Seasonal variation in abundance and diversity of zooplankton in Asu River,Ebonyi state,Nigeria

The Physicochemical variables and Zooplankton of Asu River, Ebonyi State, Nigeria were studied monthly between October 2013 and June 2014 which covered the wet and dry seasons. The study was carried out monthly in two selected sites by collecting water samples for physiochemical analysis and zooplankton identification. Shannon-Weiner diversity and Margalef's indices were used to determine the zooplankton composition. Investigation on the physiochemical variables showed that water temperature, dissolved oxygen, total dissolved solids, pH, conductivity and carbon (iv) oxide all recorded maximum values in the dry season. The present result also showed that the river is not seriously polluted. However, only carbon (iv) oxide and nitrate varied significantly between seasons (p < 0.05). Forty two (42) zooplankton species comprising Rotifera (7 families; 23 species), Copepoda (2 families; 8 species) and Cladoceran (6 families; 11 species) were identified. Rotifera spp. were numerically dominant and the most diverse group but the crustacean, Thermocyclops oithonoides dominated the total zooplankton biomass during the study. Species abundance showed inverse relationship with species richness, Shannon-Weiner diversity and Evenness. Zooplankton abundance was at its peak in the dry season while species richness, Shannon- Weiner diversity and evenness increased from dry season to wet season.     

Changes and drivers of zooplankton diversity patterns in the middle reach of Yangtze River floodplain lakes,China

Anthropogenic habitat alteration interferes the natural aquatic habitats and the system''s hydrodynamics in the Yangtze River floodplain lakes, resulting in a serious decline in freshwater biodiversity. Zooplankton communities possess major position in freshwater ecosystems, which play essential parts in maintaining biological balance of freshwater habitats. Knowledge of processes and mechanisms for affecting variations in abundance, biomass, and diversity of zooplankton is important for maintaining biological balance of freshwater ecosystems. Here, we analyzed that the temporal and spatial changes in the structure of zooplankton community and their temporal and spatial variations respond to changes in environmental factors in the middle reach of Yangtze River floodplain lakes. The results showed that zooplankton samples were classified into 128 species, and Rotifera was the most common taxa. Significant seasonal differences were found among the abundance and diversity of zooplankton. Similarly, we also found significant seasonal differences among the biomass of zooplankton functional groups. The spatial turnover component was the main contributor to the β diversity pattern, which indicated that study areas should establish habitat restoration areas to restore regional biodiversity. The NMDS plot showed that the structure of zooplankton community exhibited significant seasonal changes, where the community structure was correlated with pH, water temperature, water depth, salinity, total nitrogen, chlorophyll‐a, and total phosphorus based on RDA. This study highlights that it is very important to ensure the floodplain ecosystem''s original state of functionality for maintaining the regional diversity of the ecosystem as a whole.     

A note on the zooplankton distribution and diversity in a tropical mangrove creek system,Gazi, Kenya

Gazi Creek is situated at some 40 km south of Mombasa (Kenya 4° 25 S, 39° 50 E) sampling stations are located in the creek mouth (stn 1), in the inner creek (stn 3) and intermediate (stn 2). Sampling is done twice a month; it starts from stn 1 through stn 2 up to stn 3. A 335 µm Mesh size net is towed in near surface water for 5 minutes and the collected sample preserved in 5% formaldehyde. Hydrographic parameters are recorded during sampling.The work at Gazi is undertaken to survey the Zooplankton composition both qualitatively and quantitatively. 22 important taxa have been studied to determine their seasonal variation in abundance and distribution. Zooplankton population are highest in March (374 animals m^–3). The abundance gradually falls during the S.E. monsoon period (May–September) to the lowest value in August (30 animals m^–3) (see Fig. 1). Copepoda is the most abundant taxon throughout (48.5–92.4%) (see Table 1). This group is found throughout the creek. Nevertheless, it is evident that the creek mouth has a higher diversity of copepoda compared to the inner creek. Using the Margalef Index a consistently higher value has been observed in stn 1 compared to stn 3 (see Table 2). The surface water temperature decreases during the S.E. monsoon (28.0 to 25.5 °C) and it rises during the N.E. monsoon (29.0 to 35.5 °C). The trend in temperature variation corresponds broadly with zooplankton abundance (see Fig. 1), suggesting that zooplankton thrive best in warmer water. High Zooplankton counts were also observed around May (326 animals m^–3) during the long rains; probably due to high amounts of nutrients input. Generally, average monthly pH values vary only slightly but the pH up the creek is almost always lower than at the creek mouth. Salinity is quite constant at 35     

Influence of benthic and interstitial processes on nutrient changes along a regulated reach of a large river (Rhône River,France)

An enclosure study was conducted in Ranger Lake in south-central Ontario, Canada from 4 July to 5 August 1997 to determine predation effects of the larvae of the phantom midge fly Chaoboruson the zooplankton community. Zooplankton assemblages were established in 12 enclosures (2 m in diameter, 7.5 m deep). Three densities of fourth-instar Chaoborus trivittatus (0 l^–1, 0.1 l^–1 and 0.5 l^–1) were introduced as predator treatments to the enclosures. Temperature, dissolved oxygen and zooplankton community composition were monitored for six weeks. To determine if the zooplankton community composition changed, a repeated measures multivariate analysis was performed on percent biomass of Bosmina and calanoid copepods. There were no significant differences in mean taxon percent biomass among predator treatments. There were significant differences in mean taxon percent biomass between water layers (epilimnion and metalimnion). There were also significant differences in lengths of Bosmina and calanoid copepods among predator treatments at the end of the experiment. Crop content analysis of C. trivittatusshowed that Bosmina constituted 88–98% of the prey items found in the crops. These results demonstrate that the use of deep enclosures, a Chaoborus species which vertically migrates, and lower natural densities of Chaoborus may provide prey with an important natural refuge from predation and so allow a more accurate determination of the predation impact of Chaoborus trivittatusin temperate lakes where fish control Chaoborus densities.     

Zooplankton Composition,Diversity and Physicochemical Features of Bandam Kommu Pond,Medak District,Telangana, India

The present investigation aims to study the zooplankton composition, diversity along with physicochemical profile in a chosen pond at Medak district from December, 2010 to November, 2012. The study revealed the occurrence of 80 zooplankton species including 60 rotifers, 18 cladocerans and 02 copepods. Zooplankton density fluctuated between 119 and 26,463/L, diversity H′ = 0.89–2.68, species richness 5–21 and dominance 18.6–74.1 % over the 2 years study period. Rotifers were more predominant than other zooplankton communities, especially family Brachionidae and Lecanidae. High density of the overall zooplankton community was due to more rotifer population and the numerical dominance of the species Brachionus angularis, B. calyciflorus, B. caudatus, Keratella tropica, Filinia terminalis and Epiphanies mucronata. It was observed that the zooplankton density significantly correlates with pH values of the pond. Physicochemical profile of the pond shows tropical climate, hard water and alkaline in nature. Chloride content was found to be high may be due to the anthropogenic pressure and influx of sewage. The high content of phosphate and nitrate reveals that the pond is enriched with nutrients. This has significant correlation with zooplankton dominance. The present findings clearly indicates the eutrophication of the pond.     

Qualitative and quantitative structure,diversity and fluctuations in abundance of zooplankton in Lake Xolotlán (Managua)

The qualitative and quantitative structure of the zooplankton community was studied in 11 localities of Lake Xolotlan (Managua). Twelve rotifers, 4 cladoceran and 5 copepods species were identified. Community diversity (Shannon-Wienerindex) is low,viz. 0,83–2.20. At all times, copepods were the most abundant group. Rotifer densities were higher in zones influenced by rivers and organic pollution. Cladocerans were permanently present in low densities. Climatic events (rainfalls and dry periods) determined population fluctuations of the main zooplankton groups.     

Zooplankton in Loch Lomond: perspectives,predation and powan

Published and unpublished accounts of the zooplankton community of Loch Lomond are reviewed. Loch Lomond's zooplankton community is unique amongst those of Scotland's other large lochs. Holopedium gibberum appeared in Loch Lomond in the years between the studies of Slack & Hamilton in the 1950s and zooplankton surveys in the late 1970s.The annual cycles of Eudiaptomus gracilis, Cyclops strenuus abyssorum and Mesocyclops leuckarti are described for the mid basin of Loch Lomond. E. gracilis overwinter mainly as adult with variable egg production during their lifespan of 5–8 months. The cyclopoid copepods have variable life history characteristics. C. str. abyssorum produce a single generation per year, overwinter by means of resting eggs and a small population of planktonic adults, while M. leuckarti is present in the plankton throughout the year, but in low numbers during winter.Zooplankton populations in Loch Lomond are predated by the diverse fish community which includes a facultative planktivore in the powan, Coregonus lavaretus. Powan feed heavily on zooplankton from late spring until late autumn. Powan display selectivity in the prey species taken, in the size distribution and morph types taken within prey species. Zooplankton species, morphs and forms in Loch Lomond tend to reflect this predation.Zoology Department, University of St. AndrewsZoology Department, University of St. Andrews     

Zooplankton species diversity in Lake St. Clair,Ontario, Canada

Zooplankton species diversity and selected chemical parameters were investigated at three stations in Lake St. Clair, Ontario, Canada, from 15 June–26 August, 1971. Primary productivity and zooplankton species diversity were greatest at stations 1 and 2 which were enriched by the Thames River drainage. No significant correlation between total zooplankton diversity and chlorophyll a was found, however, within the Cladocera and Copepoda, positive correlations with chlorophyll a, reactive silicate and nitrate were shown at stations 2 and 3. Rotifer species diversity showed negative correlation with chlorophyll a, nitrate and reactive silicate.     

The longitudinal distribution and community dynamics of zooplankton in a regulated large river: a case study of the Nakdong River (Korea)

The longitudinal distribution and seasonal dynamics of zooplankton were examined along a 200-km section of the middle to lower Nakdong River, Korea. Zooplankton was sampled twice a month from January 1995 to December 1997 at five sites in the main river channel. There was considerable longitudinal variation in total zooplankton abundance (ANOVA, p < 0.001). All major zooplankton groups (rotifers, cladocerans, copepodids and nauplii) increased significantly with distance downstream along the river. There also were statistically significant seasonal differences in zooplankton abundance at the sampling sites (ANOVA, p < 0.01). Zooplankton abundance was high in spring and fall and low in summer and winter. The seasonal pattern of rotifers was similar to that of total zooplankton. This reflected the fact that rotifers (Brachionus calyciflorus, B. rubens, Keratella cochlearis and Polyarthra spp.) strongly dominated the zooplankton community at all locations. Among the macrozooplankton, small-bodied cladocerans (e.g. Bosmina spp.) dominated; the abundance of large-bodied cladocerans (e.g. Daphnia) was negligible (0–5 ind. l^–1). Among the environmental variables considered, partial residence time seemed to play the most important role in determining characteristics of the river zooplankton community.     

Characterization of Lake Michigan coastal lakes using zooplankton assemblages

Zooplankton assemblages and water quality were examined bi-weekly from 17 April to 19 October 1998 in 11 northeastern Lake Michigan coastal lakes of similar origin but varied in trophic status and limnological condition. All lakes were within or adjacent to Sleeping Bear Dunes National Lakeshore, Michigan. Zooplankton (principally microcrustaceans and rotifers) from triplicate Wisconsin net (80 μm) vertical tows taken at each lake's deepest location were analyzed. Oxygen–temperature–pH–specific conductivity profiles and surface water quality were concurrently measured. Bray-Curtis similarity analysis showed small variations among sample replicates but large temporal differences. The potential use of zooplankton communities for environmental lake comparisons was evaluated by means of BIOENV (Primer 5.1) and principal component analyses. Zooplankton analyzed at the lowest identified taxonomic level yielded greatest sensitivity to limnological variation. Taxonomic and ecological aggregations of zooplankton data performed comparably, but less well than the finest taxonomic analysis. Secchi depth, chlorophyll a, and sulfate concentrations combined to give the best correlation with patterns of variation in the zooplankton data set. Principal component analysis of these variables revealed trophic status as the most influential major limnological gradient among the study lakes. Overall, zooplankton abundance was an excellent indicator of variation in trophic status.     

北京市妫水河浮游动物群落结构与水质评价

由于浮游动物对水体环境变化敏感,可表征水体污染程度,因此在2017年对妫水河浮游动物群落结构进行调查研究,分析了浮游动物群落结构时空变化特征及其与环境因子的关系,并利用生物学评价方法对水质进行评价。结果表明:妫水河浮游动物有4门22属88种,其中原生动物种类最多,为42种,主要以轮虫和原生动物为主,浮游动物平均细胞密度和生物量分别为5041.58个/L和2.88 mg/L。浮游动物群落结构与环境因子的CCA分析显示,水温、pH、DO和氨氮是影响妫水河浮游动物群落结构变化的重要因素,其中裂痕龟纹轮虫、冠饰异尾轮虫和螺形龟甲轮虫等对水体中氮磷的相关性极为显著,具有富营养化指示作用,可作为监测水质的指示生物。妫水河浮游动物多样性指数H、均匀度指数J和丰富度指数D全年平均值分别为0.43、0.31和0.41,整体评价结果显示,妫水河水体处于中到富营养型水平,尤其是下段城区段污染严重,表明妫水河水体生态功能遭到破坏,水质还需进一步改善和治理。本研究结果可为妫水河水质评价、水环境监测及水污染治理提供基础数据资料和理论依据。     

鄱阳湖浮游动物群落结构及其与环境因子的关系

数量庞大、体积微小、高度多样化的浮游生物对淡水生态系统功能具有重要影响。为探究中国第一大淡水湖——鄱阳湖浮游动物（包括轮虫、枝角类和桡足类）群落特征及其与环境因子之间的关系,本研究在鄱阳湖设置50个采样点,分别于2017年8月（夏季）、11月（秋季）、2018年2月（冬季）和5月（春季）进行浮游动物群落与生境调查,统计分析结果表明：鄱阳湖浮游动物共记录43属99种,其中轮虫31属83种,枝角类8属11种,桡足类4属5种,春夏季节种类较为丰富。浮游动物平均丰度为1155.29 ind./L,具有极显著的季节差异（P< 0.01）,夏季（3150.37 ind./L）显著高于其他三季。四季共确定优势种14种,轮虫中优势度最高的为广布多肢轮虫（Polyarthra vulgaris）,浮游甲壳动物中仅有简弧象鼻溞（Bosmina coregoni）在秋季形成优势。优势种的季节更替明显,夏秋季节间的更替率（86.00%）高于其他季节（77.00%,66.67%）。优势种、多样性和均匀度的结果均显示鄱阳湖浮游动物群落结构较复杂,具有较好的稳定性。聚类分析（Cluster analysis）和分类回归树分析（Classification and regression trees, CART）表明,每个季节均有多种群落类型,其中春夏两季中浮游动物群落类型的划分与叶绿素a（Chlorophyll a,Chla）密切相关,化学需氧量（Chemical Oxygen Demand,COD）是影响秋季群落划分的关键环境因子。非度量多维尺度分析（Non-metric multidimensional scaling,NMDS）结果表明,温度（Water Temperature,WT）、Chla、电导率（Conductivity,Cond）是造成四季浮游动物群落显著差异的最主要环境因子。冗余分析（Redundancy analysis,RDA）显示,除Chla外,总氮（Total Nitrogen,TN）、总固体悬浮物（Total Suspended Solids,TSS）和酸碱度（Hydrogen ion concentration,pH）也是影响浮游动物群落结构和优势种分布的重要因素。     

Zooplankton community response to reservoir aging

Changes in zooplankton diversity and density in response to reservoir aging in Pawnee Reservoir were investigated. Zooplankton samples collected from April 1992 through April 1993, were compared to a similar study conducted after initial impoundment by Helzer (1971), in 1968–1970. Since this initial study, increases in turbidity and resulting changes in biotic interactions significantly altered the zooplankton community. A significant increase in total zooplankton density and a decrease in species richness were observed between study periods. Density increased from 24.6 to 95.4 individuals L^–1, while the number of taxa declined from fourteen to ten. During this time period, Cyclops vernalis became the dominant zooplankter in the reservoir. The density of this predatory copepod increased significantly, from 0.1 l^–1 in 1968–1970, to 44.3 l^–1 in 1992–1993, which accounted for most of the increase in total zooplankton density. Though a greater spring maximum of another dominant, Bosmina spp. was found during the 1992–1993 study period, the annual density of this cladoceran was not significantly different between study periods. Similar trends for Daphnia ambigua and D. parvula were also observed, as greater spring maxima levels were attained, however overall annual densities were not significantly different. The dominance of C. vernalis (46% of annual density) and Bosmina spp. (33%), indicate that these two zooplankters were tolerant of changes in physical conditions resulting from reservoir aging and biotic interactions that followed in the reservoir during the 22 years between study periods.     

A Short-Term Study of Vertical and Horizontal Distribution of Zooplankton During Thermal Stratification in Lake Kinneret,Israel

This study documents for the first time both vertical and horizontal distribution patterns of the zooplankton community in Lake Kinneret during the period of thermal stratification. The zooplankton distribution patterns were explored in relation to abiotic (temperature, oxygen) and biotic (picocyanobacteria, ciliates, flagellates, phytoplankton, fish) environmental gradients. Sampling was carried out on 6–7 July 1992 at five stations and six depths from nearshore to offshore. Zooplankton abundance and biomass varied from 5 to 267 ind. l^–1(mean: 95 ind. l^–1), and from 0.1 to 65 d.w. mg m^–3(mean: 24 d.w. mg m^–3). Zooplankton taxonomic groups (Rotifera, Cladocera, Cyclopoida, Calanoida) and size classes (micro-, meso- and macrozooplankton) showed peaks of maximal density and biomass in the epilimnetic and metalimnetic strata (5 and 14 m). Depth, accounting for 31–39% of total spatial variation, reflected the vertical distribution of zooplankton in relation to temperature and oxygen declines, and the higher concentration of food resources (protists and phytoplankton) in the epilimnion and metalimnion. Onshore–offshore distance, accounting for 17–22% of the total spatial variance, reflected different distribution patterns shown among zooplankton groups and size classes. The macrozooplankton (Copepoda, Cladocera) was more abundant offshore, whereas microzooplankton (Rotifera and nauplii) predominated nearshore. These horizontal distribution patterns were related to small increases in temperature and phytoplankton biomass, and higher concentrations of fish in the littoral zone. Although limited to a short temporal scale, our study indicated that zooplankton spatial distribution in Lake Kinneret during the period of thermal stratification was related to physicochemical, food and predation factors, manifested differently along the vertical and nearshore–offshore gradients.     

Summer zooplankton communities of selected borrow-pit ponds in Northern Illinois,U.S.A.

Zooplankton samples were collected from 7 borrow-pit ponds during the summer months of 1975 in northern Illinois. Species diversity indices and evenness values were used to characterize the ponds zooplankton community structure. Thirty-one plankton species are reported. Older borrow-pit ponds contained more species and had higher mean densities than did the newer ponds. The number of dominant species reported per pond varied from 1 to 4. Species diversity indices are higher in older ponds, and there was a general tendency for species diversity to increase with pond age. No correlations between physicochemical measurements and the structure of the zooplankton communities were found. Factors possibly governing zooplankton community structure in borrow-pits are speculated upon.     

沙颍河流域浮游动物群落结构空间变化特征与水质评价

为了解沙颍河流域浮游动物的群落结构及水质状况, 于2016年秋季对该流域设置了20个采样点, 进行浮游动物群落结构调查, 并利用生物多样性指数对水质进行评价。结果显示: 沙颍河流域共检测出浮游动物36属78种, 其中轮虫20属60种、枝角类10属12种、桡足类6属6种; 浮游动物优势种主要为长肢多肢轮虫(Polyarthra dolichoptera)、裂痕龟纹轮虫(Anuraeopsis fissa)、角突臂尾轮虫(Brachionus angularis)、萼花臂尾轮虫(B. calyciflorus)、曲腿龟甲轮虫(KeratelIa valga)和象鼻溞(Bosmina sp.); 浮游动物密度和生物量最大值出现在沙颍河流域上游, 且从上游至下游, 生物量和密度的空间变化趋势相一致, 大致呈现逐渐降低的趋势; 检测位点Shannon-Wiener 多样性指数的范围为1.03—3.51, Pielou均匀度指数的变化范围为0.26—0.70。综合分析各采样点的种群和多样性指数反映出沙颍河流域上游水体污染较为严重, 中下游水体为中度污染。水质总体呈现出中度-重度污染。     

鄱阳湖子湖“堑秋湖”过程中水位变化对浮游动物群落结构的影响

“堑秋湖”是鄱阳湖区渔民根据湖泊水位季节性涨退变化, 利用人工闸门控制子湖水位进行捕鱼的一种渔业方式。研究分析了“堑秋湖”过程中浮游动物群落结构的变化, 探讨水位变化对浮游动物群落结构的影响及其他可能的影响因素, 以期为合理管控鄱阳湖区“堑秋湖”渔业活动提供科学依据。鄱阳湖“堑秋湖”捕鱼期间(2014年11月9日至2015年1月4日), 在鄱阳湖国家级自然保护区内子湖——大湖池的敞水区设置了7个采样点进行了8次浮游动物定性、定量采集和分析。研究共发现浮游动物77种, 其中轮虫53种, 枝角类10种, 桡足类14种。在“堑秋湖”捕鱼过程中, 浮游动物物种数随水位的连续下降呈现逐渐减少趋势, 多样性指数也呈逐渐下降趋势, 密度和生物量呈现先增加后减少的变化趋势。浮游动物优势物种的密度变化具有明显的种属差异, 前节晶囊轮虫和中华窄腹剑水蚤的密度呈逐渐增加的趋势, 广布多肢轮虫、广布中剑水蚤、长额象鼻溞和桡足类无节幼体的密度呈逐渐减少的趋势。冗余分析表明: 水位、电导率、水温、溶氧、营养盐等环境因子均对浮游动物群落结构产生显著影响, 其中溶解氧是最强的影响因子。此外, 根据“堑秋湖”鱼类渔获量的变化情况推测, 捕鱼活动导致的浮游食性鱼类减少也对浮游动物的密度变化产生了影响。在“堑秋湖”过程中, 随着水位的持续下降水体理化因子发生了不同变化。浮游动物的种类和多样性指数逐渐降低, 浮游动物的密度呈现先升高后降低的变化趋势。浮游动物的群落结构主要受溶解氧、氨氮和水位的影响。捕鱼活动导致的浮游食性鱼类减少也对浮游动物的密度变化产生了影响。     

Zooplankton biomass and community structure in a Danube River floodplain system: effects of hydrology

1. Zooplankton density and biomass was examined in a Danube River floodplain section with highly variable hydrological dynamics. Temporal patterns were analysed to assess the effects of hydrological conditions on zooplankton community structure and the differential response of the two major zooplankton taxa, rotifers and crustaceans.
2. Calculated floodplain water age was used as an integrated parameter describing hydrological conditions and connectivity.
3. Total zooplankton biomass, crustacean biomass and crustacean species number were significantly positively related to water age. Rotifer biomass followed a hump-shaped relationship with water age, and rotifer species number decreased with increasing water age.
4. Rotifers dominated the community in periods of low to medium water ages. In periods of higher water ages the community was dominated by crustaceans.
5. We propose that the hydrological regime of floodplains is crucial for zooplankton biomass patterns and succession, through the alternation of washing-out effects, taxon-specific potential of reproduction and biological interactions. Flood events and high water levels reset the community to an early successional phase.     

The Zooplankton community of Croker Passage,Antarctic Peninsula

Summary Zooplankton species composition, abundance and vertical distribution were investigated in the upper 1000 m of Croker Passage, Antarctic Peninsula during the austral fall (March–April, 1983). 106 species were identified, many being mesopelagic and reported previously from the Southern Ocean. The most numerous species (>1000/100 m³) were the copepodsMetridia gerlachei, Microcalanus pygmaeus, Oncaea antarctica andOncaea curvata. Oncaea curvata alone constituted half the zooplakton population. Zooplankton biomass was dominated by three copepod species,Metridia gerlachei, Calanoides aculus andEuchaeta antarctica,which comprised 74% of the biomass. Size analysis revealed most of the zooplankton numbers were in the >1 mm fraction. The biomass distribution was polymodal with major maxima in the >1 mm and the 4–4.9 mm size classe. The >1 mm peak, exclusive of protozoans, was primarily copepod nauplii and copepodites ofOncaea, Metridia andMicrocalanus. The 4–4.9 mm peak was mostlyCalanoides acutus andMetridia gerlachei.All of the principal species had broad vertical distributions both day and night. There was some suggestion of diel vertial migration byMetridia gerlachei andEuchaeta antarctica, with segments of their populations migrating into the upper 100 m and 200 m, respectively, at night. Most of the dominant and subdominant species were concentrated below 200 m,with only the subdominantOithona similis having its maximum in the epipelagic zone. The occurrence of zooplankton at winter depths appears to have been earlier in Croker Passage in 1983 than has been generally reported for waters south of the Polar Front.Total standing stock of net-caught zooplankton (>15 mm) in the upper 1000 m was estimated at 3.1 gDW/m², which is somewhat higher than values reported for the West Wind Drift and for open ocean areas of temperate to tropical latitudes.Euphausia superba (17–52 mm) dominated the pelagic biomass, exceeding zooplankton standing stock under a square meter of ocean by a factor of 15. This is in contrast to lower latitudes where zooplankton biomass is usually greater than macrozooplankton-micronekton.     

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)。