The Community Structure And Historical Change Of Species Diversity Of Unionids In Four Lakes In The Middle And Lower Reaches Of The Yangtze River

Unionids is an important component of the macrozoobenthos community in fresh water ecological system,which has important ecological function.However,due to their slow movement and weak resistance to environment,they have become one of the most endangered aquatic animal groups in the world.The middle and lower reaches of the Yangtze River is the main distribution area of mussels in China,in where the mussel resources are very abundant.However,due to the interference of natural and human factors in recent decades,unionids population have declined significantly,the resource situation urgently needs to be ascertained and effective protection measures need to be strengthened.The survey about unionids of four lakes?Taihu Lake,Liangzi Lake,Longgan Lake,Daguan Lake?in the middle and lower reaches of the Yangtze River were conducted during 2015-2017,analyzing the unionids'species composition,standing crop,spatial distribution,floristic similarity,historical change and its relationship with environmental factors,which can provide the foundation for the protection of unionids.The main results are as follows:1.There were 18 species belonging to 10 genera were collected in four lakes,among them species of Anodonta were most up to six species,Lamprotula and Cuneopsis had two species,while there was 1 species of Schistodesmus,Unio,Hyriopsis,Cristaria,Cuneopsis,Lepidodesma and Arconaia.14 species belonging to8 genera were collected in the Taihu Lake;A total of 12 species belonging to 8 genera were collected in the Longgan Lake;There were 7 species belonging to 4 genera in the Liangzi Lake and 6 species belonging to 4 genera in the Daguan Lake.2.The average biomass of unionids in four lake was from 1.35±2.74 g/m² to14.98±16.74 g/m²;The density was from 0.02+2.63 ind./m² to 0.58+0.76 ind./m².Among them,the average biomass of Taihu Lake was 4.17+9.34 g/m²,and the density was 0.16+0.39 ind./m².The mean biomass and density differed significantly among the areas in Taihu Lake.The biomass and density were highest in eastern lakeshore area,with the values of 14.975±16.743 g/m² and 0.577±0.758 ind./m²,respectively.The lowest biomass and density were recorded in central area of Taihu Lake with the values of 0.727±1.622 g/m² and 0.029±0.071 ind./m²,respectively.The Arconaia lanceolata,Unio douglasiae and Anodonta woodiana woodiana were dominant species in Taihu Lake.The mean density and biomass of the Liangzi Lake were 0.02+2.63 ind./m² and 1.35+2.74 g/m²,the Unio douglasiae was dominant species.The mean biomass and density of the Daguan Lake were 0.08+0.10 ind./m²and 9.33+15.61g/m²,respectively,and the Unio douglasiae and Hyriopsis cumingii were dominant species.The mean density and biomass of the Longgan Lake were0.18+0.36 ind./m² and 15.71+33.22 g/m²,the dominant species were Unio douglasiae and Hyriopsis cumingii.The total species of the four lakes were Anodonta woodiana woodiana,Unio douglasiae,Anodnota euscaphys and Andonta arcaeformis.3.Eight lake areas were divided into three classes by cluster analysis.Among them,Gonghu and eastern coastal area were grouped into one class,Zhushan Bay and the western coastal areas were grouped into one class,while Meiliang Bay,East Taihu,southern coastal area and central area of lake were one class.4.The CCA results showed that the most influential factors for the distribution of the unionids in Taihu Lake were NO₃^-and BOD₅,followed by water depth and NH₄⁺,and the effect of nutrition factors on unionids was greater.5.Compared with the historical data,there was a significant decline of the resources of unionids in Taihu Lake with 9 species had reduced and the standing crop was lower than other lakes;the Liangzi Lake reduced 2 species;the remaining two lakes lacked historical data,but the status was not optimistic.The investigation found that the mussel resources of the four lakes showed obvious decline trend.