Abstract:The effect of seawater acidification on the energy budget of the mussel Mytilus galloprovincialis was studied using a combined in situ mesocosm and flow-through chambers approach in Sanggou Bay from May to June, 2016. The experimental groups of mussels were acclimated to different experimental pH values obtained by elevating seawater CO2 concentrations. Clearance rates, absorption efficiency, respiration rates, ammonia excretion rates, and O/N ratios of M. galloprovincialis were measured after 10 and 30 days of treatment. The results showed that the clearance rates, O/N ratios, and absorption efficiency of M. galloprovincialis were reduced significantly after 10 days of exposure to acidified seawater (pH 7.7) (P<0.05), whereas the rates of ammonia excretion were increased significantly (P<0.01). The respiration rates in acidified and ambient seawater did not show significant difference (P>0.05). However, after 30 days of exposure to acidified seawater, significantly increased absorption efficiency, respiration rates, and ammonia excretion rates (P<0.05), and significantly reduced clearance rates and O/N ratios were observed (P<0.05). Energy budget analysis showed that a 10-day exposure to acidified seawater resulted in significantly reduced ingestion energy, absorbed energy, and scope for growth (P<0.05), but a significant increase in excreted energy (P<0.05), whereas a 30-day exposure to acidified seawater resulted in significant reduction in ingestion energy (P<0.05), but a significant increment in absorbed energy, respiration energy, excreted energy, and scope for growth (P<0.05). The average values of O/N ratios ranged from 14.28 to 20.46 in all the experiments, suggesting that the energy source changed gradually from fats and carbohydrates to proteins under low pH conditions. These data provide theoretical insights into the possible mechanisms underlying the impact of seawater acidification on the physiological responses of mussels.
