Marine scientists in New South Wales are working to understand how reduced pH levels and increased temperatures in oceans, both projected with climate change, impact oysters.

Farmers in NSW grow approximately 4,000 tonnes of oysters each year, about one-third of Australia's total production.

Internationally, Australia's output of 12,000 tonnes per year is relatively small compared to countries like China and France.

But after a decade's work, the researchers from the NSW Department of Primary Industries (DPI) and the University of Sydney are drawing on analysis from their initial phases of research.

The scientists are now shifting their focus to understanding what are the trade-offs for those oysters which have proven to be resistant to climate change effects.

Breeding lays foundation for climate studies

This pan contains thousands of early-life oysters being grown in controlled conditions for research. ( ABC Newcastle: Robert Virtue )

The research has been a collaboration between University of Sydney's Dr Laura Parker and Professor Pauline Ross, and Dr Wayne O'Connor from the DPI's Port Stephens Fisheries Institute.

Their study began over a decade ago and looked to build on research into selective breeding of oysters undertaken at the DPI facility.

Dr O'Connor said their breeding program had produced over 200 families of oysters with various traits, including being fast-growing.

"We follow the performance of those families for things like growth, survival, shape, and their meat condition. Then we can select from those families to produce oysters that combine the characteristics most useful for industry," he said.

"The family lines also give us a really useful tool to determine what capacity natural oyster populations have to deal with various stressors.

"We can use those family lines as the basis for tests to see whether the wild population is going to be largely unaffected, or certain portions of the population may be very highly affected by certain variables."

Resilience differs in wild and selectively-bred oysters

Scientists look at how the oysters 'spend' their energy budgets. ( ABC Newcastle: Robert Virtue )

The 'normal' level of pH in the ocean is 8.2, but by the end of the century, due to climate change, the pH level is forecast to be 7.9 — the level the oysters were tested in.

The study evolved over a series of experimental phases.

Wild oysters were firstly grown in conditions simulating climate change — reduced pH levels and increased water temperature.

The scientists found wild Pacific and Sydney rock oysters were adversely affected by climate change conditions with reduced fertilisation success, developmental abnormalities, and reduced growth reported.

When fast-growing oysters from the DPI's selective breeding program were tested, they were found to have better resistance to climate change conditions.

"They had about 30 per cent better growth under ocean acidification, or those reduced pH conditions, than the wild population did," Dr Laura Parker said.

"It's to do with the way they grow their shells. One of the main impacts of reduced pH is that it's much more difficult for an oyster to lay down their shell and to maintain that shell.

"These oysters that had already been selectively bred for faster growth, they're already putting much more energy into their shell growth and are better at doing that.

"We think that's one of the reasons why they were able to grow better under those reduced pH conditions."

Further questions raised

NSW farmers grow approximately 4,000 tonnes of oysters each year. ( ABC News: Kim Honan )

While the fast-growing oysters were found to be more resistant to climate change, the results of further experiments raised other questions for the researchers which they are now considering.

Professor Ross said they studied how the offspring of both wild and selectively-bred oysters, placed in stressful conditions, coped.

"They appeared to be doing better if their parents had been in a stressed environment," she said.

"Those series of experiments told us that we could actually breed or create some more resilient oysters, even in the wild [population].

"However, the next experiment told us when we put them into multiple stressors that are in an estuary — reduced salinity, increased temperature [that we expect under climate change] — their offspring may not do as well.

"It ends up being a bit of a complex story. We can create more resilient oysters, but then there's trade-offs, and this is where we're intending to go next."

The scientists are now trying to work out what the trade-offs are for oysters resistant to climate change. ( ABC Newcastle: Robert Virtue )

Understanding those trade-offs and searching for the so-called 'Goldilocks' oyster which can adapt best, despite the challenges, is what the scientists will look at next.

"The resilience that's being created is coming at an energetic cost, so these oysters are putting more energy into growing their shell, into maintaining the pH of their blood, that's how they're able to do so well," Dr Parker said.

"But because of that they seem to have less energy available for other processes, so that might be their reproduction and other processes like that.

"What we really want to focus on now is incorporating this research within the family lines of the breeding program [and] looking at the different energy budgets.

"Whether we can find oysters which have a bigger energy budget to start with so they're able to still have energy left over to put into surviving things like elevated temperature, changes in salinity, and the other stressors that are in their environment.

"Or whether we can find oysters that use less energy to survive the reduced pH so they've got more energy left over.

"I think we're never going to find the 'Goldilocks' oyster that is the best at everything ... [but] I do think we are going to be able to find oysters that are right for the environment that we need to put them in and that do have the traits that we need them to have."