Staff writers
Marine researchers returning from reefs off the West Australian coast report minimal coral bleaching, suggesting some resilience despite a global mass bleaching event.
The field trip was conducted off Scott, Ashmore and Mermaid reefs by a team from the University of Western Australia (UWA) and the government agency Australian Institute of Marine Science (AIMS).
There was concern these reefs would suffer the same bleaching experienced by others around the world in the past year, but reef ecologists believe cyclones in the region between February and April had a cooling effect on the Indian Ocean.
The UWA and AIMS research teams were worried about the reefs due to previous susceptibility to bleaching – a phenomenon where stressed corals eject symbiotic algae that leaves the exposed calcium carbonate skeletons with a ‘bleached’ appearance.
Scott Reef had bleached in 1998 and 2006.
“It was a relief to observe that the WA oceanic reefs had not been impacted in a similar way to the Great Barrier Reef, especially considering the significant heat stress that satellite monitoring indicated had built up over the Scott and particularly Ashmore Reefs in December and January,” says AIMS reef ecologist James Gilmour.
Gilmour’s concern prior to arriving at Scott and Ashmore was prompted by satellite evidence showing reef heat stress had reached 14 degree-heating weeks (DHWs). DHWs are a ‘heat-over-time’ measurement.
“Normally you see significant bleaching and mortality at 8 DHWs,” Gilmour says.
While some evidence of bleaching and coral death was seen in the region, as well as disease and storm and cyclone damage, overall reefs in WA waters were in better condition than others off the Australian coastline.
“Our observations at Mermaid Reef in the Rowley Shoals, which is further south and previously has been less likely to bleach, indicates these reefs were less affected by the elevated sea temperatures and remain in good condition,” Gilmour says.
