Study On The Driving Factors Of Benthic Ciliate Diversity And Community Composition In Zhejiang Intertidal Wetland

The intertidal wetland is one of the most productive and fragile ecosystems.As a transitional zone between the ocean and land,the intertidal zone not only harbors rich biodiversity resources but is also an important region supporting human economic development.This area is not only strongly influenced by physical and geochemical environmental factors but also disturbed by high-intensity human activities,thus facing habitat degradation,biodiversity loss,and other issues.Studying the response of biological communities to different factors is the basis for biodiversity conservation.However,research on the mechanism of intertidal biodiversity change is often hindered by the difficulty of distinguishing the effects of natural factors,human disturbances,and inter-biological interactions.Previous studies have mostly focused on large organisms,but microorganisms,as a relatively rich and diverse population in intertidal ecosystems,are ideal model organisms for studying biodiversity.Based on this,in July 2020,this study investigated the microbe diversity and driving factors of 46 coastal sites in Zhejiang Province.Zhejiang is one of the coastal areas with a high degree of urbanization in China,and its coastal zone is strongly affected by human disturbances such as eutrophication of seawater.This study focused on ciliated protists,which have high biodiversity and are sensitive to environmental changes,and used methods such as Structural Equation Modeling(SEM),distancebased redundancy analysis(db RDA),and Variation Partitioning Analysis(VPA)to reveal the relative effects of three factors: natural environmental gradients(such as sediment grain size),human disturbance-induced eutrophication,and biotic interactions(such as the abundance of meiobenthic and benthic bacteria)on the composition(species composition,functional composition,and phylogenetic composition)and alpha diversity(taxonomic diversity,functional diversity,and phylogenetic diversity)of ciliate communities.The main results and conclusions are as follows:1)This study identified a total of 102 species of benthic ciliated protists belonging to 9 classes,23 orders,42 families,and 60 genera in the 46 coastal sites in Zhejiang.Among them,the Oligohymenophora ciliates were the dominant taxa in the sample points with larger sediment particle size(e.g.sandy sampling sites);while the Prostomatea ciliates were the dominant group in the sample points with smaller sediment particle size(e.g.mudflat sampling sites).dominant group.2)Among natural factors,sediment grain size has the highest explanatory power for the taxonomic diversity and phylogenetic diversity of benthic ciliates,and is positively correlated with both.The combination of sediment grain size and redox potential also has the highest explanatory power for the variation in ciliate community composition.This indicates that sediment grain size is the primary factor influencing alpha diversity of benthic ciliates and selecting for community composition.Moreover,the study found that an appropriate particle size range helps maintain the necessary life activities of ciliates,thereby maintaining higher diversity.3)Anthropogenic eutrophication caused by ammonium nitrogen in seawater also significantly affects the phylogenetic diversity and community composition of benthic ciliates in three facets.This is because excess nitrogen in coastal waters can cause changes in the system and functional composition(such as feeding functional groups)of ciliate communities,thereby affecting their phylogenetic diversity.4)The explanatory power of the abundance of meiobenthic representing biotic interactions on the alpha diversity of ciliates is second only to that of particle size,and the two are positively correlated.However,the abundance of benthic bacteria has no effect on ciliate alpha diversity.Therefore,the study emphasizes the importance of ciliates as a food source for benthic animals.Ciliate diversity is more regulated by the abundance of meiobenthic than by the abundance of benthic bacteria.In addition,in terms of community composition,biotic interactions have a smaller impact on ciliate community composition than natural and anthropogenic disturbances.5)The composition of ciliate communities shows a different pattern of response to different variable factors than alpha diversity,and is more sensitive to anthropogenic eutrophication than alpha diversity.Therefore,we believe that the community composition of ciliates is more suitable for indicating anthropogenic eutrophication.Overall,this study distinguishes and quantifies the relative effects of three factors:natural environmental gradients,anthropogenic eutrophication and biological interaction on the community of microbenthic ciliates in the coastal zone under multiple influences.The results obtained can provide a reference for the protection of biodiversity in the coastal zone and contributes to the formulation of ecological protection management decisions for the coastal zone.