The Response Of Benthic Ciliate Community To Scirpus Mariqueter Ecological Restoration Project In Chongming Dongtan

Scirpus mariqueter salt marsh in Chongming Dongtan is an important part of the salt marsh ecosystem in the Yangtze River Estuary,and also a necessary place for birds to inhabit and forage during their North-South migration in Asia-Pacific region.Since the 1990 s,Spartina alterniflora has invaded Chongming Dongtan,resulting in the sharp reduction of the distribution area of Scirpus mariqueter,and ecological system structure and function have been damaged.In order to prevent the further expansion of Spartina alterniflora and provide a suitable habitat for birds,the ecological restoration of Scirpus mariqueter has been carried out in the Chongming Dongtan in recent years.Previous studies have found that the change of salt marsh vegetation would affect the physicalchemical conditions of sediments environment and the benthic community,but most previous studies mainly used spatial comparison instead of time comparison,and mainly focused on marofauna and meiofauna.However,the life cycle of macrfauna and meiofauna is long,and it takes several years for the community structure to reach balance after environmental change.In contrast,Ciliate protozoa have the characteristics of short turnover time and sensitive response to environmental changes,their community structure can respond to environmental changes faster.Therefore,our research was carried out for two years(from 2019 to 2021)in two habitats which are Scirpus mariqueter ecological restoration area and Scirpus mariqueter natural growth area in Chongming Dongtan.On the one hand,we compared the species composition and diversity between the restored areas and natural areas,and analyzed the main environmental factors driving the benthic ciliate community;On the other hand,we analyzed the differences of benthic ciliate community between the restored areas and areas before restoration,and explored the most impact of ecological restoration project on benthic ciliate community.The main results and conclusions are as follows:(1)A total of 122 species of benthic ciliates were identified in the restored areas and natural areas,belonging to 10 classes,23 orders,46 families and 58 genera.The dominant species groups were Holophrya aklitolophon,Lorichophrya susannae and Kentrophyllum setigerum in the restored areas,and Holophrya aklitolophon,Pseudocyclidium marylandi,Holophrya caspica,Platynematum salinarum,Zosterodasys minutus,Kentrophyllum setigerum and Litonotus bergeri were the dominant species groups in the natural areas.NMDS analysis and PERMANOVA analysis showed that the species composition in the restored areas was significantly different from that in the natural area(P < 0.05).BIOENV analysis showed that salinity,sediment grain size,ammonium nitrogen,meiofauna abundance and meiofauna biomass are the best environmental factor group that could explain the differences in ciliate species composition between the restored areas and natural areas(R = 0.406,P< 0.05).(2)In terms of benthic ciliate community diversity,the species number,richness index,evenness index and Shannon-Wiener index in Scirpus mariqueter restored areas were significantly lower than those in natural areas(P < 0.01).Pearson correlation analysis showed that benthic ciliates community diversity is mainly correlated with salinity,sediment grain size,ammonium nitrogen,meiofauna abundance and meiofauna biomass.(3)In this study,74 species were identified in the restored areas,and 113 species were identified in the areas before restoration.The dominant species groups were Pseudochilodonopsis sp1,Spathidium sp1,Chaenea minor,Kentrophoros sp1,Holophrya caspica,Amphileptus lanceolatus,Parauronema sp2,Uronema sp1,Chlamydodon minutus,Prorodon diaphanous,Chaenea stricta,Haptorida sp2 and Pseudochilodonopsis algivora in the areas before restoration.Holophrya aklitolophon,Loricophrya susannae and Holophrya caspica were the dominant species groups in the restored areas.NMDS analysis and PERMANOVA analysis showed that the species composition was significantly different between the restored areas and areas before restoration(P < 0.05).BIOENV analysis showed that salinity and sediment grain size were the best environmental factor group to explain the changes of species composition between the restored areas and areas before restoration(R = 0.207,P < 0.05).(4)In terms of benthic ciliate community diversity,the number of species,richness index and Shannon-Wiener index of benthic ciliates in the restored areas were significantly lower than the area before restoration(P < 0.01),but the difference of evenness index was not significant(P > 0.05).Pearson correlation analysis showed that benthic ciliates community diversity is mainly correlated with salinity and ammonium nitrogen.In conclusion,there were significant differences in the species composition of ciliates community between the restored area and the natural area,and the diversity of ciliates community in the restored area is significantly lower than that in the natural area;There were significant differences in species composition between the restored areas and areas before restoration,and the dominant species groups have changed.The diversity of benthic ciliate community(species number,richness index and ShannonWiener index)in the restored areas was significantly lower than that in the areas before restoration.Therefore,we speculate that the difference in species composition and diversity between the restored areas and the natural areas is mainly affected by the Yangtze River Diluted Water,resulting in the difference of salinity,sediment grain size and nutrients,which has an impact on the ciliate community.Besides,the predation and competition of meiofauna also play an important role to control the ciliate community.The changes of species composition and diversity of ciliate community between the restored areas and the areas before restoration was affected by ecological restoration.Ecological restoration transforms the salt marsh vegetation from Spartina alterniflora into Scirpus mariqueter,which promotes the reduction of sediment particle size and indirectly improves the content of organic matter.In addition,compared with Spartina alterniflora,the Scirpus mariqueter has lower biomass that the ability of absorb nitrogen was insufficient,resulting in the increase of the ammonium nitrogen,caused a slightly eutrophication,which negatively affected the diversity of benthic ciliate community.Our aim is to explore the relationship between benthic ciliate community and environmental factors,which will provide some information for the salt marsh ecological restoration in the Yangtze River Estuary,and provide a reference for the protection and monitoring of salt marsh in the face of global climate change.