安徽省石塘湖过去百余年湖水总磷浓度的定量重建

湖水总磷浓度对湖泊富营养化有很好的预警作用,历史湖水总磷浓度的定量重建能揭示湖泊营养演化历史.依据安徽省石塘湖沉积物钻孔的高分辨率硅藻研究结果,结合长江中下游湖泊硅藻-总磷转换函数模型,定量重建了其过去百余年来硅藻组合演替与历史湖水总磷浓度的变化过程.结果表明:石塘湖硅藻经历了从颗粒直链藻(Aulacoseira granulate)优势组合(1867-1981年)向富营养属种高山直链藻(Aulacoseira alpigae)优势组合(1981年以来)的变化.1981年以前,水体ρ(总磷)为50～60μg.L-1,湖泊一直维持在中等营养水平;1981年之后水体ρ(总磷)呈现明显升高趋势(＞100 μg·L-l),硅藻组合以高山直链藻占绝对优势,同时伴有喜好富营养环境的属种如极微小环藻(Cyclotella atomus)、梅尼小环藻(Cyclotella meneghiniana)、谷皮菱形藻(Nitzschia palea)和汉斯冠盘藻(Stephanodiscus hantzschii)等的增加,标志着湖泊富营养化的发生.20世纪80年代以来,农业及城市生活污水排放、农业化学肥料的大量使用以及过度养殖是硅藻种群转变和富营养化发生的主要根源.增温在一定程度上也影响着硅藻群落变化和富营养化的加重.根据重建的硅藻-水体总磷浓度结果,提出石塘湖治理的营养物基准水体ρ(总磷)为60 μg·L-1,为该湖整治和修复方案的制定提供可参考的目标,也为当地大量类似湖泊的治理提供重要参考.     

适于北江水质生物评价的附着硅藻指数研究

采用主成分、层次聚类、箱型图和双向指示种分析(TWINSPAN)等方法,研究了15项附着硅藻指数在北江流域的适用性。在北江流域25个监测点中,共鉴定出附着硅藻2目6科30属98个种和亚种,相对丰度为5%以上的硅藻属有曲壳藻属(Achnanthes)、菱形藻属(Nitzschia)、舟形藻属(Navicula)和直链藻属(Melosira),分别为34.4%、18.1%、8.6%和7.3%。相对丰度为5%以上的硅藻种有极小曲壳藻(Achnanthes minutissima),极小曲丝藻(Achnanthidium minutissimum),克劳斯菱形藻(Nitzschia clausii)和可变直链藻(Melosira varians)。附着硅藻指数间,罗特营养指数(Rott Trophic Index,ROTT)和洛博指数(Lobo Index,LOBO)与其他指数相关性较弱,硅藻生物指数(Biological Diatom Index,IBD)和富营养污染硅藻指数(Diatom Eutrophication Pollution Index,EPI-D)呈极显著相关(r=0.915,P0.01)。硅藻指数与水质指标的相关性分析表明,斯雷德切克指数(Sláde?ek Index,SLA)和LOBO与电导率(Cond)、溶解氧(DO)和总磷(TP)等10项水质指标间均无相关性,其他指数与某个或某几个水质指标有一定的相关性。对10项水质指标加权后进行层次聚类,结果表明阿图瓦-皮卡第硅藻指数(Artois-Picardy Diatom Index,IDAP)、特定污染敏感指数(Specific Polluosensitivity Index,IPS)、硅藻属指数(Generic Diatom Index,IDG)和IBD与水质分类结果较一致。利用TWINSPAN对样点和硅藻群落进行分类后绘制箱型图,结果表明,IBD对样点水质的变化最为敏感。结果表明,IBD是适合北江流域水质评价的硅藻指数。     

九寨沟风景区秋季水体硅藻的海拔梯度变化

九寨沟是著名的世界自然遗产地,水是九寨沟自然风景的灵魂,因而关于九寨沟湿地的研究极为重要.硅藻的生长和繁殖对环境极为敏感,长期作为湿地水质监测的指标.对四川几寨沟风景区内17处采样点水体中的硅藻进行了实地调查研究,经鉴定共发现113个分类单位,包括种和变种,隶属于2纲6目10科32属.脆杆藻属、舟形藻属、桥弯藻属和异极藻属常为优势属,只在长海是以小环藻属为单一优势属的群落.首次发现典型的富营养化指示种颗粒直链藻[Melosira granulata(Ehr.)Ralfs]和星形冠盘藻[Stephanodiscus astraea(Ehr.)Grun.]在旅游旺季出现,并在淡季消失,表明旅游对九寨沟核心景Ⅸ的湖泊产生了一定的影响,而其生态系统具有较强的自我调节功能.数量统计和相关分析结果表明,硅藻细胞密度受到环境因子的综合作用而表现出与海拔显著的正相关;反映多样性的Cairns连续比较指数(SCI)普遍较高(长海除外),与海拔显著负相关,与密度极显著负相关,可以都从种间竞争得到解释;SCI不一定反映了水体水质.图2表6参25     

漓江桂林市区段夏季浮游植物群落特征与水质评价

浮游植物是水生态系统的重要组成部分,其群落结构变化与水体环境条件密切相关,能直接影响水生态系统的功能,是水环境质量优劣的重要指示因子之一。为揭示漓江流域浮游植物群落结构特征及其与水质的相互关系,2012年8月对漓江桂林市区段干流（桂林赵家桥村至桂林王家村）的理化指标及浮游植物的群落组成分布进行了分析研究,并结合水体理化指标和生物指数对漓江水质进行了评价。结果表明,漓江水体高锰酸盐指数、总氮、总磷、氨氮的变化范围依次为1.80-6.20、1.12-2.68、0.022-0.282、0.34-1.73 mg·L-1,其含量在上游变化平稳,到三条支流汇入处大幅增高,最高值均出现在南溪河入口处。共调查到浮游植物7门60属128种,其中硅藻50种（占种类组成的39.06%）,绿藻52种（占40.63%）,蓝藻16种（占12.50%）,裸藻7种（占5.47%）,黄藻、金藻和甲藻各1种（分别占0.78%）。优势种依次为冠盘藻（S. tephanodiscus）、蛋白核小球藻（C. pyrenoidosa）、喙头舟形藻（N.rhynchocephala）、短小舟形藻（N.exigua）、广缘小环藻（C.Bodanica）、四尾栅藻（S.quadricanda）和肘状针杆藻（S. ulna）。浮游植物密度为10.3×10^4-1047.0×10^4ind.·L^-1,平均密度为474.7×10^4 ind.·L^-1,其中密度最小的是赵家桥村,密度最大的是南溪河入口;种类上绿藻门占据多数,密度和优势种分布上以硅藻居多,总体上属于硅藻-绿藻型水体。浮游植物多样性指数Shannon-Wiener指数（H）在1.60-4.27之间,Simpson指数（D）在2.24-12.74之间,水质总体上为清洁-轻度污染。Margalef指数（d）在1.85-4.23之间,Pielou指数（J）在0.40-0.83之间,指数值总体较高,漓江水体中浮游植物群落结构比较稳定,受外界环境的影响较小。漓江干流水质总体上属于Ⅱ-Ⅲ类水体,在支流汇入处理化指标浓度增加,浮游植物多样性指     

基于SOM的乌梁素海浮游植物群落结构研究

浮游植物能够产生氧气并为其他生物提供食物,维持其他生命的生存,进而保证水生态系统的平衡,在水生态系统中具有重大意义。为研究寒旱区乌梁素海浮游植物群落结构特征及其与环境因子的关系,运用自组织特征映射网络(SOM),并结合完全连接法,将乌梁素海浮游植物分为8个群落类型,分别为群落Ⅰ(蓝藻Cyanobacteria-绿藻Chlorophyta-硅藻型Bacillariophyta)、群落Ⅱ(蓝藻型)、群落Ⅲ(硅藻型)、群落Ⅳ(硅藻-绿藻型)、群落Ⅴ(硅藻-蓝藻型)、群落Ⅵ(绿藻-硅藻型)、群落Ⅶ(绿藻-硅藻型)、群落Ⅷ(绿藻-硅藻-蓝藻型)。分类结果显示,各群落结构的物种组成呈现明显特征,优势种的分布具有显著的规律性。利用Kruskal-Wallis方法分析群落类型间环境因子的差异性,结果显示,各群落类型的水深、水温、p H、总磷具有极显著性差异(P0.01),而透明度、总氮、电导率显著性差异不显著(P0.05)。通过对群落类型与其环境因子的分析,结合国内外浮游植物功能群及其生境的研究,发现优势属小环藻(Cyclotella)、舟形藻(Navicula)、衣藻(Chlamydomonas)适应低温、浅水及高营养盐的水域环境;栅藻(Scenedesmus)、绿球藻(Chlorococcum)、针杆藻(Synedra)适应总氮、总磷浓度均较高的水域环境;而平裂藻(Merismopedia)、色球藻(Chroococcus)适应高温、深水、总磷浓度较低的水域环境。温度是乌梁素海浮游植物群落结构组成的决定因子,而氮磷比可能是影响群落组成的又一重要环境因子。     

粤北2座饮用水源地水库的富营养化与浮游植物群落动态

粤北地区的水库以山地型水库为主,其中有不少担负着饮用水源的功能。为了解粤北地区水源地水库的富营养化状态与浮游植物种群的动态变化,于2011年的枯水期（2―3月）和丰水期（6―7月）对花山和白水礤2座中型水库进行了采样调查,对水库的营养盐和浮游植物种群进行了分析。结果表明：2座水库均为贫营养型;浮游植物在枯水期和丰水期的种类变化不大,共鉴定出的浮游植物6门37种（属）,以硅藻为主要优势种群,优势种为小环藻（Cyclotella sp.）和颗粒直链藻（Melosira granulata）。同时,枯水期和丰水期2座水库浮游植物的丰度和生物量都比较低,其值分别为0.65×106～1.95×106cells.L-1、0.11 mg.L-1和0.73×106～8.9×106cells.L-1、0.05～0.50 mg.L-1。在浮游植物种群动态中,2座水库浮游植物丰度和生物量的季节变化主要表现为硅藻丰度和生物量的变化,低浓度的氮、磷营养盐限制是影响这2座贫营养水库浮游植物动态变化主要因素。     

太子河着生藻类群落与氮、磷营养盐的定量关系研究

着生藻类是河流水生生物群落的重要组成部分,其与栖境水环境因子有着紧密的关联性。国内外关于着生藻类群落与栖息地环境因子关系的研究多是通过多元统计分析,评价影响着生藻类群落时空分布的环境要素,这种定性分析仅能判断环境驱动因子,而无法精确定量着生藻类群落与环境因子(如氮、磷)的响应关系。本研究以辽宁省太子河为范例,基于3次全流域的水生态调查所获得的141个站位的生态数据,运用临界指示物种分析法(TITAN)和加权平均回归分析(WA),定量评价着生藻类群落与河流水环境中氮、磷营养盐的定量响应关系(最适值和阈值)。结果表明,采用TITAN在太子河共确定了22种总氮(TN)指示物种,其中,13种为负响应物种,9种为正响应物种。TN负响应指示种中,普通等片藻(Diatoma vulgare)为出现频数较高的物种; TN正响应指示种中,小片菱形藻(Nitzschia frustulum)出现的频数最高。TITAN确定的太子河流域总磷(TP)指示物种为19种,其中,9种为负响应物种,10种为正响应物种。TP指示种中,负响应种近缘桥弯藻(Cymbella affinis)出现频数最高,TP指示种所对应的正响应突变点中,小片菱形藻和急尖舟形藻(Navicula cuspidata)出现频数最高。总体上看,太子河TN和TP对着生藻类最适值范围分别为0.025～0.47 mg·L~(-1)和0.65～12.14 mg·L~(-1),直链藻属(Melosira)和菱形藻属(Nitzschia)的种类,适宜栖息于TP较高的水环境中;异极藻属(Gomphonema)和桥弯藻属(Cymbella)适宜栖息于TP较低的水环境中;裸藻属(Euglena)和菱形藻属(Nitzschia)适宜栖息于TN较高的水环境中;而桥弯藻属和舟形藻属(Navicula)适宜栖息于TN较低的水环境中。通过定量分析水环境因子氮、磷对着生藻类群落的最适值和阈值,可以相对准确地评估着生藻类群落与河流营养盐含量的定量响应关系,对于在太子河开展对氮、磷等典型营养物的流域"污染物"排放的总量控制等流域生态管理决策和环境保护提供基础数据和科学依据。     

南亚热带高产渔业水库——显岗水库敞水区浮游植物群落结构的季节变化特征

显岗水库是当地重要的饮用水水源.于2008年对南亚热带高产渔业水库——显岗水库的水文、水质和浮游植物的调查,分析了该水库敞水区浮游植物群落的结构与变化特征及其影响因子.显岗水库敞水区的总氮和总磷浓度较高,平均浓度分别为0.83mgL-1和0.046mgL-1;叶绿素a浓度的变化范围为11.02～59.34μgL-1.共检出浮游植物129种(属),隶属7门,其中绿藻占优势,共78种,其次为蓝藻和硅藻,分别为25种和16种;丰水期的浮游植物种类数量较枯水期的高.浮游植物丰度和生物量变化范围分别为0.16×108～7.49×108cellsL-1和0.63～5.09mgL-1,分别在5月、2月出现极大值,10月均具有极小值;丰水期的丰度较枯水期的高,生物量则相反.浮游植物丰度主要由蓝藻贡献,生物量则主要由硅藻贡献.拟柱孢藻Cylindrospermopsis sp.、假鱼腥藻Pseudoanabeana sp.、湖丝藻Limnthriox sp.、微小隐球藻Aphanocapsa delicatissima、针晶蓝纤维藻Dactylococcopsis rhaphidioides是主要的丰度优势种,在全年具有绝对的数量优势.小环藻Cyclotella meneghiniana、肘状针杆藻Synedna ulna、颗粒直链藻Melosira granulata、根管藻Rhizosolenia longiseta、曲壳藻Achnanthes exigua、微小隐球藻、假鱼腥藻、针晶蓝纤维藻是主要或常见的生物量优势种.根据统计分析,总磷、透明度、入库流量和降雨量是影响显岗水库敞水区浮游植物变化的主要非生物环境因子.图2表3参26     

人工湿地中试系统基质中藻类组成的研究

从2003年3月到2004年2月，在水力负荷为600mm／d的条件下研究了人工湿地中试系统（medium scale plot，MSP）基质中藻类的组成．结果表明，栅藻、小球藻、盘星藻、空星藻、纤维藻、舟行藻、小环藻、平裂藻和颤藻属的一些种类在下行池基质各层不同季节均有出现，下行池表层藻类较丰；上行池基质中不同季节的藻类组成中念珠藻和鱼腥藻均为固氮种类，菱板藻、舟行藻和卵形藻属的一些种类在上行池表层出现较多，上行池藻类组成较下行池少．本实验探讨了在人工湿地基质中存在的藻类组成，为湿地除藻机理和评估系统的稳定性提供参考．图1表2参10     

上海某河口型景观湖冬季附着藻类的建群过程初探

为了解河口型水体附着藻类的建群过程,并获得群落成熟时间,于2015年冬季采用载玻片法对上海临港地区某景观湖进行研究。结果表明,附着藻类共检测出4门37属65种,其中硅藻门数量最多,占附着藻类数量的69.57%,其次为绿藻门,占25.95%。附着藻类总丰度在27 d时达到峰值,丰度为1.13×10~4～500×10~4 cm~(-2);硅藻丰度在25 d时出现峰值,丰度为1.13×10~4～299.05×10~4 cm~(-2)。聚类分析(CA)、非度量多维尺度分析(N-MDS)和相似性分析(ANOSIM)将附着藻类建群过程分为5个阶段,各阶段主要优势属分别为菱形藻属、针杆藻属和脆杆藻属,菱形藻属和针杆藻属,菱形藻属,菱形藻属和毛枝藻属,以及异极藻属和毛枝藻属。另外,通过分析藻类群落光合荧光参数动态变化发现,PSⅡ最大光能转换效率(F_v/F_m)变化与附着藻类总丰度变化趋势较一致,可作为指示附着藻类建群过程的潜在指标。挂片后3.5～4周,附着藻类群落发育逐渐成熟,此时段采样效果较佳。     

渭河浮游生物群落结构特征及其与环境因子的关系

渭河是黄河第一大支流,是黄河流域生态保护与高质量发展的重要研究区域.为了掌握渭河浮游生物组成结构及生态环境现状,于2018—2019年分两个季节在渭河开展4次水生态调查,研究分析了渭河浮游生物群落结构特征及其影响因子.调查结果显示,浮游植物有8门53种,以绿藻门和硅藻门为主,占比分别为43.4％、33.9％;浮游动物4...     

An Evaluation of Restoration Efforts in Fishless Lakes Stocked with Exotic Trout

Abstract: Detrimental effects of introduced fishes on native amphibian populations have prompted removal of introduced cutthroat ( Oncorhynchus clarki ), rainbow ( Oncorhynchus mykiss ), and brook trout (  Salvelinus fontinalis ) from naturally fishless lakes at Mt. Rainier National Park, Washington ( U.S.A.). Using paleolimnological indicators (diatoms, invertebrates, and sediment characteristics) in eight 480-year-old sediment cores from eight lakes, we (1) derived estimates of baseline environmental conditions and natural variation, (2) assessed the effects of stocking naturally fishless lakes, and (3) determined whether lakes returned to predisturbance conditions after fish removal (restoration). Diatom floras were relatively stable between 315 and 90 years before present in all lakes; we used this time period to define lake-specific "baseline" conditions. Dissimilarity analyses of diatoms revealed sustained, dramatic changes in diatom floras that occurred approximately 80 years ago (when fish were introduced) in four of five stocked lakes, whereas the diatom floras in two unstocked lakes had not changed significantly in the last 315 years. Diatoms were not preserved in an eighth lake. State changes also occurred in two lakes over 200 years before European settlement of the Pacific Northwest. Preserved invertebrate densities fluctuated dramatically over time in all cores, providing a poor reference for assessing the effects of fishes. Nevertheless, fish-invertebrate interactions have been demonstrated in other paleolimnological studies and may be useful for lower-elevation or more productive lakes. Because diatom communities have not returned to predisturbance assemblages in restored lakes, even 20–30 years after fish removal, we conclude that Mt. Rainier lakes were not successfully restored by the removal of fishes.     

Use of epilithic diatoms to evaluate water quality in the Karasu River of Turkey

Epilithic diatom assemblages were used to evaluate water quality in the Karasu River basin (Turkey), which was polluted by industrial, agricultural and urban wastes. A total of 73 diatom taxa belonging to 22 genera were found from all seven sampling stations located in the River basin. The most pollution tolerant species Gomphonema parvulum, Nitzchia palea, Navicula cryptocephala were found in high densities at the polluted stations. Organic load (COD), biological oxygen demand in 5 days (BOD5) and concentrations of nutrients NO3(-)-N, NO2(-)-N, NH4(+)-N and PO4(3-)-P) were correlated negatively with dissolved oxygen. Except for generic index of diatoms (GI), all diatom indices were correlated significantly with COD, BOD5 dissolved oxygen and concentrations of nutrients. Saprobity index (SI), trophic diatom index (TDI) and the percentage pollution tolerant valves values suggested that the stations III, IV located in the River basin were eutrophicated and organically polluted.     

甘河着生藻类群落结构及其与环境因子的关系

2018年8月(丰水期),在嫩江支流甘河,调查了19个点位的着生藻类群落结构和水环境特征。并运用聚类分析、Mcnaughton优势度分析和IBD(biological diatom index,硅藻生物指数)3种方法研究了甘河着生硅藻群落结构和优势种清洁状况,使用主成分分析、Spearman相关分析和冗余分析等统计分析方法研究了甘河着生硅藻群落和环境因子的响应关系。结果表明:甘河共鉴定出着生藻类90种(属),以硅藻门、绿藻门和蓝藻门为主,生物量丰富。丰水期甘河水生态环境质量状况较为健康,着生硅藻主要由清洁种构成,其中Achnanthidium minutissimum优势度0.48,为绝对优势种。聚类分析结果表明,甘河采样点位可分为3组;其中组1和组2点位主要位于甘河上、中游,上、中游水质、生境质量较好,健康程度较高,优势种均为清洁种,上游Achnanthidium minutissimum优势度达到了0.64;组3点位均位于甘河下游,下游人为干扰较强,健康程度较其余两组偏低,Nitzschia palea和Nitzschia paleaeformis等耐污种在组3的优势度较高。导致甘河着生硅藻群落清洁度由上游到下游逐渐变差的主要水环境因子为电导率、总磷和高锰酸盐指数,其中影响中游硅藻群落结构变化的主要水环境因子为高锰酸盐指数,影响下游硅藻群落结构变化的主要水环境因子为电导率和总磷。由此可见,着生硅藻群落可以较好的指示甘河流域水体有机污染程度和营养富集程度。     

Experiments on resuspension of natural microphytobenthos populations

Laboratory experiments on resuspension of benthic diatoms were performed in 1988 on intact cores of sediment obtained from two transects in the Ems estuary (Dutch Wadden Sea, NW Europe). Diatoms were most abundant in sediment from sheltered stations. In the experiments, which were performed in a small carousel system, the percentage of resuspended diatoms increased concomitantly with angular velocity of the agitating paddles. Maximum microphytobenthos resuspension in terms of cell numbers was up to 45% of the total population present in the 0.5-cm top layer, and up to 11% in terms of chlorophylla. Maximum sediment resuspension was 6%. The results show that the presence of a diatom film (numerous cells on the sediment surface) increases sediment stability, thereby suppressing resuspension of sediment and diatoms. However, if the sediment contains many fine particles and much detritus, sediment stability decreases, leading to increased resuspension.These results support the contention that low detritus content and large numbers stabilize the surface layer of tidal flats, whereas high detritus content and fewer cells (<2 × 10⁵ cm^–2) do not. The stabilization is thought to be dependent on a combination of differences in sediment consolidation and in bottom roughness caused by the presence or absence of diatom films.     

Quantitative evidence concerning the stabilization of sediments by marine benthic diatoms

Six species of benthic diatoms and a natural benthic diatom community were cultured in flasks on a variety of sediments. Diatom species which secreted large quantities of mucilage were effective sediment stabilizers. These mucilage-secreting species significantly reduced resuspension and retarded laminar flow of the sediments when the culture flasks were agitated. Diatom species which secreted little or no mucilage were not effective sediment stabilizers. These non-mucilage-secreting species did not significantly effect resuspension or laminar flow of the sediments when the culture flasks were agitated. A sediment stabilizing mechanism based on the secretion of mucilage by pennate benthic diatoms is proposed. The effect such a process may have on distributional patterns of benthic invertebrates in areas where extensive diatom or other microalgal films occur is discussed.This work was supported by the Belle W. Baruch Foundation, and is Contribution No. 68 of the Belle W. Baruch Institute for Marine Biology and Coastal Research.     

Responses of phytoplankton and periphytic diatoms to environmental factors in a tropical riverine reservoir北大核心CSCD

Riverine reservoirs have a short water retention time, which is ecologically more similar to that of rivers. Generally, phytoplankton-based approaches are used for lakes and periphytic diatom-based approach for rivers. To understand the differences in the responses of phytoplankton and periphytic diatoms to environmental variables for riverine reservoirs, we collected periphytic diatom samples on artificial substrata as well as phytoplankton samples from a tropical reservoir with a resident time less than 10 days. Our results showed that 131 phytoplankton species and 138 periphytic diatoms were detected; the variation of phytoplankton community was mainly reflected by the dominant species with a strong response to the environmental variables at a time scale, whereas the variation of periphytic diatom community was noted in both the species composition and the dominant species, with a strong response at spatial-temporal scales. The multivariate regression analysis and redundancy analysis showed that environmental factors have higher explanations for the variance of the periphytic diatom community (R2 = 0.27). Temperature was the key explanatory variable for phytoplankton, planktonic diatoms and periphytic diatoms (P < 0.01). However, dissolved oxygen and nitrate were also detected as significant explanatory factors associated with periphytic diatom community (P < 0.01). Thus, the periphytic diatoms were concluded to be more sensitive to environmental change and were associated with more environmental variables than phytoplankton. Periphytic diatoms appear to provide more ecological information than phytoplankton for riverine reservoirs. © 2018 Science Press. All rights reserved.     

Growth rates of summer nanoplankton (<10 μm) populations in lower Narragansett Bay,Rhode Island,USA

Growth rates of summer (June–September) phytoplankton assemblages and constituent species were measured in 30 diffusion culture experiments. Size-fractionated (<10 m) phytoplankton assemblages were incubated in situ or under simulated in-situ conditions in outdoor tanks connected to a running seawater system. Doubling rates of important species and groups (such as microflagellates) were compared to community biomass doubling rates estimated from ¹⁴C uptake and changes in chlorophyll a concentrations. Division rates of dominant diatom species generally equalled or exceeded community biomass doubling rates, while those of flagellates and non-motile ultraplankters were slower. Maximum division rates of sixteen common diatom species exceeded 2.1 divisions d^-1, while nine had maximum division rates in excess of 3 d^-1. Mean division rates of 12 diatom species exceeded 1 d^-1. Maximum division rates of flagellated species, uncharacterized microflagellates and non-motile ultraplankton assemblages were 2.1, 1.5 and 1.4 d^-1, respectively. Microflagellate and non-motile ultraplankton assemblage doubling rates were less than 0.5 d^-1 in over half of all growth experiments.