Impact of seawater acidification on shell property of the Manila clam Ruditapes philippinarum grown within and without sediment

Although the impact of ocean acidification on marine bivalves has been previously investigated under mainly controlled laboratory conditions,it is still unclear whether the impact of acidification on sediment-burrowing species differs between those within or without sediment.In order to fill this gap in our knowledge,we compared shell properties of the infaunal Manila clam(Ruditapes philippinarum)exposed to three pH concentrations(7.4,7.7,and 8.0),within and without sediments.In the first experiment(140 d),clams were exposed to seawater in an acidification system without sediment.A decrease in shell weight corresponding to the increase in dissolution rate was observed in the group ofpH 7.4,at which shell color disappeared or whitened.SEM observations confirmed the changes of the external shell surface.In the second experiment(170 d),sediment was placed at the bottom of each exposure chamber.The effects were found obvious in shell dissolution rate and shell color in the shell specimens exposed to overlying seawater but not found in the shell specimens exposed to sediment.Although the experimental period was longer in the second experiment,shell specimens in the first experiment were more seriously damaged than those in the second experiment under acidic seawater conditions.Our results,in relation to the defense function of the shell,show that marine bivalves in burrowing behavior are more adaptable to seawater acidification than those who do not burrow into sediment.

Although the impact of ocean acidi?cation on marine bivalves has been previously investigated under mainly controlled laboratory conditions, it is still unclear whether the impact of acidi?cation on sediment-burrowing species dif fers between those within or without sediment. In order to ?ll this gap in our knowledge, we compared shell properties of the infaunal Manila clam( Ruditapes philippinarum) exposed to three pH concentrations(7.4, 7.7, and 8.0), within and without sediments. In the ?rst experiment(140 d), clams were exposed to seawater in an acidi?cation system without sediment. A decrease in shell weight corresponding to the increase in dissolution rate was observed in the group of pH 7.4, at which shell color disappeared or whitened. SEM observations con?rmed the changes of the external shell surface. In the second experiment(170 d), sediment was placed at the bottom of each exposure chamber. The ef fects were found obvious in shell dissolution rate and shell color in the shell specimens exposed to overlying seawater but not found in the shell specimens exposed to sediment. Although the experimental period was longer in the second experiment, shell specimens in the ?rst experiment were more seriously damaged than those in the second experiment under acidic seawater conditions. Our results, in relation to the defense function of the shell, show that marine bivalves in burrowing behavior are more adaptable to seawater acidi?cation than those who do not burrow into sediment.