Ocean Acidification Corroding Shells of Antarctic Sea Snails

Ocean acidification is corroding the shells of tiny marine snails living around Antarctic seas, making them susceptible to predator attacks, finds a new study.

The marine snails called pteropods play a significant role in the marine food chain and maintaining the ecosystem.

Increased emission of carbon in the atmosphere is absorbed by oceans and deposited on the floor as sediments. The rise in carbon intake has changed the chemical composition of the sea water by reducing the pH levels (concentration of hydrogen ions) and making it more acidic.

A team of international researchers studied the impact of ocean acidification on samples of pteropods (Limacina helicina Antarctica) taken during a research expedition to the Southern Ocean in 2008. They found that ocean acidity is corroding the shells of the pteropods.

The research team examined the effects of upwelling water on the shells of pteropods. Upwelling water occurs when the wind pushes the cold and dense water to the ocean's surface.  

The sea water corrodes aragonite, a type of calcium carbonate that the pteropods use to form shells when the water is pushed from a depth of around 1,000m toward the surface. This point is known as the "saturation horizon." 

The saturation horizon in some areas of the ocean was reached at a depth of around 200m, where pteropods live in the upper layer of the ocean. This is because of the combined effect of increased ocean acidity and natural upwelling, reported BBC.

This causes the shells of the sea snails to dissolve. While the snails might not die, they could become more vulnerable to predator attacks and diseases, said the researchers.

"Carbonates in shells dissolve more when temperatures are cold and pressure is high, which are the characteristic properties of the deep ocean," Dr Geraint Tarling, head of Ocean Ecosystems at the British Antarctic Survey (BAS) and co-author of the report, told BBC.

Tarling and his colleagues have projected that the increase in carbon dioxide levels would cause stronger winds, triggering the blend of deep water with acidic surface water above 200m more often, a report in Reuters said.

The team is now working on a project to study the impact of ocean acidification not only on pteropod shells, but also on different range of marine organisms.

The findings of the study, "Extensive dissolution of live pteropods in the Southern Ocean", are published in the journal Nature Geoscience.