CO2 impact on calcification in marine bivalves - a key to understand past, present and future climate records of polar ecosystems

点击翻译按钮获取中文摘要

Future ocean acidification and global warming caused by anthropogenic CO2 have the potential to adversely affect many marine organisms. Understanding what effects the rapid increase in atmospheric CO2 levels as well as associated trends of temperature rise, have on the physiological performance and calcification processes of marine organisms is an important emerging research topic. The German BMBF (“Bundesministerium für Bildung und Forschung”) has recently funded the national BIOACID research program, where many scientists from different fields and with different background look at the consequences of increasing CO2 levels in the ocean, other international programs dealing with the same query are EPOCA (“European project of ocean acidification”) and a not jet running but already accepted national project on ocean acidification in Britain. The present study will contribute to this more and more developing research field. Since CO2 rapidly equilibrates with the surface ocean, increased CO2 levels in the atmosphere will cause an increase in seawater partial pressure of CO2 (PCO2) with a concomitant decrease in seawater pH (IPCC 2007). An estimated reduction in seawater pH to 7.3 by approximately 0.7 pH units is expected within the next 300 years. Even smaller reductions in seawater pH at elevated PCO2 have an impact on physiological processes in marine organisms, in particular on those related to carbonate skeleton formation. Lower pH values decrease the availability of carbonate (CO2 −3) ions and lower the saturation state of the major shell forming carbonate minerals. The colder the water, the more CO2 is absorbed: consequently, Polar Regions will be the areas where surface seawaters will most likely become undersaturated with respect to aragonite, a form of carbonate ion cluster used by Serripes groenlandicus to build their shell. The energy budget of shell formation may be particularly sensitive to ocean acidification, as may be the quality of the shell. Present hypotheses see a key role of the capacity to regulate extracellular acid-base status in defining the sensitivity of marine ectothermic animals to elevated CO2 tensions. First results show, that Serripes groenlandicus is not able to maintain extracellular pH under elevated CO2 tensions as expected according to future scenarios. During longterm incubations (nine weeks) extracellular pH continues to be completely uncompensated. Most likely this arctic mussel is more susceptible to elevated CO2 than other marine animals like fish or crustaceans, due to their inability to maintain extracellular acid-base status.