Spatial Distribution Characteristics And Driving Factors Of Benthic Ciliates In Sandy Intertidal Zone Of China

Understanding patterns of biodiversity distribution at large spatial scales is a core objective of biogeography.In a context where global changes are profoundly affecting the coastal zone environment,leading to a dramatic loss of biodiversity and changes in the spatial and temporal distribution patterns of species,understanding the current status of regional species distribution is also a prerequisite for establishing biodiversity conservation plans.Biogeography has been studied in some depth in the field of macroorganisms,but there is still a paucity of information on the biogeographic distribution patterns of micro-organisms,especially the role of environmental and spatial factors in structuring their communities.As one of the major coastal zone ecosystems,sandy beaches,with their high shoreline occupancy and lack of vegetation zone influence,as well as being subject to multiple controls of physical,chemical and biological processes,make them ideal areas for conducting microbial biogeography experiments.In this study,ciliates,a typical micro-organism,were sampled from a sandy intertidal area of coastal China spanning a 2500 km latitudinal gradient,and relevant physicochemical parameters were determined to verify whether their community structure and diversity were driven by relevant factors such as local environmental and regional processes.This paper firstly used density gradient centrifugation combined with quantitative protein silver staining(Ludox-QPS)to obtain background information on intertidal benthic ciliates.Next,non-metric multidimensional scaling analysis(NMDS)and permutation multivariate analysis of variance(PERMANOVA)were used to reveal whether the ciliate community structure was consistent with the macrofauna-based biogeographic province classification of China’s coast.Subsequently,distance-based redundancy analysis(db RDA)was used to determine the relative importance of local and regional variables in explaining changes in community structure.Finally,a generalized linear model(GLM)was further used to explore the most important explanatory factors for ciliate alpha-diversity.The main results and conclusions of this paper are as follows:(1)A total of 177 species of benthic ciliates were detected in this study,belonging to 88 genera of 56 families in 14 orders and 25 phyla.The number of benthic ciliate species shared by the three biogeographic provinces was 68,and the number of species endemic to Provinces I and III was 30 and 10,respectively,while no endemic species existed in the communities of Province II.In terms of species composition,the PERMANOVA results showed that there were significant differences in benthic ciliate community composition among the three biogeographic provinces;however,there were no significant differences in trait composition among the three provinces.db RDA results confirmed that local environmental factors and spatial scale jointly drove variation in benthic ciliate species composition,but the former played a dominant role,while the trait composition of benthic ciliate communities was significantly influenced by salinity.A local environmental factor was significantly influenced.(2)In terms of the spatial distribution of alpha-diversity,all three indices of diversity(taxonomic diversity,phylogenetic diversity and functional diversity)were positively correlated with latitude.The hotspots of diversity were mainly concentrated in Bohai Bay,Shandong Peninsula,the northern coast of the Yangtze River estuary and the coast of Beibu Gulf.Among local environmental factors,the beach index plays a crucial role in shaping the three α-diversities of ciliates.In addition,ammonia nitrogen and the abundance of microbenthos representing biotic interactions significantly influenced the taxonomic diversity of ciliates;ammonia nitrogen similarly significantly influenced the phylogenetic diversity of ciliates;and functional diversity was significantly influenced by salinity.(3)As micro-organisms generally exhibit weaker dispersal limitations than macroorganisms,local environmental factors are more important than regional processes in driving their diversity and community structure.The significant differences in benthic ciliate community composition among the three biogeographic provinces are most likely due to the specific environmental conditions of the Yangtze River’s washed-out water flow,rather than being influenced by dispersal limitation or historical factors.This study reveals for the first time that the community distribution of marine microciliates is consistent with the biogeographic province division of macrofauna in China’s coastal zone,providing new insights into the distribution patterns of marine microfauna and their driving mechanisms,as well as a more micro-fine perspective on the conservation of intertidal biodiversity and ecosystem management in the context of future global change.