Australia floods pose dangerous ‘freshwater bleaching’ risk to vulnerable corals, research shows
Freak monsoon-like weather conditions in north-eastern Australia pose a significant risk to corals including the Great Barrier Reef, according to new research.
The impact of abnormal quantities of floodwater reaching the sea causes the salinity of the ocean to drop, which in turn provokes a similar stress response in corals as extreme heating does, researchers from James Cook University and the University of Technology Sydney found.
The phenomenon known as “freshwater bleaching” can result in coral death, the scientists said.
Extreme and sudden changes in ocean salt concentration cause a biochemical response in corals similar to that seen during marine heatwaves, but in some ways it could be even more damaging, they added in the findings which were published in the journal BMC Genomics.
“Corals are sensitive organisms, known to only tolerate slight changes in their environment. Thriving in clear, sunlit waters - the majority of reef-building corals are found in tropical and subtropical waters with a salinity between 32 to 42 parts per thousand,” said senior author Professor David Miller. “During the recent flooding, there are reports that nearshore reefs were exposed to roughly half the normal ocean salinity.”
“Our research shows that this kind of environmental change causes a shock response in corals that prevents normal cell function.”
To examine the impact floodwater entering coral seas may have, the researchers used the sequenced genome - a biological blueprint - of the common reef-building coral, Acropora millepora. Then they looked for changes in the coral’s biology.
“Using the sophisticated labs at the National Sea Simulator, we put both young and adult corals under a salinity stress test to see how they respond to differing salinity concentrations,” said co-author Dr Jean-Baptiste Raina. “We found that there was a common response between both coral life-stages - with the younger corals being more sensitive to low salinity conditions, but faring slightly better with exposure over time.”
The reaction was comparable to how corals react when exposed to warming sea waters.
“In general, we found that the coral’s cells launch a similar chemical response to reduced salinity as they do for heat stress,” Prof Miller said. “However, unlike the heat stress response, corals exposed to reduced salinity experience a complete collapse of their internal cellular protein balance, suggesting that their cells are in deep trouble.”
The findings come a few days after the Great Barrier Reef Marine Park Authority told a government committee there is a chance corals already damaged after being hit by mass bleaching in 2016 or 2017 could be damaged again by one of several impacts from the flooding disaster.
Other impacts include algal blooms which have erupted after fertilisers from farmland were washed into the sea. These form huge rafts of algae which block light from reaching the corals.
Earlier this month, floodwaters spread more than 37 miles offshore, dragging huge green clouds of algae over the reef.
Meanwhile one million tons of sludge composed of industrial residues are to be dumped on the Great Barrier Reef, after Australian authorities circumnavigated a rule which bans dumping waste at the World Heritage-listed site.
The dumping licence, awarded due to a loophole for “port maintenance waste”, was described as “another nail in the coffin” for the beleaguered reef - the biggest living structure on Earth.
Since 2016 half of all the coral in the Great Barrier Reef is estimated to have died.
