The global increase in atmospheric carbon dioxide concentration is potentially threatening marine biodiversity in two ways. First, carbon dioxide and other greenhouse gases accumulating in the atmosphere are causing global warming. Second, carbon dioxide is altering sea water chemistry, making the ocean more acidic, a phenomena known as ‘ocean acidification’. While temperature has a cardinal influence on all biological processes from the molecular to the ecosystem level, acidification might impair the process of calcification or exacerbate dissolution of calcifying organisms (Fabry et al. 2008).
The examination of six calcifying taxa routinely collected with the Continuous Plankton Recorder revealed changes in spatio-temporal distribution between 1960 and 2009. The pteropod mollusc Clione limacina (also known as sea angels) showed a reduction in both spatial extent and maximum abundance while the other pteropod Limacina spp. (i.e. sea butterflies) exhibited the same pattern although a biogeographical poleward movement is observed along the European continental shelf-edge, which is similar to biogeographical shifts reported for copepods by Beaugrand (2002). Echinoderm larvae extended their spatial distribution to the northern part of the North Sea, with an increase in average abundance in the region. Bivalve larvae exhibited a pronounced reduction in spatial extent from the 1960s to the 2000s and are now only observed in higher abundance in the northern the North Sea. Foraminifera and coccolithophores both increased in frequency of occurrence in all oceanic regions covered by this study.
Exploration of the results further indicates that changes in annual SST were positively correlated to changes in foraminifera, echinoderms and coccolithophores and negatively to alterations in pteropods and bivalves. Modifications in calcifying plankton were also correlated to changes in pH (negatively for foraminifers, coccolithophores and echinoderms and positively for pteropods and bivalve larvae). These results suggest that annual SST had a more direct effect on calcifying organisms than pH during the period 1960-2009. This supports earlier findings which suggest that we should be cautious in the attribution of current changes in calcifying plankton to ocean acidification because plankton are also highly sensitive to temperature as well as other physical and chemical factors.
Beaugrand, G., McQuatters-Gollop, A., Edwards, M. and Goberville, E., (2013). Long-term responses of North Atlantic calcifying plankton to climate change. Nature Climate Change, 3: 263-267.
McQuatters-Gollop, A., Burkill, P., Beaugrand, G., Edwards, M., Gattuso, J.-P. and Johns, D.G., (2010). Atlas of Calcifying Plankton: Results from the Continuous Plankton Recorder Survey. SAHFOS, Plymouth, UK, 20 pp.