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[AOS25-05] Effects of ocean acidification on growth and calcification in juvenile Japanese surf clam Pseudocardium sachalinense
Keywords:ocean acidification, growth effect, calcification, stable carbon isotope, Japanese surf clam
We found non-significant effects of elevated CO2 on weight (whole body, shell, and soft tissue), shell length, shell width, and shell height during experiments. Meanwhile, shell thickness at a region that grew during experiments thinned in a pCO2-dependent manner. These results suggest that effect of ocean acidification on juvenile Japanese surf clam was not the shell dissolution but the inhibition of shell formation.
We studied the contribution of acidified seawater on shell calcification by stable carbon isotope composition (δ13C). The δ13C of the shells collected from the external margin of the outer shell layer showed significant positive correlations with pH (R = 0.56, p < 0.05). The regression slope of the relationship between shell δ13C and pH was roughly the same as that between δ13C of dissolved inorganic carbon (DIC) of seawater and pH, and calcification of the experimental specimens might be strongly affected by acidified seawater. Thus, by measuring δ13C of molluscan shell and DIC of seawater, it might be possible to estimate the contribution of acidified seawater to calcification.
The concentration of carbonate ion which is necessary for calcification decreased with increasing pCO2. Because of the influx of acidified seawater into the extrapallial fluid, the decrease in carbonate ion in the extrapallial fluid might induce a thinner shell formation. Therefore, in acidified seawater, Japanese surf clam might have a poor pH regulation of the extrapallial fluid.