Ocean Acidification

Anthropogenic CO2 emissions cause rising ocean pCO2 and decreased ocean pH. This progressing ocean acidification has been shown to compromise physiological performance of many marine benthic organisms. In this study, Baltic blue mussel Mytilus edulis and common starfish Asterias rubens from Kiel Fjord were exposed to 6 different hypercapnic levels between 0.04 and 0.41 kPa pCO2 for 1–2 weeks, respectively, at 12 °C. The experiments revealed extracellular acidosis in both species with no active accretion of HCO3−. Even at moderate pCO2 levels (e.g. 0.08 kPa) pHe was significant decreased. Although shell dissolution occurred in the highest pCO2 treatment, no HCO3− or Ca2+ accumulation was observed in extracellular fluids. Gradients of pCO2 between body fluids and ambient sea water were stable at lower pCO2 levels and decreased at 0.41 kPa, which might indicate a metabolic depression. Ongoing metabolic rate and filtration rate determinations will resolve this issue. Calcification rates were only minorly impacted in the lower pCO2 treatments and became negative at 0.41 kPa pCO2. Field measurements conducted in Kiel Fjord revealed a large annual variability of surface pH and pCO2. During winter and spring, surface pH averaged 8.1 but mean summer pH values were < 7.8 and the highest measured pCO2 value exceeded 0.2 kPa (ca 2000 μatm), thus even the maximum average pCO2 values modelled for the surface ocean of the year 2300.

Experiments will be repeated at summer temperatures of 18–22 °C in June 2009 to clarify if thermal extremes increase the species' sensitivity towards hypercapnia.

Thomsen, J., Saphörster, J., Heinemann, A., and Melzner, F., 2009. Impacts of hypercapnia and temperature on physiological performance of marine invertebrates from the Baltic Sea. Comparative Biochemistry and Physiology – Part A: Molecular & Integrative Physiology 153(2): 169. Abstracts of the Annual Main Meeting of the Society of Experimental Biology, 28th June – 1st July, Glasgow, UK. Abstract.