Spatial and temporal variability in export fluxes of biogenic matter in Kongsfjorden

The marine ecosystem of Kongsfjorden experiences large variations in primary productivity due to pronounced seasonal variations in sunlight, glacier melt, and ice cover. The objective of this study was to assess spatial and seasonal variability in the downward export of biogenic matter in Kongsfjorden. Short-term sediment traps were deployed for periods ranging from 21 to 52 h at three stations from the inner fjord to the outer fjord in May, August, and October 2012 and at one mid-fjord station in January 2013. Total particulate matter, particulate organic carbon, phytoplankton cells, chlorophyll a, biogenic particulate silica, and zooplankton fecal pellet fluxes were measured to determine the magnitude and composition of the material exported in the fjord. The amount and composition of export fluxes reflected a large phytoplankton bloom grazed upon by zooplankton in May, the melting of glaciers and the intrusion of Atlantic Water in August, the end of the glacier melt period in October, and the polar night in January. Overall, seasonal changes in the phytoplankton community impacted export efficiency in the fjord, directly through phytoplankton sinking and indirectly through zooplankton grazing. Results obtained in this study may reflect the magnitude and composition of export fluxes to expect in coming years in Kongsfjorden, especially under conditions of warmer Atlantic Water and longer glacier melt periods.     

Near-bottom zooplankton aggregations in Kongsfjorden: implications for pelago–benthic coupling

Near-bottom zooplankton communities have rarely been studied despite numerous reports of high zooplankton concentrations, probably due to methodological constraints. In Kongsfjorden, Svalbard, the near-bottom layer was studied for the first time by combining daytime deployments of a remotely operated vehicle (ROV), the optical zooplankton sensor moored on-sight key species investigation (MOKI), and Tucker trawl sampling. ROV data from the fjord entrance and the inner fjord showed high near-bottom abundances of euphausiids with a mean concentration of 17.3 ± 3.5 n × 100 m^?3. With the MOKI system, we observed varying numbers of euphausiids, amphipods, chaetognaths, and copepods on the seafloor at six stations. Light-induced zooplankton swarms reached densities in the order of 90,000 (euphausiids), 120,000 (amphipods), and 470,000 ind m^?3 (chaetognaths), whereas older copepodids of Calanus hyperboreus and C. glacialis did not respond to light. They were abundant at the seafloor and 5 and 15 m above and showed maximum abundance of 65,000 ind m^?3. Tucker trawl data provided an overview of the seasonal vertical distribution of euphausiids. The most abundant species Thysanoessa inermis reached near-bottom concentrations of 270 ind m^?3. Regional distribution was neither related to depth nor to location in the fjord. The taxa observed were all part of the pelagic community. Our observations suggest the presence of near-bottom macrozooplankton also in other regions and challenge the current view of bentho–pelagic coupling. Neglecting this community may cause severe underestimates of the stock of pelagic zooplankton, especially predatory species, which link secondary production with higher trophic levels.     

钦州湾秋季和春季浮游动物分布特征及影响因素

为了解钦州湾浮游动物群落的时空分布特征及与主要环境因子的关系,于2014年10月和2015年3月进行了秋季和春季两航次的调查。结果表明:该海湾的浮游动物群落有明显的季节变化。秋季共鉴定出12类87种,其中优势种有太平洋纺锤水蚤(Acartia pacifica)、肥胖三角溞(Evadne tergestina)、亨生莹虾(Lucifer hanseni)、百陶箭虫(Sagitta bedoti)和长尾类幼虫(Macrura larvae);春季共鉴定出11类48种,优势种为中华哲水蚤(Calanus sinicus)和太平洋纺锤水蚤;秋季浮游动物的平均丰度、生物量和多样性指数(528.92个/m~3、110.60 mg/m~3和2.22)均高于春季(48.30个/m~3、61.10 mg/m~3和1.70)。空间分布上,钦州湾外湾浮游动物丰度、生物量和多样性指数的平均值皆高于内湾。多维尺度分析表明,秋季内湾群落相似性较高,春季外湾浮游动物群落相似性较高。相关性分析表明盐度与营养盐是影响钦州湾浮游动物分布的主要环境因子。与2011—2012年数据相比,钦州湾浮游动物群落结构已趋于单一化和小型化,以致生物量明显下降。这一现象主要与钦州湾海水富营养化以及大面积高密度牡蛎养殖有密切的关系。     

鸭绿江口近岸海域水质环境对冬季浮游动物群落结构的影响

定量分析滨海湿地近岸海域水质环境与浮游动物群落结构之间的关系对揭示海水水质环境健康状态具有重要意义。2019年12月在鸭绿江口湿地国家级自然保护区近岸海域开展了浮游动物和水环境因子调查,运用冗余分析和结构方程模型等方法探讨了水质环境对冬季浮游动物群落结构的影响。研究区共鉴定出浮游动物14种以及浮游幼虫5大类,桡足类最多占比52.63%;保护区不同功能分区间浮游动物群落结构总体差异不大,多样性指数、均匀度指数和丰富度指数平均值分别为1.34、0.51和0.59;浮游动物的种群分布与海水化学需氧量、溶解性无机氮、浮游植物群落多样性指数和铜元素含量关系显著;结构方程模型模拟结果表明,海水富营养化水平对浮游动物丰富度的效应系数为-0.26,具有显著的直接影响(P=0.01),重金属污染水平通过影响浮游植物丰富度(效应系数为-0.41,P<0.001)间接对浮游动物丰富度产生作用(间接效应系数为-0.2)。研究结果将有助于深化对海水环境和浮游动物群落结构协同演变过程的认识,为滨海湿地近岸海洋生态系统科学管理提供理论支撑。     

鄱阳湖丰水期水位波动对浮游动物群落演替的影响

为了解鄱阳湖夏季丰水期水位剧烈波动过程中浮游动物的群落演替特征,2012年夏季鄱阳湖水位剧烈波动期间,于6月24日、7月7日和8月27日当水位下降且接近17.6 m时,在江西鄱阳湖国家级自然保护区内的1个浅水碟形湖泊设置4个采样点进行采样调查。共发现浮游动物65种,其中轮虫52种,枝角类7种,桡足类6种,多为营浮游生活的广温性和嗜温性种类。单因子方差分析(one-way ANOVA)显示3个月之间浮游动物的密度和生物量均具有显著差异(P0.05),7月份浮游动物密度(1030.17±68.18个/L)显著高于6月份(325.16±41.60个/L)和8月份(203.79±24.91个/L);6月份浮游动物的生物量(0.56±0.04 mg/L)显著低于7月份(1.22±0.11 mg/L)和8月份(0.99±0.11 mg/L)。基于浮游动物多度的聚类分析和自组织映射神经网络图均揭示夏季3个月份的浮游动物可区分为明显的3个群落:6月群落、7月群落和8月群落。蒙特卡罗检验发现水温、电导率、浊度和溶氧与浮游动物群落结构变化显著相关(P0.05)。典型相关分析显示,6月份浮游动物群落与叶绿素a含量呈显著正相关关系,7月份浮游动物群落与水体温度呈显著正相关关系,8月份浮游动物群落与水深和电导率、浊度和溶氧呈显著正相关关系(P0.05)。在3个月均为优势物种的盖氏精囊轮虫与叶绿素a含量呈正相关关系(P0.05),与水温、pH、溶氧呈负相关(P0.05)。夏季水位波动过程中浮游动物的群落结构在时间上(月份之间)发生明显演替,呈现轮虫密度逐渐降低,枝角类和桡足类密度逐渐增加的变化规律。水位波动引起环境因子的改变,从而对浮游动物的群落演替产生了重要影响。     

南四湖浮游动物群落结构特征及其与环境因子的关系

为探讨南四湖浮游动物多样性特征及其与水质的相关性,于2012年夏季(7月)和冬季(12月)对南四湖浮游动物的群落结构进行了系统研究,结合历史数据,分析了南四湖浮游动物群落的多样性特征和时间变化。共采集到浮游动物163种,其中,轮虫78种,原生动物65种,枝角类17种,桡足类3种。夏季记录浮游动物种类数(141种)高于冬季(105种)。从四个湖区来看,微山湖浮游动物种数最多(102种),其次是南阳湖(95种)和昭阳湖(80种),独山湖(73种)较少。南四湖浮游动物全年平均密度为2 192 ind/L,平均生物量为2.27 mg/L。除原生动物外,其他三类浮游动物夏季的平均密度和生物量都高于冬季。采用丰富度指数、Shannon-Wiener指数和均匀度指数对浮游动物多样性进行了评价,结果均显示,南四湖浮游动物多样性夏季高于冬季。通过回归分析发现,总氮是影响浮游动物密度的主要因素,总氮和水温是影响浮游动物生物量的主要因素,p H和电导率是影响浮游动物多样性的主要因素。     

Year-to-year changes of the mesozooplankton community in the Chukchi Sea during summers of 1991, 1992 and 2007, 2008

A recent drastic decrease in sea ice cover area was observed in the western Arctic Ocean during summer, yet little information is available for its effect on zooplankton community. To evaluate the effect of sea ice reduction on zooplankton, we studied year-to-year changes of zooplankton community structure in the Chukchi Sea during summers of 1991, 1992 (when sea ice extended), 2007, and 2008 (when sea ice reduced). Zooplankton abundance ranged from 4,000 to 316,000 ind. m⁻² (mean: 70,000) and was greater north of Lisburne Peninsula in 2008. Zooplankton biomass ranged from 0.07 to 286 g wet mass m⁻² (mean: 36) and was greater south of Lisburne Peninsula in 2007. Cluster analysis based on zooplankton abundance showed a division of the zooplankton community into four groups. Occurrence of each group was separated geographically and interannually, and geographic distributions of each group in 1991 and 1992 were similar but those in 2007 and 2008 were shifted northward. Abundance and biomass in 2007/2008 were higher than in 1991/1992, indicating that further sea ice reduction would have a positive effect on zooplankton production (e.g. invasion of large Pacific species and temperature effects on their growth rate). The northern shift in geographic distribution of the zooplankton community in 2007/2008 indicates that sea ice reduction would have a negative effect on the zooplankton community (loss of characteristic Arctic species) in part of the Chukchi Sea. These apparently contradictory effects of sea ice reduction on zooplankton community emphasize the critical need for continued monitoring in this area.     

The relative significance of environmental and anthropogenic factors affecting zooplankton community structure in Southeast Wisconsin Till Plain lakes

Zooplankton community composition can be related to natural environmental factors such as lake morphology, lake landscape position, and water chemistry as well as anthropogenic factors such as agricultural and urban land-use. We hypothesized that within-lake factors, such as water chemistry, lake morphology, and human land-use would each be related to zooplankton community structure, but that watershed land-use would be the strongest correlate in southeast Wisconsin lakes. Zooplankton samples, collected every 3 months over a year, from 29 lakes were used to determine how lake and watershed morphology, water quality, and land-use were related to zooplankton community structure in the heavily developed Southeast Wisconsin Till Plain Ecoregion. Forward selection and a variation partitioning procedure were used to determine relative and shared contributions of each suite of variables in predicting zooplankton community structure. Redundancy analysis was used to characterize dominant gradients in pelagic zooplankton communities and related environmental factors and land-use. The major correlates of community structure included summer phosphorus, lake depth and surface area and urban and natural land. Variation partitioning illustrated that phosphorus alone accounts for the greatest part (12%) of community structure. Urban land-uses (residential, commercial and paved land) and lake morphology partially explain zooplankton community variation through combined effects with phosphorus. Small cladocerans and Skistodiaptomus pallidus were associated with higher phosphorus, shallow depth and higher urban land-use, while Daphnia pulicaria dominates in deep lakes with lower phosphorus and less urban land-use. This study contributes to the understanding of factors affecting zooplankton community structure in a largely human developed region and illustrates the importance of eutrophication in structuring zooplankton community composition.     

环境因子对唐山湾海域浮游动物群落结构的驱动作用

为研究唐山湾海域浮游动物群落结构与环境因子的关系,于2015年4月(春季)、7月(夏季)、10月(秋季)和12月(冬季)对唐山湾海域浮游动物群落结构、环境因子进行航次调查,并利用多元统计分析和相关分析法分析了浮游动物群落结构的时空变化及其主要环境驱动因子.结果表明: 影响唐山湾海域浮游动物丰度的主要环境因素为无机氮(DIN)、悬浮物(SS)、水温(T)和叶绿素a(Chl a);唐山湾海域浮游动物群落结构的空间差异主要受溶解氧(DO)、T和Chla的驱动;在唐山湾不同海域中,影响浮游动物群落结构的因素存在差异,其中乐亭海域和三岛海域浮游动物群落结构的主要影响因素为物理因素,曹妃甸海域则主要受化学因素的影响.这表明在唐山湾人类活动影响强度大的海域,浮游动物群落结构更多地受化学因素影响(DIN、活性磷酸盐),而人类活动影响小的海域则更多地受物理因素的影响(T、SS).     

东海赤潮高发区春季浮游动物生态特征的研究

根据2002年4～5月东海122°～123°30′E、29°～32°N水域海洋综合调查资料,对东海赤潮高发区浮游动物的数量分布、群落特征、种类组成及优势种等进行了分析．结果表明,在调查区共鉴定出饵料浮游动物128种[不含16种浮游幼虫(体)和仔鱼],分5门12大类,以桡足类占优势(40种,31．25％)．浮游动物群落以广温广盐生态类群为主．中华哲水蚤(Calanus sinicus)为最主要优势种(142．10ind·m-3,68．09％)．总生物量均值为243．80mg-m3(55．53～773．92mg·m-3),最高密集区(>500mg·m-3)位于长江口30°45′～31°15′N、122°45′～123°15′E水域．饵料生物量均值为195．96mg·m13(55．53～496．09mg·m。),呈长江口(30°30′N以北)水域高于舟山岛东南水域、长江口外海(122°45′E以东)高于近海水域的分布趋势．多样性指数(H′)均值为2．12(1．09～3．73)．长江口水域多样度、均匀度和丰富度低,优势度大,反映出浮游动物群落结构不够稳定．采用逐步回归分析得知,影响本区春季浮游动物生态特征值分布的主要因子是水温、硅藻和甲藻．     

Midsummer zooplankton assemblages in four types of wetlands in the Upper Midwest,USA

The objective of this study was to characterize the zooplankton and phytoplankton assemblages of four different types of wetlands and to evaluate their use as environmental indicators. Total abundances, community composition, and species diversity were evaluated for zooplankton and phytoplankton assemblages from 24 wetlands and related to water quality variables. During August 1995, six representative sites were sampled from four types of wetlands designated as constructed, impacted, non-impacted, or temporary. The plankton assemblages of all wetlands were dominated by cosmopolitan crustacean, rotifer, and phytoplankton taxa typical of lake plankton communities. Species diversity, richness, and evenness of zooplankton and phytoplankton assemblages did not differ significantly among the wetland types. Total zooplankton abundance was significantly (p < 0.01) related to chlorophyll a and total phosphorus concentrations over the range of trophic conditions. Mean zooplankton densities and phytoplankton biovolumes were similar among the wetlands, however, the relative abundances of major zooplankton groups differed among the wetland types. Cyanophytes, primarily Oscillatoria spp., were a major component of the phytoplankton across all four wetland types, and were significantly more abundant within the constructed and temporary sites. On average, rotifers accounted for 79% of total zooplankton abundance within the constructed wetlands and were much less dominant in the non-impacted and temporary wetlands. Cladoceran, copepodite, and adult copepod concentrations were low in the constructed and impacted wetlands and increased in the non-impacted and temporary wetlands in conjunction with increased chlorophytes and cryptophytes. Our preliminary survey suggests that abiotic factors which are known to directly affect phytoplankton may indirectly affect zooplankton composition in such a way as to use zooplankton assemblages as indicators of water quality. However, further study incorporating seasonal dynamics and the influence of predators on zooplankton assemblages is needed to fully assess the use of zooplankton community composition as an environmental indicator for wetland systems. This revised version was published online in July 2006 with corrections to the Cover Date.     

Fluctuation of the zooplankton community in Lake Biwa during the 20th century: a paleolimnological analysis

Detailed zooplankton records from a 26-cm sediment core with a time resolution of approximately 3–10 years were obtained from Lake Biwa, Japan, to examine the historical variations in the zooplankton community during the 20th century. In the sediments, selected zooplankton remains have fluctuated over the years. Daphnia – large zooplankton herbivores – did not occur from 1900 to 1920, and formed a very minor component of the zooplankton community in the following 30 years, while Bosmina – small zooplankton herbivores – were common during this period. In the mid-1960s, however, when eutrophication was noticeable in this lake, Daphnia numbers increased dramatically and became the dominant zooplankton thereafter. In contrast, Difflugia brevicolla and D. biwae, two amoeboid protozoans that live in connection with the lake bottom environment, occurred abundantly until the late 1950s, but gradually decreased after the mid-1960s. In particular, D. biwae, a species peculiar to this lake, was not found in sediment dated after 1980, suggesting its extinction. These results indicate that the zooplankton community structure changed greatly in the 1960s, and suggest that the eutrophication occurring at this time altered the relative strength of top-down and bottom-up forces on the zooplankton community in Lake Biwa.     

Covariation between zooplankton community composition and cyanobacterial community dynamics in Lake Blaarmeersen (Belgium)

The cyanobacterial community composition in the mesotrophic Lake Blaarmeersen was determined by denaturing gradient gel electrophoresis (DGGE) of PCR-amplified 16S rRNA gene fragments during two consecutive years to assess the importance of different classes of explanatory variables (bottom-up and top-down factors, physical variables and phytoplankton) in cyanobacterial community dynamics. The most dominant cyanobacteria in Lake Blaarmeersen were Synechococcus (three genotypes), Limnothrix redekei and Anabaena/Aphanizomenon. Analyses of Similarity revealed that the cyanobacterial community in Lake Blaarmeersen differed significantly between the growing season and the winter season as well as between the epilimnion and hypolimnion during the stratified periods. Mantel tests revealed significant correlations between the DGGE data and bottom-up factors, physical variables, the phytoplankton community composition and, interestingly, the zooplankton community composition. In general, the zooplankton community composition (especially the cladoceran community) was more important in structuring the cyanobacterial community than the total zooplankton biomass. This study shows that grazing zooplankton communities can have a relatively strong impact on the cyanobacterial community dynamics and that this impact can be equally important as bottom-up processes regulated by nutrient concentrations and/or physical variables.     

苏州工业园区湖泊后生浮游动物群落结构及影响因子

苏州工业园区地处长江流域下游,随着城市化进程的不断推进,园区水生态系统结构与功能的稳定面临严峻考验。浮游动物作为水生态系统的重要组成部分,探究其群落结构的形成机制对生物多样性保护及生态系统健康发展具有重要意义。为深入了解苏州工业园区五个主要湖泊后生浮游动物群落结构的动态变化及影响因子,于2018年7月至2019年6月进行4次调查。研究共检出后生浮游动物112种（轮虫65种、枝角类29种、桡足类18种）,其中优势种12种（轮虫10种、枝角类和桡足类各1种）。Jaccard相似性分析表明,湖泊间后生浮游动物物种组成整体处于中等相似水平。后生浮游动物密度呈现出显著的季节和湖泊差异,而生物量、Shannon-Wiener多样性指数、Pielou均匀度指数以及Margalef丰富度指数仅存在显著的季节差异。聚类分析结果表明,夏季和秋季后生浮游动物群落结构最为相似。RDA分析表明,水温、溶解氧和pH是影响园区湖泊后生浮游动物群落结构的主要环境因子。Pearson相关性分析表明,湖泊面积与后生浮游动物群落结构无显著相关关系,样点近岸距离与生物量具有显著的正相关关系。基于水质评价标准和物种多样性指数可知,园区湖泊水质整体处于轻-中度污染水平。研究表明苏州工业园区五大湖泊后生浮游动物群落结构表现出同质化趋势;季节变化、环境因子以及样点近岸距离是调控群落结构形成的主要因素。     

杭州湾内外海域秋季浮游动物群落的比较

本文比较了杭州湾湾外海域(122.10°-122.58° E, 30.54°-30.93° N)和湾内不同海域(北岸东侧: 121.67°- 121.87° E, 30.68°-30.83° N; 南岸东侧: 121.60°-121.85° E, 29.95°-30.24° N; 北岸西侧: 121.31°-121.56° E, 30.58°- 30.77° N)秋季浮游动物的群落组成、累积优势度曲线以及多样性指数(H')等群落结构特征, 并进行了差异性分析。结果表明: 湾外海域的群落组成与湾内海域的3个群落之间均有较大的差异。湾外海域的群落I是以中华假磷虾(Pseudeuphausia sinica)等近海种、背针胸刺水蚤(Centropages dorsispinatus)等沿岸低盐种为主, 其次是外海种。湾内南岸东侧海域的群落II主要以左突唇角水蚤(Labidocera sinilobata)等沿岸低盐种为主, 近海种次之。湾内北岸东侧海域的群落III是以真刺唇角水蚤(Labidocera euchaeta)等沿岸低盐种、虫肢歪水蚤(Tortanus vermiculus)等河口半咸水种组成的混合群落。湾内北岸西侧海域群落IV是以虫肢歪水蚤为代表的河口半咸水种为主的群落。总的说来, 这一水域向西和向北方向出现更低盐度适应性的群落。从累积优势度曲线来看, 湾外海域群落I与湾内北岸东侧群落III的累积优势度上升趋势均相对平缓, 但群落III的初始累积优势度略高于群落I; 而与群落I相比, 湾内南岸东侧的群落II与北岸西侧的群落IV的初始累积优势度均很高。湾外海域群落I的初始累积优势度较低, 显示出群落I的优势种较多, 而单一优势种优势度低于湾内3个群落。方差分析结果表明: 湾外海域的浮游动物多样性指数与湾内3个海域均有极显著差异(P < 0.01), 而湾内各海域之间均无显著性差异(P > 0.05)。说明湾外浮游动物群落的多样性高于湾内海域。湾内外海域浮游动物群落特征之间有较大差异, 其主要原因是影响各自群落的主导水团明显不同。     

中国近海浮游动物群落结构及季节变化

2006年7-8月、12月-2007年2月、2007年4-5月、2007年10-12月,对中国近海进行了4个航次生物、化学和水文等专业综合调查.根据采集的浮游动物样品分析鉴定结果,对中国近海浮游动物群落结构、种类组成及优势种的季节变化进行研究.结果表明,中国近海浮游动物有1330种,隶属于7门19大类群,浮游幼体47类,其中,节肢动物为最优势类群,有782种,占58.80％,其次为刺胞动物,有324种,占24.36％.在浮游动物群落结构中,4个海区均以桡足类和水母类的种类和数量占绝对优势.中国近海4个海区浮游动物种类数有明显季节变化,渤海和黄海,浮游动物种类数夏、秋季多于春、冬季;东海和南海,浮游动物种类数春、夏季多于秋、冬季.中国近海浮游动物群落大体可划分为6个主要生态类群:近岸低盐类群、低温高盐类群、高温高盐类群、低温广盐类群、高温广盐类群和广温广盐类群.结合同步调查的其它生物、水文、化学环境参数的分析结果,对中国近海浮游动物群落种类丰度与环境因子进行生物与环境变量关系分析,结果表明,浮游动物群落结构与水温、盐度、水深、溶解氧、硝酸盐和pH存在明显相关关系.水温和盐度是影响浮游动物群落结构最重要的两个环境因子.     

Seasonal zooplankton dynamics in main channel and backwater habitats of the Upper Mississippi River

This study used stratified random sampling to examine the spatial and temporal distribution of zooplankton communities in a large floodplain river (Mississippi River, USA). Potential mechanisms controlling zooplankton abundance and community structure were considered. Main channel and backwater habitats included in this study differed between a turbid upper pool reach where aquatic macrophytes were sparse and a lower pool reach which was considerably less turbid and had extensive aquatic macrophyte coverage. Samples were collected monthly during the summer over a 2-year period and multivariate analysis was used to examine the spatial and temporal distribution of zooplankton. Significant differences were found in zooplankton density and community composition among habitats and reaches within the pool. Rotifers were the dominant taxa and seasonality was pronounced, with peak densities often occurring in late-spring. Community structure varied by habitat and reach, which suggests that water quality, physical habitat characteristics, presence of aquatic macrophytes, and zooplankton sources can all influence the zooplankton communities of the Upper Mississippi River. Characterization of the zooplankton communities provides a basis for understanding changes in the river ecosystem and examination of zooplankton communities among habitats provides insight into the mechanisms affecting zooplankton dynamics.     

Influence of glacial melt and Atlantic water on bacterioplankton community of Kongsfjorden,an Arctic fjord

The Kongsfjorden, an Arctic fjord is experiencing warming due to increased input of Atlantic water masses. High-throughput sequencing was performed to examine bacterial diversity from the outer and inner zone of the fjord in summer and fall of 2012. A total of 11,999 operational taxonomic units (OTUs) were assigned into 19 known phyla and 5 genera incertae sedis. Significant variation (p = 0.001, n = 4) was observed between the bacterial community structure of outer and inner fjord while variation between summer and fall was minimum. Proteobacteria was the most abundant phylum (55.9-61.0%) in summer and fall. The most dominant alphaproteobacterial member of this phylum (OTU 263 Pelagibacteriaceae) contributed maximum to the observed dissimilarity between the outer and inner fjord community. Characterised by relatively fresher and warmer water, glacial meltwater input could be a major source of predominance of OTU 6968 Flavobacteriaceae, OTU 5552 Psychrobacter, OTU 7148 Sphingomonadales and OTU 5011 Loktanella in the inner fjord in summer. Thus, the significant variation in the bacterioplankton community composition of outer and inner fjord indicates strong and localized influence of glacial melt water in shaping the community structure.     

Strategies of zooplanktivory shape the dynamics and diversity of littoral plankton communities: a mesocosm approach

Planktivorous fish can exert strong top‐down control on zooplankton communities. By incorporating different feeding strategies, from selective particulate feeding to cruising filter feeding, fish species target distinct prey. In this study, we investigated the effects of two species with different feeding strategies, the three‐spined stickleback (Gasterosteus aculeatus (L.)) and roach (Rutilus rutilus (L.)), on a low‐diversity brackish water zooplankton community using a 16‐day mesocosm experiment. The experiment was conducted on a small‐bodied spring zooplankton community in high‐nutrient conditions, as well as a large‐bodied summer community in low‐nutrient conditions. Effects were highly dependent on the initial zooplankton community structure and hence seasonal variation. In a small‐bodied community with high predation pressure and no dispersal or migration, the selective particulate‐feeding stickleback depleted the zooplankton community and decreased its diversity more radically than the cruising filter‐feeding roach. Cladocerans rather than copepods were efficiently removed by predation, and their removal caused altered patterns in rotifer abundance. In a large‐bodied summer community with initial high taxonomic and functional diversity, predation pressure was lower and resource availability was high for omnivorous crustaceans preying on other zooplankton. In this community, predation maintained diversity, regardless of predator species. During both experimental periods, predation influenced the competitive relationship between the dominant calanoid copepods, and altered species composition and size structure of the zooplankton community. Changes also occurred to an extent at the level of nontarget prey, such as microzooplankton and rotifers, emphasizing the importance of subtle predation effects. We discuss our results in the context of the adaptive foraging mechanism and relate them to the natural littoral community.     

Glaciers caused zooplankton mortality?

Dead zooplankton were found in grab samples collected in Kongsfjorden(79N, Svalbard archipelago) in summer of 1995 and 1996. Theconcentration of dead plankters reached over 500 individualsof copepods and 130 individuals of Themicto per square metre.The biomass of dead zooplank ton reached 0.17 g C m^–2locally, and was not correlated with the depth of the locality,nor with the surface salinity. The bulk of sedimented planktonwas, however, found behind the sill of the inner fjord basin.We assume that massive discharge of glacial waters in summercauses mass mortality of surface zooplankton, which drift awayand sink in the innerfjord pool, thus supplying benthic communitieswith organic carbon.