Interactive effects of salinity and elevated CO2 levels on juvenile eastern oysters,Crassostrea virginica

Abstract

SUMMARYRising levels of atmospheric CO 2 lead to acidification of the ocean and alter seawater carbonate chemistry, which can negatively impact calcifying organisms, including mollusks. In estuaries, exposure to elevated CO 2 levels often co-occurs with other stressors, such as reduced salinity, which enhances the acidification trend, affects ion and acid-base regulation of estuarine calcifiers and modifies their response to ocean acidification. We studied the interactive effects of salinity and partial pressure of CO 2 (P CO2 ) on biomineralization and energy homeostasis in juveniles of the eastern oyster, Crassostrea virginica, a common estuarine bivalve. Juveniles were exposed for 11weeks to one of two environmentally relevant salinities (30 or 15PSU) either at current atmospheric P CO2 (~400atm, normocapnia) or P CO2 projected by moderate IPCC scenarios for the year 2100 (~700-800atm, hypercapnia). Exposure of the juvenile oysters to elevated P CO2 and/or low salinity led to a significant increase in mortality, reduction of tissue energy stores (glycogen and lipid) and negative soft tissue growth, indicating energy deficiency. Interestingly, tissue ATP levels were not affected by exposure to changing salinity and P CO2, suggesting that juvenile oysters maintain their cellular energy status at the expense of lipid and glycogen stores. At the same time, no compensatory upregulation of carbonic anhydrase activity was found under the conditions of low salinity and high P CO2 . Metabolic profiling using magnetic resonance spectroscopy revealed altered metabolite status following low salinity exposure; specifically, acetate levels were lower in hypercapnic than in normocapnic individuals at low salinity. Combined exposure to hypercapnia and low salinity negatively affected mechanical properties of shells of the juveniles, resulting in reduced hardness and fracture resistance. Thus, our data suggest that the combined effects of elevated P CO2 and fluctuating salinity may jeopardize the survival of eastern oysters because of weakening of their shells and increased energy consumption.

Impacts of ocean acidification on marine shelled molluscs

“…This suggests that well-fed healthy animals might display a higher capacity to compensate than starving individuals and that the physiological conditions of the specimens are essential (see section ''Synergistic impacts''). In contrast to Ries et al (2009) for the Eastern oyster C. virginica, Dickinson et al (2012) showed that shell growth of juvenile oysters were not affected by a pH decrease of up to -0.3 pH unit. However, the mechanical properties of the shells of the juveniles were altered under hypercapnic conditions, resulting in a reduced hardness and fracture resistance.…”

“…Oysters, the other economically very important group of species, appear less resistant than mussels to low pH conditions (three experiments showing negative impacts out of five), despite producing less soluble low-magnesium calcite shells. Moreover, the study showing no effect on oyster shell growth (Dickinson et al 2012) demonstrated that a pH decrease of less than -0.4 pH unit had significant effects on the shell hardness and fracture resistance. This could have importance consequences for this species in the field with a reduced capacity to resist to, for instance, strong currents and predators.…”

Ocean acidification and temperature increase impact mussel shell shape and thickness: problematic for protection?

“…It has been reported that ocean acidification will impact not only growth but also the ultrastructure of mollusk shells (Dickinson et al. 2012; Ivanina et al. 2013; Coleman et al.…”

“…2013) and fracture resistance after 11 weeks (Dickinson et al. 2012) in the juvenile oyster Crassostrea virginica (Dickinson et al. 2012; Ivanina et al.…”

“…2012) in the juvenile oyster Crassostrea virginica (Dickinson et al. 2012; Ivanina et al. 2013) and reduced fracture toughness in adult mussel M. edulis (Fitzer et al.…”