Physiological Responses Of Rhopilema Esculentum And Aurelia Coerulea To Ocean Acidification And Silver Nanoparticles Stress

Compared with the past few million years,the rate of global ocean acidification has increased significantly,leading to changes in the chemical environment of seawater,resulting in disturbances of physiological processes such as reproduction,development,and metabolism of marine organisms,as well as dynamic imbalances in marine ecosystems.In recent decades,silver nanoparticles(Ag NPs)have been used in various fields due to their unique properties,and subsequently released in freshwater and marine ecosystems,which in turn lead to serious impacts on the survival and health of aquatic organisms.Simultaneously,the decreased p H caused by ocean acidification can promote the dissolution of metal nanoparticles in aquatic medium,resulting in enhanced uptake of nanoparticles by organisms,thereby enhancing the synergistic toxic effect of the two environmental stress factors.As the main economic jellyfish in my country’s traditional fishery production,Rhopilema esculentum has now developed into an independent fishery industry.Aurelia coerulea is one of the main dominant populations of large-scale disaster jellyfish outbreaks in my country,and is also considered as an important indicator species for monitoring marine environmental pollution and a potential model organism for environmental toxicology research.This study aimed to elucidate the toxic mechanism of ocean acidification and Ag NPs on ephyra larvae and juvenile jellyfish of R.esculentum and A.coerulea,and to explore the physiological effects of Ag NPs on the two kinds of scyphomedusae under the background of ocean acidification.This not only fills the research gap on the effects of seawater acidification and artificial nanomaterials on jellyfish,but also provides theoretical basis and technical support for assessing the impact of global and regional marine environmental problems on marine organisms and marine environmental monitoring.The main findings of this study are as follows:(1)Taking ephyra larvae and juvenile jellyfish as research objects,the effects of ocean acidification and Ag NPs on their growth development and exercise ability were analyzed by measuring the bell diameter and pulsation rate.And we detected changes in oxidative stress,energy metabolism,acid-base balance,immunity and other related enzyme activities,to evaluate the toxic effects of two environmental stresses on R.esculentum at two different stages.The results showed that the MDA content of ephyra larvae was significantly increased,causing severe oxidative damage,resulting in negative effects on growth development and exercise capacity,under the single or combined exposure of ocean acidification and Ag NPs.Single-factor exposure to ocean acidification significantly enhanced AKP activity and inhibited ACP activity,leading to disorders of metabolism and immunity.Single exposure to Ag NPs significantly reduced the activities of ion transport enzymes in ephyra larvae,which affected the acid-base balance.Ocean acidification can alleviate the oxidative stress caused by Ag NPs on juvenile jellyfish.Ag NPs inhibited the activities of two phosphatase enzymes in juvenile jellyfish,and affected energy metabolism,resulting in slowed growth rate and decreased pulsation rate.Ocean acidification can enhance the activities of two ion transportases in juvenile jellyfish,which is beneficial to stabilize the concentration of various ions in the intracellular environment and maintain the osmotic pressure balance.(2)In this study,we measured the growth,motility,and various enzyme activities,to explore the physiological effects of ocean acidification and Ag NPs on A.coerulea at different stages,and to clarify the mechanism of the toxicity of Ag NPs on A.coerulea under the background of ocean acidification.The results showed that Ag NPs exposure had negative effects on the growth and contraction frequency of ephyra larvae and juvenile jellyfish.Ocean acidification significantly reduced the activities of CAT and SOD in ephyra larvae,resulting in an increase in the content of MDA,leading to lipid peroxidation.Under the combined exposure of ocean acidification and high concentration(200 μg/L)Ag NPs,the activities of two ion transportases in ephyra larvae were significantly increased,which promoted the transport of calcium ions and maintained osmotic pressure balance,that is the opposite in juvenile jellyfish.Ocean acidification can significantly inhibit the activities of ACP and AKP,resulting in energy metabolism limitation and reduced immunity.In summary,Rhopilema esculentum and Aurelia coerulea have different physiological responses to ocean acidification and Ag NPs,and the two environmental factors have distinct effects on different life stages of the same jellyfish.Therefore,this study can more effectively predict the changing trend of R.esculentum and A.coerulea populations under future marine environmental conditions,which is of great significance for protecting wild R.esculentum resources,preventing and controlling catastrophic A.coerulea outbreaks.