The Mechanism Concerning The Mitigating Effect Of Ocean Acidification On Mercury Toxicity In Marine Copepod Pseudodiaptomus Annandalei

Mercury,as a global pollutant,has high toxicity,persistence and mobility.The emission of mercury pollutants into environment due to hunman activities will eventually be deposited in the ocean,resulting in marine mercury pollution.The ocean is the largest carbon sink on the earth's surface,as it can absorb one third of CO2 emission caused by human acitivities each year.When a large amount of CO2 is dissolved into the ocean,the seawater carbonate system will be changed greatly,which is exemplified by reduced pH level,that is,ocean acidification.Since the industrial revolution of 18th century,human activities expecially fossil fuel burning have emitted large amounts of CO2 and mercury into the atmosphere simutaneously,both of which will finally enter into marine environments.Accordingly,ocean acidification and mercury pollution may co-occur in marine environments,which,in turn,will threaten the fitness of the global marine ecosystem.As a crucial part in marine plankton,marine copepod has been considered as a good model organism because of its small individual,short generation time and strong fecundity.Pseudodiaptomus annandalei is one of few marine copepod which can be cultivated continuously under laboratory conditions.Nevetheless,so far,very scare information has been provided for this species in marine ecotoxicologys.In this study,the marine copepod P.annandalei was used as a testing organism.That is to say,P.annandalei were exposed to ocean acidification and mercury pollution(pCO2 400 ?atm+Control,pCO2 800 ?atm+Control,pCO2 400 ?atm+1.0?g/L Hg,pCO2 800 ?atM+1.0 ?g/L Hg,pCO2 400 ?atm+2.5 ?g/L Hg,pCO2 800?atm+2.5 ?g/L Hg)for three consecutive generations,and it was followed by a recovery of one generation in clean seawater.Metal accumulation and six important life history traits(i.e.,survival,development time for nauplius phase,development time to maturation,number of nauplii/clutch,number of clutches,and total fecundity)were examined for each generation.Specifically,TMT-based quantitative proteomics was analyzed to study the crital functional proteins and biological processes for the first and third generation of P.annandalei under ocean acidification and mercury pollution(along and combined).As a consequence,this study was aimed to reveal the response and adaptation mechanisms of P.annandalei against ocean acidification and mercury pollution(along and combined),and reveal the mechanism concerning the mitigating effect of ocean acidification on mercury toxicity in marine copepod.The main fingings are described as following:(1)Under Hg polluiton and the combined exposure,mercury signficantly accumulated in the treated copepods specifically with a concentration dependent manner during F0-F2.Interestingly,ocean acidification signficantly reduced mercury accumulation of in P.annandalei during F0-F2(2)Ocean acidification had insignificant effect on the development and reproduction of P.annandalei.However,mercury significantly displayed adverse impacts on development and reproduction.In addition,ocean acidification signficantly alleviated mercury toxicity to development and reproduction in P.annandalei ·(3)During the recovery generation(F3),mercury slightly accumulated in the treated copepods,but all the six important life history traits were insignificantly affected.(4)Our proteomic analysis showed that P.annandalei probably initiated adaptive mechanism as exemplied by an increased expression of carbohydrate metabolism and glycoprotein degradation,as a consequence,which could be used to increase energy allocation into displaying resilience against ocean acidification.By contrast,mercury toxicity significantly inhibited many important processes/pathways in P.annandalei,primarily including amino acid metabolism,nucleotide metabolic process and nucleosome assembly,and they were ultimately translated into population-level adverse outcome,that is,development retardation and restrained reproduction.Under combination,P.annandalei might launch more stress-related defense pathways,such as an increased expression of carbohydrate metabolism,glycoprotein degradation,and oxidative defense,to counteract mercury toxicity to the exposed copepods.Overall,the shotgun-based quantitive proteomics provided mechanistic explanation to the alleviating effect of ocean acidification on mercury toxicity to development and reproduction in marine copepod.