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[WillowLuman]

SO2 (sulfur dioxide) is a major volcanic gas. It also has a whole classification of chemotrophic lifeforms that use and hydrogen sulfide for respiration.

Oxygen breathing life is only *one* option.

Given the lack of any other energy source to drive the ecosystem, chemotrophs look very attractive as a prospect.

A non-bacterial chemotroph ?

Also, GCS are predators. They use carbon based compounds as an energy source.

And there's (95% of the time) no contact between magma and the caverns, how could SO2 enter the caverns ?

Magma pools, but indeed those can be rare. Seepage?

[KodKod]

This could all be solved using the time honoured tradition: A wizard did it.

I think it's safe to say by now that at least some of us have come to a collective conclusion that GCS are either impossible or mindbogglingly unlikely. That leaves magic or divine influence, and as stubborn as people are not to resort to that, sometimes it's the only, dare I say it, "realistic" solution.

Quelle surprise.

[WillowLuman]

This could all be solved using the time honoured tradition: A wizard did it.

I think it's safe to say by now that at least some of us have come to a collective conclusion that GCS are either impossible or mindbogglingly unlikely. That leaves magic or divine influence, and as stubborn as people are not to resort to that, sometimes it's the only, dare I say it, "realistic" solution.

Quelle surprise.

Although again, we are talking about arguably the most realistic fantasy game. We could go for the Pratchettian magitek sort of compromise though. Background magical energy and whatnot.

[wierd]

Really? I find magma in the cavern layer frequently....


That aside, SO2 is a gas. It seeps through cracked/fractured rock formations.

A multicellular autochemotroph is silly, but a multicellular heterochemotroph isn't so much.
A lightless environment like the cavern layer needs energy of some form. The only energy sources available are chemical and thermal.  Most likely, the slime on the walls and floors of the cavern system are the lynchpin of the ecosystem, providing the raw energy production to sustain larger organisms, such as the fungi trees, and their associated fauna.

GCS would be an apex predator, but that doesn't mean it can't have formed symbiotic relationships with cavern microfauna. (Much like large surface organisms have symbiotic gut bacteria, GCS may have symbiotic lung bacteria.)

[Sadrice]

Documentaries with sound effects seems very dishonest to me.

It's pretty much necessary, and nigh universal.  It's very hard to get good quality audio recording in the field.  Fun fact: the planet earth crew carried no audio equipment at all, and added everything in later.

What's really dishonest is using rented animals, which is very common, especially in "wildlife" photography.

As for spiders, the issue isn't so much taking in the gas, but distributing it.  Arthropods have an open circulatory system, meaning they have a heart like pump, but it is like an aquarium motor, and just keeps things mixing.  This works alright at their size, but doesn't scale up well.  Insects have their tracheal system, where they basically have tubes that bring air directly to the tissue that needs it, which allows them to have higher metabolic rates than things like spiders.

Another issue for spiders is that they lack limb extensor muscles, and use hydraulic pressure.  This is why jumping spiders have ordinary sized legs, unlike pretty much every other specialized jumping creature.  I suspect that if you scaled that up, the pressures required would be formidable, and might pose problems.

True. By metabolism, I meant the oxygen metabolism... Of course, that isn't technically a correct use, either, but insufficient O2 to breath is what I was meaning.

That is actually the most correct use.

Also, all spiders have lungs of a sort.  In some cases, they don't have book lungs proper, but they still have a hollow cavity where they would otherwise be, which they use for gas exchange.  Some other arachnids don't have any lung like structures, and do gas exchange through the skin, but that's mostly mites and harvestmen.

[Rude]

I'm a little shocked that no one has pointed out the creeping eye yet...

[wierd]

Clearly, must be an evolutionary camoflauge technique for a more active form of slime mold.

Looks like an eye, but actually isn't.

[Sadrice]

The main biological problem with the caverns is how much living stuff there is in there.  Sure, there could be some sort of chemosynthetic bacteria forming the base of the energy chain, but there would still need to be a significant source of carbon, which is not a major component of most rocks.  In DF cave ecosystems, there's such an excess of energy containing organic matter that there can be whole fungal forests underground.  Maybe it's dwarf powered?  Dwarven settlements are so common, and so often meet sticky ends in the caverns, that they actually form the base of the foodchain?  Perhaps various cavern creatures use the stairways that the dwarves leave to go up to the surface and import plant material?  Or maybe most dwarven settlements are too lazy to dig a dumping chute all the way to magma, and just dump their waste into the caves.

[Rude]

The main biological problem with the caverns is how much living stuff there is in there.  Sure, there could be some sort of chemosynthetic bacteria forming the base of the energy chain, but there would still need to be a significant source of carbon, which is not a major component of most rocks.  In DF cave ecosystems, there's such an excess of energy containing organic matter that there can be whole fungal forests underground.  Maybe it's dwarf powered?  Dwarven settlements are so common, and so often meet sticky ends in the caverns, that they actually form the base of the foodchain?  Perhaps various cavern creatures use the stairways that the dwarves leave to go up to the surface and import plant material?  Or maybe most dwarven settlements are too lazy to dig a dumping chute all the way to magma, and just dump their waste into the caves.

Quick an easy experiment to disprove this: gen a world without dwarfs.

[wierd]

The main biological problem with the caverns is how much living stuff there is in there.  Sure, there could be some sort of chemosynthetic bacteria forming the base of the energy chain, but there would still need to be a significant source of carbon, which is not a major component of most rocks.  In DF cave ecosystems, there's such an excess of energy containing organic matter that there can be whole fungal forests underground.  Maybe it's dwarf powered?  Dwarven settlements are so common, and so often meet sticky ends in the caverns, that they actually form the base of the foodchain?  Perhaps various cavern creatures use the stairways that the dwarves leave to go up to the surface and import plant material?  Or maybe most dwarven settlements are too lazy to dig a dumping chute all the way to magma, and just dump their waste into the caves.

Carbondioxide is also a common volcanic gas.

A thriving chemotrophic "sponge" ecosystem, especially with gasses bubbling through water, would probably be sufficient for the mushroom forests.

Dunno about macrofauna deriving sufficient energy from the mushrooms though.

[WillowLuman]

The breakdown of rock and organic processes have created a soil layer in the caverns (the mud), which acts somewhat like normal soil.

[Sadrice]

snip

Carbondioxide is also a common volcanic gas.

A thriving chemotrophic "sponge" ecosystem, especially with gasses bubbling through water, would probably be sufficient for the mushroom forests.

Dunno about macrofauna deriving sufficient energy from the mushrooms though.

Right!  Hadn't thought of that, I was thinking of CO2 as being primarily a product of photosynthesis.

[wierd]

The problem is energy in, energy out, and entropy.

The chemical energy supplied by the volcanic gasses are the substitute for sunlight.

Dirt isn't the problem.  Energy is.

The chemosynthetic sludge on the walls and floor of the cavern system absorb volcanic gasses, and use the chemical energy to drive their cellular processes.

The mushroom fungi "consume" the sludge using enzymes in their mycelial structures, and literally steal energy from the chemotrophic slime. The problem is that by the time it filters through the mushrooms, most of the energy will either have been expelled as heat energy, or bound up in inedible chemical structures like cellulose.

The whole ecosystem would be dependant upon how efficiently the cavern ooze is at converting co2 and SO2 into useful organic compounds for more advanced life forms.

[Naryar]

snip

Carbondioxide is also a common volcanic gas.

A thriving chemotrophic "sponge" ecosystem, especially with gasses bubbling through water, would probably be sufficient for the mushroom forests.

Dunno about macrofauna deriving sufficient energy from the mushrooms though.

Right!  Hadn't thought of that, I was thinking of CO2 as being primarily a product of photosynthesis.

So can someone explain why dwarves tend to die more at the claws of a beast than of CO2 poisoning ? I know than living underground they should have a better oxygen absorption than elves (which must be ridiculously high on oxygen considering they live around plants) and humans, but still...

[wierd]

Depends on how efficiently the cavern ooze can anerobically convert those two gasses (SO2 is far more toxic, btw.) Into oxygen breather friendly waste products. (Oxygen, water, mineral sulfur, simple sugar analogs.)