The latest findings on New Zealand's ocean acidification have been published in the Journal of Marine and Freshwater Research.

NIWA scientists found pH measurements taken from off Otago's coast is showing water acidifying at the same rate as carbon dioxide rising in the atmosphere.

The scientists are continuing studies into what decreasing pH in our oceans will mean for it's inhabitants.

They're halfway through a study called CARIM, which focuses on establishing the scale of ocean acidification and how it affects coastal ecosystems.

Dr Cliff Law said they're building an idea of how pH varies from 14 different coastal locations around the country.

He said significant testing is involved.

"The thing about pH is it's really difficult to look for long term trends because particularly in coastal waters there's such a large variation in on a day to day basis and also from site to site."

Law said marine organisms have a variety of responses to ocean acidification, but some shellfish might struggle.

"They're having to put more of their energy into having to maintaining that carbonate shell and that means they've got less energy available for other things like growth and reproduction, so the first off we might see for example smaller paua."