Nature

Sydney’s famous rock oysters are getting smaller as oceans become more acidic

New study finds that climate change is causing oysters in New South Wales to become smaller and fewer in number

PUBLISHED : Thursday, 16 August, 2018, 4:20pm
UPDATED : Thursday, 16 August, 2018, 4:40pm

The famous Sydney rock oyster is shrinking as oceans become more acidic, new research has found.

In news that will rock seafood lovers, a study released by academics in the United Kingdom found oysters in New South Wales (NSW) have become smaller and fewer in number because of coastal acidification.

It is part of what researchers fear is a worldwide trend driven by climate change and coastal run-off.

Headed by University of Stirling academic Susan Fitzer, the study looked at oyster leases at Wallis Lake and Port Stephens, both on the NSW coast north of Sydney.

They make up the two largest Sydney rock oyster production areas in NSW.

The study found the oysters’ diminishing size and falling population is due to acidification from land and sea sources, part of a global trend.

“Sydney rock oysters are becoming smaller and their population is decreasing as a result of coastal acidification,” Fitzer said.

“The first thing consumers will notice is smaller oysters, mussels and other molluscs on their plates, but if ocean acidification and coastal acidification are exacerbated by future climate change and sea level rise, this could have a huge impact on commercial aquaculture and populations around the world.”

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The risk to oyster populations around the globe from soil run-off has long been recognised.

In 2014, oyster farmers in Port Stephens released an industry-driven environmental management policy which recognised that damage to oyster leases from the drainage from acid-sulphate soils was both “likely” to occur and “severe” in consequence.

But Fitzer’s research argues that run-off is not caused by agricultural activity and is rather the consequence of the impacts of climate change.

“A lot of work has been done near to Australia’s oyster fisheries to mitigate the impact of sulphate soils causing acidification, and there has been a marked decline in levels,” she said.

“The run-off from sulphate soils aren’t produced by agricultural activity, they occur as a natural result of climate change-driven increases in rainfall and sea-level rise. But the trend persists and small changes in pH are having a huge impact on these molluscs.”

Increased acidification affects oyster growth by limiting the amount of carbonate in the water.

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“Acidic water is damaging oysters’ ability to grow their shells. We see lots of disorder in the calcite layers, because there isn’t enough carbonate in the water for the oysters to draw on for optimal shell formation and growth,” Fitzer said.

The issue is not confined to Australian oyster production.

Ocean acidification has been reported globally, while coastal acidification from the land, as freshwater run-off from acid sulphate soils, is driven by rising sea levels and flooding also decreases environmental pH.

Fitzer has previously linked rising acidification to weaker shells in mussels in Loch Fyne, Scotland.

“This is the first time that the Sydney rock oysters’ shell crystallography has been studied, and we now know disruption to this process could have a significant impact on Australian aquaculture,” she said.

Fitzer’s research was published in the Journal of Ecology and Environment.

Mike Webb, the head of research at the Natural Environment Research Council, said the aim of the study was to contribute “to the understanding of how climate change will affect food production around the world, and lead to collaboration between researchers and industry to solve some of the challenges our society faces”.