| Microplastics（MPs）pollution in Lagoon is a prominent problem in marine environment.Xincun Bay,a typical tide-influenced lagoon with weak hydrodynamic,is a national first-class good port.Its aquaculture industry plays an important role in the fishery industry of Hainan Province.In addition,mangroves,seagrass beds and other important coastal wetland ecosystems are also located in the lagoon,which plays a vital role in protecting the coast,purifying seawater and maintaining biodiversity.Ecological impact of numerous microplastics,produced by fishing rafts,nets,fishing boats and activity of Danjia in Xincun Bay,should not be underestimated.Due to the large specific surface area,MPs could be attached microorganisms through biofilm called“plastisphere”,which may carry and even spread harmful microorganisms,thus affecting the surrounding ecosystem.Therefore,an extensive and in-depth study on the distribution characteristics of microplastics and its ecological risk in Xincun lagoon is to be carried out urgently to control microplastics pollution in lagoon and protect the surrounding typical marine ecosystem.Firstly,this study analyzed the abundance,morphology,particle size,color and polymer types of microplastics in surface seawater,adult mangrove,young mangrove sediments and surface water,and seagrass patch sediments of different sizes in Xincun Bay aquaculture area.The results showed that:（1）The abundance of microplastics in surface seawater at different sampling locations was 5.2±2.7 n·L-1.Densely populated areas with poor hydrodynamic force had significantly higher abundance than others（P<0.05）.Among them,polyethylene（PE）,polystyrene（PS）and polypropylene（PP）ranked the top three type,which was highly consistent with plastic materials used in aquaculture;（2）The abundance of microplastics in seagrass sediments in lagoon is significantly different due to size of patches.The abundance of microplastics in long patches（W≈3m）is significantly higher than that in round patches（R≈3m）;A higher proportion of fibrous microplastics were also found in the middle of long patches;The abundance of microplastics was not significantly correlated with shoot density of seagrass.（3）Forest age and tide level had significant effects on the distribution of microplastics in mangrove in lagoon.The abundance of MPs in surface seawater and sediments of adult mangrove(91.2±15.0 n·L-1,1972.9±805.2 n·kg-1)was significantly higher than that of young mangrove(49.1±7.3 n·L-1,686.2±64.3 n·kg-1);Mangrove ecosystem can trap MPs,and landside mangrove has the strongest ability.Furthermore,three polymer types of MPs（PE,PS and PP）with the highest abundance in above typical ecosystem and one natural material particles（Wood,WD）were cultured in situ in Xincun aquaculture area for 60 days.The diversity and succession characteristics of microorganisms on the surface of samples retrieved on10d,30d and 60d,were studied by 16S r RNA high-throughput sequencing.PS,PP and WD samples were transferred to seagrass bed and mangrove ecosystem and retrieved on 3d,10d and 10d to study community succession characteristics in seagrass bed and mangrove ecosystem by 16S r RNA high-throughput sequencing.PE,PS and PP retrieved on 60d in Xincun aquaculture area were transferred to indoor seagrass culture system for 12 hours.The surface microorganisms of various parts（seagrass leaves,seagrass rhizomes,seawater and sediments）were sampled at the 12th hour.The transfer characteristics of typical microplastic surface microbial communities in the seaweed culture system were studied by 16S r RNA high-throughput sequencing.Study using microbial communitiesαDiversityβThe results showed that:（1）with the extension of exposure time,the biofilm on the surface of MPs became thicker,among which PS biofilm was the thickest;MPs bacteriaαThe diversity index was higher than that of water body（WR）,and some microorganisms were unique to microplastics;Compared with WR,the microbial network structure of MPs is more complex and dispersed;Through the analysis of potential degrading bacteria and pathogens with abundance of more than 0.01%,it was found that the abundance of several potential degrading bacteria on microplastics was higher than that in water,and no potential pathogens were enriched on microplastics;WR and MPs bacterial communities have significant differences in carbon and nitrogen cycle of metabolic function and drug resistance.（2）After the three materials were transferred to mangrove and seagrass bed ecosystems,theαdiversity of microplastic surface microorganisms showed different changes,and the seagrass ecosystem showed various changes on theαdiversity indexes decreased while mangrove increased;There were similar changes at the level of microbial community composition,the proportion of Proteobacteria and cyanobacteria increased,and the proportion of Firmicutes and actinobacteria decreased;The abundance of the top 25 species at PCo A and genus levels showed that there were significant differences in the composition of microplastic surface microorganisms between aquaculture areas and mangrove or seagrass beds;（3）Three MPs were transferred to seagrass culture system.It was found that compared with the bacteria in CK,the treatment with microplastic had significantly higher bacterial richness,and there were significant differences in community composition,aggregation,cluster analysis and biomarker groups,indicating that the bacteria would transfer to seaweed culture system with micro plastic as carrier.Microplastics are widely distributed in the lagoon ecosystem of aquaculture in Xincun.Microplastics are found in the surface water,mangrove sediments,surface water and seagrass bed sediments in the aquaculture area,and their abundance is at the middle level.According to the material of microplastics,it can be concluded that they come from the materials used in aquaculture.The microorganisms on the surface of microplastics in aquaculture area were significantly different from those in water,and no obvious pathogenic bacteria were found;When microplastics spread to seagrass beds and mangroves in aquaculture areas,obvious community succession occurred on their surface to adapt to the new environment;When the microorganisms in the aquaculture area are transferred to the seaweed culture system,the microbial community characteristics different from the control group can be found in the water body,sediment,seagrass leaves and seagrass rhizomes of the seagrass culture system.In short,the typical ecosystem of Xincun Bay has obvious microplastic pollution,and the spread of microorganisms on the surface of microplastics has potential ecological risks to the system. |
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