Relationship Between Macrobenthos Community Structure And Environmental Factors In Karst Caves In Zhenning County,Guizhou Province

Caves are special subsurface ecosystems,and are the gathering place of "extreme subsurface biodiversity".Cave macrobenthos is an important part of the cave water ecosystem,located in the middle of cave aquatic food web,and plays an important role in processes such as energy flow,material cycling and maintaining the integrity of ecosystem function.At present,there are few studies on cave macrobenthos in China,especially on the community structure of cave macrobenthos and its relationship with the environment.To this end,we investigated and collected macrobenthos and environmental factors in 14 caves in Zhenning County,Guizhou Province in January 2021(dry season)and July 2021(wet season),studied the spatial and temporal changes of cave macrobenthos community structure and functional feeding groups,explored the relationship between cave macrobenthos community structure and environment using correlation analysis and constrained ordination analysis.Preliminary estimates of the secondary productivity levels of cave macrobenthos were made and the environmental quality of cave water was evaluated by using the macrobenthos biology index.This study aims to provide basic information for understanding the material cycle and energy flow of the cave water ecosystem,provide data support for the response of the cave water ecosystem to environmental changes,and provide theoretical references for the conservation of cave aquatic biodiversity and the exploitation,utilization and protection of cave water resources in Zhenning County.The main research results are as follows.(1)A total of 5,902 cave macrobenthos were obtained in the two surveys,with 121 species belonging to 4 phyla,7 classes,22 orders and66 families.The species composition was mainly insects and mollusks.The number of species and individuals of macrobenthos did not differ significantly between different seasons and light zones,but there were significant differences between different caves.(2)The composition of the dominant species differs in different seasons,the dominant species in the wet sesason were Physa foncinalis,Simulium sp.,Baetis sp.,Hydropsyche sp.and Caenis sp.,while in the dry season were Ephemera sp.,Macromia sp.,Physa foncinalis and Parafossarulus sp..The distribution of dominant species varied widely among caves,with the Physa foncinalis and Baetis sp.occurring most frequently and being dominant in about 60% of the caves,and the mollusks being relatively dominant in all caves.(3)The density and biomass of macrobenthos fauna differed significantly between the two seasons,with arthropods dominating the density and mollusks the biomass.The density,biomass,diversity index(H?)and evenness index(J?)of macrobenthos did not differ significantly between different seasons,caves and light zones,and the richness index(D)only differed significantly between caves.Cluster analysis showed that the similarity of macrobenthic communities between adjacent light zones in the same cave was high,and the similarity between macrobenthic communities in different light zones in different caves was low.(4)The species composition of the functional feeding groups of macrobenthos in the caves in Zhenning was dominated by predators,and the number of individuals was dominated by scrapers and collectors.The number of species,individuals,density and biomass of functional feeding groups did not differ significantly between different seasons,and the functional feeding groups with the highest density and biomass in the wet season were scrapers,while those with the highest density and biomass in the dry season were scrapers and filter feeders,respectively.There were no significant spatial differences in the density and biomass of the functional feeding groups,except for the biomass of scrapers,which differed significantly between caves.(5)Pearson correlation analysis showed that water temperature and water depth were the main environmental factors influencing the community structure of cave macrobenthos in the wet season,and dissolved oxygen,cave light intensity and sediment organic matter content were the main environmental factors influencing the community structure of cave macrobenthos in the dry season.The CCA/RDA analysis showed that dissolved oxygen and cave light intensity were the main environmental factors affecting the distribution of macrobenthos in the light zone;flow rate was the main environmental factor affecting the macrobenthos community structure in the weak light zone;and sediment organic matter was the main environmental factor affecting the macrobenthos community structure in the dark zone.The RDA analysis showed that dissolved oxygen and cave light intensity were the main environmental factors affecting the functional feeding groups of cave macrobenthos.(6)The water quality of the caves was evaluated based on biological indexes of macrobenthos.The evaluation results of Shannon-Weiner index show that the overall water quality of light pollution?heavy pollution level in Zhenning caves;BI index shows that the overall water quality of good?medium pollution level in Zhenning caves.The evaluation results of different indices have large differences,Due to the uneven distribution of macrobenthos in the caves,the diversity index is generally low,so Shannon-Weiner index are not suitable for cave water quality evaluation.BI index takes into account the pollution tolerance and relative number of different groups,and the evaluation results are closer to the actual cave water environment,which is more suitable for cave water quality evaluation.