Search

枝角类体内氮磷比与生活史策略的选择密切相关，大型枝角类通常体内含磷量高、个体生长快、生殖率高，而小型枝角类体内含磷量低，个体生长相对较慢、生殖率低.由于大型枝角类对磷的需求比较高，我们假设大型枝角类生活史各参数对食物磷缺乏比小型枝角类更为敏感.本研究比较分析了食物碳磷比对流溪河水库两种枝角类（盔型溞（Daphnia galeata）和脆弱象鼻溞（Bosmina fatalis））生活史各参数的影响.实验设计了3个食物质量处理组：高磷（碳：磷=105）、中磷（400）和低磷（1450），食物浓度均为2 mg C/L的蛋白核小球藻（Chlorella pyrenoidosa）.脆弱象鼻溞内禀增长率、幼溞生长速率、平均每窝产仔量和首次生殖时体长均随着食物碳磷比的升高而显著下降；首次生殖时间则随着食物碳磷比的升高而显著延长；新生幼溞体长在各食物处理中无显著差异.盔型溞幼溞生长速率、平均每窝产仔量和首次生殖时体长均随着食物碳磷比的升高而显著下降；内禀增长率和新生幼溞体长在高磷处理组显著高于中磷和低磷处理组，但在中磷和低磷处理组无显著差异；首次生殖时间在高磷处理组显著短于中磷和低磷处理组，但在中磷和低磷处理组无显著差异.结果表明，食物的磷缺乏降低了两种枝角类的内禀增长率和幼溞生长速率，并延长了性成熟时间；盔型溞的内禀增长率、首次生殖时间和平均每窝产仔量等生活史参数受食物磷限制的程度小于脆弱象鼻溞，导致盔型溞对脆弱象鼻溞有竞争优势.

异尾轮虫是热带亚热带地区轮虫的重要优势类群.为了解其在水库中的分布模式和潜在影响因素，于2013-2014年对广东流溪河水库河流区、过渡区及湖泊区的异尾轮虫群落及环境因子进行逐月调查.2年共采集到异尾轮虫11种，其中对棘异尾轮虫（Trichocerca similis）、圆筒异尾轮虫（T. cylindrica）、暗小异尾轮虫（T. pusilla）和刺盖异尾轮虫（T. capucina）为优势种，主要出现在丰水期，具有明显的季节分布模式.2013-2014年河流区、过渡区和湖泊区异尾轮虫丰度平均值分别为142.9、102.5和53.6 ind./L，3个水域的异尾轮虫总丰度在夏季（5-9月）较高.从水库上游到下游，异尾轮属的物种丰富度和Simpson多样性指数呈现递减趋势，体现了群落对环境的分区和稳定性变化的响应.群落丰度组成的主成分分析表明，主要优势种的丰度全年分布差异较大，而多数种类全年分布差异小.冗余分析表明，叶绿素a浓度、晶囊轮虫丰度、水温+磷酸盐浓度分别为影响河流区、过渡区和湖泊区异尾轮虫群落结构的关键变量，而降雨则是影响整个库区异尾轮虫群落结构的潜在变量.

Although diatom has been widely used in biological or ecological monitoring of rivers,there is little information on diatom communities in most of Chinese rivers.In this study,we reported periphytic diatoms on artificial substrata(tile)in the Huizhou section of the Dongjiang River.We analyzed seasonal variations of the species composition and the relationship between the relative abundance and seasonal environmental factors at five sampling stations in 2010.A total of 153 periphytic diatom species,belonging to 40 genera,were identified.Dominant genera included Achnanthidium,Gomphonema,Melosira,Navicula,Nitzschia and Synedra.Gomphonema parvulum and Nitzschia palea were the common species in all the sampling sites with relative abundance1%.However,the relative abundance of the two species varied largely in seasons.Chl.a concentrations of the periphytic algae were positively correlated with the temperature.Redundancy analysis showed that water temperature,DO,NH+4-N,PO3-4-P,conductivity and pH were the major factors influencing the community structure of periphytic diatoms.Furthermore,hydrographic condition was crucial to some mobile species such as Nitzschia palea,whose relative abundance was low in summer mainly due to flushing in flood season.

Rotifers were sampled monthly from February to November in 2009 in Lake Erhai,Yunnan Province,China,in order to study their diversity and seasonal dynamics.Lake Erhai has a rotifer composition with tropical-subtropical characteristics: 68 species belonging to 25 genera of 17 families were identified,the majority of which were eurythermal or mesophilic.The genera of Trichocerca,Lecane and Brachionus were more abundant than others,accounting for 37% of the total community.Lecane arcuata and Trichocera inermis are new records in China.Biomass of the rotifer communities in Lake Erhai exhibited a bimodal seasonal cycle.An increase occurred during spring from low winter levels to an annual maximum in the mid fishing moratorium and a second increase in the early fishing season.In the mid fishing moratorium,the rotifer biomass was dominated by Asplanchna priodonta;while in the early fishing season,it was dominated by the small-sized Keratella cochlearis and Polyarthra vulgaris,then by A.priodonta again.The seasonal fishing moratorium affected not only the predation pressure on rotifers,but also competitive pressure on rotifer through influencing the community structure of Cladocera.Through the influence of predation and competition,rotifers were dominated by large omnivorous A.priodonta,which showed a bimodal seasonal distribution pattern.

Fifteen species of planktonic crustaceans,including 7 species of copepod and 8 species of cladoceran,were identified in an investigation for seven reservoirs of Hainan Island in the dry season(December,2006) and flooding season(May,2007).All the species were eurythermal or mesophilic,and their communities were dominated by small-sized species.Mesocyclops thermocyclopoides,Bosmina fatali and Bosminopsis deitersi were common species in all the reservoirs.The species richness,in the oligotrophic and oligo-mesotrophic reservoirs were much higher in flooding season than in dry season,but had a reverse pattern in the eutrophic reservoirs.The abundance of Bosmina fatali and Diaphanosoma dubium was positively related with majority of species,and Thermocyclops taihokuensis and Mesocyclops thermocyclopoides were negatively but weakly related with the cladoceran species in correlation analysis.This weak correlations indicated a weak interaction between the species and other influence factors existed,such as fish predation affected coexistence of planktonic zooplankton species.

Liuxihe Reservoir, located at the tropic of Cancer, is a large valley-type reservoir. In order to understand its limonological features, main limnological variables including hydrological and environmental factors were observed monthly in 2006. Surface water temperature ranged from 14.9 ℃ to 31.6 ℃ . The thermal stratification was monomictic, initiating in the early March when the water temperature reached 20 ℃, and lasting until December. The total precipitation in 2006 was 2960mm, but mainly distributed in wet season (from April to September). The mean water residence time was about 170 days, being more short in the flooding season (65 days). The mean concentrations of TN, TP, chlorophyll-a and SD were 0.66mg/L, 0.016mg/L, 2.2mg/m3 and 3.1m, respectively, indicating that the reservoir was oligo-mesotrophic. Mass ratio of TN/TP is around 41, 78 for DIN/DIP. Both ratios were much higher than the Redfield ratio, and mean that growth of phytoplankton was strongly limited by phosphorus. The high N/P ratio was attributed to the tropical red soil containing rich iron. A distinct longitudinal pattern and seasonal variability in limnological variables were observed in this reservoir. At the beginning of wet season (April and May), all nutrient concentrations were significantly higher than other period. It confirmed that surface runoff was the main path for nutrient loading into the reservoir. The longitudinal pattern of nutrient and chlorophyll-a concentrations was typical as follows as riverine zonetransition zonelacustrine zone, and the water transparency correspondingly showed an opposite one. High inflow with monsoon was the main driving force in seasonality of limnological variables, and resulted finally in a significantly longitudinal gradient of these variables by interacting with the reservoir own morphology.

Dajingshan Reservoir,located in Zhuhai City,South China,is a medium-size water body.It supplies drinking water for the Zhuhai City and Macau in dry seasons.Water is pumped into the reservoir from a nearby river in dry seasons so as to enhance the water storage.Pumped water modified the hydrodynamic processes and ecosystem dynamics.In order to understand the dynamic of rotifer community and the relationships between specific composition of rotifers and the environmental variables,an investigation was conducted monthly in 2005.Altogether 32 species of rotifer were identified,among which 12 species were belonged to Brachionidae,4 species to Trichocereidae and 4 species to Lecanidae.The majority of the species are tropical or sub-tropical species. Keratella tropica,Trichocerea stylata,Keratella cochlearis,Filinia maior,Anuraeopsis fissa,Brachionus angularis,Brachionus forficula,Ascomorpha ovalis and Collotheca pelagica were the dominant species.They had small body size and Iorica.The diversity index of rotifers ranged from 0.29 to 0.8,which were lower than that in Lake Donghu and Lake Xinghu.The abundance and biomass of rotifers ranged from 21 to 1094ind./L and from 4.04 to 1127μg/L,respectively.The maximal abundance and biomass occurred in February and May,respectively.The body length of rotifers ranged from 50μm to 620μm.The total abundance of rotifers was contributed by of small-sized species with a body size less than 200μm,while the rotifers biomass was dominated by medium-sized species with body size from 200-400μm.Secchi disk depth,temperature,total phytoplankton biomass and Cyanophyta biomass were the main factors affecting the species composition and quantitative dynamics of the rotifer community.

Gancun Reservoir was a tropical high-yield fishery reservoir located in the Leizhou Peninsula of Guangdong Province. In order to understand the dynamic characteristics of rotifer community in the reservoir in dry season, rotifers were investigated once a week in three dry seasons in 2006-2007. Rotifer was sampled with vertical tows of a mesh plankton net (64μm mesh size) and preserved in 5% sucrose formalin and counted under a binocular microscope. We analyzed the rotifer’s species composition, abundance, biomass and their correlations with ecological factors. Altogether 32 species were identified, the most frequent species were ones from the genera of Brachionus: Brachionus caudatus and Anuraeopsis fissa. Because of the high predation pressure from fishes, the rotifer species in Gancun Reservoir were dominated by the small-sized species with hard armor. In the three dry seasons the rotifer abundance ranged from 170 to 2152ind./L, the difference in abundance was significant in the three dry seasons. The rotifer abundance in the first dry season was much higher than that in the other two seasons, the rotifer abundance in the second dry season was the lowest, because the dry season had just experienced the summer flood period, in which the phytoplankton as food of rotifers was largely reduced, while the fish predation pressure increased. The rotifer biomass ranged from 10.6 to 677.5μg/L, there was no significant difference among the biomasses of the three dry seasons. Cluster analysis of rotifer community structure indicated that rotifer species composition in the two dry seasons before and after the flooding season, were classified into two relatively independent groups, however, the first 8 dominant species of rotifers contributing above 75% of total biomass, which strongly suggestted that the rotifer community structure in the tropical reservoir kept rather stable in the dry seasons.

Cladocerans in 19 reservoirs of Guangdong Province,South China were investigated in 2000.Among them,3 typical with different retention time were sampled in the later 4 years.As a result,24 species in 16 genera were identified,including 13 eurythermal species,7 thermophilic species,3 psychrophilic species and 1 endemic species.There are 5 or 6 species on average in an individual reservoir.The majority of the species were composed of small-bodied species that were abundant and dominant over large-bodied species.These small sized species had a body length less than 1 mm.Small-bodied species such as Bosmina longirostris,Bominopsis deitersi,Diaphanoso- ma brachyurum,Diaphanosom birger,Ceriodaphnia cornuta and Moina micura were the dominant species.They occurred in all reservoirs less regarding of reservoir trophic states.Among large-bodied species,only Daphnia hya- line and Leptodora kindti can be found frequently in several oligotrophic or mesotrophic reservoirs.The average a- bundance of cladocerans was very low.In flood season,the average abundance was less than 10 ind./L in 14 in- vestigated reservoirs,and ranged from 10 to 20 ind./L in 5 reservoirs.In dry season,the average abundance was less than 10 ind./L in 12 reservoirs,between 10 ind./L and 20 ind./L in 5 reservoirs,but reach 67 ind./L in 2 reservoirs:Gaozhou Reservior and Hexi Reservoir.Because of the difference in food quality and quantity of zoo- plankton,the species composition and population abundance of cladocerans in reservoirs at different trophic states are different to some extent,however,the dominant species were almost the same in these reservoirs.The cladocer- an' s abundances were related to water retention time in the investigated.The abundance of cladocerans and their food concentration were significantly affected by flushing in the flow-through reservoirs.As most sampling sites are located near dams,the species are mainly contributed by the pelagic group and the composition of species has a typical structure of tropical zooplankton.Cladocerans are dominated by small-sized species;the large sized species have a transparent body that is helpful to survive in high predation in tropical/subtropical reservoirs.

Spatial and temporal variation in metazooplankton biomass size spectrum was studied from April 2001 to December 2002 , in a tropical reservoir, Liuxihe reservoir (South China). The SheldonWest Laketype size spectrum of metazooplankton (50 to 512μm equivalent spherical diameter) was not uniform, but showed an increase in biomass between successive size classes. Within rotifers (50μm to 160μm ESD) , biomass decreased slightly in size, while cladoceras ( 100μm to 512μm ESD) had maximum biomass concentration per size class at medium ranges of body size. Copepods was the most important zooplankton fraction ( contributed more than 60% of total zooplankton biomass) , and covered all 10 size classes from 50 to 512μm in this study. Biomass of copepods showed an overall increase in size. As man-made lakes, reservoirs occupy an intermediate position between rivers and natural lakes by combining numerous features of rivers and lakes. Due to this unique feature, metazooplankton size distribution changed spatially in the reservoir, and the slopes of size spectra showed a different seasonal pattern between the riverine /one and the lacustrine zone. On average, small sized organisms, rotifers and nauplii, contributed a relatively more percentage biomass in the riverine zone than in the lacustrine zone, whereas adult Mesocyclops thermoryrlopoids, Phyllodiaptomus tunguidus and their late stage copepodites contributed less percentage biomass in the riverine zone. As a result, the slope of normalized biomass spectrum was more negative in the riverine zone than that in the lacustrine zone. In the riverine zone, slopes were more negative than -0.75 when water level decreased in the dry seasons and the reverse when water level increased in flood seasons. The temporal variations might be attributed to the water level fluctuation in the riverine zone. In contrast to the riverine zone, as the depth is deep enough in the lacustrine zone, and water level fluctuation showed no effect on the size distribution of melazooplankton. Size distribution of metazooplankton was relatively stable over seasons.