Seawater acidification induced immune function changes of haemocytes in Mytilus edulis: a comparative study of CO ₂ and HCl enrichment

Abstract

The present study was performed to evaluate the effects of CO ₂− or HCl-induced seawater acidification (pH 7.7 or 7.1; control: pH 8.1) on haemocytes of Mytilus edulis, and the changes in the structure and immune function were investigated during a 21-day experiment. The results demonstrated that seawater acidification had little effect on the cellular mortality and granulocyte proportion but damaged the granulocyte ultrastructure. Phagocytosis of haemocytes was also significantly inhibited in a clearly concentration-dependent manner, demonstrating that the immune function was affected. Moreover, ROS production was significantly induced in both CO ₂ and HCl treatments, and four antioxidant components, GSH, GST, GR and GPx, had active responses to the acidification stress. Comparatively, CO ₂ had more severe destructive effects on haemocytes than HCl at the same pH level, indicating that CO ₂ stressed cells in other ways beyond the increasing H ⁺ concentration. One possible explanation was that seawater acidification induced ROS overproduction, which damaged the ultrastructure of haemocytes and decreased phagocytosis.