You're welcome, and I should have pointed out that it was anecdotal, so thank you.
hehe, don't get me started! Fascinating observation and question. Something I've thought about many times.
Let me start off with a couple points (all my questionable knowledge - research further if interested):
1. Corals, well, *MOST* corals (especially in the shallower ranges) are symbiotic creatures. They host a type of algae called zooxanthellae. The zooxanthellae use respiration (nutrients) and light to create simple sugars which provide energy to the corals. Oftentimes reefkeepers rely almost 100% on this relationship to feed corals and never actually feed them directly.
zooxanthellae are also largely responsible for the corals gorgeous florescent coloration under certain lighting (around 420nm wavelength if memory serves)
2.Corals reproduce by two means; fragmentation, just breaking off a piece - or cutting of soft-bodied, and sexually (releasing ova and sperm into the water column). Corals release MASSIVE amounts of sperm and ova when they breed, but mortality is high - alas, filter feeders (inlcluding themselves) are effecient. Interestingly - at least as of the last time I studied it about a decade ago - we don't know how to trigger sexual reproduction in captivity, so we just use "fragging". It's something to do with temperature, moon-phase, blah blah, who knows? hehe
3. Unrelated trivia: Had to look it up because I hated that I forgot the exact numbers - IN THE HOBBY, we shoot for a ph between 8.0-8.4. I don't think I've ever exceeded 8.2 for any extended amount of time.
Ok, now to your questions, I think the answer is, for the most part, adaptation, within the bounds of chemistry, anyway. No skeletal material is going to survive for long under 7 or so. Terminators notwithstanding.
So let's talk about bleaching - bleaching isn't actually the coral dying - it's the zooxanthellae dying - thus the loss of color and the term bleaching. That said, corals typically don't last long after, and I'm not aware of any success in reseeding the algae in a bleached coral. Being an algae zooxanthellae can reproduce fairly quickly (assumption) and therefore mutations can happen on a more rapid basis. As long as the negative environmental factors doin't outpace, timewise, the ability/chance of an appropriate mutation then they can adapt and go on to breed more resilient zooxanthellae themselves.
As mentioned earlier corals also reproduce (sexually) pretty prolifically, even with the high mortality rate. So plenty of chance to mutate there as well and add onto that an increased growth of zooxanthellae population of a new coral and you're chances get even greater (within context).
So yes, coral bleaching is disastrous, especially en-mass. However, there are populations that are gaining resilience to some of the environmental pressures.
The environmental runoff factor is an entirely different discussion and as I haven't thought about it as much I'll just make a couple points but avoid any strong conclusions.
The primary environmental runoff into the oceans (that I'm addressing, anyway - sulfuric acid is sulfuric acid, after all - are fertilizers and sewage. Both are extremely high nutrient sources (by definition). Look up the "nutrient cycle" if you're interested in more - same processes work on solid ground as well . Specifically the migration of ammonia to nitrite to nitrate. If your at all familiar, these are the components of fertilizer and biological waste.
Plants (including zooxanthellae) consume these nutrients and use them for growth and energy. This is why you can see algae blooms in stagnate areas or areas of high runoff.
So, I would think that too much of a good thing could be an issue. Or, perhaps, algae blooms cutting off light to more benthic organisms?
Definitely a very interesting question that I haven't thought about before - and the above is very much my thought-train first ramblings on the subject.
Temperature also, of course, plays a part. Increased temperature means increased metabolism, etc.
Thanks for the interesting discussion, now I'm going to have to go down a rabbit hole! hehe