Physiological And Molecular Underlying Mechanisms Of The Early Life History Stages Of The Moon Jellyfish Aurelia Coerulea To Ocean Acidification And Warming

Since the industrial revolution,the oceans have absorbed approximately 30%of human CO₂emissions,causing seawater acidification and increasing ocean surface temperatures.Under environmental stresses such as ocean acidification（OA）and ocean warming（OW）,the physiological characteristics and gene expression patterns such as oxidative stress,energy metabolism and immune response of marine animals are changed,thus affecting the growth,development,reproduction and survival of the organism.However,as one of the important ecological groups of marine animals,jellyfish have the potential to tolerate seawater acidification and warming environments to gain a population competitive advantage.Moon jellyfish（Aurelia coerulea）is widely distributed in temperate coastal waters around the world.It is the dominant species of large-scale disaster jellyfish in China and plays an important role in the biogeochemical cycle and marine ecosystem.The early life history stage of polyps and ephyrea is important for the proliferation and growth of jellyfish populations,which is the key to determining jellyfish outbreaks.Therefore,in this study,the physiological response strategies and molecular regulatory mechanisms of A.coerulea in response to future changes in the marine environment were analyzed in the context of seawater acidification and warming,and the early life history stages of polyps and ephyrea were used to provide a scientific basis for predicting future changes in jellyfish populations.This study is mainly divided into the following four parts:（1）Two seawater acidification exposure experiments（p H 7.8;p H 7.6）were conducted with A.coerulea polyps in short generations（F0）and multiple generations（F0-F4）.The physiological indicators of asexual reproduction rate,respiration rate and enzyme activities such as SOD,CAT,Na⁺K⁺-ATPase,Ca²⁺-ATPase,ACP and AKP were measured in polyps,and combined with the transcriptomic data were used to explore the physiological responses and molecular regulation mechanism of A.coerulea polyps in response to seawater acidification.The results showed that in the F0 generation,the asexual reproduction rate of polyps exposed to very low p H（p H=7.6）was significantly lower than that of the control group（p H 8.1）;short-term seawater acidification severely inhibited the activities of SOD,CAT,Na⁺K⁺-ATPase and ACP,affecting the acid-base balance,immune response and antioxidant response.In addition,transcriptomic analysis showed that the expression patterns of genes associated with microtubules and Ca²⁺binding were significantly altered in A.coerulea polyps in response to elevated CO₂levels.However,when the A.coerulea polyps were exposed to seawater acidification for five generations,the physiological characteristics and transcript expression of the polyps were not significantly different from those of the controls.Therefore,based on the response characteristics of A.coerulea polyps to seawater acidification,we speculate that they can strongly adapt to future OA.（2）The effects of short-term seawater acidification exposure on the community composition,structure and function of the A.coerulea polyp-associated microbial communities were investigated by Biolog-ECO and metagenomic methods to explore the role of microorganisms in response to seawater acidification.The results showed that the structures and functions of the microbial communities associated with A.coerulea polyps were conserved in future seawater acidification（p H 7.8;p H 7.6）.Biolog-ECO results showed that seawater acidification had little effect on the microbial metabolic activity,diversity index and carbon source utilization of the associated microbial community of A.coerulea polyps.The metagenomic results showed that four categories,including Tenericute,Proteobacteria,Firmicutes and Bacteroidetes,were the dominant groups of polyp microorganisms,and the community structure was not significant among different acidification groups;moreover,the functions of the associated microbial community of A.coerulea polyps were exposed to different acidification conditions.Thus,OA may not affect polyps by changing the microbial community structure.（3）The physiological response and molecular mechanisms of A.coerulea ephyrea to seawater acidification were studied through morphological,behavioral,physiological and transcriptomic methods.The results showed that seawater acidification significantly inhibited the growth,contraction behavior and feeding rate of A.coerulea ephyrea.Based on transcriptomic technical findings,acidification exposure significantly altered the gene expression pattern of A.coerulea ephyrea.Differentially expressed genes enriched in the growth-related Wnt signaling pathway and Notch signaling pathway inhibited the growth of A.coerulea ephyrea.In addition,the expression of genes related to toxin production and neurotransmission was significantly downregulated;therefore,seawater acidification may reduce the feeding efficiency and locomotor behavior of A.coerulea ephyrea by inhibiting toxin production and weakening nerve transmission.Thus,combining physiological indicators and histological data,we hypothesize that A.coerulea ephyrea will be negatively affected by seawater acidification in the short term.（4）The effects of seasonal seawater warming on A.coerulea polyps were evaluated by measuring physiological indicators such as the asexual reproduction rate,feeding rate and respiration rate.The results showed that the feeding rate and asexual reproduction rate of A.coerulea polyps increased after 42 d of seasonal warming exposure;the asexual reproduction rate of A.coerulea polyps was highest when exposed to summer warming seawater;and the respiration rate of A.coerulea polyps was significantly suppressed after winter warming,indicating that energy was allocated to asexual reproduction rather than metabolism after winter warming.Thus,A.coerulea polyp populations would benefit from increased seawater temperatures in all seasons due to climate change,which may further increase A.coerulea outbreak potential and size,especially in summer.In summary,the two early life history stages of A.coerulea（polys and ephyrea）have different response strategies to seawater acidification.Although A.coerulea polyps were negatively affected by short-term acidification,their physiological and transcriptional levels showed adaptation to seawater acidification after long-term exposure.However,A.coerulea ephyrea showed significant inhibition of growth and development,locomotor behavior and predation under seawater acidification stress.The asexual reproduction rate of A.coerulea polyps increased after seasonal warming exposure,suggesting that A.coerulea may benefit from future ocean temperature increases.In the context of global climate change,this study will provide a scientific basis for predicting future changes in A.coerulea populations.