On the seabed of Kaneohe Bay, in Hawaii, divers lowered heavy concrete pyramids back onto the reef — and with them, a coral that had been declared gone from the wild forever. That coral lived nowhere else on Earth except this one bay on the island of Oahu. Yet after deadly heat waves and storms swept through in 2015, its natural colonies vanished completely. The only survivors were the fragments scientists had rescued just in time.
That rescue began with a race against the clock. In 2015, marine biologists from the Hawaii Coral Restoration Nursery, run by the state's Division of Aquatic Resources, pulled living pieces of the rare knobby coral from Kaneohe Bay. They placed the fragments into a special living collection called the Rare Hawaiian Coral Ark — a kind of emergency bank for corals found nowhere else on the planet. Almost a quarter of Hawaii's coral species exist only there, so if one is lost, nothing can replace it. Soon after that urgent collection, the wild colonies died out from heat-related bleaching and storm damage. The Ark held the only surviving representatives of that population.
This matters because Hawaiian corals grow painfully slowly — often less than one centimetre a year. At that pace, a damaged reef might take hundreds of years to recover. So the nursery, based at the Anuenue Fisheries Research Center on Sand Island, turned to a clever trick called microfragmentation. Biologists sliced the rescued coral into tiny one-centimetre pieces and attached them to concrete pyramids called modules. Inside tanks with carefully controlled light, temperature and water flow, the small pieces grew quickly across the concrete. When the growing edges met, they fused into large adult colonies. The result: fully reef-ready corals in just one to two years — less than one-twentieth of the natural timeline.
"The ultimate goal is to have corals on the reef that, if you swim over it, you would have no clue that it was grown in a coral nursery," said Christina Jayne, curator at the nursery, "and that they would contribute to maintaining that reef ecosystem, and reproduce."
Before the coral went home, it passed through a strict quarantine to make sure no pathogens came along. Now, divers have placed the modules back in Kaneohe Bay, and field checks show the newcomers are thriving. The colonies developed strong bases, grew living tissue down onto the natural reef, and showed no signs of disease or heavy predation. The long-term hope is that these corals will blend seamlessly into the reef, reproduce on their own, and help the whole ecosystem bounce back. For a creature that once seemed gone for good, that is a second chance worth swimming over.