Ecotoxicological Effects Of Porites Lutea Under Single And Combined Stresses Of Acidification And Benzo[a]pyrene

In recent years,with global climate change and human activities,corals have been affected by multiple stressors,such as ocean acidification and persistent pollutant pollution.The balance of the "coral-Symbiodiniaceae-microbial" symbiosis is an important guarantee to maintain the health of coral reef ecosystem,and its dynamic relationship can objectively respond to the environmental stresses.However,most studies have focused on the stress effects of a single factor on coral symbiosis,and few studies have been reported on the mechanism of coral symbiotic microorganisms in response to acidification-benzo[a]pyrene complex stress.Porites lutea from Sanya coral reef area,which is more tolerant to environmental changes,was selected as the subject of this study.In this study,the acidification,BaP single and complex stress groups were set up to investigate the toxicological effects of stress on corals by monitoring their antioxidant enzyme activities,functional gene expression and photosynthetic physiological indicators in response to different stresses,and then based on ITS2 and 16 S rRNA high-throughput sequencing techniques,the community characteristics of coral commensal Symbiodiniaceae and coral commensal microorganisms(bacteria,archaea)were investigated under different treatments.The main results are as follows:(1)Different stresses can cause changes in coral antioxidant enzyme activities,and a single stress has a greater effect on antioxidant enzyme activities than a combination of stresses.Acidification stress inhibited the activity of anti-oxidative enzymes,BaP stress induced an increase in enzyme activity,and acidification-BaP stress inhibited the activity of POD enzymes,which were more sensitive to the three stresses and could be used as biomarkers of acidification-BaP stress.Complex stress induced up-regulation of Hsp90 gene,calcium ion transport-related genes(VAMP4,NCX1)expression,and the effect of complex stress on calcification-related genes was greater than that of single stress,and the expression of trapping light complex-related genes was more sensitive to single stress.(2)The photosynthetic physiology of Cordyceps showed differences in response to different stress modalities.Acidification stress had no significant effect on the photosynthetic physiological effects of Symbiodiniaceae.BaP stress reduced the chlorophyll a content of symbiotic Symbiodiniaceae,and acidification-BaP complex stress increased the density of Symbiodiniaceae.Acidification and BaP single stress caused a large change in the diversity and structure of the Symbiodiniaceae,lineages.Acidification stress led to a decrease in the alpha-diversity of Symbiodiniaceae,with highly significant increases in the relative abundance of the dominant subpopulations C15.6 and C15.9 under acidification and BaP single stress.Significant decreases in the relative abundance of the rare subclade C15.2,C1 s,C1#,C91 d,Cspc,and the C15.3.C15.4 subclade group showed a significant increase in abundance,and C15.2,C1# rare subclade group showed a significant decrease under compound stress.The corals responded to seawater acidification and organic matter pollution stress by changing the phylogenetic structure of their symbiotic.Such as decreasing the number of sensitive phylogenetic groups and increasing the abundance of tolerant phylogenetic groups.(3)Both single and complex stresses caused significant changes in microbial community diversity,structure and function,with the greatest changes in microbial community structure and function occurring under combined stresses,with the greatest changes in microbial community diversity under combined stress,an increase in bacterial community diversity,richness and evenness,and a decrease in archaeal diversity,richness and evenness.At the taxonomic level of phylum and genus,compound stress had a greater effect on the community composition and relative abundance of coral commensal microorganisms than single stress,causing a significant decrease in the probiotic coral bacteria Endozoicomonas.With significant increase in the relative abundance of the dominant archae phylum(Crenarchaeota)and a significant increase in metabolism-related functions.In addition,compared to the control,Aestuariibacter and Acanthopleuribacter at the genus level and Methanococcoides at the archaeal level all showed consistent and significant decreases in response to the three stress treatments,which can be used as sensitive indicator microorganisms for subsequent studies of coral symbiosis in response to environmental stress.The results of this study contribute to the understanding of the interaction between symbiotic microorganisms and corals under multiple environmental stresses.It provides a new perspective on the environmental adaptations and endosymbiotic mechanisms of coral symbionts,and also provides an important scientific basis for studying the endosymbiotic response mechanisms of coral symbionts to environmental stresses.