Why corals in American Samoa are thriving despite warmer oceans
Ropati Opa sat in the shade on the side of the road beside a carpet of tropical greenery with a massive, fringing coral reef sitting just offshore.
He is the mayor of Leone, a seaside village on American Samoa, an island in the South Pacific between Hawaii and New Zealand. As such, it’s his responsibility to help ensure that the coral there stays healthy.
Corals attract fish that are beneficial to the Samoan ecosystem, and they buffer the island from strong waves. They also attract tourists who snorkel in the ocean to explore the reefs.
“We need to have a good coral in this ocean,” Opa said. “It’s very important. They have good fish.”
Despite prevailing narratives of coral bleaching and decline, the reefs of American Samoa have been particularly resilient to warming temperatures that have laid waste to other corals. Scientists there are finding out why, and looking for ways to use this knowledge to help reefs in other parts of the world.
Dan Barshis, a coral biologist at Old Dominion University, has worked on the American Samoan reefs for 19 years.
“It’s like a black-sand beach, almost,” Barshis said of the shoreline, where gentle waves lapped against sand the color of coffee grounds.
“We’re going to go swim out and show you what a real South Pacific reef looks like,” he said, a pile of snorkeling gear beside him.
He donned his gear, fell back into water the temperature of a warm bath, and swam out to the reef in about five minutes.
Rising ocean temperatures due to global warming have led to the demise of other reefs. Ocean warming often leads to bleaching, when corals jettison the colorful algae that nourish them.
“Looks like somebody poured bleach on the coral,” Barshis explained. “And they can starve and die if they’re not able to recover.”
Globally, coral cover has been declining over the last 15 years. But the picture is different here in American Samoa. The reefs here have bleached on occasion, but it has ultimately managed to shake the worst of it off and rebound. There are other rare bright spots dotted across the world’s oceans.
“Our central question is what makes certain corals more tolerant to temperature,” Barshis said. “And what makes the strongest corals strong.”
That means looking at their genes.
“We’re sequencing their genomes to see what genes and what mutations might be causing them to be adapted for high-temperature events.”
Genome sequencing could help scientists look for those genes in corals elsewhere in the world to identify and protect similarly resilient reefs. They could rebuild beleaguered reefs by seeding them with hardier young reefs from nearby. This approach would effectively buy corals time while humanity works to lower its emissions.
Barshis’ work adds to a backdrop of coral conservation work on the island, championed by the American Samoa Department of Marine and Wildlife Resources.