Ocean Acidification

Highlights

• Combined acidification and hypoxia trigger significant mortality in Magallana gigas.
• Seawater acidification suppresses the nonspecific immune response in Magallana gigas.
• Gill histopathology and immunosuppression are most pronounced with combined exposure.

Abstract

Rising atmospheric carbon dioxide leads to oxygen depletion and increased acidification in marine areas worldwide. The combined effects of these two stressors on the health of commercially important bivalves have not been sufficiently studied. We experimentally studied the effects of water acidification in combination with normoxic and hypoxic conditions on the parameters of cellular immunity and the gills microstructure of the Magallana gigas. We evaluated the hemolymph cellular composition, the total number and phagocytosis capacity of hemocytes, and also evaluated the histopathology of oyster gills during an 8-day experimental period. The oysters were exposed to low pH conditions (7.3), either under normoxic conditions (dissolved oxygen concentration of 8.0 mg/L) or hypoxic conditions (dissolved oxygen concentration of 2.0 mg/L). The parameters were assessed at days 1, 3, 6, and 8 of the experiment. It was shown that acidification of the aquatic environment causes significant suppression of oyster immunity in both normoxia and hypoxia, leading to a decrease in phagocytic capacity and ROS production by hemocytes. The combined effect of these factors increased the negative impact, ultimately leading to the oyster death at the end of the experiment. In addition, the effects of acidification caused serious and progressive histopathological damage to the oyster gills, while the most severe and frequent pathologies, such as almost complete expansion of the water chambers and severe dilation of the hemal sinuses, were caused by the combined effects of acidification and hypoxia. Therefore, the synergistic impact of acidification and hypoxia poses a substantial threat to oyster health.

Kukhareva T. A., Kladchenko E. S., Podolskaya M. S., Gavruseva T. V., Tkachuk A. A., Bogacheva E. A., Chelebieva E. S., Lavrichenko D. S., Borovkov A. B. &Andreyeva A. Y.., 2026. Immunosuppression and gill damage of acidification and hypoxia on the Pacific oyster Magallana gigas. Estuarine, Coastal and Shelf Science 337: 109922. doi: 10.1016/j.ecss.2026.109922. Article (subscription required).