Synergistic effects of ocean acidification and warming on overwintering pteropods in the Arctic

• Published in: Global Change Biology
• Main Authors: Lischka, Silke, Riebesell, Ulf
• Format: Article in Journal/Newspaper
• Language: English
• Published: Wiley 2012
• Subjects: Arctic; Climate change; Ocean acidification
• Online Access: http://dx.doi.org/10.1111/gcb.12020; https://api.wiley.com/onlinelibrary/tdm/v1/articles/10.1111%2Fgcb.12020; https://onlinelibrary.wiley.com/doi/pdf/10.1111/gcb.12020

Abstract Ocean acidification and warming will be most pronounced in the A rctic O cean. Aragonite shell‐bearing pteropods in the A rctic are expected to be among the first species to suffer from ocean acidification. Carbonate undersaturation in the A rctic will first occur in winter and because this period is also characterized by low food availability, the overwintering stages of polar pteropods may develop into a bottleneck in their life cycle. The impacts of ocean acidification and warming on growth, shell degradation (dissolution), and mortality of two thecosome pteropods, the polar L imacina helicina and the boreal L . retroversa , were studied for the first time during the A rctic winter in the K ongsfjord ( S valbard). The abundance of L . helicina and L . retroversa varied from 23.5 to 120 ind m −2 and 12 to 38 ind m −2 , and the mean shell size ranged from 920 to 981 μm and 810 to 823 μm, respectively. Seawater was aragonite‐undersaturated at the overwintering depths of pteropods on two out of ten days of our observations. A 7‐day experiment [temperature levels: 2 and 7 °C, p CO 2 levels: 350, 650 (only for L . helicina ) and 880 μatm] revealed a significant p CO 2 effect on shell degradation in both species, and synergistic effects between temperature and p CO 2 for L . helicina . A comparison of live and dead specimens kept under the same experimental conditions indicated that both species were capable of actively reducing the impacts of acidification on shell dissolution. A higher vulnerability to increasing p CO 2 and temperature during the winter season is indicated compared with a similar study from fall 2009. Considering the species winter phenology and the seasonal changes in carbonate chemistry in A rctic waters, negative climate change effects on Arctic thecosomes are likely to show up first during winter, possibly well before ocean acidification effects become detectable during the summer season.