Well, for one how long are we talking about, a few years, a few decades? What's the success rate at 5 years, 10 years, 20 years?(1) One of the interesting things research is showing is the DOC from corals promotes autotrophic microbial processes which helps maintain healthy conditions for corals. But as time goes by without water changes unhealthy types of DOC and associated microbial processes are going to start building up. Skill is certainly needed to maintain systems for years and decades but there's a whole lot going on in our systems and we've only scratched the surface.
Here's a paper that looks at excess labile carbon and it's association with reef degradation. https://www.ncbi.nlm.nih.gov/pubmed/28895945
And here's one looking at antagonistic interactions of coral associated bacteria https://www.researchgate.net/public...ssociated_bacteria_Environ_Microbiol_12_28-39
One intriguing expereiment are two mesocosms set up in London to study spawning in 4 species of acros: http://onlinelibrary.wiley.com/doi/10.1002/ece3.3538/full They started with gravid colonies which spawned soon after introduction and were able to get them to spawn simultaneously with wild colonies a year later. Since this is an ongoing and tightly controlled experiment with benchmarks it will be fascinating to see what happens over time.
Sadly there's very little research I've found. To use a gardening analogy, If I plant a bunch of different species together but use just one mainteneance regime most if not all the plants will certainly sprout but as they grow the individual species will have different requirements, not meeting their individual requirements will mean after a while some thrive, some will decline and die.
This paper looked at just 3 species, Porites compressa, Montipora capitata and Pocillopora damicornis. The researchers found the requirements for growth differed for each one. Meeting the needs of one would necessitate the other two would not do as well.
And this paper, https://www.advancedaquarist.com/2008/3/aafeature1, looked at how 10 different acros and montis looked and grew under different color temps. What one species liked another grew poorly under. If we keep a coral under less than ideal conditions how many years should we expect it to live?
(1) And are they actually going as long as they say, locally one aquarist liked to say he went years without a water change when he had never gone more than two, less if you add the water he had to replace for skimming [1/2 gallon a week in a 200 gallon system is at least 10% a year.]
