Pāua shells 'at risk' as climate changes

Pāua is NZ's most internationally well-known shellfish. Photo / Getty Images

The "devastating" effects of climate change on the ocean are also threatening pāua, New Zealand's most internationally well-known shellfish, new research shows.

The research, including by National Institute of Water & Atmospheric Research (Niwa) and University of Otago scientists, shows that higher seawater temperatures and ocean acidification will affect the thickness of pāua shells.

"It seems obvious that a healthy planet requires a healthy ocean," Professor Abby Smith, of the University of Otago, said yesterday.

"What we need to realise is that big, planet-wide changes can affect even very small shells living under a rock in New Zealand," Smith, of Otago marine science department, said.

The research team, including Niwa scientists Dr Vonda Cummings, Peter Marriott and Jane Halliday, as well as Smith and recent Otago graduate Dr Bryce Peebles, has discovered the effects of warmer seawater and ocean acidification on young pāua.

Cummings said that, in the future, seawater would be warmer and more acidic, and this would affect the thickness of pāua shells, meaning they were not as resistant to waves and predators.

The scientists grew young pāua — less than 24mm long — in seawater with different combinations of temperatures and pH levels and investigated aspects of the creatures' survival, growth and general health, as well as their shells' thickness, integrity and composition.

The study showed that juvenile pāua were good at surviving and growing in warmer, more acidic water.

But the outer layer of their shells was etched by seawater at lower pH, especially if the water was warmer, Cummings said.

This etching reduced the level of protection for pāua.

Smith is trying to raise awareness about climate change and its "devastating" effect on the ocean, and organised a special, marine-themed march, held alongside the recent climate march in Dunedin.

New Zealand exported both pāua meat and shell and almost nothing was "so quintessentially New Zealand" as an artwork or jewellery made of pāua shell.

"Ocean acidification could make shells thinner, or chemically different, or even impossible," she said.

Pāua shell was unique — "no other abalone species is blue and as lovely. It's also endemic.

"The species only lives in New Zealand", she said.

The research has been published in PeerJ, a peer-reviewed international scientific journal.