Effects Of Diel-Cycling Seawater Acidification And Hypoxia On Development,Acid-Base Regulation And Energy Budget Of Thick Shell Mussel Mytilus Coruscus

Over the past few decades,due to the excess nutrients delivered to the water environment by human activities,some estuaries and coastal waters have experienced both acidification and hypoxia.In the natural ecological environment,the respiration and photosynthesis of plants and animals can cause fluctuations in p H and dissolved oxygen in seawater,presenting a certain pattern of day and night cycles.Compared with the effects of continuous hypoxia and acidification on marine animals,the impact of rhythmic factors in accordance with the state of the natural environment on marine bivalves has not been fully studied.Therefore,in order to study the effects of circadian acidification and hypoxia on the early development of marine bivalves,thick shell mussels Mytilus coruscus were exposed to seven experimental treatments:two dissolved oxygen?DO?levels?the hypoxia 2 mg/L,the normal level 8 mg/L?,two p H treatments?7.3 for acidification,8.1for environmental p H?,p H fluctuations?8.1-7.3?,DO fluctuations?8-2 mg/L?and joint fluctuations in p H and DO?p H:8.1-7.3 and DO:8-2 mg/L?,and then temperature difference flowing water was used to stimulate the oxytocin.Offspring exposure was conducted for 4 days to record and study the development of fertilized eggs.The results showed that continuous low p H and its combined stress with continuous low DO significantly reduced the fertilization rate,cleavage rate,and shell length and height of D-type larvae.The combined stress of circadian low p H and DO significantly reduced the cleavage rate and the shell length and height of D-type larvae.Both continuous and circadian low DO significantly reduced the cleavage rate,but did not significantly affect the fertilization rate and the distortion rate.A significant interaction between acidification and hypoxia was observed during the experiment.Short-term exposure tests showed that circadian and continuous acidification and hypoxia impeded the early development of thick-shell mussels.In order to study the effects of circadian ocean acidification and hypoxia on the internal environmental stability of marine bivalves,thick shell mussels Mytilus coruscus were exposed 3 weeks to seven experimental treatments:two dissolved oxygen?DO?levels?the hypoxia 2 mg/L,the normal level 8 mg/L?,two p H treatments?7.3 for acidification,8.1 for environmental p H?,p H fluctuations?8.1-7.3?,DO fluctuations?8-2mg/L?and joint fluctuations in p H and DO?p H:8.1-7.3 and DO:8-2 mg/L?.The results showed that continuous acidification and hypoxia significantly reduced the extracellular p H value?p H_e?of mussels and increased the concentration of HCO₃^-,p CO₂,calcium concentration,osmotic pressure and standard metabolic rate?SMR?of mussels in hemolymph.Hypoxia and acidification of circadian rhythm also significantly reduced p H_e and increased SMR,but had no significant effect on p CO₂,HCO₃^-,calcium concentration and osmotic pressure.The combined stress of hypoxia and acidification had a significant effect on the physiological parameters,and the differences between the groups were significant.An obvious interaction between acidification and hypoxia was observed in the experiment.The results showed that mussels'resistance to the acidification and hypoxia of the circadian rhythm was stronger than that of sustained stress.In conclusion,sustained and intermittent stress negatively affected hemolymph homeostasis in thick shell mussels.In order to study the effects of short-term exposure to hypoxia and acidification and their rhythmicity on the energy budget and growth performance of marine bivalves,thick shell mussels Mytilus coruscus were exposed 3 weeks to seven experimental treatments:two dissolved oxygen?DO?levels?the hypoxia 2 mg/L,the normal level 8mg/L?,two p H treatments?7.3 for acidification,8.1 for environmental p H?,p H fluctuations?8.1-7.3?,DO fluctuations?8-2 mg/L?and joint fluctuations in p H and DO?p H:8.1-7.3 and DO:8-2 mg/L?.The results showed that continuous acidification and hypoxia significantly reduced clearance rate,absorption rate,ammonia excretion rate,scope for growth and condition index of thick shell mussels,while respiration rate and O:N significantly increased.The circadian hypoxia and acidification also significantly reduced clearance rate,absorption rate,ammonia excretion rate,scope for growth and condition index of thick shell mussels,and significantly increased respiration rate and O:N.During the experiment,there were significant differences between groups,and an obvious interaction between acidification and hypoxia was observed.Therefore,the circadian and the continuous acidification and hypoxia significantly reduce the net energy and condition index of mussel growth,threaten the survival of individual mussels and the development of the population,and lead to the decline of the production and quality of mussels in fishery and aquaculture.