Pesticide toxicity endpoints in aquatic ecosystems

To adequately protect aquatic ecosystems from impactby anthropogenic perturbations it is necessary todistinguish what is safe from what is not. Thisreview examines approaches to this problem in relationto primary and secondary effects of pesticides.Understanding nutrient – plankton and plankton –plankton interrelationships on both spatial andtemporal scales is important if secondary or indirecteffects are to be assessed. Before defining ormeasuring a toxicity endpoint, consideration must begiven to whether to use single species or multispeciestests. Each has its strengths and weaknesses and isreviewed. In single species testing, toxicityendpoints can be more clearly defined butextrapolation of effects to an ecosystem is moredifficult than with multispecies testing and can oftenlead to incorrect conclusions. Interpretation ofmultispecies testing results are challenging andnumerical analysis techniques including methods whoseobjectives are inference, classification andordination are required. Conceptual and fuzzy logicmodelling techniques promise a solution to theinterpretation of multispecies tests.     

Stomach content analyses of Simulium perflavum Roubaud 1906 (Diptera: Simuliidae) larvae from streams in Central Amazônia, Brazil

Stomach contents of Simulium perflavum Roubaud larvae were analyzed and compared with plankton and periphyton collected in five streams, in Central Amazonia (Manaus and Presidente Figueiredo counties), in Sep./Oct.1996 (dry season) and Feb./Mar. 1997 (rainy season). A total of 1,400 last-instar larvae were dissected; the stomach contents were analyzed using different methods: fresh and after oxidation. A total of 87 taxa (algae, diatoms and rotifers) were found in the stomach contents. In each stream, qualitative samples of plankton and periphyton were collected; these were mounted between slides and cover slips. A total of 94 taxa of plankton and 54 taxa of periphyton were collected. One species of Rotifera was present in the stomach contents, plankton and periphyton. Cluster analysis based on species composition of the organisms present in the stomach contents grouped the streams into two major groups, each belonging to a different drainage area. Correlations based on presence/absence of species of microalgae in the stomach contents, plankton and periphyton indicated significant associations (p<0.05) between stomach contents and plankton and between plankton and periphyton (z test); the Sorensen coefficient and cluster analysis corroborate the same associations.     

DNA metabarcoding reveals that 200‐μm‐size‐fractionated filtering is unable to discriminate between planktonic microbial and large eukaryotes

Microeukaryotic plankton (0.2–200 μm) are critical components of aquatic ecosystems and key players in global ecological processes. High‐throughput sequencing is currently revolutionizing their study on an unprecedented scale. However, it is currently unclear whether we can accurately, effectively and quantitatively depict the microeukaryotic plankton communities using traditional size‐fractionated filtering combined with molecular methods. To address this, we analysed the eukaryotic plankton communities both with, and without, prefiltering with a 200 μm pore‐size sieve –by using SSU rDNA‐based high‐throughput sequencing on 16 samples with three replicates in each sample from two subtropical reservoirs sampled from January to October in 2013. We found that ~25% reads were classified as metazoan in both size groups. The species richness, alpha and beta diversity of plankton community and relative abundance of reads in 99.2% eukaryotic OTUs showed no significant changes after prefiltering with a 200 μm pore‐size sieve. We further found that both >0.2 μm and 0.2–200 μm eukaryotic plankton communities, especially the abundant plankton subcommunities, exhibited very similar, and synchronous, spatiotemporal patterns and processes associated with almost identical environmental drivers. The lack of an effect on community structure from prefiltering suggests that environmental DNA from larger metazoa is introduced into the smaller size class. Therefore, size‐fractionated filtering with 200 μm is insufficient to discriminate between the eukaryotic plankton size groups in metabarcoding approaches. Our results also highlight the importance of sequencing depth, and strict quality filtering of reads, when designing studies to characterize microeukaryotic plankton communities.     

Interaction among Non-toxic Phytoplankton,Toxic Phytoplankton and Zooplankton: Inferences from Field Observations

We explore the mutual dependencies and interactions among different groups of species of the plankton population, based on an analysis of the long-term field observations carried out by our group in the North–West coast of the Bay of Bengal. The plankton community is structured into three groups of species, namely, non-toxic phytoplankton (NTP), toxic phytoplankton (TPP) and zooplankton. To find the pair-wise dependencies among the three groups of plankton, Pearson and partial correlation coefficients are calculated. To explore the simultaneous interaction among all the three groups, a time series analysis is performed. Following an Expectation Maximization (E-M) algorithm, those data points which are missing due to irregularities in sampling are estimated, and with the completed data set a Vector Auto-Regressive (VAR) model is analyzed. The overall analysis demonstrates that toxin-producing phytoplankton play two distinct roles: the inhibition on consumption of toxic substances reduces the abundance of zooplankton, and the toxic materials released by TPP significantly compensate for the competitive disadvantages among phytoplankton species. Our study suggests that the presence of TPP might be a possible cause for the generation of a complex interaction among the large number of phytoplankton and zooplankton species that might be responsible for the prolonged coexistence of the plankton species in a fluctuating biomass.     

Plankton Community Succession in Artificial Systems Subjected to Cyanobacterial Blooms Removal using Chitosan-Modified Soils

Using artificial systems to simulate natural lake environments with cyanobacterial blooms, we investigated plankton community succession by polymerase chain reaction–denaturing gradient gel electrophoresis (PCR-DGGE) fingerprinting and morphological method. With this approach, we explored potential ecological effects of a newly developed cyanobacterial blooms removal method using chitosan-modified soils. Results of PCR-DGGE and morphological identification showed that plankton communities in the four test systems were nearly identical at the beginning of the experiment. After applying the newly developed and standard removal methods, there was a shift in community composition, but neither chemical conditions nor plankton succession were significantly affected by the cyanobacteria removal process. The planted Vallisneria natans successfully recovered after cyanobacteria removal, whereas that in the box without removal process did not. Additionally, canonical correspondence analysis indicated that other than for zooplankton abundance, total phosphorus was the most important environmental predictor of planktonic composition. The present study and others suggest that dealing with cyanobacteria removal using chitosan-modified soils can play an important role in controlling cyanobacterial blooms in eutrophicated freshwater systems.     

Distribution of potentially pathogenic bacteria as free living and plankton associated in a marine coastal zone

AIMS: To determine the abundance of faecal and nonfaecal bacteria related to human and animal health, as free living or associated with small (>64 microm) and large (>200 microm) plankton, samples were collected monthly from the coastal zone at Messina (Italy). METHODS AND RESULTS: Different enrichment and selective cultural methods were used to determine the abundance of bacteria in sea water and plankton. The bacteria were more frequently isolated from water and large plankton than from small plankton. Vibrio and Aeromonas spp. showed different distribution patterns in water and plankton. Faecal indicators were always present in water and the large size class plankton samples. Enterococci associated with large plankton were more abundant than E. coli in the winter. Vibrio species distributions were different in water and plankton samples. Among arcobacters only A. butzleri was isolated from water and plankton samples. Campylobacter spp. was always absent in small plankton and more frequent in large plankton than in water. CONCLUSIONS: The colonization of zooplankton by potentially pathogenic bacteria is a widespread phenomenon. SIGNIFICANCE AND IMPACT OF THE STUDY: The presence of potentially pathogenic bacteria in sea water and associated with plankton can have ecological and epidemiological implications.     

Estimation of the biomass of plankton

Summary A mathematical function is demonstrated in the numbers of individuals of the various species in a planktonic biocoenosis. The logarithms of the numbers form a Gauss or normal probability curve. A similar probability relation is found in the volumes of the individuals of the various species as well as in the biomass of the various populations.This relationship in the numbers is caused by the effect of the numerous ecological factors influencing the rate of proliferation of the various plankton species. The cause of this relationship concerning the volumes of the various species is not understood. The relationship between the various biomasses is the mathematical product of number and mean volume.An approximate hyperbolic function can be derived from the population volumes and with the aid of a simple equation the plankton biomass is calculated. A modus operandi is given to abbreviate the work necessary to determine the plankton biomass with Lohmann's method. Only ten or twenty of the most dominant populations out of all species present in a plankton sample, have to be counted and measured.The biomasses of the populations in various plankton samples may easily be compared using the hyperbolic or the probability relationship.The biomasses of plankton in various habitats may easily be compared in a graphic way. The logarithms of the biomasses found during the year follow a probability curve and may be plotted and compared on a cumulative logarithmic probability graph.The number of organisms of each species to be counted depends on the degree of accuracy and has to be about a hundred. A chance determined spread is always found in plankton counts.The spatial distribution of most plankters shows a very broad spread. Therefore, sampling at ten places and working with the mean of the ten samples is compulsory.Some gregariously living zooplankters form bunches in the water. A reliable mean may be calculated using the hyperbolic function which seems to describe their densities at the various places.From the existing methods of collection of plankton the rotary, electric pump is chosen. A translucent hose with a special and moving mouth is let down into the water. First the water passes through the plankton-net and after that through the pump and the water-meter. A series of 7 samples of increasing decimal volumes is drawn in this way. From these samples the plankton is concentrated and fractionated by means of two sedimentation chambers, four small plankton sieves and three plankton nets. The sieves and nets have various standardized meshes.Square counting chambers of 10 cm² area are used. These chambers have a thin glass bottom and a broad rim. The sedimentation chambers and the small plankton sieves fit on and into the chambers thus minimizing the loss of organisms.The plankton organisms are enumerated by means of an inverted microscope projecting the image on a ground glass which makes counting easier. Only those organisms seen within a measured square on the ground glass are counted.By standardization of the sample volumes, the magnifications of the microscope and the dimensions of the squares the conversion factors are so simple that only zeros or a decimal point have to be placed in the number counted to obtain the result.International standardization of the method of estimation of the biomass of plankton and the expression of the results is proposed.     

Association of the gonyaulacoid dinoflagellate Alexandrium ostenfeldii with spirolide toxins in size-fractionated plankton

Spirolides are pharmacologically active macrocyclic imines discoveredin shellfish and plankton size-fractions collected from near-surfacewaters along the southeastern coast of Nova Scotia (NS), Canada.These compounds are most prevalent in the water column withinplankton size-fractions from 21 to 56 µm during late spring.Analysis of bulk plankton material by liquid chromatographycombined with ion-spray mass spectrometry indicated that gonyaulacoiddinoflagellates were domin-ant members of the plankton assemblagein these fractions when spirolides were abundant at Graves Shoal,NS, but that spirolides disappeared from the water column aftera shift to diatom dominance. Spirolide composition in the planktonwas rather consistent over time and among different sizefractionswithin a site, but the profile was radically different betweensites in Nova Scotia. At Ship Harbour, NS, spirolides A, B,C and desmethyl-C were the major constituents, whereas at GravesShoal, the primary spirolide derivatives were B, D and an isomerD2. Correlation analysis of spirolide abundance and the occurrenceof particular taxa in size-fractionated plankton showed thatthe highest correlations were with Alexandrium species (r² =0.93) and GB42 cells (r² = 0.83). These latter cells are nowrecognized as athecate forms of gonyaulacoid dinoflagellates,primarily of Alexandrium ostenfeldii. By analysis of size-fractionatedplankton and comparison with cultured plankton isolates fromspirolide-rich areas, we have substantiated the primary roleof A. ostenfeldii as the source of spirolides in the water column.     

三峡库区浮游生物群落DNA结构与水体理化因子的分析

本文对三峡水库大坝至香溪河段所设A、B、C、D、E、F和G等7个站点浮游生物群落DNA进行了RAPD分子生物学研究,并分析了其与水体理化因子的关系。各站点间RAPD研究表明：D和E首先聚到一组, 然后与A聚到一起, 最后与C聚成一大类;B和F聚成一大类;而站点G独自归于一类。而理化因子聚类结果显示：B首先与C聚为一小类,再与D聚到一起,然后与G、F聚成的小类聚为一类,而E与A分别单独归为一类。比较发现,RAPD聚类结果中相距较近的站点在理化因子聚类中显示为相距较远的站点（如站点A、C、D、E之间）,而在RAPD聚类中相距较远的站点在理化因子聚类中显示为相距较近的站点（如站点B、F分别与G之间）,这可能因为它们之间存在负相关性,也可能部分因为试验条件本身所造成的误差。为确定浮游生物DNA指纹结构与理化因子的关系提供了新的信息,进而为建立一种新的水质评价体系积累了理化因子的一些背景资料。     

Chaos and Peak-to-Peak Dynamics in a Plankton–Fish Model

A plankton–fish model, comprising phosphorus, algae, zooplankton, and young fish, with light intensity and water temperature varying periodically with the seasons, is analyzed in this paper. For realistic values of the parameters the model behaves chaotically, but its dynamics within the strange attractor can be described by a few one-dimensional maps that allow one to forecast the next yearly peak of plankton or fish from the last peaks. This property is an unambiguous mark of a special form of chaos. Unfortunately, the estimate of such peak-to-peak maps from field data is possible only if plankton or young fish biomass has been sampled accurately and frequently for a paramount number of years. In conclusion, the analysis shows that it might be that plankton dynamics are characterized by an interesting and peculiar form of chaos, but that inferences from recorded data on the existence of these forms of chaos are premature.     

Comparative metagenomics of bathypelagic plankton and bottom sediment from the Sea of Marmara

To extend comparative metagenomic analyses of the deep-sea, we produced metagenomic data by direct 454 pyrosequencing from bathypelagic plankton (1000 m depth) and bottom sediment of the Sea of Marmara, the gateway between the Eastern Mediterranean and the Black Seas. Data from small subunit ribosomal RNA (SSU rRNA) gene libraries and direct pyrosequencing of the same samples indicated that Gamma- and Alpha-proteobacteria, followed by Bacteroidetes, dominated the bacterial fraction in Marmara deep-sea plankton, whereas Planctomycetes, Delta- and Gamma-proteobacteria were the most abundant groups in high bacterial-diversity sediment. Group I Crenarchaeota/Thaumarchaeota dominated the archaeal plankton fraction, although group II and III Euryarchaeota were also present. Eukaryotes were highly diverse in SSU rRNA gene libraries, with group I (Duboscquellida) and II (Syndiniales) alveolates and Radiozoa dominating plankton, and Opisthokonta and Alveolates, sediment. However, eukaryotic sequences were scarce in pyrosequence data. Archaeal amo genes were abundant in plankton, suggesting that Marmara planktonic Thaumarchaeota are ammonia oxidizers. Genes involved in sulfate reduction, carbon monoxide oxidation, anammox and sulfatases were over-represented in sediment. Genome recruitment analyses showed that Alteromonas macleodii ‘surface ecotype'', Pelagibacter ubique and Nitrosopumilus maritimus were highly represented in 1000 m-deep plankton. A comparative analysis of Marmara metagenomes with ALOHA deep-sea and surface plankton, whale carcasses, Peru subsurface sediment and soil metagenomes clustered deep-sea Marmara plankton with deep-ALOHA plankton and whale carcasses, likely because of the suboxic conditions in the deep Marmara water column. The Marmara sediment clustered with the soil metagenome, highlighting the common ecological role of both types of microbial communities in the degradation of organic matter and the completion of biogeochemical cycles.     

Feeding and gut contents in Cephalodiscus nigrescens (Hemichordata, Pterobranchia) from the Weddell Sea

The gut of the pterobranch hemichordate Cephalodiscus nigrescens contains plankton of sizes from less than 1 μm to over 100 μm in diameter. Some of the smaller plankton are clumped together in spherical bolus that is mucus-bound. Most plankton types known from the habitat are respresnted amongst the gut contents.     

不同类型湖泊夏季浮游生物多元聚类分析

为深入了解湖泊环境生态系统的变化规律,为湖泊渔业和湖泊管理提供基础数据,于2007年夏季测定了武汉市梁子湖、斧头湖、柴泊湖、南湖和野芷湖5个养殖湖泊的浮游生物的数量和生物量。利用SPSS软件,对5个湖泊浮游植物6个门和浮游动物4个类的数量和生物量进行了主成分分析和因子分析。主成分分析和因子分析的结果是不相同的,其原因是两种方法的差异所致。两种方法结合使用,将有效地提高分析结果的准确度。分析结果表明,影响5个湖浮游生物的第1至第6个主成分分别为枝角类桡足类数量和重量因子、轮虫数量重量和绿藻门数量因子、隐藻门数量和重量因子、原生动物数量和重量因子、蓝藻门数量因子、硅藻门数量和绿藻门重量因子。使用SPSS软件,对5个湖泊13个点的浮游生物的数量和生物量予以了层次聚类法,并将5个湖泊的13个点分为5类,即梁子湖和斧头湖敞水区的3号和5号点为一类;梁子湖和斧头湖围拦养殖区的1号和4号点,以及梁子岛附近的2号点为一类;柴泊湖的6、7、8号3个点为一类;南湖原排污口附近的10号点为一类;南湖与野芷湖的其他9、11、12和13号4个点为一类。经分析认为,形成这个结果是由城市废水、生活污水和养殖生产所致。       

Scaling patterns of plankton diversity: a study of ciliates in a tropical coastal lagoon

Although spatial and temporal variation in plankton diversity is regularly investigated in surveys, experiments, and models, there is a lack of methods for predicting spatial patchiness of plankton diversity. We develop and apply a suite of geostatistical and multiple-regression analysis tools to assess ciliate diversity in a tropical coastal lagoon; these methods can predict spatial and temporal patterns of diversity, provide error estimates associated with these predictions, and assess which environmental factors may drive diversity patchiness. Geostatistical analysis was applied to H′ (Shannon diversity index) from 25 to 35 data collected from a sampling grid (40 × 40 m), and 10 dispersed lagoonal sites, in the dry and rainy seasons, on numerous occasions. Conditional simulation and kriging were used to predict diversity at the lagoonal and small scales, respectively. The relationship between diversity (H′) and the environment was examined by multiple-regression analysis. Thirty-six ciliate morphospecies occurred; H′ ranged from 0 to 1.9 and was patchy. Multiple regression indicated ciliate diversity changed seasonally, increasing when the sand bar was open and the lagoon was connected with the sea. Geostatistical analysis extended the recognition that seasonal changes alter diversity: when the rainy season produced a variable environment, relatively small scale patches and diversity gradients occurred; in the dry season, when the lagoon was physically uniform, larger and fewer diversity patches occurred; at the sublagoonal scale, diversity patches were similarly structured in the two seasons. Results indicate environmental variability and immigration can be the main drivers behind ciliate diversity in the lagoon. We recommend the patterns these data reveal and methods we employ be considered when further studies are continued to examine diversity on local and larger scales. Handling editor: S. Declerck     

Cultivation of seaweed Gracilaria lemaneiformis enhanced biodiversity in a eukaryotic plankton community as revealed via metagenomic analyses

Plankton diversity reflects the quality and health of waters and should be monitored as a critical feature of marine ecosystems. This study applied a pair of 28S rRNA gene‐specific primers and pyrosequencing to assess the effects of large‐scale cultivation of the seaweed Gracilaria lemaneiformis on the biodiversity of eukaryotic plankton community in the coastal water of Guangdong, China. With 1 million sequences (2,221 operational taxonomic units [OTUs]) obtained from 51 samples, we found that the biodiversity of eukaryotic plankton community was significantly higher in the seaweed cultivation area than that in the nearby control area as reflected in OTU richness, evenness (Shannon–Wiener index) and dominance (Simpson index) for total plankton community and its four subcategories when Gracilaria biomass reached the maximum, while no such a significant difference was observed before seaweed inoculation. Our laboratory experiment using an artificial phytoplankton community of nine species observed the same effects of Gracilaria exposure. Principal component analysis and principal coordinates analysis showed the plankton community structure in cultivation area markedly differed from the control area when Gracilaria biomass reached its maximum. Redundancy analysis showed that G. lemaneiformis was the critical factor in controlling the dynamics of eukaryotic plankton communities in the studied coastal ecosystem. Our results explicitly demonstrated G. lemaneiformis cultivation could enhance biodiversity of plankton community via allelopathy, which prevents one or several plankton species from blooming and consequently maintains a relatively higher biodiversity. Our study provided further support for using large‐scale G. lemaneiformis cultivation as an effective approach for improving costal ecosystem health.     

The biogeography of marine plankton traits

Changes in marine plankton communities driven by environmental variability impact the marine food web and global biogeochemical cycles of carbon and other elements. To predict and assess these community shifts and their consequences, ecologists are increasingly investigating how the functional traits of plankton determine their relative fitness along environmental and biological gradients. Laboratory, field and modelling studies are adopting this trait‐based approach to map the biogeography of plankton traits that underlies variations in plankton communities. Here, we review progress towards understanding the regulatory roles of several key plankton functional traits, including cell size, N₂‐fixation and mixotrophy among phytoplankton, and body size, ontogeny and feeding behaviour for zooplankton. The trait biogeographical approach sheds light on what structures plankton communities in the current ocean, as well as under climate change scenarios, and also allows for finer resolution of community function because community trait composition determines the rates of significant processes, including carbon export. Although understanding of trait biogeography is growing, uncertainties remain that stem, in part, from the paucity of observations describing plankton functional traits. Thus, in addition to recommending widespread adoption of the trait‐based approach, we advocate for enhanced collection, standardisation and dissemination of plankton functional trait data.     

鄱阳湖不同水文期浮游生物群落结构特征和影响因素及水质评价

为阐明鄱阳湖不同水文期浮游生物群落结构特征及其影响因素,研究于2017年8月(丰水期)和12月(枯水期)在鄱阳湖湖区典型水域设置5个采样点进行浮游生物采样调查。研究期间共鉴定浮游植物8门75属186种,丰水期与枯水期均以硅藻门和绿藻门为主。共鉴定浮游动物4类76种,丰水期与枯水期均以原生动物和轮虫为主。方差分析显示:浮游植物密度与生物量在不同水文期之间的差异均为极显著(P<0.01),浮游动物丰水期密度高于枯水期,但无显著差异(P>0.05),浮游动物生物量(P<0.05)在不同水文期差异显著。冗余分析(RDA)显示:丰水期透明度和浮游生物呈显著负相关关系,电导率和浮游生物呈显著正相关。透明度、电导率与营养盐是影响丰水期浮游生物群落结构的主要环境因素,枯水期水温和溶解氧是驱动鄱阳湖浮游生物群落生态分布的主要环境因素。基于Shannon-Wiener(H′)、Margalef(d)和Pielou(J)等生物多样性指数的水质评价结果表明:鄱阳湖研究区域水质状态处于寡污-中污之间。研究揭示了2个水文期对通江湖泊浮游生物的影响:季节变化不改变湖泊浮游生物的物种组成及优势种,但...     

Seasonal variation of gelatinous plankton consumption by fish in the South-western Atlantic Ocean: a question of strategy*

Gelatinous plankton is an important food resource for several species of fishes in the Southwestern Atlantic Ocean. Some fish depend heavily on these organisms and are specialized to feed on ctenophores, salps and medusae, while others only consume gelatinous plankton occasionally. We hypothesize that consumption of gelatinous plankton by fishes represents an alternative food resource when primary prey are not available during cold periods in the study area. To determine seasonal variations of gelatinous plankton consumption by fishes, data samples were grouped into cold and warm periods. A total of 64,567 stomachs belonging to 106 species of fish were analysed, of which 32,943 (51%) contained food items. Of those containing food items, 2719 (8.2%), from 38 fish species, contained gelatinous items. Fourteen species ingested gelatinous in warm period, nine in cold period, and 15 in both periods. The proportion of stomachs with gelatinous was significantly greater during the cold period. Ctenophores were the most predominant prey in both periods, followed by salps and medusae. Consumption of ctenophores, salps and medusae was unevenly distributed within the area during the different periods. Classification methods (group average sorting utilizing Bray–Curtis similarity measures based on log (X + 1) identified eight areas of consumption. SIMPER (similarity percentages) analyses revealed that nine fish species contributed most to gelatinous plankton consumption. The seasonal and spatial variation of gelatinous consumption by fish would be related to the availability of food in each period. Strategies of gelatinous consumption, including survival, feeding opportunities and prey specialization, are discussed.