Abstract
This study investigated the combined effects of seawater acidification and hypoxia on the antioxidant response in gonads of the thick shell mussel Mytilus coruscus. Mussels were collected along the Shengsi Island, East China Sea, where oxygen and pH fluctuations frequently occur in summer. Mussels were exposed to three pH (8.1, 7.7, and 7.3) and two dissolved oxygen (DO) levels (6 and 2 mg L-1) for 21 days followed by a 10-day recovery period (pH 8.1 and DO 6 mg L-1). Gonad surface area (GSA) and activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPX), glutathione (GSH), glutathione S-transferase (GST), and malondialdehyde (MDA) in gonad were measured at days 21 and 31. Complex and enzyme-specific responses were observed after the 21-day exposure period. Overall, PCA analysis revealed a stronger effect of pH than DO. Integrated biomarker response (IBR) analysis demonstrated that low pH and DO decreased mussel's antioxidant system and increased oxidative damage with potential consequences for gonad development. Mussels exposed to low pH and DO were only partly able to recover a normal enzymatic activity after 10-day recovery period. This suggests that mussels exposed to short-term pH and DO fluctuations event in the field may suffer lasting negative impacts.
Highlights
Ocean acidification (OA) refers to the process in which absorption of excess carbon dioxide from the atmosphere causes a chemical reaction to lower the pH of the ocean (Birchenough et al, 2015; Orr et al, 2005; Feely et al, 2004)
This study investigated the combined effects of seawater acidification and hypoxia on the gonadal antioxidant response of the thick shell mussel Mytilus coruscus mainly distributed along the Shengsi Island, East China Sea, where hypoxia and pH fluctuations frequently occur in summer
Our results clearly showed that acidification and hypoxia synergistically exert negative impact on the antioxidant system and gonad development of mussels, and the effect of acidification was more significant
Summary
Ocean acidification (OA) refers to the process in which absorption of excess carbon dioxide from the atmosphere causes a chemical reaction to lower the pH of the ocean (Birchenough et al, 2015; Orr et al, 2005; Feely et al, 2004). The atmospheric CO2 concentration has increased from 280 ppm to 380 ppm since the industrial age. It may reach 1200 ppm and the pH may reduce 0.4 units by the end of this century according to an earth biochemical model The effects on marine bivalves are especially significant (Tan & Zheng, 2020). OA exerts plenty of impacts on survival, calcification, growth and reproduction of marine bivalves by breaking the acidbase balance and reducing the saturation state of CaCO3 (Anthony et al, 2008; Doney et al, 2009; Nakamura et al, 2011; Orr et al, 2005). Since different species and even various life stages of the particular specie showed different responses to OA (Ries et al, 2009; Melzner et al, 2009), the understanding of these impacts is still weak
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