Labelling patterns of carbon-14 in net plankton during a winter-spring bloom

Weekly surface samples were collected in lower Narragansett Bay, Rhode Island, during the 1975 winter-spring bloom and fractionated by nets to nannoplankton (<20 μm) and total (< 158 μm) size fractions. Each size fraction was assayed for paniculate carbon, nitrogen, carbohydrate, protein, chlorophyll a, and cell counts. The <20 μm values were subtracted from the <158 μm values to estimate the composition of the 20 μm to 158 μm fraction (termed net plankton). As nutrients (primarily nitrogen) decreased to undetectable levels with the culmination of the diatom bloom, the ratios of protein/carbohydrate, carbohydrate/carbon, and carbon/chlorophyll a in the net plankton indicated the diatom population was increasingly nutrient-limited. Each size fraction was also incubated at a saturating light intensity with carbon-14; following filtration, the cells were extracted with solvents to obtain labelled polysaccharide and protein. The daily rates of polysaccharide and protein synthesis in the net plankton declined as the bloom entered the stationary phase. When the diatom population was at its maximum density the majority of the carbon-14 was found in the ethanol-soluble fraction; this may be due to high light intensities or nutrient effects.     

The size structure of plankton during a deep bloom in a stratified reservoir

In this paper we describe the main features of planktonic size structure in a stratified reservoir during a summer, deep bloom due to the dinoflagellate Ceratium hirundinella (O. F. Müller) Bergh. As one might expect from the eutrophic character of the ecosystem, the complete size-biomass spectrum is dominated by large phytoplankton and small zooplankton. The relation between numerical abundance (N, organisms per ml) and body size (V m³) for the overall size spectrum is described by the model log N = 7.25–0.99 log V (r ² = 0.93). However, the existence of tendencies in the points around the regression line suggest limiting linear scaling to the size range of unicells (log N = 6.34–0.51 log V, r ² = 0.85). The size structure shows the less negative slope at the level of the thermocline and when the bloom of C. hirundinella reaches its maximum. In the epilimnion, important taxonomic changes have no effect on the size structure, which appears to be a conservative character of the planktonic community at this level.     

Seasonal plankton dynamics along a cross-shelf gradient

Much interest has recently been devoted to reconstructing the dynamic structure of ecological systems on the basis of time-series data. Using 10 years of monthly data on phyto- and zooplankton abundance from the Bay of Biscay (coastal to shelf-break sites), we demonstrate that the interaction between these two plankton components is approximately linear, whereas the effects of environmental factors (nutrients, temperature, upwelling and photoperiod) on these two plankton population growth rates are nonlinear. With the inclusion of the environmental factors, the main observed seasonal and inter-annual dynamic patterns within the studied plankton assemblage also indicate the prevalence of bottom-up regulatory control.     

Evolution as a critical component of plankton dynamics

Microevolution is typically ignored as a factor directly affecting ongoing population dynamics. We show here that density-dependent natural selection has a direct and measurable effect on a planktonic predator-prey interaction. We kept populations of Brachionus calyciflorus, a monogonont rotifer that exhibits cyclical parthenogenesis, in continuous flow-through cultures (chemostats) for more than 900 days. Initially, females frequently produced male offspring, especially at high population densities. We observed rapid evolution, however, towards low propensity to reproduce sexually, and by 750 days, reproduction had become entirely asexual. There was strong selection favouring asexual reproduction because, under the turbulent chemostat regime, males were unable to mate with females, produced no offspring, and so had zero fitness. In replicated chemostat experiments we found that this evolutionary process directly influenced the population dynamics. We observed very specific but reproducible plankton dynamics which are explained well by a mathematical model that explicitly includes evolution. This model accounts for both asexual and sexual reproduction and treats the propensity to reproduce sexually as a quantitative trait under selection. We suggest that a similar amalgam of ecological and evolutionary mechanisms may drive the dynamics of rapidly reproducing organisms in the wild.     

The effects of abrupt topography on plankton dynamics

Plankton population dynamics in the upper layer of the ocean depends on upwelling processes that bring nutrients from deeper waters. In turn, these depend on the structure of the vertical velocity field. In coastal areas and in oceanic regions characterized by the presence of strong submarine topographic features, the variable bottom topography induces significant effects on vertical velocities and upwelling/downwelling patterns. As a consequence, large plankton and fish abundances are frequently observed above seamounts, canyons and steep continental shelves. In this work, the dynamics of an NPZ (nutrient-phytoplankton-zooplankton) system is numerically studied by coupling the ecosystem model with a quasi two-dimensional (2D) fluid model with topography. At variance with classical 2D approaches, this formulation allows for an explicit expression of the vertical motions produced when fluid columns are squeezed and stretched as they experience changes of depth. Thus, input or output of nutrients at the surface are associated with fluid motion over the bottom topography. We examine the dynamics of a cyclonic vortex over two basic topographies: a steep escarpment and a submarine mountain. We show that plankton abundance over the escarpment is modulated by the passing of topographic Rossby waves, generated by the vortex-topography interaction. In such configuration, advection effects driven by the flow over the escarpment are of limited relevance for the dynamics of biological fields. By contrast, we find that the flow resulting from the interaction of a vortex with a seamount is sufficiently strong and persistent to allow for a remarkable increase of nutrients, and a corresponding enhancement of phytoplankton and zooplankton concentrations. Over the seamount, advection effects associated with trapped flow perturbations around the summit play an essential role.     

春季和夏季巢湖浮游生物群落组成及其动态分析

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The effects of abrupt topography on plankton dynamics

Plankton population dynamics in the upper layer of the ocean depends on upwelling processes that bring nutrients from deeper waters. In turn, these depend on the structure of the vertical velocity field. In coastal areas and in oceanic regions characterized by the presence of strong submarine topographic features, the variable bottom topography induces significant effects on vertical velocities and upwelling/downwelling patterns. As a consequence, large plankton and fish abundances are frequently observed above seamounts, canyons and steep continental shelves. In this work, the dynamics of an NPZ (nutrient-phytoplankton-zooplankton) system is numerically studied by coupling the ecosystem model with a quasi two-dimensional (2D) fluid model with topography. At variance with classical 2D approaches, this formulation allows for an explicit expression of the vertical motions produced when fluid columns are squeezed and stretched as they experience changes of depth. Thus, input or output of nutrients at the surface are associated with fluid motion over the bottom topography. We examine the dynamics of a cyclonic vortex over two basic topographies: a steep escarpment and a submarine mountain. We show that plankton abundance over the escarpment is modulated by the passing of topographic Rossby waves, generated by the vortex-topography interaction. In such configuration, advection effects driven by the flow over the escarpment are of limited relevance for the dynamics of biological fields. By contrast, we find that the flow resulting from the interaction of a vortex with a seamount is sufficiently strong and persistent to allow for a remarkable increase of nutrients, and a corresponding enhancement of phytoplankton and zooplankton concentrations. Over the seamount, advection effects associated with trapped flow perturbations around the summit play an essential role.     

Specific growth rates of heterotrophic plankton organisms in a eutrophic lake during a spring bloom

The in situ growth of the dominating pelagic organisms at severaltrophic levels was investigated during a spring bloom characterizedby well-mixed cold water. The study includes primary productionand the carbon flow through the nano-, micro- and mesozooplanktonpopulations based on population dynamics and specific growthrates. The phytoplankton biomass and production were totallydominated by small algae <20 µm. of which {small tilde}5%were <3µm. potentially a food source for the nano-and microzooplankton. The mean carbon-specific primary productionwas 0.15 day^–1 and was regulated solely by light. Themean volume-based specific growth rate of bacterioplankton wasmodest. 0.1 day^–1. and probably controlled by the lowtemperature. The volume-based specific growth rates of heterotrophicnanoflagellates. ciliates. rotifers and copepods were 0.35.0.13. 0.16 and 0.03 day^–1, respectively. The observedgrowth of the heterotrophic plankton was generally not foodlimited, but was controlled by temperature. The stable temperatureduring the experiment therefore allows a cross-taxonomic comparisonof specific growth rates. The b exponent in the allometric relationship(G = aV^th) between volume-specific growth rate (G) and individualbody size (V) was –0.15 ± 0.03 for all filtratingzooplankton. indicating an in situ scaling not far from thephysiological principles onginally demonstrated for laboratorypopulations.     

Effects of disturbance on phosphorus turnover and plankton dynamics

In coastal lagoons, one common type of anthropogenic disturbanceis opening of the sand barriers that isolate these lagoons fromthe sea. We investigated how a disturbance caused by an artificialopening of the sand barrier affects phytoplankton and bacterioplanktondynamics and alkaline phosphatase activities (APA) in a Braziliancoastal lagoon. We propose an index of potential phosphorusturnover time (PPTT) calculated as the ratio of total phosphorus(TP) and APA in an attempt to quantify the effect of disturbanceson phosphorus recycling within the plankton community. Openingthe barrier caused increased phytoplankton biomass, TP concentrations,APA and PPTT, and decreased bacteria to phytoplankton biomassratio. PPTT is easily calculated and may be used to detect planktonresponses to anthropogenic disturbances.     

Modelling the dynamics of biosystems

The need for a more formal handling of biological information processing with stochastic and mobile process algebras is addressed. Biology can benefit this approach, yielding a better understanding of behavioural properties of cells, and computer science can benefit this approach, obtaining new computational models inspired by nature.     

Modelling spatial dynamics of fish

Our ability to model spatial distributions of fish populations is reviewed by describing the available modelling tools. Ultimate models of the individual's motivation for behavioural decisions are derived from evolutionary ecology. Mechanistic models for how fish sense and may respond to their surroundings are presented for vision, olfaction, hearing, the lateral line and other sensory organs. Models for learning and memory are presented, based both upon evolutionary optimization premises and upon neurological information processing and decision making. Functional tools for modelling behaviour and life histories can be categorized as belonging to an optimization or an adaptation approach. Among optimization tools, optimal foraging theory, life history theory, ideal free distribution, game theory and stochastic dynamic programming are presented. Among adaptation tools, genetic algorithms and the combination with artificial neural networks are described. The review advocates the combination of evolutionary and neurological approaches to modelling spatial dynamics of fish.     

The ecophysiology and bloom dynamics of Prymnesium spp.

Members of Prymnesium belong to the division Haptophyta, class Prymnesiophyceae, order Prymnesiales and family Prymnesiaceae. As most haptophytes, members of the genus Prymnesium are unicellular and planktonic. The most known of these species is the ichthyotoxic P. parvum, which may form nearly monospecific dense blooms in coastal and inland waters. This species possesses extraordinary plasticity concerning life survival strategies, and is specifically addressed in this review.Toxins produced by P. parvum have hemolytic properties, that not only kill fish but also co-existing plankton. These substances are allelopathic (when other algae are killed) and grazer deterrent (when grazers are killed). Allelopathy enables P. parvum to utilize inorganic nutrients present in the surrounding water without competition from other algal species; and by eliminating its grazers P. parvum reduces cell losses. The paralized microalgae and/or zooplankton, are therefter ingested by the P. parvum cells, a process called phagotrophy. P. parvum is also able of osmotrophy, i.e. utilization of dissolved organic matter. In this review, the cellular characteristics, life cycles, bloom formation, and factors affecting toxicity, allelopathy, phagotrophy, and osmotrophy of P. parvum are discussed.     

Temporal plankton dynamics in an oligotrophic maritime Antarctic lake

• 1 The population density, diversity and productivity of the microbial plankton in an oligotrophic maritime Antarctic lake were studied for a 15‐month period between December 1994 and February 1996.
• 2 In the lake, concentrations of nutrients and dissolved organic carbon were uniformly low, temperature varied over a small annual range of 0.1–3 °C, and the surface was ice‐covered except during a period of approximately 6 weeks in summer.
• 3 The total of 57 morphotypes of protozoa observed during the study is a higher taxonomic diversity than previously reported from continental Antarctic lakes, but lower than that found in more eutrophic maritime Antarctic lakes. Likewise, planktonic abundance and productivity were lower than has been reported in other lakes on Signy Island, but generally higher than those of lakes on the Antarctic continent.
• 4 There were marked seasonal and interannual variations in planktonic population density.
• 5 Chlorophyll a concentrations ranged from undetectable to 4.2 µg L^‐1 and the greatest rate of primary productivity measured was 4.5 mg C m^‐3 h^‐1. The phytoplankton was dominated by small chlorophytes and chrysophytes, with phototrophic nanoflagellate abundance ranging from 1.1 × 10³ to 1.2 × 10⁷ L^‐1.
• 6 Bacterial densities of 3.6 × 10⁸ to 1.9 × 10¹⁰ L^‐1 were recorded and bacterial productivity reached a peak of 0.36 µg C L^‐1 h^‐1. Numbers of heterotrophic nanoflagellates between 5.0 × 10⁴ and 1.8 × 10⁷ L^‐1, and of ciliates from undetectable to 1.1 × 10⁴ L^‐1 were observed. Naked amoebae were usually rare, but occasionally reached peaks of up to 1.5 × 10³ L^‐1.

     

Time delay as a key factor of model plankton dynamics

Studies of the mechanisms underlying complex dynamics of ecological systems at various spatial and time scales bring increasing awareness that complexity is an intrinsic feature of ecological functioning. This paper is to investigate the role of such an ecologically significant parameter as the time delay due to maturation processes in the complex plankton dynamics. We show that the time lag T1, associated with the zooplankton maturation period can lead to essential changes in the plankton dynamics. Particularly, we show that the coexistence of limit cycle and chaotic attractor we have recently found to be typical of the system at T1 = 0 [A.B. Medvinsky, I.A. Tikhonova, R.R. Aliev, B.-L. Li, Z.-S. Lin, H. Malchow, Patchy environment as a factor of complex plankton dynamics, Phys. Rev. E 64 (2001) 021915] is replaced by pure chaotic plankton dynamics as T1 becomes more than a critical value. The results obtained imply that chaos is a rather common phenomenon in the plankton functioning.     

Life-history stages of natural bloom populations and the bloom dynamics of a tropical Asian ribotype of Alexandrium minutum

In 2015, a remarkably high density bloom of Alexandrium minutum occurred in Sungai Geting, a semi-enclosed lagoon situated in the northeast of Peninsular Malaysia, causing severe discoloration and contaminated the benthic clams (Polymesoda). Plankton and water samples were collected to investigate the mechanisms of bloom development of this toxic species. Analysis of bloom samples using flow cytometry indicated that the bloom was initiated by the process of active excystment, as planomycetes (>4C cells) were observed in the early stage of the bloom. Increase in planozygotes (2C cells) was evident during the middle stage of the bloom, coinciding with an abrupt decrease in salinity and increase of temperature. The bloom was sustained through the combination of binary division of vegetative cells, division of planozygotes, and cyst germination through continuous excystment. Nutrient depletion followed by precipitation subsequently caused the bloom to terminate. This study provides the first continuous record of in situ life-cycle stages of a natural bloom population of A. minutum through a complete bloom cycle. The event has provided a fundamental understanding of the pelagic life-cycle stages of this tropical dinoflagellate, and demonstrated a unique bloom development characteristic shared among toxic Alexandrium species in coastal embayments.     

Modelling the dynamics of senescence spread

Cellular senescence is a cell surveillance mechanism that arrests the cell cycle in damaged cells. The senescent phenotype can spread from cell to cell through paracrine and juxtacrine signalling, but the dynamics of this process are not well understood. Although senescent cells are important in ageing, wound healing and cancer, it is unclear how the spread of senescence is contained in senescent lesions. In the absence of the immune system, senescence could theoretically spread infinitely from one cell to another, but this contradicts experimental evidence. To investigate this issue, we developed both a minimal mathematical model and a stochastic simulation of senescence spread. Our results suggest that differences in the number of signalling molecules secreted between subtypes of senescent cells can limit the spread of senescence. We found that dynamic, time-dependent paracrine signalling prevents the uncontrolled spread of senescence, and we demonstrate how model parameters can be determined using Bayesian inference in a proposed experiment.     

Modelling the impact of benthic filter-feeders on the composition and biomass of river plankton

SUMMARY 1. The POTAMON model [Everbecq E. et al . (2001) Water Research , 35 , 901] has been used to simulate the effect of benthic bivalves (mainly Dreissena polymorpha ) on the phytoplankton and zooplankton in a lowland Western European river (the Moselle). Here we use a modified version of the POTAMON model with five categories of phytoplankton ( Stephanodiscus , Cyclotella -like, large diatoms, Skeletonema and non-siliceous algae) to model filter-feeding effects of benthic bivalves in the Moselle. Zooplankton has been represented in the model by two categories, Brachionus -like and Keratella -like rotifers.
2. According to density estimates from field surveys (Bachmann V. et al . (1995) Hydroécologie Appliquée , 7 , 185, Bachmann V. & Usseglio-Polatera P. (1999) Hydrobiologia , 410 , 39), zebra mussel density varied among river stretches, and increased through the year to a maximum in summer. Dreissena filtration rates from the literature were used, and mussels have been assumed to feed on different phytoplankton categories (but less on large and filamentous diatoms) as well as on rotifers.
3. The simulations suggest a significant impact of benthic filter-feeders on potamoplankton and water quality in those stretches where the mussels are abundant, their impact being maximal in summer. Consequently, different plankton groups were not affected to the same extent, depending on their period of development and on indirect effects, such as predation by mussels on herbivorous zooplankton.
4. A daily carbon balance for a typical summer shows the effect of benthic filter-feeders on planktonic and benthic processes: the flux of organic matter to the bottom is greatly enhanced at high mussel density; conversely, production and breakdown of organic carbon in the water column are reduced. Mussel removal would drive the carbon balance of the river toward autotrophy only in the downstream stretches.     

Modelling viral and immune system dynamics

During the past 6 years, there have been substantial advances in our understanding of human immunodeficiency virus 1 and other viruses, such as hepatitis B virus and hepatitis C virus, that cause chronic infection. The use of mathematical modelling to interpret experimental results has made a significant contribution to this field. Mathematical modelling is also improving our understanding of T-cell dynamics and the quantitative events that underlie the immune response to pathogens.