal]

I watched an old eposide of jacque cousteau where they were pulling baskets of stuff off of the bottom of the Mariana Trench. They were looking for giant squid. Two thing stand out in my memory.

1) Giant jellyfish liek creatures the size of a football field, and a diver swimming among them

2) the basket from the bottom contained a totally clear shrimp and fish. Both were alive and well after the 7 mile journey to the surface.

If anybody knows the name of this episode or has a copy of it...

Bean

[pch90265]

Sounds like Barry is a bit more qualified than I am to address the topic of pressure in marine life, but there was quite a bit of discussion on this topic on a thread a while back on Dendros. If you search "Dendro study group" you should find it.

I asked the same question in that context -- if Dendros are most commonly found below 30m, and really thrive at 60m (that's the land of tri-mix and long decompression dives for folks that venture down that deep) then I would assume part of the reason we land lubbers have such a hard time with them is the lack of pressure in our tanks.

However, there were a number of scholarly types that refuted that line of thinking... I'd still like to see someone try Dendro's in a hyperbaric chamber, but I certainly don't have the cash for that kind of fun.

--Sean--