Schade, Hanna (2012) Influence of seawater acidification on benthic bivalve communities. (Master thesis), Christian-Albrechts-Universität Kiel, Kiel, Germany, 65 pp.

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Abstract

Marine organisms have to cope with increasing CO2 partial pressures in the oceans. The ocean acidifies as an effect of ongoing pCO2 increase and as a possible result of leakage at carbon capture and sequestration (CCS) storage sites. Leakage at CCS storage sites has the potential to cause a localized very strong increase in pCO2. This is the first study testing the effects of moderately to highly elevated pCO2 on three marine infauna bivalve species during a 12 week period using six different pCO2 levels (900, 1,500, 2,900, 6,600, 12,800, 24,000 μatm) were applied. In this study the effects of high pCO2 on mortality, shell free dry mass, corrosion, behavior and tissue malondialdehyde (MDA) content of different size classes of the cockle Cerastoderma edule were investigated. For the same treatment levels, mortality and behavior of Mya arenaria and Macoma balthica were assessed. C. edule was found to be highly sensitive to possible leakage as pCO2 had a significant influence on mortality for levels > 6,600 μatm. Mortality decreased with size, larger animals were less susceptible than smaller animals. In the highest treatment even larger specimens were strongly impacted by elevated pCO2 and mortality was high. C. edule was found to be influenced at lower pCO2 as corrosion of the shell, visualized using SEM analysis, occurred at a level of 1,500 μatm. This value will occur due to general CO2 increase, even without the added influence of potential CCS leakage. Visible macroscopic corrosion could be shown for 2,900 μatm. Shell free dry mass decreased in the highest pCO2 level indicating starvation and tissue metabolization. MDA content and filtration rate tended to increase until a pCO2 of 2,900 μatm and decrease at higher levels. Significant correlation between both parameters suggest a decrease in metabolism at the highest pCO2 levels tested. At very high levels of pCO2, cockles move to the sediment surface prior to death and are easily visible. This behavior is applicable as a monitoring technique for possible leakages. C. edule was found to be highly sensitive towards acidification within the water column. Future ocean acidification scenarios (< 3000 μatm) were shown to be not lethal but did influence shell morphology, while leakage scenarios (> 6,000 μatm) led to increased mortality. Mortality and behavior were not significantly influenced by pCO2 at any of the applied levels for M. arenaria and M. balthica, suggesting a very high resistance of both species towards increasing pCO2 in the ocean.

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