The Resurrection Coral, AKA Zombie Coral
Marine biologist Kate Furby is on Palmyra Atoll (near Hawaii) investigating recovery mechanisms for damaged and bleached corals. Of particular interest is Porites superfusa, a SPS with seemingly supernatural resiliency. Her research team has observed this coral remarkably spring back to life, emerging through the algae and sponges covering its tissue-less skeleton many months after "death." She hopes that Porites superfusa and corals like it can teach us how corals might cope with catastrophies.
Zombies in our reef tanks?
I've observed this phenomenon over the years, and I suspect many reefkeepers have seen mysterious corals appear out of their live rock too. Perhaps more interestingly, it's always been one of two genera of SPS in my experience: Porites and Leptastrea. After months of apparent lifelessness (algae has overgrown the once-white skeletons), new polyps will emerge and reestablish a colony.
Perhaps the secret to these corals' amazing resiliency is their skeletal structure consisting of corallites with elaborate columella providing cryptic coral cells a safe place to "hide" (like a coral apocalypse bunker) until conditions for life are favorable again.