Distributions and Biomass of Benthic Ciliates,Foraminifera and Amoeboid Protists in Marine,Brackish, and Freshwater Sediments

The quantitative importance of ciliates, foraminifers, and amoebae was investigated in marine, brackish, and freshwater sediments from 15 littoral stations. Total protozoan communities were usually dominated by ciliates in term of abundance, while amoebae often dominated in terms of biomass. Applying the biomass‐metabolic rate equation, ciliates, amoebae, and foraminifera were estimated to contribute 66% of the total abundance and 33% of the biomass, but up to 55% of the combined metabolic rate to the micro‐ and meiobenthos in the 15 sediments. Statistical analyses using ciliate data demonstrated: (1) species composition and community structures represented significant differences between freshwater and marine/brackish sediments, and subsequently between temperate and arctic sampling sites; (2) the occurrence of dominant ciliates and their allocation to feeding types indicated that herbivory was the most common feeding strategy in these sediments; (3) multivariate analyses showed all of the tested environmental factors (temperature, salinity, silt/clay, carbon, nitrogen, and chlorophyll a) to be important to varying degrees, but especially the combination of salinity, temperature, and silt/clay. Multiple factor effects or comprehensive influences might be important in regulating the distribution of protozoa in sediments. The importance of protozoa in sediment systems and the potential ecological significance of cysts are discussed.     

Contrasting dynamics of ciliate communities in sandy and silty sediments of an estuarine intertidal flat

During a 1-year study of the ciliate faunas of a silty and a sandy site on an intertidal flat in the Westerschelde estuary, a total number of 107 taxa were recorded belonging to at least 52 genera and 15 orders. Our results suggest that physical properties of the sediment were more important in regulating ciliate abundance, diversity and community composition than food availability, predation, temperature or oxygen concentration. Ciliate abundance and diversity were positively related to sediment grain size and the ciliate community of silty sediments was found to be a subset of that of sandy sediments. At the sandy site, where the sediment composition was stable, seasonal changes in the ciliate community were related to changes in food availability and/or temperature. At both the sandy and silty sites, a clear vertical gradient in the ciliate community was observed that appeared to be linked to gradients in food availability and oxygen concentration. These vertical gradients in ciliate community composition, however, were less steep than the measured oxygen gradients, probably due to the presence of oxic microniches in the anoxic zone.     

Zonation of intertidal macrobenthos in the estuaries of Schelde and Ems

Based on data, collected in 1980–1990, the intertidal benthic macrofauna of the Schelde and Ems estuaries was compared. The spatial occurrence of the benthic macrofauna along the salinity gradient, including the freshwater tidal area was emphasized. Both estuaries appeared to have a very similar species composition, especially at genus level. The higher number of species observed in the Schelde estuary was probably due to a greater habitat diversity. In both estuaries species diversity decreased with distance upstream. The total density did not vary along the estuarine gradient, whereas biomass is highest in the polyhaline zone.In both estuaries distinct intertidal benthic communities were observed along the salinity gradient: a marine community in the polyhaline zone, a brackish community in the mesohaline zone, and a third community in the oligohaline and freshwater tidal zones of the estuary. These three communities were very similar between both estuaries. Their main characteristics were discussed together with the occurrence and distribution of the dominant species.For the Schelde estuary and to a lesser extent also for the Ems estuary, there was evidence that anthropogenic stress had a negative effect on the intertidal macrobenthic communities of the oligohaline/freshwater tidal zone. Only Oligochaeta were dominating, whereas the very euryhaline and/or true limnetic species were missing. In the mesohaline zone, the Schelde estuary was dominated by large numbers of short-living, opportunistic species, whereas in the Ems estuary relatively more stable macrobenthic communities were observed. A comparison with some other European estuaries showed in general similar trends as those observed for the Schelde and Ems estuaries.     

Respiration rates in heterotrophic,free-living protozoa

Published estimates of protozoan respiratory rates are reviewed with the object of clarifying their value in ecological studies. The data show a surprisingly large variance when similarly sized cells or individual species are compared. This is attributed to the range of physiological states in the cells concerned. The concept of basal metabolism has little meaning in protozoa. During balanced growth, energy metabolism is nearly linearly proportional to the growth rate constant; at the initiation of starvation, metabolic rate rapidly declines. Motility requires an insignificant fraction of the energy budget of protozoans. For growing cells, metabolic rate is approximately proportional to weight^0.75 and the data fall nearly exactly on a curve extrapolated from that describing the respiration rates of poikilotherm metazoans as a function of body weight. It is conceivable that protozoan species exist with lower maximum potential growth and metabolic rates than those predicted from cell volume and the equations derived from the available data. However, the lack of information concerning the state of the cells studied prevents verification of this idea. Laboratory measurements of protozoan respiratory rates have no predictive value for protozoa in nature other than delimiting a potential range. For small protozoans, this range may, on an individual basis, represent a factor of 50.     

中国淡水原生动物多样性及其所受威胁

概述了地球上原生动物多样性现状,指出它在生物学界中的地位及其对人类的作用。从生态学概念出发,把淡水原生动物作为一个集合类群,对其多样性和所受威胁进行了讨论。以武汉东湖为例,讨论了半个世纪来由于人类活动的影响引起湖泊富营养化后,原生动物丰度增长了10倍,优势种出现替代现象,并有明显的小型化倾向。以长江三峡地区为例,分析了工业污染能损伤70％原生动物种类。原生动物多样性指数变化表明：在有机污染影响下作为饮用水的汉江其水质已达临界边缘。对待开发的西南武陵山地区生物资源考察中,用原生动物多样性现状阐明该地区水生态系的稳定性。     

Functional Groups in the Protozoa: Roles in Differing Ecosystems1,2

Feeding habits of freshwater protozoa were used to group species into functional, trophic groups. Community structure in differing ecosystems was examined in relation to the number of species occurring in the functional group categories. Six wetland ecosystems and a large river ecosystem were studied. Changes in community structure during the colonization of artificial substrates were also examined. Changes during colonization were studied in a mesotrophic lake, in low-order streams, and in laboratory microecosystems. In the latter case, the response of colonizing communities to a heavy metal toxicant was studied. All communities studied were dominated by bactivorous-detritivorous species and, to a lesser extent, by photosynthetic species. The chief functional role of substrate-associated protozoans appears to be the processing of dead organic matter and its associated bacterial flora. Functional groups utilizing resources other than detrital or mineral nutrients (saprotrophs, algivores, omnivores, and predators) were always minor community components. Colonizing communities were often dominated by photosynthetic species during early colonization stages but were again dominated by bactivorous-detritivorous species at species equilibrium. Low levels of toxicant (Cd) reduced numbers of both photosynthetic and bactivorous-detritivorous species. Higher toxicant levels virtually eliminated photosynthetic species and reduced bacterial detritivores by over one-half. Roles of protozoan species in ecosystems are closely tied to the processing of detritus and the recycling of mineral nutrients. Enumeration of individuals in functional categories is proposed as a simplified method for studying the abundance and activity of protozoa in ecosystems. Examination of changes in functional group composition and the relationship of functional group abundances to rates of carbon processing are suggested for studies of the importance of protozoa to the flow of energy and materials in ecosystems.     

The distribution of protozoa across a trophic gradient, factors controlling their abundance and importance in the plankton food web

The relative contribution of protozoan biomass to whole planktoniccommunities (phytoplankton, picophytoplankton, bactenoplankton,protozoa and zooplankton) and factors important in controllingprotozoan abundance were investigated at two eutrophic coastalsites and two meso-oligo trophic offshore sites in the centralbasin of Lake Erie, USA, from May through August in 1993 and1994. The abundance and biomass of heterotrophic nanoflagellates(HNAN) and ciliates (and also other plankton components) weresignificantly higher at the coastal sites than at the offshoresites. HNAN dominated numerically at all sites most of the time,but the biomass of phototrophic nano flagellates (PNAN) wasas high as that of HNAN, indicating that the average size ofPNAN was larger. Percent protozoan carbon content was alwayshigher at the offshore sites than the coastal sites, due torelatively lower phyto-and zooplankton biomass at the offshoresites. The percent contribution of heterotrophic protozoans(both HNAN and ciliates) also showed the same trend. Correlationsbetween protozoan abundance and other parameters were strongerat the offshore sites than the coastal sites. When correlatingdata over the coastal to offshore transect, both HNAN and ciliateabundances were significantly correlated with total phosphorus(TP) and the abundance of bacteria, nauplii and copepods. Theseresults suggest that both bottom-up and top-down factors maybe important in controlling protozoan abundance, and suggestthat protozoans are important as a carbon link in the microbialfood web of Lake Erie. ¹Present address: Ecosystem Restoration Department, South FloridaWater Management District, West Palm Beach, FL 33416-4680, USA     

Freshwater protozoa: biodiversity and ecological function

The purpose of this article is to pull together various elements from current knowledge regarding the natural history of free-living protozoa in fresh waters. We define their functional role, set the likely limits of biodiversity, and explore how the two may be related. Protozoa are unicellular, phagotrophic organisms, and 16 phyla of protists contain free-living freshwater protozoan species. They are the most important grazers of microbes in aquatic environments and the only grazers of any importance in anoxic habitats. In sediments, ciliates are usually the dominant protozoans. Benthic ciliate biomass accounts for slightly less than 10% of total benthic invertebrate biomass, but ciliate production may equal or even exceed invertebrate production. Freshwater protozoan species are probably ubiquitous, although many may persist locally for long periods in a cryptic state – as potential rather than active biodiversity. As protozoa are among the largest and most complex of micro-organisms, it follows that bacteria and all other smaller, more numerous microbes are also ubiquitous. The number of protozoan species recorded in local surveys (232) is about 10% of the estimated global species richness (2390). The 'seedbank of protozoan (and microbial) species ensures that local microbial diversity is never so impoverished that it cannot play its full part in ecosystem functions such as carbon fixation and nutrient cycling.     

Spatial variability in structural and functional aspects of macrofauna communities and their environmental parameters in the Jade Bay (Wadden Sea Lower Saxony, southern North Sea)

Spatial distribution and functional structure of intertidal benthic macrofauna in relation to environmental variables in the Jade Bay (southern North Sea) were studied and compared with other intertidal areas of the Wadden Sea. A total of 128 stations covering the whole Jade Bay were sampled in summer 2009. A total of 114 taxa were found. Highest species numbers occurred in the subtidal areas, whereas highest mean abundances were found in the upper intertidal areas. Based on species abundance data, six significantly distinct macrofauna communities in the Jade Bay were identified and evaluated with multivariate statistics, univariate correlations and canonical correspondence analysis. Differences in these community patterns were caused by the response of the dominant species (Hydrobia ulvae, Tubificoides benedii, Pygospio elegans, Caulleriella killariensis, Scoloplos armiger, Urothoe poseidonis, Microprotopus maculatus) to prevailing environmental conditions along the gradient from the lower and exposed sandy intertidal areas via intermediate mixed sediments to the upper mudflat areas. Distribution patterns in relation to tidal zonation were best explained by variability in submergence time, Chlorophyll a (chl a) content and sediment composition (mud content), which are proxies for hydrodynamic conditions and food availability. Species inventory and species richness were comparable with other intertidal areas of the Wadden Sea, but the Jade Bay differs from these areas regarding dominant species. Differences in sediment composition and morphological characteristics (macrotidal versus mesotidal Wadden Sea areas) are discussed for comparison of regional differences.     

Mesocosm experiments: mimicking seasonal developments of microbial variables in North Sea sediments

This study investigated the suitability of mesocosms for studying the seasonal development of microbial variables in the benthic system of the North Sea. Undisturbed sediment cores were taken from two locations in the North Sea, one with sandy sediment (28 m depth) and the other with silty sediment (38 m depth) and installed in mesocosms in January–April 1989. Cores were kept as in situ temperature in the dark until December 1989. One set of sandy and silty sediments was starved and the other set received a supply of organic matter in May–June, simulating the settlement of the spring bloom of Phaeocystis pouchetii. Seasonal developments in bacterial production (methyl ³H-thymidine incorporation), abundance and biomass of bacteria and nanoflagellates and oxygen consumption were compared between the mesocosms and the field in surface sediments every 1.5 to 2.5 months. Effects of seasonal temperature variations (range 6–17.5 °C) on microbial variables in starved mesocosms were limited, which possibly indicates a subordinate role of temperature in microbial processes in North Sea sediments. Organic matter produced a direct response in bacterial production and oxygen consumption in mesocosms. Bacterial and protozoan abundance also increased. The effect of the organic input disappeared within 2 months and values of enhanced variables declined to initial levels. The organic matter enrichment in mesocosms apparently did not provide sufficient energy to keep the microbenthos active at field levels through summer.These results suggest that in the silty sediments in the field, organic matter is available for bacterial production throughout summer. In sandy sediments, the major organic matter input, which sets the seasonal pattern, appears to be in June. Apparently the seasonal development of microbial variables can be mimicked in mesocosms with organic matter supplies. Differences between the field and mesocosms are further illustrated by carbon budgets. Recycling of bacterial biomass was required to meet the bacterial carbon demand in the budget.Publication No. 22 of the project Applied Scientific Research Neth. Inst. for Sea Res. (BEWON).     

Macrobenthic Distribution within the Sediment along an Estuarine Salinity Gradient

The distribution of the macrobenthic infaunal community within the upper 25 cm of the sediment was studied at 16 stations in the lower Chesapeake Bay. Stations were located from the tidal freshwater to the polyhaline zone of major tributaries (James, York and Rappahannock Rivers) and in the polyhaline portion of the lower bay mainstem. Profiles for total number of individuals, total ash-free dry weight biomass and species encountered with depth were calculated. Except for the deep dwelling bivalve, Macoma balthica, tributary macrobenthic communities had a shallow depth distribution compared to the mainstem sites which were found in generally coarser sediments in the higher salinity region of the estuary.     

Temporal and Spatial Abundance of Naked Amoebae (Gymnamoebae) in Marine Benthic Sediments of the Clyde Sea Area, Scotland

ABSTRACT. The abundances of benthic naked amoebae in the sediments of the Clyde Sea Area, Scotland, were studied throughout 1991. Four sites differing in sediment grain size and organic carbon content were chosen for study. Amoebae were enumerated by enrichment cultivation methods and found to be numerically important, attaining densities of up to 14,883 amoebae/cm³ on one occasion. They were most abundant, and temporally stable, in finer sediments where they averaged 2,224 cells/cm³ and lower and more variable in the sandy sediments, averaging 874 cells/cm³ throughout the year. In general, amoebae were most abundant in the surface sediment layers. Around 70 different morphotypes were recorded, and 61% of all amoebae counted were less than 10 μm in length. This is the first detailed quantitative study of benthic marine gymanamoebae and shows that naked amoebae and flagellates are numerically the dominant interstitial fauna in sediments of this area. Moreover, the gymnamoebae comprised the largest proportion of total protozoan biomass (excluding foraminiferans) and clearly need to be considered in future models of benthic carbon flow.     

Sulphate,dissolved organic carbon,nutrients and terminal metabolic products in deep pore waters of an intertidal flat

This study addresses deep pore water chemistry in a permeable intertidal sand flat at the NW German coast. Sulphate, dissolved organic carbon (DOC), nutrients, and several terminal metabolic products were studied down to 5 m sediment depth. By extending the depth domain to several meters, insights into the functioning of deep sandy tidal flats were gained. Despite the dynamic sedimentological conditions in the study area, the general depth profiles obtained in the relatively young intertidal flat sediments of some metres depth are comparable to those determined in deep marine surface sediments. Besides diffusion and lithology which control pore water profiles in most marine surface sediments, biogeochemical processes are influenced by advection in the studied permeable intertidal flat sediments. This is supported by the model setup in which advection has to be implemented to reproduce pore water profiles. Water exchange at the sediment surface and in deeper sediment layers converts these permeable intertidal sediments into a “bio-reactor” where organic matter is recycled, and nutrients and DOC are released. At tidal flat margins, a hydraulic gradient is generated, which leads to water flow towards the creekbank. Deep nutrient-rich pore waters escaping at tidal flat margins during low tide presumably form a source of nutrients for the overlying water column in the study area. Significant correlations between the inorganic products of terminal metabolism (NH₄ ⁺ and PO₄ ³⁻) and sulphate depletion suggest sulphate reduction to be the dominant pathway of anaerobic carbon remineralisation. Pore water concentrations of sulphate, ammonium, and phosphate were used to elucidate the composition of organic matter degraded in the sediment. Calculated C:N and C:P ratios were supported by model results.     

东海原甲藻（Prorocentrum donghaiensis）对原生动物群落结构影响的现场船基实验

2005年在长江口赤潮频发海域调查期间,分别于4月27日、5月4日和5月8日,在zzf1、zc18a和ra5站位利用现场船基培养的方法,研究了添加到赤潮密度106 cells L-1的东海原甲藻（Prorocentrum donghaiense）对原生动物群落结构的影响。结果发现,赤潮密度的东海原甲藻抑制了小型无壳纤毛虫的种群数量,而没有抑制中大型砂壳纤毛虫和夜光虫（Noctiluca scintillans）的种群数量,从而使得原生动物群落向中大型种类演替,这种影响的程度与原生动物本身的群落组成和浮游植物的组成密切相关。添加东海原甲藻72 h后,在以小型无壳纤毛虫管游虫（Cyrtostrombidium sp.）为优势种的zzf1站位,演替为以大型原生动物夜光虫为优势种的群落;在以中大型原生动物百乐拟铃虫（Tintinnospsis beroidea）和夜光虫为优势种的zc18a站位,仍然是以此为优势种,且大型原生动物夜光虫在群落中的比例上升;在以小型无壳纤毛虫急游虫2（Strombidium sp.2）为优势种的ra5站位,演替为以中大型原生动物百乐拟铃虫和亚速岛网纹虫（Favella azorica）为优势种的群落。zzf1和ra5站位实验组中原生动物的总丰度都呈下降趋势,而zc18a站位变化不明显,这是由于前两个站位的最优势种管游虫（zzf1站位）和急游虫2（ra5站位）的丰度迅速下降,而zc18a站位的优势种百乐拟铃虫和夜光虫的丰度比较稳定造成的。在zzf1和zc18a站位,对照组和实验组中原生动物的总生物量在实验前后都没有大的变化,而在ra5站位却均呈下降的趋势。这可能与浮游植物的组成有关,zzf1和zc18a站位是以无毒的锥状斯氏藻（Scrippsiella trochoidea）和螺旋环沟藻（Gyrodinium spirale）为主,而ra5站位是以有毒的亚历山大藻（Alexandrium sp.）为主。综上可见,可预测当东海大规模赤潮爆发时,会使原生动物群落向中大型种类演替,进而可能影响海洋生态系统的结构和功能。     

Morphological and compositional changes in a planktonic bacterial community in response to enhanced protozoan grazing

We analyzed changes in bacterioplankton morphology and composition during enhanced protozoan grazing by image analysis and fluorescent in situ hybridization with group-specific rRNA-targeted oligonucleotide probes. Enclosure experiments were conducted in a small, fishless freshwater pond which was dominated by the cladoceran Daphnia magna. The removal of metazooplankton enhanced protozoan grazing pressure and triggered a microbial succession from fast-growing small bacteria to larger grazing-resistant morphotypes. These were mainly different types of filamentous bacteria which correlated in biomass with the population development of heterotrophic nanoflagellates (HNF). Small bacterial rods and cocci, which showed increased proportion after removal of Daphnia and doubling times of 6 to 11 h, belonged nearly exclusively to the beta subdivision of the class Proteobacteria and the Cytophaga-Flavobacterium cluster. The majority of this newly produced bacterial biomass was rapidly consumed by HNF. In contrast, the proportion of bacteria belonging to the gamma and alpha subdivisions of the Proteobacteria increased throughout the experiment. The alpha subdivision consisted mainly of rods that were 3 to 6 microm in length, which probably exceeded the size range of bacteria edible by protozoa. Initially, these organisms accounted for less than 1% of total bacteria, but after 72 h they became the predominant group of the bacterial assemblage. Other types of grazing-resistant, filamentous bacteria were also found within the beta subdivision of Proteobacteria and the Cytophaga-Flavobacterium cluster. We conclude that the predation regimen is a major structuring force for the bacterial community composition in this system. Protozoan grazing resulted in shifts of the morphological as well as the taxonomic composition of the bacterial assemblage. Grazing-resistant filamentous bacteria can develop within different phylogenetic groups of bacteria, and formerly underepresented taxa might become a dominant group when protozoan predation is the major selective pressure.     

A Doubling of Microphytobenthos Biomass Coincides with a Tenfold Increase in Denitrifier and Total Bacterial Abundances in Intertidal Sediments of a Temperate Estuary

Surface sediments are important systems for the removal of anthropogenically derived inorganic nitrogen in estuaries. They are often characterized by the presence of a microphytobenthos (MPB) biofilm, which can impact bacterial communities in underlying sediments for example by secretion of extracellular polymeric substances (EPS) and competition for nutrients (including nitrogen). Pyrosequencing and qPCR was performed on two intertidal surface sediments of the Westerschelde estuary characterized by a two-fold difference in MPB biomass but no difference in MPB composition. Doubling of MPB biomass was accompanied by a disproportionately (ten-fold) increase in total bacterial abundances while, unexpectedly, no difference in general community structure was observed, despite significantly lower bacterial richness and distinct community membership, mostly for non-abundant taxa. Denitrifier abundances corresponded likewise while community structure, both for nirS and nirK denitrifiers, remained unchanged, suggesting that competition with diatoms for nitrate is negligible at concentrations in the investigated sediments (appr. 1 mg/l NO₃^-). This study indicates that MPB biomass increase has a general, significantly positive effect on total bacterial and denitrifier abundances, with stimulation or inhibition of specific bacterial groups that however do not result in a re-structured community.     

The temporal variation of intertidal nematodes in the Westerschelde I. The importance of an estuarine gradient

Biannual meiobenthic sampling (Spring and Autumn) was carried out in 1983–1989 at two fine sandy intertidal stations in the Westerschelde estuary. Both stations are exposed daily for more than one hour and are situated in the polyhaline and the mesohaline zone of the estuary. Average density data of non-selective deposit-feeders > predators > epigrowth-feeders > selective deposit-feeders for both stations are presented in spite of different nematode species composition. No difference between Spring and Autumn nor trend over 7 years could be detected. Higher total nematode densities are found at the polyhaline station (average 3200 ind. 10 cm^?2) in comparison with the mesohaline station (average 2300 ind. 10 cm^?2), a difference mainly due to higher non-selective deposit-feeders and predators densities in the polyhaline station. Each year, heterogeneous variance is found for all feeding types at the mesohaline station, but only for epigrowth-feeders and predators at the polyhaline station. The higher nematode density at the polyhaline station is probably caused by the more stable nematode structure. An unstable nematode temporal pattern at the mesohaline station is suggested to be combined with the detritus food chain system in the mesohaline zone. The unstable estuarine habitats are mainly caused by their upstream effects: the River Schelde, which clearly influences the stability of the nematode communities.     

Factors structuring the heterotrophic flagellate and ciliate community along a brackish water primary production gradient

A seasonal study of dominant protozoa, heterotrophic flagellatesand ciliates, was performed along a primary production gradientin the northern Baltic Sea. The abundances of protozoa increasedwith increasing primary production from north to south. Smallcells dominated in the low productive north, while larger cellsbecame more dominant in the south. The highest biovolume concentrationof protozoa was observed in summer in the north and during springin the south. The seasonal succession of protozoa followed ageneral pattern: choanoflagellates, large flagellates and ciliatesshowed peaks during spring and autumn, while small bacterivorousnanoflagellates peaked during the summer. An in situ experimentindicated that the inverse relationship between loricated choanoflagellatesand other small flagellates may be explained by a seasonal changein the predator community and a seasonal change in the accessto surface-attachment sites. Principal component regressionanalyses including all data showed that 46% of the variationof small flagellates and 20% of the variation of large flagellatescould be explained by temperature and bacterial biomass. Ciliatesshowed a significant relationship to latitude and salinity,explaining 12–24% of the variation. In conclusion, thefield data indicated that the protozoan community in generalwas resource controlled.     

东海原甲藻(Prorocentrum donghaiensis)对原生动物群落结构影响的现场船基实验

2005年在长江口赤潮频发海域调查期间,分别于4月27日、5月4日和5月8日,在zzf1、zc18a和ra5站位利用现场船基培养的方法,研究了添加到赤潮密度10^6cells L^-1的东海原甲藻（Prorocentrum donghaiense）对原生动物群落结构的影响。结果发现,赤潮密度的东海原甲藻抑制了小型无壳纤毛虫的种群数量,而没有抑制中大型砂壳纤毛虫和夜光虫（Noctiluca scintillans）的种群数量,从而使得原生动物群落向中大型种类演替,这种影响的程度与原生动物本身的群落组成和浮游植物的组成密切相关。添加东海原甲藻72h后,在以小型无壳纤毛虫管游虫（Cyrtostrombidium sp．）为优势种的zzf1站位,演替为以大型原生动物夜光虫为优势种的群落;在以中大型原生动物百乐拟铃虫（Tintinnospsis beroidea）和夜光虫为优势种的zc18a站位,仍然是以此为优势种,且大型原生动物夜光虫在群落中的比例上升;在以小型无壳纤毛虫急游虫2（Strombidium sp．2）为优势种的ra5站位,演替为以中大型原生动物百乐拟铃虫和亚速岛网纹虫（Favella azorica）为优势种的群落。zzf1和ra5站位实验组中原生动物的总丰度都呈下降趋势,而zc18a站位变化不明显,这是由于前两个站位的最优势种管游虫（zzf1站位）和急游虫2（ra5站位）的丰度迅速下降,而zc18a站位的优势种百乐拟铃虫和夜光虫的丰度比较稳定造成的。在zzf1和zc18a站位,对照组和实验组中原生动物的总生物量在实验前后都没有大的变化,而在ra5站位却均呈下降的趋势。这可能与浮游植物的组成有关,zzf1和zc18a站位是以无毒的锥状斯氏藻（Scrippsiella trochoidea）和螺旋环沟藻（Gyrodinium spirale）为主,而ra5站位是以有毒的亚历山大藻（Alexandriumsp．）为主。综上可见,可预测当东海大规模赤潮爆发时,会使原生动物群落向中大型种类演替,进而可能影响海洋生态系统的结构和功能。     

Protozooplankton in the Weddell Sea,Antarctica: Abundance and distribution in the ice-edge zone

Summary Protozooplankton were sampled in the iceedge zone of the Weddell Sea during the austral spring of 1983 and the austral autumn of 1986. Protozooplankton biomass was dominated by flagellates and ciliates. Other protozoa and micrometazoa contributed a relatively small fraction to the heterotrophic biomass. During both cruises protozoan biomass, chlorophyll a concentrations, phytoplankton production and bacterial biomass and production were low at ice covered stations. During the spring cruise, protozooplankton, phytoplankton, and bacterioplankton reached high concentrations in a welldeveloped ice edge bloom 100 km north of the receding ice edge. During the autumn cruise, the highest concentrations of biomass were in open water well-separated from the ice edge. Integrated protozoan biomass was <12% of the biomass of phytoplankton during the spring cruise and in the autumn the percentages at some stations were >20%. Bacterial biomass exceeded protozooplankton biomass at ice covered stations but in open water stations during the fall cruise, protozooplankton biomass reached twice that of bacteria in the upper 100m of the water column. The biomass of different protozoan groups was positively correlated with primary production, chlorophyll a concentrations and bacterial production and biomass, suggesting that the protozoan abundances were largely controlled by prey availability and productivity. Population grazing rates calculated from clearance rates in the literature indicated that protozooplankton were capable of consuming significant portions of the daily phyto- and bacterioplankton production.