At the beach? Meet global warming’s evil twin

By Lynley Hargreaves 15/01/2015

Kina, or New Zealand sea urchin
Kina, or New Zealand sea urchin

One third of our carbon dioxide emissions are absorbed by the world’s oceans, which increases the acidity of the water and affects marine life. The University of Auckland’s Associate Professor Mary Sewell looks into the impacts on kina, or the New Zealand sea urchin, and how their fertilisation, early development and metabolism change. She tells us what ocean acidification will mean for your local beach.

Why did you chose to work on kina?

Marine organisms that have a calcium carbonate skeleton, such as kina, are vulnerable to the effects of ocean acidification as the skeleton can dissolve or is more difficult to lay down in lower pH conditions. This is true of both the adults and the larval stages that are the focus of our studies. The choice of species was also influenced by the fact that I have been working on echinoderms for my entire research career.

Associate Professor Mary Sewell
Associate Professor Mary Sewell

What are your results?

We produce larval stages in the laboratory from adult sea urchins collected at Matheson’s Bay near the Leigh Marine Laboratory. These larval stages are found naturally in the water column during the summer months. We manipulate the pH by bubbling buckets of seawater with a CO2/air mix and then grow the embryos and larvae in these conditions. We have shown that kina larvae are affected by a lower pH – they are smaller, have reduced skeletons, and our physiological measurements show that they are under considerable stress at a CO2 concentration expected before the year 2100 (540 ppm). If the larvae cannot complete development, then we might see lower populations of kina in New Zealand in the near future.

Can’t sea life just adapt to ocean acidification?

The rate of change of CO2 concentration is unprecedented in Earth’s history, with CO2 rising at nearly two parts per million each year. As well as ocean acidification, marine organisms are also facing challenges from warming seawater temperatures, changing oxygen conditions, and the addition of nutrients from land-based agriculture. In combination, these “multiple stressors” will mean that many species will struggle to survive in their current geographical distributions.

Will ocean acidification affect human food stocks?

Kina are an important customary and recreational food for many New Zealanders, so lower numbers of kina will impact people who like to eat them (not me…), and the subtidal kelp forests where they, and many commercially-important fish species, live. Other research in New Zealand is showing that ocean acidification has an impact on species with shells, such as mussels, oysters, and paua, which has implications for both human food stocks and our aquaculture industry.

These interviews showcase researchers supported by the Marsden Fund which, since 1994, has been supporting fundamental, investigator-led research in New Zealand.