枯水季节赣江近岸水洼与浅滩中浮游动物的群落差异

为探究水洼与邻近浅滩中浮游动物群落是否存在差异, 于2015年1月22日和3月1日, 选择赣江南昌段的3个水洼和邻近浅滩采集浮游动物, 对浮游动物的物种组成、密度、生物量、多样性指数和群落结构进行比较研究。通过单因子方差分析(One-way ANOVA)检验水洼与浅滩中水环境因子及浮游动物密度和生物量的差异。使用非度量多维尺度分析(Non-metric multi-dimensional scaling, NMDS)和群落相似性分析(Analysis of similarity, ANOSIM)对暂时性水洼及邻近浅滩的浮游动物群落进行排序。1月和3月共发现浮游动物44种, 轮虫有30种, 占总捕获数的68%。枝角类和桡足类各有7种, 分别占总捕获数的16%。相对重要性指数(Index of relative importance, IRI)大于1000的优势物种有5种, 分别为汤匙华哲水蚤Sinocalanus dorrii、长肢多肢轮虫Polyarthra dolichoptera、桡足类无节幼体Copepod nauplii、角突臂尾轮虫Brachionus angularis和长圆疣毛轮虫Synchaeta oblonga。单因子方差分析表明, 1月份水洼的水深、电导率和总氮含量显著高于浅滩(P<0.05), 浅滩的水温、pH、溶解氧、浊度和总磷含量略高于水洼。3月份水洼的水深、pH和总氮含量略高于浅滩, 浅滩的溶解氧、浊度和总磷含量较水洼高, 水温和电导率在2种水体中非常接近。1月份水洼中浮游动物的密度(7.90 ind./L)和生物量(7.78 μg/L)均低于浅滩(9.34 ind./L, 19.03 μg/L), 3月份水洼中浮游动物的密度(24.27 ind./L)和生物量(332.14 μg/L)均高于浅滩(22.86 ind./L, 146.10 μg/L)。浅滩中浮游动物的多样性指数(H′)、均匀度指数(J)和物种丰富度指数(D)均大于水洼。非度量多维尺度分析和群落相似性分析表明, 仅1月份水洼与浅滩的浮游动物群落结构具有边缘显著差异(P=0.067), 可大致划分为2个: 水洼群落和浅滩群落。3月份由于水位上涨, 研究的水洼与赣江河道处于连通或半连通状态, 2种生境中浮游动物群落结构无显著差异(P=0.313)。斯皮尔曼相关分析(Spearman correlation coefficient)发现水深和溶解氧是导致水洼和浅滩中浮游动物密度差异的主要环境因子。2种生境中浮游动物的密度与pH、电导率、总氮和总磷均具有显著相关性(P<0.05)。

VARIATION OF ZOOPLANKTON COMMUNITIES IN ALONGSHORE TEMPORAL POOLS AND RIFFLES OF GANJIANG RIVER DURING DRY SEASON

Water level fluctuations mediate species composition and abundance dynamics of zooplankton to impact the structure and function of aquatic ecosystems. There are many temporary pools formation along the bed of Ganjiang River due to water level decline in dry season. To explore the variation of zooplankton communities in pools and adjacent riffles, three pools and riffles, located in Nanchang section of Ganjiang River, were used to collect zooplankton in January and March of 2015 to investigate species composition, density, biomass, species diversity, and community structure. Water environment factors, zooplankton density and biomass in pools and riffles were analyzed by one-way ANOVA to test the variance. Zooplankton communities in pools and riffles were analyzed by Non-metric multi-dimensional scaling (NMDS) and analysis of similarity (ANOSIM) with software Primer 5.0. A total of 44 species of zooplankton were identified. Among them, 30 rotifers (68%), 7 cladocerans (16%) and 7 copepods (16%) were recorded. There were five dominant species with index of relative importance greater than 1000, which were Sinocalanus dorrii, Polyarthra dolichoptera, Copepod nauplii, Brachionus angularis and Synchaeta oblonga. The results of one-way ANOVA suggested that water depth, conductivity and total nitrogen of pools were significantly higher than those of riffles (P<0.05). In January, the water temperature, pH, dissolved oxygen, turbidity and total phosphorus of riffles were slightly higher than those of pools. In March, the water depth, pH and total nitrogen of pools were slightly higher than those of riffles. Dissolved oxygen, turbidity and total phosphorus of riffles were higher than pools. The water temperature and conductivity in the two water bodies were very close. In January, the total density (7.90 ind./L) and biomass (7.78 μg/L) of zooplankton in pools were lower than those in riffles (9.34 ind/L, 19.03 μg/L). On the contrary, the total density (24.27 ind./L) and biomass (332.14 μg/L) of zooplankton in pools were higher than those in riffles (22.86 ind./L, 146.10 μg/L). The Shannon-winner index (H'), Pielou evenness index (J) and species richness index (D) of zooplankton in riffles were higher than those in pools. Marginally significant difference in zooplankton communities between pools and riffles in January (P=0.067) were found by non-metric multi-dimensional scaling and similarity analysis. Zooplankton communities in January showed two communities: pool community and riffle community. In March, pools and riffles were gradually connected with the rising water level. There were no significant differences in zooplankton communities between the two habitats (P=0.313). Spearman correlation coefficient showed that water depth and dissolved oxygen were main environmental factors in variation of zooplankton density between pools and riffles. Zooplankton communities had significant correlations with pH, conductivity, total nitrogen and phosphorus (P<0.05) in the two habitats.