Sydney rock oysters shrinking due to coastal acidification


16 August 2018 by Sarah McDaid

Sydney rock oysters, found only in the waters of Australia and New Zealand, are getting smaller due to coastal acidification, a new report has found.

A NERC study carried out by Scottish and Australian scientists at two commercial oyster farms in Wallis Lake and Post Stephens, both in the Mid North Coast, New South Wales, confirmed that the oysters' diminishing size and falling population is due to acidification from land and sea sources.

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

Dr Susan Fitzer, a NERC independent research fellow at the University of Stirling in Scotland, reported her findings in the journal Ecology & Environment. While the research project focused on Australian aquaculture, Dr Fitzer warns that seafood lovers around the globe could begin to find smaller and smaller oysters on their plates.

Dr Fitzer said:

Sydney rock oysters are becoming smaller and their population is decreasing as a result of coastal acidification. A lot of work has been done near to Australia's oyster fisheries to mitigate the impact of sulfate soils causing acidification, and there has been a marked decline in levels. The run-off from sulfate 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.

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.

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.

While the Sydney rock oyster is native to Australia and New Zealand, Dr Fitzer has previously linked rising acidification to weaker shells in mussels in Loch Fyne, Scotland and sees global ramifications for the study.

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.

Dr Fitzer's findings are from a five-year NERC-funded project that is investigating biomineralisation in commercially farmed and wild shellfish, to understand how climate change will affect global aquaculture.

NERC Head of Research, Oceans, Mike Webb said:

By supporting research projects like Dr Fitzer's work in Scotland and Australia, NERC is contributing to the understanding of how climate change will affect food production around the world, and leading to collaboration between researchers and industry to solve some of the challenges our society faces.