流溪河水库敞水区轮虫多样性与群落的动态特征

流溪河水库是位于北回归线上的大型峡谷型供水水库,于2013—2014年对该水库敞水区轮虫群落及其环境因子进行观测,分析敞水区轮虫多样性与群落动态特征。流溪河水库介于贫营养到中营养水平之间,丰水期(5月—9月)的总磷、透明度均高于枯水期(10月—4月),两年的总磷的平均值为0.019mg/L,透明度为2.55m。两年共检出轮虫40种,单月检出物种数波动范围为8—19种,月均检出轮虫13种。螺形龟甲轮虫、真翅多肢轮虫、沟痕泡轮虫和胶鞘轮虫是主要优势轮虫。2013、2014年轮虫年均总丰度分别为68.9、66.9个/L,两年物种丰富度在丰水期大于枯水期,但枯水期轮虫群落Simpson多样性指数均大于丰水期。采用Bray-Curtis距离测度群落之间的相异性,计算表明两年的枯水期轮虫群落之间的平均距离均大于丰水期,即丰水期时轮虫群落相似性较高,枯水期时轮虫群落变异较大。丰水期的水温和水质参数的变化相对稳定,种类的优势度更为明显,导致丰水期群落之间更为相似。主成分分析表明,无柄轮属、胶鞘轮属、多肢轮属、异尾轮属、泡轮属、晶囊轮属和皱甲轮属的主要种类的全年分布有较大的差异,而其余多数轮虫种类全年分布差异较小,反映了我国南亚热带地区水温全年变幅小,可维持较多的全年性种类共存。群落的方差解析与RDA分析表明,相对于生物与化学变量,物理环境变量主导了流溪河水库敞水区轮虫群落的变异,就单个变量而言,水温和食物是影响流溪河水库敞水区轮虫群落结构的重要因素,降雨则是影响轮虫群落结构变异的宏观因素。绝大多数轮虫为滤食性的,处于食物链底端,个体小、生活史短,轮虫群落在对环境因子变化的响应上与浮游植物具有相似性。

Rotifer species diversity and community structure in the pelagic zone of the Liuxihe Reservoir

The Liuxihe Reservoir is a large canyon reservoir located on the Tropic of Cancer in Guangdong Province, and is used as a source of drinking water. The diversity and dynamics of rotifer species as an indicator group of water quality and ecosystem health, and environmental variables were investigated monthly in the pelagic zone of the reservoir from 2013 to 2014. We used the R language program (MASS, vegan, and packfor packages) to analyze the species diversity and community structure of rotifers in the pelagic zone of Liuxihe Reservoir. The rotifer community structure was analyzed using principal component analysis (PCA), redundancy analysis (RDA), nonmetric multidimensional scaling (NMDS), and variation partitioning. In the present study, Liuxihe Reservoir is an oligotrophic or mesotrophic water body, with annual averages of total phosphorus of 0.019 mg/L and water transparency of 2.55 m. Both total phosphorus and water transparency were slightly higher in the wet seasons from May to September than dry seasons (October to April). In total, 40 species were observed during the two-year investigation. The observed species richness ranged from 8 to 19 monthly, with a monthly average of 13. Keratella cochlearis, Polyarthra euryptera, Pompholyx sulcata, and Collotheca sp. were the dominant species. The average total abundance was 68.9 and 66.9 individuals/L in 2013 and 2014, respectively. The species richness was higher in wet than in dry seasons, whereas the Simpson index showed the opposite pattern. The average community distance, which was measured by the Bray-Curtis distance, was higher in dry than wet seasons, indicating that the rotifer community similarity was higher in wet than dry seasons. Water temperature and other variables of water quality were more stable in wet seasons. As a result, species dominance became stronger and rotifer communities were more similar. PCA indicated that Ascomorpha, Collotheca, Polyarthra, Trichocerca, Pompholyx, Asplanchna, and Ploesoma species showed significant temporal variation. This rotifer community structure is representative of tropical and subtropical China, where there is less water temperature fluctuation, allowing more species to occur throughout the year. Variation partitioning and RDA of the rotifer community with environment variables demonstrated that physical environment variables including temperature, dissolved oxygen, Secchi disk depth, precipitation, and water retention time explained the variance of the rotifer community, and among all the measured variables, water temperature and food availability were the two key factors explaining community structure variation, and precipitation was a macroscopic indirect factor affecting the variation of rotifer community. Most rotifer species are filters at low tropic levels in the pelagic zone of the Liuxihe Reservoir, with a small body size and short life span, and their communities responded to the variation of environmental factors similarly to phytoplankton communities.