A coral species that all but disappeared from waters off the main Hawaiian islands thousands of years ago could be making a comeback to the area, a recent surprise discovery off the southern shore of Oahu indicates.
A group of coral ecology scientists with the National Oceanic and Atmospheric Administration stumbled upon what one of them called a "sizeable" table coral colony during a routine training dive last November, roughly a mile from the Ewa Plain. There had been only one other previous sighting of the distinctive plate-shaped coral around the main islands — off Kauai several years ago — but that budding colony swiftly disappeared, said Randall Kosaki, deputy superintendent for research and one of the four scientists who made the recent Oahu discovery.
The table coral colony near Oahu, on the other hand, measured more than a meter across and was estimated to be 10 to 14 years old, Kosaki said. It’s about 60 feet below the surface, officials say.
NOAA publicized the discovery in a release this week after it was peer-reviewed and published last month in the Bulletin of Marine Science.
Table coral, also known as acropora, is typically found in warmer, tropical waters and grows abundantly at Johnston Atoll, 830 miles west-southwest of Hawaii, NOAA officials say.
It does flourish in the northwestern Hawaiian islands that make up the Papahanaumokuakea Marine National Monument, but "it’s essentially absent in the main Hawaiian islands," Kosaki said.
With the Oahu encounter, "it may be in the process of spreading," he added.
Table coral opens out faster than other species and helps build the reef structures essential to marine life relatively quickly, Kosaki said. Despite its flat top, table coral actually provides plenty of underwater shapes and "structure complexity," as Kosaki described it, for marine animals to use.
Fossilized records suggest table coral last flourished around the main islands tens of thousands of years ago, he said.
A resurgence could help to sustain local reefs as warmer waters and coral bleaching due to climate change threaten coral species, Kosaki said.
However, the table coral could simultaneously be threatened in the tropical regions where it currently thrives if those waters get too warm, he added.
The colony near Oahu was discovered during a dive with closed-circuit "rebreathers," which Kosaki described as "scuba on steroids."
While regular scuba divers exhale bubbles into the water, rebreathers "recycle" those gases and scrub them of carbon dioxide so divers can reuse the air. The method, which has become more mainstream in the past five to 10 years thanks to technological advancements, allows divers to reach greater depths and stay underwater for hours longer at a time, Kosaki said.
"You’re going to find more interesting and unusual things," he said.