Effect of zinc sulphate on the growth of mono- and multispecies cultures of some marine plankton algae

The effect of zinc sulphate has been investigated in mono- and multispecies cultures of the dinoflagellatesScrippsiella faeroense, Prorocentrum micans andGymnodinium splendens and of the diatomsSchroederella schroederi andThalassiosira rotula. Multiplication rate, in vivo chlorophyll fluorescence, maximum cell densities and Zn-conditioned disturbance of the species equilibrium of the multispecies cultures were used as criteria of sublethal toxic inhibition. In monocultures, the first effect became manifest after addition of 0.01 to 0.1 mg Zn⁺⁺ · l^–1. Diatoms proved to be more sensitive than dinoflagellates. In multispecies cultures, the growth of each species depended on the ratio of the inocula. Interrelation between interspecific competition and Zn-caused decrease in the number of algal cells regulated further growth of the cultures. Algal sensitivity to zinc increased with the number of species combined in the test medium: in a 5-species culture sublethal changes appeared already after addition of 0.005 to 0.01 mg Zn⁺⁺ · l^–1. In a few cases, interspecific competition depressed the growth of some species to an appreciable extent, even in the control cultures. At the resulting low cell numbers, the effect of zinc became apparent only in higher concentrations from 5 to 10 mg Zn⁺⁺ · l^–1. Morphological aberrations became manifest inScrippsiella faeroense and in the diatoms in concentrations from 1 and 0.01 mg Zn⁺⁺ · l^–1 respectively. The results show that multispecies experiments are a more sensitive test method for investigating the influence of zinc on plankton algae than are monoculture experiments. In natural plankton communities, however, the toxicity of heavy metals may become effective at considerably lower limit concentrations; this is suggested by the simplified model investigations in the laboratory.     

Statistical mechanics of relative species abundance

Statistical mechanics of relative species abundance (RSA) patterns in biological networks is presented. The theory is based on multispecies replicator dynamics equivalent to the Lotka–Volterra equation, with diverse interspecies interactions. Various RSA patterns observed in nature are derived from a single parameter related to productivity or maturity of a community. The abundance distribution is formed like a widely observed left-skewed lognormal distribution. It is also found that the “canonical hypothesis” is supported in some parameter region where the typical RSA patterns are observed. As the model has a general form, the result can be applied to similar patterns in other complex biological networks, e.g. gene expression.     

Seasonal cycle of the microbial plankton in Crooked Lake,Antarctica

Summary Changes in the abundance of the components of the microbial plankton between July 1990 and March 1991 in Crooked Lake, one of the largest and deepest freshwater lakes in Antarctica, are described. Chlorophyll a concentration is low (0.2–0.4g·1^–1) and there is no discernable spring increase. The phytoplankton is largely dominated by flagellates. Bacterioplankton exhibits a seasonal pattern of abundance ranging from 1.0 × 10⁸·1^–1 in July to 3.25 × 10⁸·1^–1 in September. Changes in bacterial abundance probably relate to temperature and grazing by heterotrophic and mixotrophic flagellates. Total flagellated protozoan concentrations ranged between 25–136 × 10²·l^–1. Autotrophic and heterotrophic flagellate abundances were coupled and peaks in their abundance oscillated with peaks in bacterioplankton concentration. Four species of ciliated protozoa, dominated by oligotrichs, particularly the plastidic Strombidium, inhabit the lake. The plankton is characterised by the presence of floes which act as loci for bacteria, flagellates and amoebae and feeding sites for the ciliates and the two sparce metazoan components of the plankton. Crooked Lake is extremely oligotrophic but nonetheless supports a plankton community with a low species diversity and simple trophodynamics.     

Structure and dynamics of zooplankton communities,Alligator Rivers Region,N.T., Australia

Biological monitoring in the Alligator Rivers region, northern Australia, provides baseline ecological information to assess the impact of uranium mining and milling and settlement in the area. Spatial and temporal variations 1978–1980 in zooplankton communities of the Magela Creek, a tributary of the East Alligator River, are described. Extremely diverse plankton assemblages occur late in the wet season (Dec.–May), with up to 80 taxa of rotifers and microcrustacea in some billabongs (= ox-bows), while there is a decrease in diversity but increase in population density as the dry season progresses. Natural fluctuations in water quality may be extreme, and limiting to plankters common elsewhere in the tropics. The plankton is composed largely of littoral or epiphytic taxa, with endemic species in all groups.     

Interannual Dynamics of the Trophic Structure of Zooplankton of the Southern Kuril Region

Based on the data on feeding ecology of common species of zooplankton, the main trophic groups of plankton of the southern Kuril region are identified. These are phytophages, zoophages, and omnivores. The interannual dynamics of trophic characteristics of the plankton community are examined. Predatory plankton significantly dominated in 1992–1994; however, in 1995–1996 its biomass decreased markedly. The biomass dynamics of predatory and nonpredatory zooplankton, as well as changes in the structure of nonpredatory zoolankton, suggest structural changes in the planktonic community.     

The microbial plankton of freshwater lakes in the Vestfold Hills,Antarctica

Summary The plankton of twelve freshwater and slightly saline lakes in the Vestfold Hills, Antarctica was sampled in February 1991. All of the lakes are oligotrophic. The chlorophyll a concentrations in the lakes ranged from 0.10–2.69 g · 1^–1. The majority of the phytoplankton were flagellates or picoplanktonic cyanobacteria with the species composition varying between the lakes. Cyanobacteria were found in five of the lakes. Five to 6 species of ciliated protozoa occurred, among them oligotrichs, including the mixotrophic species Strombidium viride. The concentrations of protists and bacteria were an order to several orders of magnitude lower than reported from lower latitude oligotrophic lakes. Low species diversity and low numbers in the plankton characterise these eastern Antarctica lakes which reflects their low nutrient status and isolation.     

春季长江口邻近外海网采浮游生物的生物量谱

对2005年春季黄海南部、东海北部近江口外海水域网采的浮游生物个体大小的粒径分布进行研究,确定各粒级大小的功能群组成,建立此季该调查水域网采浮游生物的生物量谱.样品是用小、中、大型浮游生物网(网孔径为77、160、 505μm)采集所得.三网具采集浮游生物个体大小粒径是连续的,其中浮游植物,其等效粒径(ESD)和含碳量范围分别为5～250μm、15pg～146ng;浮游动物,含碳量范围为115ng～7.5mg,ESD分别为120μm～5.8mm、200μm～2cm.所得网采浮游生物的标准生物量谱,总测区的斜率为-0.607±0.059、截距为19.45±0.46;各站位的生物量谱斜率为-0.889～-0.455、截距为12.866～16.863,两特征参数分布规律为南高北低,且具有显著的站位间差异.相关性分析表明截距和回归系数与粒级多样性有关.     

Copepod nauplii from the barrier reef of Belize

A study of areal distribution of the copepod nauplii near mangrove covered cays on the barrier reef of Belize was begun in the summer of 1989 and continued in the spring of 1990 with the collection of twenty samples from four locations. At distances in the order of 100 of meters to 1000 from the mangrove prop roots there were thousands of nauplii m^–3. In the samples from Twin Cays where the plankton tows were made 15 m from the prop roots or less the average was 387 nauplii m^–3. Copepod nauplii compose 60% of the metazoan plankton abundance in all of the samples. Harpacticoid nauplii were the largest single component of the plankton in every sample; they account for 42% to 76% of the copepod nauplii. Cyclopoid nauplii represent 13 to 40% and are second to the harpacticoid nauplii. Calanoid nauplii account for 2% to 23% of the copepod nauplii.     

Seasonal variability of lipophilic toxins during a Dinophysis acuta bloom in Western Iberia: Differences between picked cells and plankton concentrates

This work describes and compares the seasonal variability of toxin profiles and content, estimated by LC–MS analyses, in picked cell of Dinophysis acuta Ehrenberg, in plankton concentrates rich in this species, and in extracellular lipophilic toxins collected by adsorbent resins during weekly sampling in a Galician ría (Western Iberia) from October 2005 to January 2006. Picked cells of D. acuta—which exhibited a fairly stable OA:DTX2 ratio, close to 3:2, but a variable okadaates:PTX2 ratio—showed a 9-fold variation in cell toxin quota, which was partly related to cellular volume, with maximum values (19 pg cell⁻¹) observed during the exponential decline of the population. Large differences in toxin profiles and content were observed between picked cells and plankton concentrates (up to 73 pg cell⁻¹ in the latter), that were most conspicuous after the bloom decline. The toxin profile of picked cells was more similar to that observed in the adsorbent resins than to the profiles of plankton concentrates. Their continued detection several weeks after the disappearance of Dinophysis spp. indicates that these toxins may take a long time to be degraded. It is concluded that analyses of picked-cells are essential to determine the contribution of each species of Dinophysis to a toxic outbreak. Estimates of cellular toxin content from plankton concentrates can lead to considerable overestimates after Dinophysis blooms decay due to extracellular toxins that persist in the water column, possibly bound to organic aggregates and detritus, and are retained (>0.22 μm) in the filters.     

Phytoplankton community response to reservoir aging, 1968–92

The effects of reservoir aging on the phytoplankton community of amidwestern U.S. reservoir constructed in 1965 (Pawnee Reservoir) werestudied by comparing algal biovolume and species composition from April 1992through November 1992 to surveys conducted in 1968–73 and 1990. Meansummer total phosphorus, nitrate-nitrogen, Secchi disk depth, totalsuspended solids, chlorophyll a, and phytoplankton species composition datacharacterized Pawnee Reservoir during 1968–69 as a high nutrient,relatively clear water environment. Phytoplankton biomass was relativelylow, consisting mainly of cyanophytes and non-flagellated chlorophytes.During 1970–73, water clarity was poor, total suspended solids werehigh, and total phosphorus was lower, but was still greater than 100 µgl^–1. The 1970–73 phytoplankton biomass was high and wasdominated by cyanophytes. Mean summer total phosphorus remained >100µg l^–1, water clarity remained poor, but phytoplanktonbiomass decreased significantly during 1990–92. The dramatic drop inchlorophyll a and low mean volatile suspended solids indicated thatinorganic suspended sediments, rather than phytoplankton, accounted for themajority of the turbidity in 1990-92. In addition to lower phytoplanktonbiomass, community composition shifted away from buoyancy-regulatingcyanophytes toward flagellated chlorophytes. These data suggest that asreservoirs located in agricultural watersheds age, (1) inorganic suspendedsediments have a significant effect on the light environment as well asphytoplankton biomass and species composition, (2) the control ofphytoplankton biomass and species composition shifts away from nutrients tolight and suspended sediments, and (3) there is a 1–2 year lag in theresponse of phytoplankton biomass to maximum nutrient loading during thetrophic upsurge period. Thus, sedimentation has been shown to be a primarydeterminant of plankton and benthic macroinvertebrate community compositionas Pawnee Reservoir aged.     

Finding of the Hydromedusa Hydractinia minima (Trinci, 1903) (Cnidaria: Hydrozoa: Hydractiniidae) in Peter the Great Bay, Sea of Japan

The first finding of the hydromedusa Hydractinia minima (Trinci, 1903) in plankton of Peter the Great Bay (Sea of Japan) is reported. The hydromedusae are 0.24–0.51 mm in bell diameter and 0.25–0.53 mm in height. The size characteristics of the nematocysts of this species (desmonemes and microbasic euryteles) are given. H. minima is present in the plankton of Peter the Great Bay from June through October at water temperatures of 16.4 to 22°C with the highest mean monthly density of 151 ind./m³. The finding of H. minima in Peter the Great Bay extends the area of this species in the North Pacific to the low-boreal subzone.Original Russian Text Copyright © 2005 by Biologiya Morya, Chaplygina, Dautova.     

How to calculate the optimal density of food for fish larvae

Synopsis The optimal density of plankton required for the growth and development ofCoregonus lavaretus (L.) larvae is calculated on the basis of the volume of water searched, the probability of successful feeding responses, and the results of experimental growth studies. This amounts to 200–260 individual food organisms 1^–1 (individual plankton 0.004 mg), or 14–17 individuals 1^–1 (individual plankton 0.057 mg). The feeding optimum depends on water temperature and the time at which feeding begins.     

Effects of mineral turbidity on freshwater plankton communities: Three exploratory tank experiments of factorial design

We conducted three exploratory experiments of factorial design on the effects of mineral turbidity in 18 large (7 000 1) fiberglass tanks containing plankton communities derived from Lake Texoma (Oklahoma-Texas), a large reservoir often subject to turbid inflows. Replicate plankton communities developed for 30–45 d in response to 4–9 treatments of planktivorous fish, dead fish, nutrient additions and artificial removal of zooplankton with plankton netting (or combinations of these manipulations). In one experiment we then added three concentrations of kaolin and in the other two experiments we added bentonite or powdered silica to the replicate tank communities. We measured the responses of the diverse plankton communities to the addition of mineral turbidity for an additional period of 30–45 d.Effects of introduced minerals (quality or concentration effects) and food web treatments after mineral addition (fish, nutrients, etc.) were determined by analysis of covariance after observations were adjusted for the value of each response variable at the time of mineral addition. Covariance analysis resulted in a statistical model explaining > 80% of the variance for most response variables. The values of response variables at the time of mineral addition were often the most important source of variation, suggesting the importance of biotic community resiliency to the effects of mineral turbidity. There were few effects of mineral particles on physical or chemical (temperature, conductivity, oxygen, pH), nutrient (nitrate, phosphate, alkalinity) or biotic (algal or zooplankton populations) components of the tank communities. Mineral effects were found for several measures of water clarity (Secchi depth, turbidity, and the concentration of small sestonic particles).     

Developing a statistical support system for environmental hazard evaluation

Estimating the hazard or risk to both human health and the environment has been based almost exclusively on single species toxicity tests low in environmental realism and without validation of their accuracy in more complex systems. While this may be quite appropriate for humans in a large variety of circumstances, there is no substantive body of direct experimental evidence indicating that precise predictions of harm from hazardous materials can be extrapolated from single species laboratory tests (or even multispecies laboratory tests) to the more complex highly variable natural systems. Now added to the hazardous chemical assessment problem is the accidental or deliberate release of genetically engineered microorganisms into the environment that have the additional capability of multiplying and expanding their numbers and also transferring genetic information to other organisms. This paper focuses entirely on hazard evaluation for organisms other than humans, namely predicting the potential risk or probability of harm to natural systems based on laboratory toxicity testing using single species. Not only will the basic risk assessment strategy itself be examined but also the question of determining the statistical reliability of various extrapolations from one level of biological organization to another. ‘For every complex problem, there is a simple, direct solution ... and it is invariably wrong!’ H. L. Mencken     

Rotifer distribution in relation to temperature and oxygen content

Lunzer Obersee, a small lake located at an altitude of 1100 m above sea level, was investigated from July 1985 to October 1987. The rotifer community consists of 7 dominant species, 7 subdominant species and 34 species which occasionally occurred in the plankton. The dominant species show rather different demands in relation to temperature and oxygen content; e.g.: Filinia hofmanni was found at a wide range of oxygen concentrations (0.6–13.3 mg O₂l^–1) and low temperatures (4–6 °O, living in the upper water layers (1–7 m) during spring and in the deeper, anoxic zone in summer. In contrast, Asplanchna priodonta was found at rather high oxygen contents (> 9 mg O₂ l^–1), ), and showed a wide range of temperature tolerance (4–15 °C).On the basis of field data the temperature and oxygen requirements of several species are described and discussed.     

Are single species toxicity tests alone adequate for estimating environmental hazard?

Most biologists agree that at each succeeding level of biological organization new properties appear that would not have been evident even by the most intense and careful examination of lower levels of organization. These levels might be crudely characterized as subcellular, cellular, organ, organism, population, multispecies, community, and ecosystem. The field of ecology developed because even the most meticulous study of single species could not accurately predict how several such species might interact competitively or in predator-prey interactions and the like. Moreover, interactions of biotic and abiotic materials at the level of organization called ecosystem are so complex that they could not be predicted from a detailed examination of isolated component parts. This preamble may seem platitudinous to most biologists who have heard this many times before. This makes it all the more remarkable that in the field of toxicity testing an assumption is made that responses at levels of biological organization above single species can be reliably predicted with single species toxicity tests. Unfortunately, this assumption is rarely explicitly stated and, therefore, often passes unchallenged. When the assumption is challenged, a response is that single species tests have been used for years and no adverse ecosystem or multispecies effects were noted. This could be because single species tests are overly protective when coupled with an enormous application factor or that such effects were simply not detected because there were no systematic, scientifically sound studies carried out to detect them. Probably both of these possibilities occur. However, the important factor is that no scientifically justifiable evidence exists to indicate that degree of reliability with which one may use single species tests to predict responses at higher levels of biological organization. One might speculate that the absence of such information is due to the paucity of reliable tests at higher levels of organization. This situation certainly exists but does not explain the lack of pressure to develop such tests. The most pressing need in the field of toxicity testing is not further perfection of single species tests, but rather the development of parallel tests at higher levels of organization. These need not be inordinately expensive, time consuming, or require any more skilled professionals than single species tests. Higher level tests merely require a different type of biological background. Theoretical ecologists have been notoriously reluctant to contribute to this effort, and, as a consequence, such tests must be developed by associations of professional biologists and other organizations with similar interests.     

Observations of seasonal changes in diatoms at inshore localities near Davis Station,East Antarctica

Seventy-five diatom taxa were identified from net plankton samples collected inshore during winter, spring and summer 1977–8 near Davis Station, East Antarctica. Species richness was found to be higher in winter than in summer; this is the first time this trend has been reported in antarctic coastal regions.When these taxa were grouped according to the general habitats in which they normally occur, the benthic assemblages dominated the planktonic ones.Of the plankton, most species were of oceanic origin in winter and late summer and are thought to have been swept inshore by a cyclonic gyre which is known to occur in summer but has not been studied in winter.     

An overview of the multispecies VPA — theory and applications

Summary Multispecies virtual population analysis is an attempt to take species interactions into account when assessing the status of fish stocks. It was introduced primarily with the aim of lowering the uncertainty in the natural mortality rate as used in single species VPA and to take account of variability between years and ages by calculating inside the model the part of the mortality rate caused by predation. The output of the MSVPA is therefore —in addition to stock sizes and fishing mortality rates as in single species VPA —the amounts consumed of the various species by the predators included in the analysis.The MSVPA model of the predation interactions results in a set of coupled non-linear equations which must be solved for each time step in the analysis. Key parameters in the model are the so-called suitability coefficients, measuring the relative suitability of one species as prey for another species. These parameters must be estimated inside the model and this estimation requires data on the stomach contents of the predators in the model. The MSVPA makes two key assumptions: constant ration size (i.e. independent of time for each species-age combination) and hence fixed weights-at-age and a model of prey selection which leads to a type ii functional feeding response. These assumptions do not hold for all areas and therefore limit the applicability of the MSVPA in its present form.The MSVPA is probably one of the more successful multispecies models in fisheries. Its main application to date has been to the North Sea, and although it has not been used directly as a management tool it has provided input values of parameters used in assessment models as well as valuable insights into the system. For example, it has demonstrated that an increase in mesh size can result in lower long-term yields, an effect opposite to what is predicted if species interactions are ignored. Such insights into the dynamics of the system are useful and MSVPA may therefore have an indirect role to play in management. Nevertheless, due to many uncertainties involved in multispecies modelling in general and MSVPA in particular, it seems doubtful that the use of MSVPA in fisheries management will be much greater in the immediate future than it is at present.     

Factors regulating summer phytoplankton in a highly eutrophic Antarctic lake

Lakes from Maritime Antarctica are regarded as systems generally inhabited by metazoan plankton capable of imposing a top-down control on the phytoplankton during short periods, while lakes from Continental Antarctica lacking these communities would be typically controlled by scarcity of nutrients, following a bottom-up model. Otero Lake is a highly eutrophic small lake located on the NW of the Antarctic Peninsula, which has no metazoan plankton. During summer 1996, we studied the density, composition and vertical distribution of the phytoplankton community of this lake with respect to various abiotic variables, yet our results demonstrated neither light nor nutrient limitation of the phytoplankton biomass. Densities of heterotrophic nanoflagellates (HNAN) and ciliates from three different size categories were also studied. Extremely low densities of HNAN (0–155 ind. ml^–1) could be due to feeding competition by bacterivore nanociliates and/or predation by large ciliates. A summer bloom of the phytoflagellate Chlamydomonas aff. celerrima Pascher reached densities tenfold those of previous years (158.10³ ind. ml^–1), though apparently curtailed by a strong peak of large ciliates (107 ind. ml^–1) which would heavily graze on PNAN (phototrophic nanoflagellates). Top-down control can thus occur in this lake during short periods of long hydrologic residence time.