Green sea urchins
Photo: R. Wollocombe

Ocean acidification has been studied in relation to marine animals with calcium carbonate shells. Oysters, sea butterflies, shrimp – all are affected by acidification when their outer shells don’t develop properly.

According to this article, ocean acidification has increased by 25-30% since the beginning of the Industrial Revolution.

A new study published in Nature Climate Change looks at a different key species in kelp forests in temperate and subpolar oceans, green sea urchins. But it’s not their shells that are at risk.

In a first demonstration that ocean CO2 levels can affect the digestion of a marine creature, German and Swedish researchers showed that the larval stage of green sea urchins (Strongylocentrotus droebachiensis) have difficulty digesting in water with higher levels of acidity.

Green sea urchin
Source: OhDeer

The sea urchins compensate by eating 11-33% more, but if additional food is unavailable, their growth, fertility and survival can be compromised.

So while some studies have shown that ocean acidification varying levels of impact on different marine life.

Unlike the effects on oysters and sea butterflies, increased acidity (up to a given threshold) has less of an effect on certain marine animals with substantial shell coverings – like the temperate sea urchin.

Unfortunately, being protected by a thick shell may not be all that’s necessary to survive in an acidified ocean.

Green sea urchin endoskeleton
Photo: galewhale/Project Noah