Krome, Carsten (2009) pH-, calcium homeostasis and hematology in a high pCO2-environment in the eastern oyster Crassostrea virginica. (Diploma thesis), Christian-Albrechts-Universität zu Kiel, Kiel, Germany, 78 pp.

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Abstract

Rising pCO2 levels in the atmosphere, predominantly attributable to fossil-fuel combustion, are causing a steady decrease in oceanic pH. Various publications have highlighted negative effects of lower pH upon organisms that produce calcium carbonate, including lower shell production in marine bivalves. As shell construction in the Eastern Oyster (Crassostrea virginica) has been shown to be mediated by granular hemocytes, circulating cells with diverse functions, the present study investigated physiological capacity of these cells to respond to extracellular acidification, especially concerning pH and calcium homeostasis. Initial calcium-carbonate crystallization leading to shell construction is thought to occur within specialized organelles, which would have high internal pH as well as high ionic calcium and bicarbonate concentrations to form calcium carbonate crystals that are then deposited at the shell-construction site. Adult Eastern oysters exposed to a strong decrease in external pH (6. 7) for a period of 9 days showed a sustained decrease in hemolymph pH, but no changes in intracellular hemocyte pH, which remained at control values near 7.2 throughout all measurement days (0, 3, 6, 9) of the exposure period. Intracellular calcium, however, declined significantly on day 9 of the experiment in acidified oysters, compared to controls. To further document the equilibration process within hemocytes exposed to low extracellular pH, a method was developed to demonstrate immediate reaction of granulocytes to hypercapnia. When exposed to pH 6.7 seawater, hemocytes showed a significant drop in intracellular pH, compared to the initial value. These values subsequently increased steadily and were no longer significantly different than initial values after 1 O min. These results demonstrate high capacity in granular hemocytes to maintain intracellular pH despite sharp decreases in extracellular pH. It appears, therefore, that reduction in shell production is not attributable to low pH within these cells. The loss of intracellular calcium concentration in response to seawater acidification may represent, however, a decrease in calcium concentration in cellular compartments normally responsible for calcium-carbonate crystal formation.

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