Ocean acidification impacts on Southern Ocean Pteropods

Laboratory experiments suggest that decreased carbonate saturation will lower calcification rates of marine calcifiers, particularly aragonite producers such as shelled pteropods.Observations of impacts of decreased carbonate saturation on these at risk taxa in nature are, as yet, limited. The Southern Ocean presents a unique opportunity in which to observe in situ responses of pteropods to changes in ocean carbonate chemistry as these waters contain a disproportionate amount of the oceanic inventory of anthropogenic CO2 and will experience aragonite undersaturation earlier than other areas of the global ocean. Through a sustained sediment trap monitoring program in the deep (2000 m) subantarctic (47°S, 142°E) Southern Ocean we infer a slight decline in mean shell weight, and contribution to total pteropod flux, of the common shelled pteropod Limacina helicina antarctica forma antarctica from 1997-2006.Attribution of this trend to acidification is unclear. However, these small but discernible interannual decreases may represent an emerging response to changing carbonate saturation in the Southern Ocean, which does have a clear, if slow, decadal decline. As pteropods are important biogeochemically and nutritionally in the Southern Ocean ecosystem there is a particular urgency in determining the impact of ocean acidification on these calcifiers. And as we are unable to access pre-industrial baselines of calcification for pteropods in the Southern Ocean our results point to the importance of continued in situ observations in this at risk marine ecosystem as a means of detecting impacts of ocean acidification on the most vulnerable calcifiers as early as possible.