Characteristics Of Geographical Distribution Pattern Of Snail Assemblages In Typical Marsh Wetlands In Northeast China

Understanding the spatial distribution characteristics of organisms,the spatial differences of biodiversity and its influencing factors is one of the cores of Macro-ecology,Biogeography and Environmental science.Gastropoda(snail)is the second class of aquatic macro-invertebrates.At present,in Northeast China,basic data of species composition and diversity of snails are lacking,and distribution pattern at different scales of snails,the influence of environmental factors and human activities on the distribution pattern of snails are still unclear.We studied the composition of snail assemblages and geographical distribution pattern of typical marsh wetlands in four regions(Sanjiang Plain,Songnen Plain,Changbai Mountain,Daxing'an Mountains)of Northeast China.The species composition and diversity characteristics of snail assemblages of Northeast China region and in different wet areas were made clear.The influence of human disturbance on the distribution pattern of snail assemblages was clarified.The distribution characteristics of snails at regional and local scales are studied.The influencing environmental factors of distribution patterns of snail assemblage at regional and local scales were analyzed.This research provided a scientific basis for the protection of biodiversity and the management of biological resource of marshes.The main conclusions are as follows:A total of 65 species of snails were collected from marsh wetlands in Northeast China,including 58 species of Heterobrania and 7 species of Caenogastropoda.Terrestrial snails in marshes(11 species)were richer when compared with other aquatic ecosystems.Snail assemblages of marsh wetlands at four regions had different dominant species,representative indicator species and exclusive species.Species richness of snail assemblages first increased and then decreased with the increase of latitude and longitude.Species richness of snail assemblages gradually decreased with the increase of altitude.Species richness and taxonomic diversity of snail assemblages in marshes of Sanjiang Plain and Daxing'an Mountains were higher than those of Songnen Plain and Changbai Mountains.Altitude and salinity were the most important environmental variables in explaining the dissimilarities of snail assemblages among the four wetland regions.Salinity was the first driving environmental variables,and altitude was second to salinity.Under the influence of salinity and altitude,various factors drived the distribution pattern of snail assemblages in marsh wetlands of Northeast China.Type of water supply of marsh wetlands is one of the important driving factors affecting the distribution pattern of snail assemblages in the Sanjiang and Songnen plain.In the Sanjiang Plain,snail assemblages in permanent inundated marshes were significantly different with seasonal flooded marshes.Species of snail assemblages in seasonal flooded marshes was richer than permanent inundated marshes.Abundance of snail assemblages in permanent inundated marshes was significantly higher than seasonal flooded marshes.Indicator species of in seasonal flooded marshes were mostly non-pulmonate snails,which are common in lotic habitats.Indicator species of permanent inundated marshes were pulmonate snails,which are common in lentic habitats.We also found that the composition of snail assemblages of Deyeuxia angustifolia,Carex schmidtii,Carex lasiocarpa,Carex pseudocuraica association were corresponded to the water depth and plant composition in the depressional marshes of the Sanjiang Plain.Marshes in the Songnen Plain were divided into seasonal inundated saline-alkaline marshes,Permanent inundated saline-alkaline marshes and an unclassified group according to the snail assemblages.Snail assemblages of these three groups of saline-alkaline marshes were significantly different from each other.Five environmental variables(salinity,p H,dissolved oxygen,total suspended solids,and chlorophyll)are best explained the snail assemblage distribution and structural patterns in the saline-alkaline marshes of Songnen Plain.Marshes in mountain regions were sampled in Daxing'an mountains and Changbai mountains.In Daxing'an mountains,groups of snail assemblages was corresponded to the types of marshes(temporary marsh,floodplain swamps,terrace swamps and piedmont plain marshes).Snail assemblages of four type marshes were significantly different from each other.Four terrestrial snails were indicator species of temporary wetlands;eight snails were indicator species of terrace swamps;two snails were indicator species of piedmont plain marshes;only one snail species was indicator of river floodplain marshes.In the Changbai mountains,snail assemblages of two groups of moss peatland and one group of herbaceous peatland were significantly different from each other.One type of moss peatland and herbaceous peatland had indicator snail species.Altitude is the most relevant environmental variable explained the snail assemblage distribution patterns of wetlands both in the Daxing'an mountains and Changbai mountains.Snail assemblages in 16 wetlands across a range of human impacts showed that abundance was higher in the reference marshes than the impacted marshes.Five pulmonate snail species were indicators of reference marshes.Two non-pulmonate species were indicators of one group of impacted marshes.Snail assemblages in 12 floodplain wetlands and 10 levee-isolated marshes along Wusuli River(headwater,mid,and downstream reaches)demonstrated that the snail assemblages were concurrently being impacted by river reach,and whether the wetlands were connected with the river,or not.Seven snail species were significant indicators of these wetland groups.Snail assemblages of seven natural marshes,nine wetland ditches,and nine agricultural ditches differed significantly in the Sanjiang Plain of northeastern China.Species richness and abundance of snail assemblages in wetland ditches were similar with natural marshes.Although lower,species richness and abundance of snail assemblages in agricultural ditches still accounted for 22% and 52%,respcetively,of that in natural wetlands.Dissolved oxygen in combination with p H was the most important environmental factors in explaining the dissimilarities of snail assemblages among the three different habitats.