Deepwater coral also affected by climate change
AUCKLAND: Even the darkest depths of Australia’s worldrenowned Great Barrier Reef might not be safe from the impacts of climate change, a New Zealand researcher says.
Victoria University’s Dr Alice Rogers was among an international team that investigated a mass bleaching event in 2016 that wiped out about a third of shallowwater corals at the Queensland natural wonder.
Coral bleaching, named because of the lightenedwhite appearance the coral takes on when it expels algae from its tissue, is driven by rising sea temperatures.
The new study, published in scientific journal Nature Communications, showed that while deeper reefs suffered less damage, corals tens of metres below the surface still showed significant signs of bleaching.
‘‘We know little about bleaching temperature thresholds for corals living beyond the wellstudied shallow reef,’’ said Dr Rogers, from Victoria’s School of Biological Sciences.
‘‘We hope that this study and further science in this area will help us learn more about deepreef response to coral bleaching.’’
The study’s lead author, Dr Pedro Frade, from Portugal’s Centre of Marine Sciences, was alarmed at the new findings.
‘‘It was a shock to see that the impacts extended to these dimly lit reefs, as we were hoping that their depth may have provided protection from this devastating event,’’ he said.
The team sent remotely operated vehicles and divers down to survey the reef.
Their findings showed that bleaching affected almost a quarter of corals at a depth of 40m, compared with about half the corals at shallower depths.
During the bleaching event, coldwater upwelling initially provided cooler conditions on the deep reef.
But when this upwelling stopped towards the end of summer, temperatures rose to recordhigh levels even at depth.
‘‘Unfortunately, this research further stresses the vulnerability of the Great Barrier Reef,’’ said study coauthor Prof Ove HoeghGuldberg, of the University of Queensland.
‘‘We already established that the refuge role of deep reefs is generally restricted by the limited overlap in species with the shallow reef,’’ he said.
‘‘However, this adds an extra limitation by demonstrating that the deep reefs themselves are also impacted by higher seawater temperatures.’’
The research team planned to study the process of recovery from these bleaching events, examining how deeper and shallower reefs differ in their recovery. — NZME