4 Oct 2019

Climate change consequences for the iconic paua shell

From Afternoons with Jesse Mulligan, 1:17 pm on 4 October 2019

Researchers have found that changes to seawater temperatures combined with acidity levels dropping will compromise the iconic pāua shells.

Niwa researchers alongside Otago University scientists have been looking at how predicted climate change impacts on the ocean will affect the unique New Zealand pāua.

Professor Abby Smith told Afternoons it will affect the thickness of their shells, which subsequently puts them at risk.

Paua held by Mike Vincent.

Pāua shell. Photo: RNZ / Rebekah Parsons-King

Ocean acidification is one of the major side effects of climate change – it’s when CO2 gets absorbed by the sea, however, the more CO2 that's dissolved in the ocean then the lower the pH is, meaning there’s a little bit a more acid.

Prof Smith says it goes from a pH of 8.1 to a pH of 7.8, which doesn’t sound like a lot but makes a huge difference to animals that depend on particular pH levels to be able incorporate, carbon and oxygen and calcium into their shell.

She says previous studies have observed adult pāua, but their study looked at young pāua and subjected them to different combinations of temperature and pH for a period of time, then looked at the quality of shell, how well it survived, and the metabolism as well.

“We found that juvenile pāua … are able to step up their effort to create the shell they need at least under the range [of conditions] that we subjected them to.

“But what we also found is that once they’ve made it, under low pH situations it starts to degrade – it gets a bit moth-eaten, it gets pitted and edged - from its exposure to lower pH water.

“And that’s where a little wee pāua who counts on his shell to save him, from predators and strong waves and rocks fall and earthquakes in Kaikōura, is not going to be as well protected in a shell that’s got pits and has been edged and is thinner.”

But it’s not just the aesthetic of the shell that a lower pH water threatens, it’s also potentially harmful to their survival and long-term existence, prof Smith says.

“It’s when circumstances change really fast, like they are now, that they can’t [evolve and adapt], and that’s what I’m concerned about and what we’re all concerned about.

“The sea’s acidity has gone up and down over time but always very slowly and gradually, and what’s happening right now is that it’s culminating at a speed never before seen and things like pāua can’t keep up.”

If there’s one thing New Zealanders can do to help is to be more cautious of their carbon emissions, prof Smith says, and that’ll pave the way for other countries to be more conscious.

“Every time we make small efforts to control our carbon emissions, we make small increments, but the most important part of visibly standing up and controlling your carbon emission is that other people notice and then they start doing it too, and that’s also true of New Zealand.”