MIAMI — With a gentle pat, Wajahat Shera cemented a four-inch staghorn coral fragment onto a patch of seafloor two miles east of Key Biscayne — one of many planted Friday as part of an unusual undersea experiment being run by University of Miami scientists. These corals, previously collected from a range of reefs off South Florida, are being put to a critical heat-stress test. Some likely won’t survive the high ocean temperatures off the state that threaten to devastate much of the natural reef tract. But if some do — and that’s the hope — it could help identify coral types more likely to endu...