Abstract
Varying salinities of coastal waters are likely to affect the physiology and ion transport capabilities of calcifying marine organisms such as bivalves. To investigate the physiological effect of decreased environmental salinity in bivalves, adult oysters (Crassostrea gigas) were exposed for 14 days to 50% seawater (14) and the effects on mantle ion transport, electrophysiology and the expression of Ca2+ transporters and channels relative to animals maintained in full strength sea water (28) was evaluated. Exposure of oysters to a salinity of 14 decreased the active mantle transepithelial ion transport and specifically affected Ca2+ transfer. Gene expression of the Na+/K+-ATPase and the sarco(endo)plasmic reticulum Ca2+-ATPase was decreased whereas the expression of the T-type voltage-gated Ca channel and the Na+/Ca2+-exchanger increased compared to animals maintained in full SW. The results indicate that decreased environmental salinities will most likely affect not only osmoregulation but also bivalve biomineralization and shell formation.
Highlights
Intertidal organisms face a fluctuating environment where the salinity can exhibit drastic changes during a single day (Geng et al, 2016)
The transepithelial potential (TEP) was maintained at the same level irrespective of the salinity of the external environment (Figure 2C)
Ca2+ transfer across the outer mantle epithelium (OME) was higher in salinity 28, 498 ± 37.1 nM/min (N = 9), compared to 14, 393 ± 36.1 nM/min (N = 10), by 21% (P = 0.021) (Figure 3)
Summary
Intertidal organisms face a fluctuating environment where the salinity can exhibit drastic changes during a single day (Geng et al, 2016). These natural variations in salinity may be further accentuated by the changes occurring in oceans due to climate change, which is expected to modify water evaporation and precipitation patterns in the near future (Ipcc, 2014). Salinity stress has been shown to trigger multiple physiological responses in marine calcifying invertebrates including changes in protein and mRNA expression, enzyme metabolism, cell signaling, amino acid content and ion regulation (Shumway, 1977a; Berger and Kharazova, 1997; Zhao et al, 2012; Meng et al, 2013). A decrease in environmental water salinity was shown to decrease shell calcification and/or affect shell properties in species such as Crassostrea virginica and Diluted Seawater Affects Ca2+ Transport
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