Seawater acidification affects the immune enzyme activities of the Manila clam Ruditapes philippinarum

Ocean acidification leads to changes in physiological and immune responses of bivalves, but the effect on the immune enzyme activities of the Manila clam, Ruditapes philippinarum , when the pH is lower than the normal value has not been studied in detail. In this study, experiments were conducted to determine how pH (7.4, 7.7, 8.0) affects the immune enzyme activities in the gill and hemocytes of the Manila clam. Membrane stability and phagocytosis increased with decrease of pH from 8.0 to 7.7 and then decreased at pH 7.4. The total protein content in the hemocytes and gills decreased with decreasing pH. Lysozyme content in the hemocytes increased with decreasing pH, and the differences were significant among the different pH groups ( P < 0.05). Adenosine triphosphatase activity at pH 7.4 was significantly higher than in the other two groups, but no significant difference was observed between pH 7.7 and 8.0. Catalase activity decreased from pH 8.0 to 7.7 and then increased at pH 7.4, and the differences were significant among the experimental groups ( P < 0.05). These findings provide valuable information about the immune response of R. philippinarum to reduced water pH and insights for future research investigating exposure of bivalves to elevated CO 2 conditions.