Is it possible for there to be live coral trees, or even live coral cliffs and mountains?

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Corals are tiny animals who rely on Phytoplankton and Zooplankton for survival. Since planktons do not exist on dry land, no corals would survive outside the oceans.

But coral also get energy from photosynthetic algae in their skeletons. If a form of coral evolved that drew all of its energy from such algae, could it not move out of the ocean?

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Then they would be plants. They would also need something other than calcium carbonate for their skeletons since they won't be able to extract it from sea water. Cellulose wood do.

We might have to increase the atmospheric pressure and perhaps world temperature to get higher humidity. Then perhaps we could have floating air plankton for the land coral to feed off.

Coral polyps are tiny animals - carnivores. They need protein from Zooplankton as part of their diet to survive. I suppose it’s possible that a vegetarian species could derive a selection advantage as we continue to degrade the health of our oceans but it would take millions of years, at best. Coral are extremely fragile creatures and I personally think it would be unlikely for them to survive such a transition.

As Brak said, this wouldn't be possible without the final result being some creature other than coral. Corals--hexacorals, specifically--are colonial organisms with rigid carbonate substrates. In the ocean, there's plenty of carbonate for use, and it has the added benefit of anchoring the colony in shallow water. On land, there's no easily available carbonate, so no substrate; in any event, the rocky skeletons would be even more vulnerable to erosion and collapse on land. No floating plankton, either, and making it wholly photosynthetic and removing the carbonate skeleton would leave us with...well...some kind of algae.

I hate to say it's impossible, because evolution is more inventive than we are, but I don't think it's likely.

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Hmmm, have it grow in a form that traps rainwater and attracts insects and the energy problem is solved, leaving "only" the skeleton problem.
Reuse the kitin from the insects perhaps?
Would be very slow growing, but that's not a problem for coral.

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It seems that if coral colonies were going to adapt sufficiently to survive above the tidal zone, we would no longer be describing corals but a newly evolved species ...

For a long time, geologists and palaeontologists have used fossil corals and reefs as an indicator of the environmental setting ... it was believed that all corals existed within a fairly narrow range of temperature and depth limits ... so that a fossil coral community indicated a warm shallow marine environment ...

Recent living coral discoveries must challenge that view somewhat ... cold deepwater corals have been found off Norway and in other parts of the Atlantic ... and some of these appear to be closely related (think identical) to some of the fossil forms ... one conclusion proposed is that these ancient corals did not die out but migrated to the deepwater environments and the more recent forms filled the niches thus created ...

but I wonder if these ancient corals were always deepwater forms, and the modern corals expanded into the shallow regions? ... of course, to consider that means overturning some longstanding beliefs about a number of geological settings ... and finding valid explanations for the underlying and overlying strata ... plus a plausible mechanism for vertical transport without destroying the fossil structures ...

so, a third possibility is that the ancient corals were pandemic, and occupied all marine settings ... and lost the warm shallow regions to modern forms, leaving only the deepwater settings where modern corals cannot survive ...

sorry ... just rambling on about the versatility of corals over time ...

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Corals rely on water for dispersal of their free-floating laval stage; maybe this gives them some ability to migrate to or colonise new more suitable habitats.

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There is an analogy in the form of air plants I guess.

Doug

The only reason I don’t like this analogy is because corals are commonly mistaken for plants. While corals do maintain a symbiotic relationship with algae, they are tiny colonizing animals. While an entire reef structure could be interpreted as being both plant and animal, there are in fact several unique species involved in the composition of a collective reef biosystem.

If a photosynthetic form of land coral evolved, it could grow to large size using a built substrate consisting of the skeletal remains of previous individuals. You might get a coral-like colonial tree structure, raising the individual phytocoral higher that their rivals in a quest for sunlight. More like a land stromatolite, really. In regions where the rock is mostly calcite such a structure might be doable.
Except that such a structure would face the same problems a tree faces; the phytocoral would need to obtain water and minerals from the soil. So the land phytocoral would need to have fluid transport systems similar to xylem and phloem in its structure; it may just be possible for colonial organisms to form specialised tissues capable of nutrient transport alone.

Carbonic acid could form and eat away the coral- unless it was protected by a living outer skin.

Basically I am describing a colonial tree with a calcareous heartwood instead of a woody heart. Not impossible; but perhaps such organisms would be out-competed by woody trees in most cases.

I can't see much advantage for animal-like land coral; sea coral adopts that habit to pluck food particles floating in the water; unless the atmosphere is thick enough to have numerous food particles suspended in it, a land coral is not a very sensible form for a heterotroph.

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Surely the problem is basically one of water.

All living things that live in water have immediate access to it. Those things that live on land have three options.

A. They move about until they can reach a source of water when they need it. Which is what most animals do.

B. They hijack the water they need from other living things that they take as food - again some animals do that also.

C. They transport water from the water table to the rest of their cells which is what trees and all other land plants do.

How can a tiny individual organism survive on land if it does not obtain the water it needs in one of those ways. If it is going to rely on A or B then it really needs to be mobile because trying to obtain the water it needs from chance encounters of passing organisms is a high risk strategy. A small organism could not hope to store rainwater for its needs either. It would need to be much larger in which case it would be plant (probably a cactus). If it is going to rely on C and draw water from the water table then it needs long transport structures in which case it is not going to be a colony of tiny individuals but a larger form of life like a plant. So I do not see how something like coral could grow on land without ceasing to be coral and instead becoming some form of plant (regardless of whether it caught and digested passing animals) Compared to seawater and pondwater the atmosphere is a pretty sterile medium for life.

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D. They gather a reserve from rainwater for use when it's not raining.

The existence of epiphytes shows your list to be incomplete.

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OK I will admit I did not list an Item D. But I did suggest that such a small organism likc coral would not be substantial enought to store rainwater thus I recognised the problem and dismissed it as a method that a tiny colony organism could apply unlike a much larger plants which can grow the structures to store rain water

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HenrikOlsen added:

--- D. They gather a reserve from rainwater for use when it's not raining.

Could "living on land" include the idea of "living outside the boundaries of oceans?" (In water, but just not ocean water.)

There's a Wikipedia article on what is known as "freshwater coral" which exists in Pavilion Lake in British Columbia. Perhaps they represent options A and D at work. (Option D, in this case, would be like a cup overrunning.)

http://en.wikipedia.org/wiki/Pavilion_Lake

This text was copied from the wikipedia article.

Pavilion Lake is a lake in Marble Canyon, British Columbia, Canada. It is located between the towns of Lillooet and Cache Creek (18.3 miles WNW, as the crow flies, from Cache Creek) and lies along BC Highway 99, five and a half highway miles (northeast then southeast) from Pavilion, British Columbia. Part of a karst formation, the lake is most notable for being home to colonies of microbialites, a type of stromatolite, otherwise known as "freshwater coral", and has become the subject of astrobiology research by NASA. The lake area and its foreshore were added to Marble Canyon Provincial Park in order to protect its special scientific and heritage values.

The Wikipedia article on "Marble Canyon" says that the microbialites are
unusual carbonate structures built by bacteria.

http://en.wikipedia.org/wiki/Marble_...sh_Columbia%29

I take your point but my earlier argument still holds true. For a small organism that simply lives in a colonial structure it has no capacity to store water in order to survive even a day or two exposed to a the drying effect of the atmosphere. Small organisms can survive close to or within the water table. they can also live in the water stored by large organisms but neither of these solutions would compare to a coral forest on land. We therefore come back to the same problem in order to form something like a forest on land the coral would need to evolve methods to either capture and store or transport from the water table. To do either of these the coral would need to evolve complex multicellular structures with specialised functions just as plants do. Therefore the result of this would no longer be a colony of organisms like a coral but instead a single organism like a plant. If you combine that with its probable need to abandon calcium carbonate as its skeletal base and instead use cellulose or some hardened protein then one can see that you no longer have coral what you have is a tree.

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By and large this is still true. Fossil coral reefs are in almost all cases shallow water features, from multiple lines of evidence.

Not that recent. Deep water coral build ups have been known for many decades. While some ancient deep water builp ups may have been mistaken for shallow water reefs, in general deep and shallow water build ups have very different characteristics. Depwater corals are still "modern" at the taxonomic level, being all scleractinians. No rugose or tabulates have been found in deep water, unfortunately.

It's probably the other way round, corals first appeared in shallow water and only later moved into deep water enironments. The earliest corals in the Cambrian are in shallow water environments.

Something like this appears to have happened with brachipods, stalked crinoids, and bryozoans, which are less common in shallow tropical environmnets than they were previously.

But palaeoenvironmnetal interpretation is probably a subject for another thread!

Jon