An increase in the number and severity of marine heatwaves is forcing the seafood industry to temperature-test oyster beds and breed more resilient varieties to combat climate change.

A heatwave in NSW waters from late January to mid-March caused an acceleration in bacteria in oysters, forcing farmers to dump stocks and temporarily shut down operations, as water temperatures shot up in some areas.

Ocean acidification, greater incidents of flooding from repeated La Nina weather patterns over the past five years and polluted waterways, have all contributed to a rise of more than 20 per cent in farmgate oyster prices in the past two years.

“We went from selling 3,000-dozen a week to zero for the last month,” said Dominic Boyton of Merimbula Gourmet Oysters at Merimbula Lake, on the far south coast of New South Wales.

The manager of the farm and lake coordinator, who is in charge of water testing at the lake, added: “The oysters didn’t like the heat at all.

“The naturally occurring bugs went crazy because it was nice and warm for them. That’s what we’re putting down as our major issue.” 

The Climate Council has recorded double the amount of marine heatwaves since 1980, putting New South Wales’ seafood industry under increased pressure.

Marine heatwaves occur when excess heat in the atmosphere is trapped by greenhouse gas emissions and absorbed by oceans. The ocean has already absorbed 93 per cent of this excess heat, damaging the world’s marine life.

We knew there were probably some changes coming but we all, even the authorities, were like ‘oh!’…we’ve never had this before’.

Oysters have been particularly affected by recent marine heatwaves along the coast of NSW.

The farming of them has been the most valuable aquaculture industry in NSW for over 100 years, with Sydney Rock Oysters accounting for over 90 per cent of the state’s oyster production.

Dr Elliot Scanes, a postdoctoral research fellow at the University of Technology Sydney’s Climate Change Cluster, said: “Oysters are the number one seafood product from New South Wales… they’re worth over $200 million to the state every year, and they support a lot of employment in regional areas.”

“Heat waves lower oysters’ immune systems and make them vulnerable to bacteria and other diseases.” 

He said the flow-on affects the entire marine ecosystem.

“We may see a degradation in the health of our coastal ecosystems because oysters cannot provide services they used to, like filtering and shoreline protection,” he said.

According to the Climate Council’s report, the ocean is absorbing enough excess heat energy to boil Sydney Harbour every eight minutes.

Sydney’s water temperature has already risen to tropical levels, with waters so warm that coral has been growing in Sydney Harbour.


Oyster beds at Brunswick Heads, NSW. Source: Wikimedia.


Economic conditions have also affected oyster prices, with Pez Collier, from Melbourne restaurant Pearl Diver, telling the Sydney Morning Herald last year they were up 20 to 25 per cent.

He attributed it to a combination of factors including higher freight and transport costs, as well as three years of La Nina weather.

At the top of Merimbula Lake, which is shallow and so naturally warmer than the water at the entrance to the sea, the cooler ocean water usually lowers temperatures as the tide comes in. 

However, with marine heatwaves off the coast of NSW, Boyton recorded water temperatures up to 4 degrees celsius above normal.

“You couldn’t tell the difference between the tide going in or going out,” he said.

“In summer, the entrance to the lake would usually be 20 to 22 degrees, we were sitting up around the 26-degree mark.”

He added the farm was unprepared for the extremity of the marine heatwaves.

“We knew there were probably some changes coming but we all, even the authorities, were like ‘oh!’…we’ve never had this before,” he said.

While oyster farmers are bearing the brunt of the effects of the marine heatwaves, there’s nothing they can do to prevent them. 

Instead, the focus is on minimising the effects.

We’ve got these new rules coming in after we harvest our oysters, all about temperature control. I think it will change for the whole NSW oyster industry.

“Now that we know the consequences of marine heatwaves,” Boyton said, “we just have to better manage.”

Merimbula Gourmet Oysters is now being used by the NSW Food Authority as a test case for other oyster farms in the state. 

Boyton said new rules will soon be put in place by the NSW Food Authority covering water temperature testing and control to ensure affected oysters, which may make people sick, will not be sold.

“We’ve got these new rules coming in after we harvest our oysters, all about temperature control,” said Boyton. “I think it will change for the whole NSW oyster industry.”

Changes, however, will only escalate as marine heatwaves continue to grow in severity, escalating economic and environmental loss which comes with oyster degradation.

“Archaeological evidence has shown that oysters have been actually cultivated by Indigenous peoples in Australia for thousands and thousands of years,” Dr Scanes said.

“It is important to maintain that and ensure that the connection is not lost.”

Dr Scanes is working closely with scientists, Indigenous communities, and the NSW Department of Fisheries to combat marine heatwaves’ effects, and said there are a number of solutions being worked on that would soon be implemented.

 “What we’re able to do is selectively breed to help oysters evolve more quickly,” he said. “We’ve been able to select oysters that are much more resilient to climate change.

“I do think that there is an opportunity for the marine environment to respond and overcome some of the challenges.”

Main image by Paul Arps/Flickr.