It's a neat picture. But I might present a counter-opinion.
corals exposed at high tide doesn't demonstrate their "hardiness" per se, but it does demonstrate what sort of conditions they have adapted to over countless millenia. Think about the intensity of light they are exposed to in that shallow water, what they are exposed to during low tide, and the pounding of the waves. Those exact conditions are going to be near impossible to replicate in an artificial environment - however, luckily we know that their tolerances are wide enough to include those which we can nearly replicate. However those corals we see in the picture have been in the low tide conditions since they settled out as planktonic larva - taking a deep water acropora and putting them at the same depth might show that extreme changes in conditions are enough to ... well, do them in.
Sorry for the counterpoint but felt compelled to share MY thoughts on it
