Some effects of enclosure on the zooplankton in a small lake

Observations on the effect of enclosure on zooplankton by introducing two experimental tubes, each holding some 18 000 m³ of water, into a small lake, showed that a limnetic community could be maintained within tubes of this capacity throughout a period of 22 months. Two species, the copepod Diaptomus gracilis and the cladoceran Daphnia hyalina were dominant both in the open lake and in each tube, but Diaptomus gracilis was relatively more abundant in the tubes than in the lake, whereas Daphnia hyalina, especially in spring and autumn, was more abundant in the lake than in the tubes. Several scarce species became relatively more abundant in the tubes than in the lake. These changes are more probably associated with reduced predation, especially by larvae of Chaoborus, than with artificially induced changes in the phytoplankton, changes only poorly correlated with changes in the zooplankton.     

太湖梅梁湾大型控藻围栏对浮游甲壳动物群落结构的影响

2005年对太湖梅梁湾大型鲢、鳙控藻围栏内外浮游甲壳动物群落结构的季节变化进行了监测.结果表明:围栏内外的环境因子、浮游植物生物量、浮游甲壳动物种类组成无显著差异.但鲢、鳙放养对浮游甲壳动物的生物量产生了较大的影响,围栏内浮游甲壳动物的总生物量和枝角类的生物量显著低于围栏外.总体上,枝角类各种类的生物量受鲢、鳙放养的影响程度大于桡足类的种类.太湖梅梁湾浮游甲壳动物的季节演替明显,大部分种类只是季节性出现.冬季和春季以溞(Daphnia sp.)和近邻剑水蚤(Cyclops vicnus)等大型种类为主,夏季和秋季以象鼻溞(Bosmina sp.)、角突网纹溞(Ceriodaphnia cornuta)和中华窄腹剑水蚤(Limnoithona sinensis)等小型种类为主.典范对应分析表明,透明度、温度和浮游植物的生物量是影响浮游甲壳动物季节变化的主要因素.     

Composition and Structure of Zooplankton Communities in Eighteen Arctic and Subarctic Lakes

The factors influencing the composition and structure of zooplankton communities in 18 lakes in the Canadian arctic and subarctic were determined during 1975 and 1976. Phytoplankton were consumed in very low numbers by all species (Diaptomus sicilis, Heterocope septentrionalis, Cyclops scutifer, Daphnia longiremis, Bosmina longirostris, Holopedium gibberum, Keratella cochlearis, Kellicottia longispina) and therefore differences in algal productivity among the lakes had little effect on the zooplankton. Variations in surface area, maximum water depth, pH and the ionic composition of the water were also unimportant in controlling the communities. However, low temperature exerted strong influence over the diversity, abundance, fecundity and vertical distribution of most species.     

Seasonal dynamics and composition of cladoceran and copepod assemblages in ponds of a Hungarian cutaway peatland

Seasonal dynamics of cladoceran and copepod zooplankton were studied over a one‐year period in five permanent ponds of a cutaway peatland, situated in the Danube−Tisza Interfluve, Central Hungary. 17 cladoceran, 11 cyclopoid copepod and 6 harpacticoid copepod species were identified and most of them were typical of small lowland ponds. Nevertheless, some taxa like Cyclops insignis, Ceriodaphnia setosa and Macrocyclops distinctus are considered to be rare in Hungary. The microcrustacean assemblages exhibited apparent seasonal succession with typical seasonal species. There appears to be at least two main successional patterns in the five ponds. After general cyclopoid copepod dominance in winter (Cyclops strenuus and Cyclops insignis), at sites with higher proportion of open water and submerged vegetation, spring was characterized by the dominance of the large cladoceran Daphnia curvirostris, which declined during summer, when microcrustacean assemblages composed mainly of smaller, littoral cladocerans. At these sites, species richness and diversity reached their maximum in autumn. In the case of duckweed covered ponds, succession led to less diverse autumn assemblages with fewer species, dominated by Simocephalus exspinosus. Our results draw the attention to the importance of long‐term investigations and the often neglected winter sampling in the accurate evaluation of species richness (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Zooplankton composition, dominance and abundance as indicators of environmental compartmentalization in Jurumirim Reservoir (Paranapanema River), São Paulo, Brazil

Spatial and temporal patterns in the distribution of the zooplankton in a large tropical reservoir were investigated for a year. The zooplankton was sampled at 10 limnetic stations. Rotifera were richest in number of species and individuals, especially in transitional river–lake zones. They were dominant during the summer in nine sampling stations, and decreased in spring. The main species were Polyarthra vulgaris, Keratella americana, K. cochlearis and Conochilus unicornis. Polyarthra vulgaris was widely distributed. Keratella was more abundant at upstream stations, and a dense population of C. unicornis was observed in a lateral, sheltered compartment. Among copepods, Calanoida were more abundant in spring and Cyclopoida in autumn. Longitudinal gradients in the Calanoida/Cyclopoida relation were observed, with the predominance of Cyclopoida at upstream sampling stations and Calanoida in more lacustrine zones towards the dam. Notodiaptomus iheringi, Thermocyclops minutus and T. decipiens were the main species. Diaphanosoma birgei, the most abundant cladoceran, mainly occurred in lacustrine zones, while Moina minuta was more abundant at riverine sampling stations, generally in association with Bosminopsis deitersi. Peaks of tintinnid protozoans were observed in upstream zones during summer and spring.     

Vertical and temporal distribution of two copepod species, Cyclops scutifer and Diaptomus pribilofensis, in 24 h arctic daylight

Factors structuring zooplankton communities in areas with 24h of sunlight are not well understood. In stratified temperatelakes with fish, zooplankton generally undergo a diel verticalmigration (DVM) to avoid predation. Zooplankton abundance mayalso be linked to the quality and quantity of food. To explorefactors that determine vertical structure of zooplankton whereDVM does not occur, we obtained time-series data on the verticaldistribution of the two dominate copepods, Cyclops scutiferand Diaptomus pribilofensis, in Toolik Lake, Alaska, a sitewithin the Arctic Long Term Ecological Research area. Thesetwo species compose 80–90% of pelagic mesozooplanktoncommunity density. Temperature plays a large role in the verticaldistribution of these two species. During the summers of 2002and 2003, C. scutifer underwent a seasonal vertical migrationfrom the epilimnion to the hypolimnion as water temperaturesincreased. Diaptomus pribilofensis exhibited a strong preferencefor warmer water and were not present in the water column untilepilimnetic temperatures reached 9°C. During both yearsof this study, C. scutifer and D. pribilofensis segregated verticallyin the water column along thermal gradients when the two speciesoverlapped temporally.     

Diverse Responses of Planktonic Crustaceans to Fish Predation by Shifts in Depth Selection and Size at Maturity

We investigated the behaviour and life histories of large zooplankton in the Esch-sur-Sûre reservoir (Luxembourg). We found that the decrease in size at maturity, as well as diurnal refuge in deep waters, were the adaptive responses (concurrently or alternatively) adopted by large zooplankters to cope with the increasing predation risk throughout the summer. Daphnia galeata initiated a more severe trade-off to cope with high summer predation relative to other cladoceran species. Diaphanosoma brachyurum and Daphnia cucullata seem less susceptible to fish predation as indicated by the low alteration of their size structure and their vertical distribution. The copepod Eudiaptomus gracilis took refuge in deep waters and achieved important modifications of its mature size.     

Seasonal variations in copepod size: effects of temperature, food abundance, and vertebrate predation

Seasonal dry weights of female and male Cyclops bicuspidatusthomasi, Diaptomus ashlandi and Diaptomus minutus were studiedin southeastern Lake Michigan during 1975–1981. Smallestanimals occurred during summer and early fall, and largest animalsin winter and spring, a pattern reported for other copepods.The range of weights for the species and sexes decreased fromwinter to summer, and converged in summer to a value of approximately2 µg/animal. Surface water temperature and abundancesof young-of-the-year (YOY) fish were inversely correlated withweights of males and females of the three copepod species. Standingstocks of important phytoplankton groups, especially pennatediatoms and flagellates, were positively correlated with copepodweight. Seasonal change of copepod body size appears to be morethan simply a function of temperature; seasonal predation byYOY fish may be a factor influencing sizes of adult copepods.     

Effects of predation by Chaoborus flavicans on crustacean zooplankton of Lake Lenore, Washington

1. After Chaoborus flavicans became established in 1974, the species composition of zooplankton in Lake Lenore changed. Diaptomus nevadensis disappeared and densities of Diaptomus sicilis were reduced.
2. A transplant experiment showed the D. nevadensis could survive in Lake Lenore water in the absence of Chaoborus . The disappearance of D. nevadensis was probably a consequence of Chaoborus predation.
3. Although densities of Daphnia pulicaria † were similar before and after the colonization of C. flavicans , juvenile D. pulicaria began producing neck-teeth during the first summer Chaoborus was present.
4. The seasonal pattern of neck-teeth production by juvenile D. pilicaria did not correlate with density of Chaoborus but rather with a combination of water temperature and Chaoborus density, suggesting that metabolic processes are a component of induction of neck-teeth in this species.     

Seasonal vertical distribution and diel migration of zooplankton in a temperate stratified lake

The investigation of the vertical distribution of the zooplankton community in the temperate Lake Trichonis during four seasons in 2005, showed the existence of vertical segregation among species, ontogenetic stages and sexes within and between the major groups. In each season, the two or three more abundant rotifer species distributed at separate depth layers, while this feature was maintained during the entire 24 h period, since no diel vertical migrations (DVM) were performed. In contrast, the crustacean community, comprised mainly by the calanoid copepod Eudiaptomus drieschi and the cladoceran Diaphanosoma orghidani, showed various patterns of DVM, being more pronounced in spring and summer. Females of E. drieschi distributed deeper than males, while the copepod nauplii were found mainly in the surface layer in all four seasons. Temperature was the most important abiotic factor affecting directly and indirectly the vertical distribution and migration of various species. During stratification, the metalimnion was the most productive layer in Lake Trichonis, having maximum values of dissolved oxygen and low transparency due to high concentration of organic matter and phytoplankton. The DVM patterns of the crustaceans indicate that the metalimnion acts probably as a daylight refuge against predation by Atherina boyeri, which is the dominant planktivorous fish in the lake.     

Zooplankton densities in a Hydrilla infested lake

The number of individuals and species of zooplankton were sampled concurrently with Hydrilla biomass and water quality for one year in a small, eutrophic central Florida lake. Throughout the study, rotifer species and individuals dominated the zooplankton. The abundance of the zooplankton tended to remain high when Hydrilla biomass was at its seasonal low during late winter and early spring. When hydrilla growth increased in the late spring and summer months causing a decrease in total alkalinity, specific conductivity, water color, turbidity, orthophosphate and chlorophyll a concentrations; the abundance of the zooplankton declined. During this time, there was a shift from limnetic to littoral species, principally rotifers. Hydrilla growth did not affect the mean number of cladoceran or copepod species, but may have led to an increase in rotifer species.     

The effects of selective fish predation on the horizontal distribution of pelagic Cladocera in a southern French reservoir

A four-year study showed a clear seasonal succession of species within the cladoceran community of the large, oligotrophic Sainte-Croix reservoir (S.E. France). Diaphanosoma brachyurum and Ceriodaphnia pulchella were strictly limited to the warm stratified period (July to October), whereas Bosmina longirostris and Bosmina coregoni were dominant during spring and autumn. Daphnia longispina was the only species to occur throughout the year with higher densities in spring.In spring and late autumn, the discharge of the inflowing river Verdon was high and the abundance of all species showed a gradient over the whole lake with lower densities close to the inflow. During the stratified period, water inflow was very low and species showed different patterns. Densities of the small form Ceriodaphnia pulchella were similar all along the long axis of the lake, whereas Daphnia densities were significantly higher near the dam. The distribution pattern of Diaphanosoma, an intermediate-sized species, showed similar trends to that of Daphnia. The only planktivorous fish in the pelagic zone, the bleak (Alburnus alburnus), fed mostly on large-bodied species (> 1.0 mm) and was more abundant close to the inflow current. A comparison between the length frequency distributions of cladocera upstream and downstream provided a clear demonstration of the effects of size-selective predation on prey populations. Finally, the interactions between spatial heterogeneity and long-term development of the zooplankton community and the indirect effects of predation are discussed.     

浙江水源地水库浮游动物丰度和生物量与水质参数的通径分析

为探明浙江水源地水库浮游动物群落特征及与环境因子的关系, 达到用浮游动物群落参数监测水源地水库水质的目的。于2014年1月至2016年10月, 对10个饮用水源地水库(K1—K10)展开了水质参数、浮游动物丰度和生物量的季节调查。采用多元逐步回归与通径分析的方法, 研究了浙江水源地水库环境因子与浮游动物群落之间的相互关系和作用过程。结果表明, 2014—2016年水库浮游动物平均密度97.5 ind./L, 主要由桡足类无节幼体(占36.3%)、轮虫(28.4%)和剑水蚤(20.0%)组成。平均生物量289.3 μg/L, 主要由枝角类(占39.3%)、剑水蚤(29.0%)和哲水蚤(14.5%)组成。Chl. a含量是春、夏季水库浮游动物丰度的决策因子, TP含量是秋、冬季群落丰度波动的限制因子, 春季TN通过N﹕P比率影响群落丰度。DO含量是冬季和夏季水库浮游动物生物量发展的决策因子, 冬季DO通过降低N﹕P比促进群落生物量发展。水库浮游动物现存量受到了TP含量消长、N﹕P比率变化, 以及最终反映的水体Chl.a含量共同影响。     

苏州工业园区水体浮游甲壳动物群落特征及其与环境因子的关系

于2012年6月至2013年5月,对苏州工业园区湖泊和河流水体的浮游甲壳动物组成及群落结构进行了研究,分析了浮游甲壳动物的密度和生物量的年度变化,探讨其分布与水体理化因子间的关系.结果表明：园区水体有枝角类6科12属24种,桡足类7科13属18种,其中短尾秀体溞、长额象鼻溞、汤匙华哲水蚤及近邻剑水蚤在不同水体中不同季节均为优势种.在湖泊水体和河流水体中,浮游甲壳动物的密度和生物量表现为夏、秋季较高,冬、春季较低,且在夏、秋季分别具有2个峰值.枝角类平均密度和生物量在河流水体中均高于湖泊水体,两者间均具有显著差异;桡足类的平均密度在河流水体和湖泊水体间差异不显著,而平均生物量要显著高于湖泊水体.湖泊水体和河流水体在溶解氧、pH、透明度、总溶解固体、盐度、总磷、总氮及铵氮含量上均存在显著差异;冗余分析表明无论是湖泊水体还是河流水体,多数浮游甲壳动物的分布与水温、盐度、化学需氧量(COD_Mn)和总磷等指数呈正相关,只有枝角类中的溞属、船卵溞属种类的分布与水体溶解氧、pH值及透明度呈正相关.     

Predation pressure induced by seasonal fishing moratorium changes the dynamics of subtropical Cladocera populations

Seasonal fishing moratorium with selective fish harvesting is a common means of increasing fish production in Asia. Such manipulation might be expected to lead to a seasonal variation in abundance and composition of fish and predation pressure on zooplankton, and consequently a seasonal change in the Cladocera populations. In this study, we examined the seasonal dynamics of cladocerans in a subtropical plateau lake in southwestern China, Lake Erh, in which a fishing moratorium was implemented in spring and early summer. Cladocerans showed a bimodal seasonal distribution linked to variations in predation pressure induced by the seasonal fishing moratorium. When predation was low in winter because of cool water temperatures and decreasing fish density, Daphnia galeata appeared in the water column and increased towards spring. The cladoceran peaked in the middle of the fishing moratorium, coinciding with a clear water phase. The feeding rate increased with temperature in the late moratorium, allowing planktivorous fish to strongly suppress large daphnids. Small cladocerans benefited from the reduced competition with large daphnids by increasing their numbers rapidly, which resulted in a second peak of cladocerans in the fishing season.     

福建北部近海浮游动物数量分布与水团季节变化的关系

根据2015—2016年在福建北部近海水域(120.10°E—120.65°E, 26.35°N—27.07°N)夏、秋、冬、春4个季节的海洋生态调查资料, 探讨了该水域浮游动物的数量分布、季节变化及其与水团变化的关系。结果表明, 调查水域浮游动物的平均生物量依次是: 夏季(479.51 mg/m3)>秋季(257.37 mg/m3)>春季(241.86 mg/m3)>冬季(84.05 mg/m3), 平均丰度依次是: 夏季(156.36 ind./m3)>春季(91.57 ind./m3)>秋季(40.34 ind./m3)>冬季(21.82 ind./m3), 生物量和丰度均值都呈现出夏季、秋季到冬季依次减少, 春季增多的趋势, 不同的是秋季生物量均值高于春季, 而丰度均值低于春季。在夏、冬和春三季, 浮游动物的总生物量和总丰度的分布总体较为一致; 而在秋季, 浮游动物的总生物量和总丰度的分布几乎相反。百陶箭虫(Sagitta bedoti)和微剌哲水蚤(Canthocalanus pauper)是影响夏季总丰度分布最主要的种类; 链钟水母(Desmophyes annectens)是影响秋季总丰度分布最主要的种类; 驼背隆哲水蚤(Acrocalanus gibber)、亚强真哲水蚤(Eucalanus subcrassus)和百陶箭虫对冬季总丰度的分布起到了重要影响; 五角水母(Muggiaea atlantica)和微剌哲水蚤是春季占总丰度比例较高的种类。浮游动物数量各季不同分布模式的根本原因是台湾暖流和浙闽沿岸流水团的季节性变化所致。研究结果不仅对了解与评价区域海洋生态系统动态和生物多样性变化具有重要的理论意义, 而且还可以丰富我国近海水域浮游动物的生态特征与水团变化之间的关系。     

Daphnia lumholtzi and Daphnia ambigua: population comparisons of an exotica and a native cladoceran in Lake Okeechobee, Florida

The population dynamics of an exotic cladoceran (Daphnia lumholtzi Sars) and a native cladoceran (Daphnia ambigua) were studied over a 12 month period in subtropical Lake Okeechobee, Florida (USA), to quantify the extent of invasion of the exotic species and compare ecological niches. Daphnia lumholtzi accounted for up to 70% of the Daphnia assemblage during the summer months (June-August), while D.ambigua accounted for up to 97% of the Daphnia assemblage from fall to spring (October-April). The densities of the two species were inversely corelated. The exotic species was most concentrated in the shallower, warmer, north and south ends of the lake during the summer. It also was present, but at much lower densities, in the central lake region during the fall. The native species displayed a ubiquitous distribution throughout the lake during spring and winter, but was concentrated in the deeper, cooler, central region during the summer. Relationships of the two species with environmental conditions indicate that water column temperature might affect the seasonal and spatial distribution of the two Daphnia species. The results also indicate that D.lumholtzi may be filling a 'vacant' seasonal or spatial niche when conditions are unfavorable for D.ambigua.      

福建中部近海浮游动物数量分布与水团变化的关系

根据2009—2010年在福建中部近海24°55'—25°13'N、119°11'—119°32'E水域冬、春、夏3个季节的调查资料,探讨了该水域浮游动物总丰度与生物量的平面分布、季节变化及其与台湾海峡水团变化的关系。结果表明,调查水域浮游动物的数量在冬、春之交变化较大,而在春、夏季变化较小。浮游动物冬、春两季的平均丰度分别为8.90 个/m³和245.65 个/m³,夏季为236.82 个/m³。冬、春两季,该水域浮游动物的分布特征相近。其数量在近岸较高,向外侧水域逐渐降低。冬季浮游动物的丰度最高为31.56 个/m³,春季最高达到831.67 个/m³。中华哲水蚤(Calanus sinicus)是冬、春季影响总丰度变化最主要的种类。与冬、春季不同,夏季浮游动物的数量在离岸水域较高,丰度最高达1053.13 个/m³,而在近岸较低,最低值仅19.17 个/m³。汉森莹虾(Lucifer hanseni)、双生水母(Diphyes chamissonis)是影响总丰度变化最主要的种类。浮游动物在各季的不同分布特征与台湾海峡的季节性水团变化有关。受季风转换影响,从冬季到夏季,海峡内沿岸流势力逐渐减弱,台湾暖流水势力逐渐增强,并影响到沿岸的水文环境。这导致调查水域内浮游动物的优势种类由暖温种向暖水种演替。由于冬、春季的重要优势种类中华哲水蚤与夏季的汉森莹虾、双生水母具有不同的温度适应性,受不同性质水团的影响,在近岸和离岸水域各自呈现出不同的数量高低。从而进一步影响到各季浮游动物总数量的分布。     

武汉三角湖浮游甲壳动物群落结构

三角湖是长江中下游地区典型的小型城市湖泊,近年来其富营养化趋势明显。2014年7月至2015年6月对湖中浮游甲壳动物群落及其影响因子进行了调查,旨在为湖泊污染防治和生态修复提供依据。在三角湖共采集浮游甲壳动物9科17属22种。浮游甲壳动物全年平均密度为(3.7±3.6)ind/L,各月密度变化范围为0.6~13.1 ind/L,夏季和秋季密度较低,密度峰值出现在2月。浮游甲壳动物全年大部分时间(5、6月除外)以桡足类及无节幼体占优势,其比例为55.2%~95.4%。浮游甲壳动物物种丰富度变化范围为6~15,平均值为10±3,夏季浮游甲壳动物物种丰富度较低。浮游甲壳动物群落Simpson指数变化范围为0.76~0.90,平均值为0.80±0.04。Pearson相关分析表明,浮游甲壳动物总密度与水深呈显著负相关(r=﹣0.636,P0.05,n=11),显示季节性的水位波动影响浮游甲壳动物密度。典范对应分析(CCA)显示,水温和透明度是影响浮游甲壳动物物种组成季节变化的主要环境因子(P0.05)。高密度的鲢(Hypophthalmichthys molitrix)、鳙(Aristichthys nobilis)放养引起的摄食压力可能是三角湖浮游甲壳动物密度较低的主要原因之一。     

Seasonal changes in zooplankton abundance in the lower Rhine during 1987–1991

Zooplankton in the River Rhine was surveyed for five years at the Dutch sampling stations, Lobith (German/Dutch border) and Maassluis (at the point of discharge of the river into the North Sea). The zooplankton abundance showed an apparent seasonal pattern at both stations, characterized by low densities during the winter period, and higher densities during the summer period, with a spring peak. Zooplankton was dominated by rotifers at both stations, although during the winter periods the contribution of copepods was considerable. The rotifers were dominated byBrachionus angularis, B. calyciflorus, Keratella cochlearis andK. quadrata; the copepods by cyclopoid nauplii; the cladocerans by small-sized species mainly belonging toBosmina. At Maassluis the relative contribution of copepods was higher than at Lobith. Furthermore, the zooplankton at Maassluis included the speciesEurytemora affinis, characteristic for estuarine conditions. In spring, the rotifer density and water temperature and rotifer density and chlorophylla concentration were positively correlated. Furthermore, both rotifer density and chlorophylla were inversely correlated with discharge. The possible role of environmental factors (water temperature, chlorophyll content, discharge and biotic factors) controlling the river zooplankton dynamics is indicated.