Abstract
The present study was performed to evaluate the effects of CO2− 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 CO2 and HCl treatments, and four antioxidant components, GSH, GST, GR and GPx, had active responses to the acidification stress. Comparatively, CO2 had more severe destructive effects on haemocytes than HCl at the same pH level, indicating that CO2 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.
Highlights
Balance[13,14]
The percentages of haemocytes that were found to be nonviable were very low in the control (2.8 ± 0.37%) and acidified groups (7.7 HCl group (HG): 4.1 ± 0.42%; 7.7 CO2 group (CG): 4.5 ± 0.48%; 7.1 HG: 3.9 ± 0.52%; 7.1 CG: 4.0 ± 0.34%;)
We found that the haemocytes in the CO2-seawater were more vulnerable compared to those in the HCl-seawater at the same pH level, which was presumed to imply that factors other than H+ might play an essential role in the negative impacts
Summary
Balance[13,14]. Li et al.[15] showed that ocean acidification (−0.3 and −0.6 pH units) decreased the haemolymph pH value of Pinctada fucata by 0.45–0.55 pH units[15]. Matozzo et al.[16] demonstrated that seawater acidification significantly affected the immune parameters in two species of bivalves, M. galloprovincialis and Chamelea gallina[16]. Bibby et al.[17] found that CO2-induced acidification (−0.2 to −1.1 pH units) had an obvious impact on the physiological condition and functionality of M. edulis haemocytes, and their phagocytosis was strongly decreased with decreasing pH levels[17]. There are few studies on the overall effects of elevated oceanic CO2 on haemocytes from M. edulis, especially in terms of the toxic mechanism of acidification in different biospectra of haemocytes and their immune function. We conducted a 21-day experiment to investigate the impact of CO2 enrichment-induced seawater acidification on key aspects of the haemocyte structure and immune function of M. edulis. The results in the present study shed light on how seawater acidification contributes to the structure and function of the haemocytes of M. edulis
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