Resource Status, Diversity Patterns Of Freshwater Mussels In Poyang Lake Area And Its Response To The Different Environmental Factors

Freshwater mussels is one class of very important aquatic organisms in freshwater ecosystems. With slow motion, living area relatively fixed, weak tolerance to environmental change, freshwater mussels that one of the freshwater taxonomic groups is the most vulnerable to the threat and its distribution is the widest. Freshwater mussels which can be used as food for the small animals, groundfish and birds is an important part of the food chain and important component of the freshwater biomes. As filter feeders, freshwater mussels can improve water quality through filtering food nutrients, organic matter and plankton. Freshwater mussels play an important role in freshwater ecosystems whose biomass and density are often dominant in the benthic animals. It will cause a series of ecological problems if freshwater mussels disappear in the freshwater lakes or rivers.There are complicated habitats, abundant species and rich resources of freshwater mussels in Poyang Lake, however, many habitats of freshwater mussels have been seriously damaged by human activity. Over the years, many scholars have systematically investigated and studied the resources of freshwater mussels in Poyang Lake, but their methods are basically qualitative collection and analysis, so it is very necessary to carry out a quantitative survey on the resources of freshwater mussels in Poyang Lake. In this article, freshwater mussels' quantitative collection and investigation had been systematically done according to different sampling areas, different types of uses and different habitats of Poyang Lake area, and the response of freshwater mussels to different environmental factors had been analyzed, both of which will provide information on species composition and resources status of freshwater mussels in Poyang Lake and they also have great reference value on the utilization and protection of freshwater mussels and the impact of the proposed hydro projects on freshwater mussels in Poyang Lake.The main results are as follows:1. There are 42 species belonging to 13 genera of freshwater mussels in Poyang Lake, of which 32 species are the Chinese endemic species. Both Unio douglasiae (Gray) and Lamprotula caveata (Heude) are dominant species and they are distributed in all sampling areas of Poyang Lake. The difference among genera, species and relative abundance of every sampling area is quite large, so it is with the species and relative abundance contained in genera and the biomass and density of all sampling areas and genera. The density and biomass of freshwater mussels in the whole lake are (0.28±0.22) ind/m2 and (4.08±3.96) g/m2 respectively. In terms of population structure, the growth form concludes Anodonta eascaphys, Cristaria plicata, Lamprotula leai, Cuneopsis pisciculus, Lamprotula rochechouarti, Arconaia.lanceolata, Acuticosta chinensis, Lanceolara eucylindrica, Lamprotula caveata, Anodonta woodiana oodiana, Anodonta woodiana pacifica, Lamprotula scripta, Lamprotula fibrosa and Cuneopsis heudei; the stable form concludes Lanceolara grayana, Schistodesmus lampreyanus, Anodonta arcaeformis and Unio douglasiae; the involution form concludes Lamprotula polysticta, Anodonta woodiana elliptica, Anodonta globosula and Schistodesmus spinosus.2. Qinlan Lake is a natural lake which has 35 species belonging to 11 genera of freshwater mussels. Chinese endemic species is 28. The dominant species are Unio douglasiae-Lamprotula caveata and Acuticosta chinensis which take a large proportion in specimens of each season. Freshwater mussels have small difference with seasons. The number of genera and species of freshwater mussels in autumn is 11 genera and 21 species respectively, being the maximum. Species of each genus of specimens are quite different, up to a maximum of 9 species belonging to Lamprotula and 8 species belonging to Anodonta. The biomass and density in summer are the maximum, being 22.75 g/m2 and 0.81 ind/m respectively; while those in autumn are the minimum, being and 10.00 g/m2 0.31 ind/m2 respectively. The average annual biomass and density are (15.94±5.26) g/m and (0.59±0.21) ind/m2 respectively. In terms of population structure, the growth form concludes Anodonta globosula, Schistodesmus lampreyanus, Lamprotula bazini, Anodonta woodiana pacifica, Arconaia lanceolata and Anodonta arcaeformis; the stable form concludes Unio douglasiae, Lamprotula caveata, Acuticosta chinensis, Cristaria plicata, Lanceolara grayana and Schistodesmus spinosus; the involution form concludes Anodonta fluminea, Hyriopsis cumingii, Lanceolara eucylindrica, Acuticosta ovata, Anodonta woodiana elliptica and Cuneopsis pisciculus.3. Junshan Lake is a proliferative lake which has 16 species belonging to 9 genera of freshwater mussels. The number of Chinese endemic species is 9. The dominant species are Unio douglasiae and Lamprotula caveata. The density and biomass of Unio douglasiae are 0.10 ind/m2 and 0.24g/m2 respectively, which is 52.47% and 31.07% of the total density and biomass of Junshan lake; the density and biomass of Lamprotula caveata are 0.04 ind/m2 and 0.26g/m2 respectively, which is 21.30% and 33.83% of total density and biomass of Junshan lake. Species of each genus of specimens are quite different, up to a maximum of 4 species belonging to Anodonta and 3 species belonging to Lanceolara. The density and biomass of freshwater mussels of Qinglan Lake are about 3 times and 20.70 times as much as those of Junshan Lake. The community similarity coefficient between the two lakes is 41.67. Qinglan Lake is a natural lake and its area is more diminutive than that of Junshan Lake which is a proliferative lake. But the resources of freshwater mussels in Qinglan Lake are more abundant than those in Junshan lake, which explains that artificial proliferating has major influence on resources of freshwater mussels in Junshan Lake.4. Dahuchi Lake, Shentanghu Lake and Donghu Lake are all shallow lakes in Poyang Lake area. Taizihe River is a gully while Raohe River, Xiuhe River, Xinjiang River and Ganjiang River are all the important river systems of Poyang Lake. The total freshwater mussels of all sampling areas are 40 species belonging to 14 genera, of which the number of Chinese endemic species is 32. Lamprotula caveata, Unio douglasiae and Anodonta arcaeformis are distributed in all sampling areas. There are 23 species belonging to 10 genera and 16 Chinese endemic species in Taizihe River, 17 species belonging to 8 genera and 10 Chinese endemic species in Raohe River,7 species belonging to 4 genera and 3 Chinese endemic species in Dahuchi Lake,6 species belonging to 5 genera and 2 Chinese endemic species in Shentanghu Lake,7 species belonging to 3 genera and 2 Chinese endemic species in Donghu Lake,14 species belonging to 10 genera and 7 Chinese endemic species in Xiuhe River,27 species belonging to 12 genera and 22 Chinese endemic species in Xinjiang River and 29 species belonging to 13 genera and 21 Chinese endemic species in Ganjiang River respectively. The number of genera, species and Chinese endemic species, densities and biomasses of freshwater mussels in rivers is more than that in shallow lakes, so it is with the number of overall species belonging to each genus. All indicate that the resources of freshwater mussels in rivers are much more abundant than those in shallow lakes.5. Freshwater mussels produce different responses to different environmental factors. The average number of species of freshwater mussels in silt sediment is the most, being 5.67 species; in aquatic sediment is the least, being 1.84 species.The density and biomass of freshwater mussels in silt sediment are 0.62 ind/m2 and 13.42 g/m2 as the most; in aquatic sediments are the least, being only 0.002 ind/m2 and 0.044 g/m2 respectively. The average number of species of freshwater mussels living in the depth from 0 to 2 meters are the most, being 5.71 species; while that exceeding 6 meters are 1.14 species as the least. The density and biomass of freshwater mussels living in the depth from 0 to 2 meters are 0.71 ind/m2 and 13.09 g/m2 as the most; that exceeding 6 meters are the least, being only 0.04 ind/m2 and 0.62 g/m2 respectively. The average number of species of freshwater mussels in moderately flowing water are the most, being 5.18 species; while that in gently flowing water are 1.92 species as the least. The density and biomass of freshwater mussels in moderately flowing water are the most, being 0.63 ind/m2 and 13.74 g/m2 respectively; while those in gently flowing water are 0.004 ind/m2 and 0.086 g/m2 as the least. The average number of species of freshwater mussels are the most when the transparency is 30 to 50 centimeters, being 5.83 species; while that exceeding 70 centimeters are 1.63 species as the least. The density and biomass of freshwater mussels are the most when the transparency is 30 to 50 centimeters, being 0.73 ind/m2 and 16.33 g/m2 respectively; while that exceeding 70 centimeters are 0.08 ind/m2 and 1.64 g/m2 as the least.6. Different freshwater mussels have different median effective time [ET50 (d)] of drying death. The general trend is:Lamprotula caveata> Acuticosta chinensis> Cristaria plicata> Arconaia.lanceolata> Schistodesmus lampreyanus> Lanceolara grayana> Lanceolara eucylindrica> Anodonta woodiana pacifica> Anodonta arcaeformis> Anodonta globosula, indicating that freshwater mussels of thick shells are more resistant to drought than those of thin shells. To freshwater mussels of different size, the bigger ones are more resistant to drought than the smaller ones. And the larger the difference is, the more obvious the trend is, which indicate that the adult mussels'drought-resistant capacity is stronger than the juvenile mussels'.