The Ocean in a High-CO2 World: Science highlights from the symposium
The impact of ocean acidification on calcification has been investigated for over 20 years. However, few taxonomic groups of calcifying organisms have been studied in acidified conditions: among them are reef-building corals and phytoplankton (coccolithophores). Yet, there are more than 16 phyla of calcifying organisms, some of them critically important due to their role in biogeochemical cycles or because they are host to ecosystems with high biodiversity. Arctic pteropods, or marine snails, and deep-sea corals thrive in areas that will be among the first affected by changes in ocean acidification. The polar pteropod Limacina helicina (Figure 1) is a major dietary component for zooplankton and higher predators such as herring, salmon, whale and birds. Its fragile aragonite shell plays a vital protective role and forms an external skeleton. Perturbation experiments, carried out under controlled pH conditions representative of carbonate chemistry for 1990 and 2100, show calcification rates decreased by 28% for the pteropod L. helicina when pH was lowered by 0.3 units. An even larger reduction of 50% was seen in response to a decrease of 0.3 pH units for the cold-water coral Lophelia pertusa (Figure 2). While tropical coral reefs are formed by a large number of coral species, the structure of a cold-water coral reef is made by one or two coral species that form the basis of a very diverse ecosystem. A reduction in skeletal growth as a consequence of ocean acidification can therefore become detrimental to the whole ecosystem.
These first results presented during the Monaco Symposium raise great concern for the future of pteropods and cold-water corals, and organisms that depend on them as a food source or habitat. One role of the recently launched national or international research projects on ocean acidification will undoubtedly be to generate data on other taxa, longer time scales and on the interactive impacts of ocean acidification and other global changes such as temperature on these organisms.