Climate change: Scientists seek to find the ‘tipping point’ of ocean acidification around NZ

Kiwi scientists are simulating how New Zealand’s coastal environment will respond to potentially disastrous effects of acidification caused by climate change.

The new study aims to pinpoint a possible “tipping point” at which ecosystems could collapse – potentially threatening our aquaculture industry.

Ocean acidification, often receiving less public attention than other major climate change impacts like sea level rise and violent storms, is increasingly concerning scientists because of the global threat it poses to coral communities and shellfish aquaculture.

It’s driven by increasing carbon dioxide in the atmosphere, which is absorbed by oceans and causes pH levels to drop and waters to become more acidic.

Scientists are particularly worried about the survival of organisms that have shells composed of calcium carbonate, ranging from corals to shellfish, as it becomes more difficult to grow and maintain in a more acidic ocean.

In a new study, the first of its kind in the world, New Zealand researchers will test how microbes in near-shore sediments respond to pH levels simulated to reflect those projected in 50 years’ time.

Waikato University microbiologist Professor Craig Cary, leading the million-dollar study, said little was known about how microbial communities would handle more acidic waters, despite their critical function in regenerating the nutrients that sustain food webs many marine species rely on.

“In terms of the health of the planet, the bacteria are the rapid responders – they are the guys who always take care of the things we mess up in the marine environment, be it oil spills, pollution and nutrient runoff from agriculture,” he said.

“In the sedimentary environment, bacteria take organic carbon, regenerate it and release it as nutrients, which then powers the system from the bottom up to keep the natural system operating – this is called ecosystem function.”

But major changes had the potential to significantly affect productivity of wild fisheries and aquaculture, worth hundreds of millions of dollars to the New Zealand economy and prized by tangata whenua.

Combining lab experiments, DNA analysis and field sampling, the team will investigate whether microbial systems can adapt to lower pH levels – or whether there’s a tipping point where they will fail.

“If it’s found the system does crash, we will be able to provide a baseline where we see the tipping point happening, which can then be put into a model to see how the industry might have to respond.”

Cary said the findings would also be valuable to many other countries, as the effects of ocean acidification would impact the entire planet.

“Every place in the global ocean is likely to be affected by it in the end.”

While there could be ways to locally “buffer” the system by adding calcium carbonates to the sediment – something his team would also explore – these approaches were still being developed.

The study, also being carried out by Auckland University of Technology marine scientist Dr Kay Vopel and Professor Conrad Pilditch and Charles Lee of Waikato University, is funded by the Ministry of Business, Innovation and Employment.

Jamie Morton, New Zealand Herald, 25 October 2016. Article.

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