An international team of researchers, including a scientist from The University of Western Australia, has warned of the devastating consequences for shallow reef ecosystems when global warming combines with local weather anomalies.
In the research published today in Scientific Reports, scientists found that a 2 degree Celsius rise in sea temperatures surrounding the Dongsha Atoll, a shallow coral reef in the northern South China Sea, was intensified to 6 degree Celsius on the reef, causing mass coral bleaching that killed 40 per cent of the resident coral community.
Lead author of the study Dr Thomas DeCarlo, who recently joined the UWA Oceans Institute after completing his PhD at the Woods Hole Oceanographic Institution, said the corals at the Dongsha Atoll were typically very healthy and should have shown resiliency, but that wasn’t the case.
“This reef is typically hit with tropical storms and strong winds in June, which keep the corals as cool as the open ocean,” Dr DeCarlo said.
“But in 2015, the weather in June was exceptionally calm – at one point, there was basically no wind and no waves, making the sea surface so mirror-like that it was difficult to tell where the horizon was.
“This had an intensifying effect on the water temperatures that were already warmer than usual due to global warming and El Niño, causing the whole reef to become a giant swimming pool that just sat there and baked in the sun. Nearly half of the corals died within the space of one month.”
Once the water temperatures had stabilised, the researchers drilled core samples from the corals living on the reef and used Computed Tomography scans to look for thermal stress signals, a sign this had occurred in the past.
While there were signs of bleaching, nothing appeared as damaging as the 2015 event, suggesting global projections for coral reefs may not accurately account for the local weather anomalies that occurred at the Dongsha Atoll.
Dr DeCarlo said most projections of coral-reef futures relied on estimates of open-ocean warming and were overly optimistic for many shallow coral-reef ecosystems.
“Models based on open-ocean warming already paint a dire picture for coral reefs, but the scary reality is that they are probably too optimistic for many shallow reefs,” he said.
Dr Thomas DeCarlo (UWA Oceans Institute) (+61 8) 6488 4486 / (+61 4) 09 895 484
David Stacey (UWA Media and Public Relations Manager) (+61 8) 6488 3229 / (+61 4) 32 637 716