Coral reefs around the world are dying. A few exceptions have been found, but they're small and isolated. Now, however, a larger example has been reported, with the reefs of the Turks and Caicos islands apparently sailing through global bleaching events relatively unscathed. Even corals that did suffer damage have bounced back surprisingly well.
Coral reefs are being hit by multiple threats at once, including pollution, over-fishing, introduced species, and being loved to death by tourists. Even reefs well protected from all these things are dying as water temperatures rise. When corals overheat, they expel the symbiotic photosynthetic algae that give them both their color and much of their food, creating a white appearance called bleaching. Corals can recover from bleaching, but if it lasts too long they die.
The Caribbean has been hit particularly hard, losing 80 percent of its coral cover since the 1970s. An already bad situation became much worse during the 2014-17 global bleaching event, when particularly warm waters pushed a record number of reefs over the edge.
Since 2012, a citizen science program in the British Overseas Dependency of the Turks and Caicos Islands has been surveying 104 dive sites off South Caicos Island. When Abby Knipp, an undergraduate at the University of Illinois at Urbana-Champaign, reviewed their data she was pleasantly surprised. Their findings are reported in Applied Sciences.
“Boulder-type corals on the Turks and Caicos Islands demonstrated no significant bleaching as a result of the peak thermal stress in late 2015,” she said in a statement. “Plate-type corals did suffer bleaching, but they quickly rebounded. Their pigmentation levels were back to normal within months of the anomalously high thermal stress.”
Turks and Caicos boulder corals were more pigmented in 2017 than three years earlier, implying greater health. Plate type corals' algae are less resistant to high temperatures but they were able to rebound.
Hurricane Irma and Maria, which passed the islands on either side, helped. Direct hits from large hurricanes can turn coral colonies to rubble, but big storms also churn up colder water from the depths. For places near, but not right in, the hurricane path, this can be enough to survive otherwise lethal heat. Moderate tourist pressure and less damage to surrounding ecosystems are also part of the South Caicos picture.
However, these reefs may have something currently unknown going on that can be used to save corals elsewhere if we can identify it. Some reefs off Hawaii and at the southern end of the Great Barrier Reef have also been found to be resisting the global trend, but the latest discovery is on a larger scale.