Effect Of Ocean Acidification Stress On Physiological Activity Of Mytilus Galloprovincialis And Crassostrea Gigas And Mitigation Measures

Since the industrial revolution,due to the influence of human activities,the content of carbon dioxide（CO₂）in the atmosphere has continued to increase,resulting in the rapid increase of CO₂ content dissolved and absorbed by the ocean,which in turn has led to an increase in the concentration of seawater H⁺,and the occurrence of carbonate systems in seawater.The fluctuation is ocean acidification.According to the report of IPCC,the pH in the ocean has been declining year by year from the Industrial Revolution to 2000,the pH of the ocean has rapidly dropped by 0.1 units;by 2200,the pH of the ocean will drop by 0.3-0.5 units;by 2300,the pH of the ocean will drop by 0.7 units or even lower.The mussels and oysters,which belong to the bivalves,are widely distributed in the northern coast of China,and the Yellow Sea as well as Bohai Sea regions are not only important economic shellfish in China,but also in the intertidal ecosystem.One of the group-building species plays an important role in improving the diversity of the intertidal ecosystem.In this study,we selected the mussels Mytilus galloprovincialis and the Oyster Crassostrea gigas as the experimental subjects.We used the experimental methods of combining wild outside compartment and site flow water to systematically study and analyze the effects of ocean acidification on the feeding physiology,metabolic physiology,and growth activities of M.galloprovincialis and C.gigas.As well as the effects on the key enzymes of C.gigas,the role of the integrated aquaculture in mitigating the negative effects of ocean acidification in the bivalves was explored.（一）The effect of ocean acidification on the physiological activities of the Mytilus galloprovincialis and Crassostrea gigasFrom May to June 2016,the effect of acidification stress on the growth physiology of the M.galloprovincialis and C.gigas was studied in the bay of Hudao,Sanggou Bay,Rongcheng City,Shandong Province.According to the IPCC prediction of ocean acidification in 2100,two pH groups were set up,pH 8.0 and pH 7.7.Using the wild outside compartment experiment,the key physiological parameters,such as the clearance rate,absorption efficiency,Respiration rate,ammonia excretion rate,and scope for growth,were determined on the 10th and 30th days of acidification,respectively.The distribution of energy in the mussels and the oyster was analyzed,and the changes of Na⁺/K⁺-ATPase,CAT enzyme in the C.gigas were analyzed.The main results were as follows:1)Effects of seawater acidification on the feeding physiology of the Mytilus galloprovincialis and Crassostrea gigas:acidification stress for 10 days,the clearance rate of the M.galloprovincialis and C.gigas decreased significantly（P<0.05）,and the absorption efficiency significantly decreased（P<0.01）.After 30 days of acid stress,the clearance rate of M.galloprovincialis and C.gigas was significantly decreased（P<0.05）;the absorption efficiency of M.galloprovincialis was significantly increased（P<0.05）,and the absorption efficiency of C.gigas was significantly reduced（P<0.01）.2)Effects of seawater acidification on the metabolic physiology of the Mytilus galloprovincialis and Crassostrea gigas:Oxygen stress for 10 days,the respiration rate of M.galloprovincialis and C.gigas did not change significantly（P>0.05）;the ammonia excretion rate of M.galloprovincialis was significantly increased（P<0.05）.There was no significant change in the ammonia excretion rate of the C.gigas（P>0.05）,and the O:N ratios of the M.galloprovincialis and C.gigas both decreased significantly（P<0.05）.After 30 days of acid stress,the respiration rate of M.galloprovincialis and C.gigas increased significantly（P<0.05）,the ammonia excretion rate of M.galloprovincialis increased significantly（P<0.05）,and the ammonia excretion rate of C.gigas increased significantly（P<0.05）;the O:N ratios of M.galloprovincialis and C.gigas were all significantly decreased（P<0.05）.3)Effects of seawater acidification on the energy allocation of the Mytilus galloprovincialis and Crassostrea gigas:seawater acidification changes the proportion of energy distribution in shellfish,the energy used for respiration and excretion gradually increases,and the proportion of energy used for growth decreases,especially for oysters.With the increase of acidification time,the growth of shellfish increased.Compared with the control group,seawater acidification for 10 days,the growth of M.galloprovincialis decreased by 28.65%,growth of C.gigas could drop by 41.45%,acidification stress for30d,M.galloprovincialis growth can increase by 26.95%;C.gigas growth can be reduced by 36.92%.In addition,it was found that after the acidification stress,the specific growth rates of M.galloprovincialis and C.gigas decreased significantly（P<0.05）.4)Effect of seawater acidification on the Na⁺/K⁺-ATPase and CAT activities of C.gigas:The activity of Na⁺/K⁺-ATPase in the oyster gill was significantly reduced after acidification（P<0.05）.The activities of Na⁺/K⁺-ATPase and CAT enzyme in oyster mantle were significantly increased（P<0.01）.（二）Integrated aquaculture of Seashell Algae in Relieving the Negative Effects of Ocean AcidificationFrom May to June 2017,an experiment was seted to study the role of algae culture in the mitigation of the negative effects of ocean acidification on Sanggou Bay in the Rongcheng City,Shandong Province.According to the IPCC prediction of changes in seawater acidification during the 21^th,two experiments were conducted as pH 8.0 and pH7.7;two treatments,a single oyster group,and an algae cultivation group.Using the wild-outside experiment,after 30 days of the experiment,the key physiological indicators such as the clearance rate,absorption efficiency,respiration rate,ammonia excretion rate,and scope for growth were determined.The results of the experiment were as follows:The clearance rate of oysters at the pH7.7 integrated-aquaculture group was significantly higher than that of the oysters at the pH 7.7 single-group（P<0.01）,but there was no significant difference between the oyster clearance rate and the pH8.0 control group;The absorption efficiency of oysters in the pH7.7 integrated-aquaculture group was significantly lower than that of the oysters in the pH 7.7 single-group（P<0.01）,which was significantly lower than that of the pH8.0 control group（P<0.05）.From the point of view of respiratory metabolism,the respiration rate of oysters in the pH7.7 integrated-aquaculture group was significantly lower than that of the oysters in the pH 7.7 single-group（P<0.01）,and was significantly lower than that of the oysters in the pH8.0 control group（P<0.05）.From the results of ammonia excretion rate,the ammonia excretion rate of oysters in the pH7.7 integrated-aquaculture group was significantly lower than that of the pH 7.7 single-group（P<0.01）,and was significantly lower than that of the pH8.0control group（P<0.05）.From the perspective of energy allocation,the energy distribution of oysters in the algae cultivation group under seawater acidification stress tends to be normal,the total energy absorbed by the shellfish increases significantly,the energy used for respiration and excretion gradually decreases,and the proportion used for growing energy rises significantly high.The algae cultivation model is an effective way to respond positively to the negative effects of ocean acidification.