| Artificial reef(AR)is an important basic ecological project in marine ranching construction with the main functions of improving the marine ecological environment,providing habitats for reproduction,growth,feeding and shelter of marine organisms,and protecting and enhancing marine resources.The biological effect is one of the most important ecological functions of ARs.So far,the basic researches on the biological effects of ARs were mainly from the macro level and focused on investigating the structural characteristics of marine flora and fauna in the AR area,ignoring the importance of microorganisms and microecology,which is difficult to explain the ARs’ biological effects.Microbes are major primary producers and environmental indicator organisms that play an important role in the biochemical cycle and stability of the marine ecosystem,and induce the settlement and recruitment of macroalga spores and invertebrate larvae.Exploring the structure and succession of microbial communities therefore contributes to understanding the ecological effects of ARs.The present study was conducted with the help of high-throughput sequencing technology and bioinformatics methods.The typical AR areas in Weihai were selected as the sampling points,and the microbial communities from the sediments and reef surface were taken as the research objects,considering factors such as AR age,material,flow direction,and dominant macroalgae attached to the reef,combined with the results of environmental factors.The development and succession of microbial communities were systematically studied,to analyze the dynamic changes of the structure and diversity of microbial community,and the interactions between microbial communities,to reveal the relationships between microorganisms and macrobenthic community,as well as the environmental factors driving the dynamic changes of microbial communities.The present study could provide a theoretical basis for the evaluation of the ecological effects of ARs.The main results are as follows:(1)In order to explore the impact of AR deployment on the microbial community structure of sediments,a total of eight times were continuously collected before and after ARs’deployment from July 2018 in Shuangdao Bay.The richness and diversity of microbial communities changed dynamically over time.The linear fitting analysis showed that the values of the Shannon index and Chao1 index were significantly positively correlated with temperature,and negatively correlated with dissolved oxygen(P<0.05).Proteobacteria was the most dominant phylum,varying 38.54%to 61.89%.Except for the samples collected in winter,Bacteroidetes was the second predominant phylum(from 13.17%to 22.61%).Thaumarchaeota had a high abundance only in early autumn and winter samples.At the genus level,the dominant bacterial genus showed distinct temporal succession,and Woeseia was the most dominant bacterial genus in the vast majority of sample groups.The number of core OTUs at different stages was just 12.34%.Except for November and December,the unique OTU numbers in different periods were relatively small.LefSe analysis showed significant differences in microbial community structure were mainly concentrated in November and December.Temperature and dissolved oxygen were the main factors driving the succession of microbial communities.(2)There are obvious seasonal changes in the composition and diversity of the sediment microbial community surrounding the AR area.The values of diversity and richness of microbial communities were higher in summer,and lower in spring or winter.Proteobacteria,Bacteroidetes,and Desulfobacterota were the dominant phyla,with a relative abundance of 60.37～68.76%.The relative abundances of dominant flora in different seasons and different sampling areas were quite different.The PERMANOVA analysis showed that seasons,sampling area,and seasons × sampling area had significant effects on the microbial community structure.The abundant ASV numbers of the microbial community between different seasons were only 5-12,with a relative abundance of 8.35%-25.53%.While the number of rare ASVs accounted for more than 85%,and the proportion of rare ASVs was even more than 95%in different seasons.The co-occurrence network showed that the microbial interaction might be more intensive in AR than the control area.The microbial communities were significantly correlated with temperature,DO,salinity,pH,TOC,D50,and TN(P<0.001).(3)The ecological succession of the microbial community on concrete and wooden AR blocks was explored.The richness and diversity index of microbial communities were significantly higher in concrete than in wood,and there were significant differences in microbial community structure between these two AR materials.The microbial community of concrete and wooden ARs showed temporal succession,but the trends were not exactly the same.The relative abundances significantly decreased over time for Proteobacteria,Cyanobacteria and Gracilibacteria in wood,as did that of Cyanobacteria in concrete.Co-occurrence network analysis showed that the microbial interaction might be more intensive in wood than concrete.The macrobiotic compositions were broadly similar on the concrete and wooden AR blocks,and the dominant species changed dynamically with time,especially in the first five weeks,whereas the Pacific oyster(Crassostrea gigas)became the absolute dominant species from the sixth week to the end of the study.The organism coverage on the concrete blocks was higher than that of wood at most time points,the Shannon index of microbial community was significantly positively correlated with the organism coverage.(4)The composition and diversity of the microbial community at different flow sides of ARs showed distinct changes over time.The diversity and abundance of bacterial and archaeal communities on the stoss side were higher than those on the lee side(P>0.05).However,the fungal community was significantly higher than that on the lee side(P<0.05).There were differences in the composition of absolute dominant phyla in bacterial and archaeal communities,while Ascomycota and Basidiomycota were always the dominant phyla in fungal community.Linear regression analysis showed that the relative abundances of Cyanobacteria and Verrucomicrobiota significantly decreased over time(P<0.05),while Crenarchaeota increased significantly on both sides(P<0.05).The relative abundances of Proteobacteria and Bacteroidetes significantly decreased with time on the lee side(P<0.05).PERMANOVA analysis showed that flow side,sampling time,and flow side × sampling time had significant effects on the microbial community structure.The proportion of the core OTU number of the bacterial and archaeal communities,and fungal community was only 2.80%and 0.207%.Co-occurrence network analysis showed that the microbial interaction was more intensive and complex on the lee side.The species composition of the macrobiotic communities colonized on both sides changed with time.The Margalef index,Shannon index,and Pielou index of the macrobiota on the stross side were higher than those on the lee side,while the biomass and coverage were lower than those on the lee side.The values of the microbial shannon index showed a significant positive correlation with organism coverage in the stross side groups(P<0.05),while the correlation on the lee side was not significant(P>0.05).(5)To further explore the effect of the macrobiota on the microbial community structure on ARs,investigation in the rocky intertidal zone was carried out on a stretch of rocky beach in the north of Weihai City,Shandong Province,China.The epiphytic microbial communities on four macroalgae(Corallina officinalis,Rhodomela confervoides,Sargassum thunbergii,and Ulva linza)and their rocky substrates were characterized using high-throughput sequencing technology.The Shannon and Chao 1 indices were greater in rocky substrates than that in macroalgae.Except for the exposed rock matrix,the values of the Pielou index were also higher in in rocky substrate samples than that in macroalgae samples except that of the blank rocky substrate samples.The microbial community on U.linza displayed the lowest level of species richness,diversity,and evenness among samples groups.The NMDS ordination showed the microbial communities on macroalgae and rocky substrates formed clear separate clusters.The results of PERMANOVA and ANOSIM further confirmed that the microbial communities on macroalgae were significantly different from those on rocky substrates.The microbial similarities among macroalgae and rocky substrate groups tended to decrease from the high taxonomic ranks(at phylum and class levels)to lower ranks(at genus and species levels).The number of unique ASVs in rocky substrates was far greater than that of macroalgae,and each macroalga and its’ respective substrate also followed a similar trend.Only 22.69%of the total amplicon sequence variants(ASVs)were shared.PICRUSt2 was used to analyze and predict the functional capabilities of microbial communities inhabiting macroalgae and rocky substrates.At the primary level,metabolism was the highest in abundance in all samples,followed by genetic information processing.There were no significant differences in these metabolic pathways among groups(p>0.05). |
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