Weak Armor

Marine animals are already feeling the effects of higher carbon dioxide levels near the ocean’s surface. In Nature Geoscience, researchers have reported finding live molluscs called sea butterflies with partly-dissolved shells in the Southern Ocean.

The organism in question, Limacina helicina antarctica, needs a form of calcium carbonate called aragonite to build its shell. But as the ocean surface absorbs more carbon dioxide from the atmosphere, the water becomes more acidic and carbonate ion levels drop. Lab experiments have shown that sea butterflies’ shells become deformed under high carbon-dioxide conditions, but “such effects have not been documented on live animals extracted directly from the natural environment,” the study authors write.

The team collected live sea butterflies from part of the Southern Ocean where deep water often rises close to the surface, bringing more carbon dioxide along with it. Using a scanning electron microscope, the researchers found that some organisms showed “severe levels of shell dissolution,” according to the study. While these weakened shells aren’t fatal, the animals have less protection against diseases and predators.

The low aragonite levels in that part of the ocean were due partly to carbon dioxide emissions from human sources and partly to the upwelling of water high in carbon dioxide, the authors say. They note that the Southern Ocean is expected to get windier as the climate changes, which could trigger more upwelling.  Roberta Kwok | 27 November 2012

Source: Bednarsek, N. et al. 2012. Extensive dissolution of live pteropods in the Southern Ocean. Nature Geoscience doi: 10.1038/ngeo1635.

Image © R. Giesecke | Wikimedia Commons