Abstract
As ocean acidification (OA) is gradually increasing, concerns regarding its ecological impacts on marine organisms are growing. Our previous studies have shown that seawater acidification exerted adverse effects on physiological processes of the blue mussel Mytilus edulis, and the aim of the present study was to obtain energy-related evidence to verify and explain our previous findings. Thus, the same acidification system (pH: 7.7 or 7.1; acidification method: HCl addition or CO2 enrichment; experimental period: 21d) was set up, and the energy-related changes were assessed. The results showed that the energy charge (EC) and the gene expressions of cytochrome C oxidase (COX) reflecting the ATP synthesis rate increased significantly after acidification treatments. What’s more, the mussels exposed to acidification allocated more energy to gills and hemocytes. However, the total adenylate pool (TAP) and the final adenosine triphosphate (ATP) in M. edulis decreased significantly, especially in CO2 treatment group at pH 7.1. It was interesting to note that, TAP, ATP, and COXs gene expressions in CO2 treatment groups were all significantly lower than that in HCl treatment groups at the same pH, verifying that CO2-induced acidification exhibited more deleterious impacts on M. edulis, and ions besides H+ produced by CO2 dissolution were possible causes. In conclusion, energy-related changes in M. edulis responded actively to seawater acidification and varied with different acidification conditions, while the constraints they had at higher acidification levels suggest that M. edulis will have a limited tolerance to increasing OA in the future.
Highlights
Oceans have absorbed a large amount of anthropogenic carbon dioxide (CO2) since the industrial revolution, leading to ocean acidification (OA; Caldeira and Wickett, 2003; Doney et al, 2009)
In gills (Figure 1), total adenylate pool (TAP) changed little in either HCl treatment group (p > 0.05) compared with the control group; TAP decreased significantly (p < 0.05) in both CO2 treatment groups compared with the control group, significantly lower at pH 7.1 than pH 7.7
adenosine triphosphate (ATP) declined significantly in both CO2 treatment groups compared with the control group (p < 0.05), significantly lower at pH 7.1 than pH 7.7, while it only decreased significantly in the HCl treatment group at pH 7.1 (p < 0.05)
Summary
Oceans have absorbed a large amount of anthropogenic carbon dioxide (CO2) since the industrial revolution, leading to ocean acidification (OA; Caldeira and Wickett, 2003; Doney et al, 2009). Owing to relatively low metabolic rates, poor acid-base regulation capacities and calcareous skeletal structures or shells, a large fraction of mollusk species presented a high vulnerability to OA (Thomsen et al, 2010; Wittmann and Pörtner, 2013; Wang and Wang, 2020). In the early stages of their life, can react with decreased rates of growth and calcification, as well as a decreased shell strength toward elevated seawater pCO2 (Beniash et al, 2010; Gazeau et al, 2010; Talmage and Gobler, 2010; Gaylord et al, 2011; Stevens and Gobler, 2018). The slowness of growth and calcification seen in bivalve mollusks under acidic conditions was attributed to a higher energy consumption for the maintenance of physiological homeostasis (Lannig et al, 2010; Thomsen and Melzner, 2010; Melzner et al, 2020). Beniash et al (2010) found that Crassostrea virginica greatly increased its energy consumption and standard metabolic rate to maintain its internal stability when it was exposed to an acidic environment at pH 7.5
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