Vertical Distribution Of Phytoplankton Research Articles

A simple model illustrating the role of turbulence on phytoplankton blooms.

The problem of the vertical distribution of phytoplankton is considered in the presence of gravitational settling, turbulent mixing, population growth due to cell division and a constant rate of loss due to predation and natural death. Nutrients are assumed to be plentiful so that the production rate depends only on the light available for photosynthesis. The non-linear saturation of plankton growth is modeled by allowing the attenuation rate of light to be a linear function of the plankton density. The turbulent diffusivity is assumed constant which corresponds to a mixed layer depth very much greater than the depth of light penetration (euphotic depth). It is shown that an exact analytical solution of this non-linear problem is possible for an idealized model in which the functional dependence of production on light intensity is assumed to be a step function. Non-zero solutions are shown to exist only if the parameters characterizing the system are above a certain critical curve in a two dimensional parameter space. Numerical simulations using functional forms of the production curve that resemble the measured photosynthetic response of plankton, show, that the qualitative behavior of the system is similar to that of the idealized model presented. Comparisons are made with other analytical approaches to the problem.

Tidal and diel periodicities of size-fractionated phytoplankton pigment signatures at an offshore station in the southeastern English Channel

The influence of the tidal cycle on the vertical distribution of phytoplankton was investigated in neap-tide conditions during a 36 h sampling period in the southeastern English Channel. Phytoplankton distribution was investigated through algal pigment signatures analyzed by HPLC, in three size fractions: 0.7–5 μm, 5–20 μm and ≥20 μm. In spite of the physical homogeneity of the water column, vertical and temporal variabilities were observed in the size-class distribution and phytoplankton-community composition (revealed by biomarker pigments). Microplankton biomass (chl. a, ≥20 μm) dominated the community, accounting for up to 60% of the total chl. a. Tidal current cycles were responsible for periodical horizontal advection of biomass in the surface layer with every low tide moving from the coastal waters to the offshore. Tidal currents were responsible for cyclical vertical advection of phytoplankton through the water column, such as for the resuspension of benthic and/or tychoplanktonic diatoms from the bottom. Time-dependent biological variability was also related to the diel scale, with vertical migration of phytoflagellate cells (especially Cryptophytes). Over the daily cycle, it appeared that physiological changes (through measurements of in vivo chl. a fluorescence) occurred in the sub-surface layer, revealing photoinhibition under high light.

Small-scale vertical distribution of phytoplankton, nutrients and sulphide below the oxycline of a mesotrophic lake

A characteristic vertical sequence of phytoplankton populations was observed below the metalimnetic oxycline of a stratified, mesotrophic lake. Ceratium spp., Closterium acutum and Aphanizomenon flos- aquae were present in the epilimnion but had distinct population maxima in the microaerobic chemocline. Below these populations, Cryptomonas phaseolus, Planktothrix clathrata, Pseudanabaena catenata and Limnothrix sp. followed each other in the transition zone between the chemocline and the sulphide-containing hypolimnion. The dominating populations of P. clathrata and P. catenata caused a deep chlorophyll maximum. Phytoplankton structure was determined by the vertical gradients of sulphide and light. Compared with the epilimnion, nutrient availability was not fundamentally better below the oxycline but the algae might have benefited from reduced grazing pressure in their habitat.

The role of advection and turbulent mixing in the vertical distribution of phytoplankton

The purpose of this study is to analyse the role of the flow field on the horizontal and vertical distributions of different phytoplankton populations thriving in the water column of a shallow coastal ecosystem. Two extreme flow conditions are illustrated. The first was a low energetic flow, under calm meteorological conditions and a stratified temperature of the water column. The second flow, coincident with the passage of a storm front, was more energetic resulting in increased mixing that homogenized the temperature in the whole water column. Although the mixing level homogenized the temperature of the water column in the high-energy period, it was not enough to homogenize the temperature in the low-energy period. In contrast, in both periods, the mixing level was enough to homogenize the vertical distribution of particles. A decrease in the concentration of particles from the calm period to the high-energy period was attributed to an advection event with warmer water of lower plankton concentration that resulted in a decrease of the total concentration of suspended particles in the water column. Data are used to test a model of plankton mixing proposed by Ruiz et al. (J. Plankton Res., 18 (1996) 1727).

Identifying characteristic chlorophyll a profiles in the coastal domain using an artificial neural network

To estimate primary production in the marine environment, knowledge of the vertical distribution of phytoplankton is needed. The measurement of ocean colour by satellite remote sensing makes it possible to map the near-surface phytoplankton distribution, although the subsurface vertical structure cannot be measured. In this study, we investigated the shape of vertical chlorophyll profiles from the Benguela upwelling system seasonally and with respect to environmental variables such as surface temperature and chlorophyll, and mixed layer and water column depth. We used an artificial neural network technique called a self-organizing map to identify characteristic classes of vertical chlorophyll profiles, and then classify existing profiles into these representative classes. The self-organizing map identified a continuum of patterns, ranging from those with small deep peaks (1 mg m(-3), 45 m) to those with large near-surface peaks (9 mg m(-3), 7 m). Although profile shape varied seasonally, profiles were very variable within each season, making chlorophyll profiles averaged seasonally meaningless. A canonical succession in profile shape following upwelling of cold water in spring and summer could be identified, with large surface peaks in cool water and small deep peaks in warm water. The approach presented here can be used in a semi-quantitative manner to predict the subsurface chlorophyll field from known (water column depth) or easily measured variables from satellites (surface temperature or surface chlorophyll), as the relative frequency of each characteristic profile under different environmental conditions is presented. This approach enables prediction of profile shapes in the dynamic coastal domain and thus superior regional estimates of primary production.

Vertical distribution of phytoplankton in a pampean shallow lake

Vertical distribution of phytoplankton in a pampean shallow lake

The phytoplankton vertical distribution and diurnal migration in three quarry lakes in South Bohemia, Czech Republic

The summer phytoplankton communities of three lakes, originated in flooded quarries, were investigated. All lakes were small (0.35-0.42 ha), wind protected, oligo- or mesotrophic water bodies with high relative depth (>10 %). Their phytoplankton was dominated by flagellates, forming a heterogeneous distribution with metalimnetic maxima of abundance. In Skali and Pasticky lake, these maxima were formed by Cryptophyceae mostly. The diurnal vertical migration patterns were investigated for 10 species in Pasticky lake. Cryptomonas curvata and C. phaseolus were located at the boundary between oxic and anoxic water layer, at night C. curvata descended into anoxia. Similar pattern showed Euglena acus. On the other hand, Synura sp. and Ceratium hirundinella had their maxima between 3 m and above upper boundary of anoxia. Paulschultzia pseudovolvox, coccal desmid Cosmarium pygmeum and Rhodomonas lacustris occurred in epilimnium. The small proportion of coccal forms in phytoplankton biomass and dominance of flagellates is probably the result of unmixed water column, where the forms dependent on the dwelling caused by water turbulence are outcompeted by flagellates, able to eliminate sedimentation loss, having acces both to hypolimnetic nutrients and sufficient light for their photosynthesis.

Catastrophic Transition in Vertical Distributions of Phytoplankton: Alternative Equilibria in a Water Column

We showed a catastrophic transition between a surface maximum pattern and a subsurface maximum pattern of phytoplankton in a water column by a mathematical model considering the vertical distribution of phytoplankton and two resources, light and a limiting nutrient. In our model, we assumed that a water column consists of two layers: a complete mixing layer above a seasonal thermocline and an incomplete mixing layer below it. From numerical calculation of the model, we obtained that there are two stable vertical patterns of phytoplankton over a certain range of parameters of the model: a pattern having its maximum below the thermocline and another having its maximum above the thermocline. As other models having multiple stable equilibria, our model also exhibits a hysteresis effect and catastrophic transition when one of the parameters of the model changes continuously. These results indicate the possibility of the existence of alternative equilibria of vertical patterns of phytoplankton even if the trophic status and physical condition of the water column are similar. Moreover, the catastrophic transition between the steady states suggests one of the possible mechanisms of autumn algal blooms.

Spatial variability of chlorophyll- a in the Marginal Ice Zone of the Barents Sea, with relations to sea ice and oceanographic conditions

The distribution of chlorophyll- a in the Barents Sea was observed from the optical satellite instrument Sea-viewing Wide Field-of-view Sensor (SeaWiFS) during May 1999. In the same period water samples were collected in situ and analysed. Contrary to previous studies of phytoplankton distribution in the Barents Sea, we rigourously analysed the chlorophyll- a distribution characteristics with respect to sea ice and oceanographic conditions, spatially and temporally. The spatial distribution of surface chlorophyll- a was analysed and related, statistically, to the ice edge and sea ice concentrations from the Special Sensor Microwave Imager (SSM/I) satellite instrument. The highest chlorophyll- a concentrations were observed near the ice edge, and then decreased further into the ice. The spatial variability of the chlorophyll- a concentrations in this region was high, even in open water along the ice edge. The chlorophyll- a observations indicated a strong primary bloom about 2 weeks after the ice edge had retreated from a given measurement point. There were also indications of several minor blooms about 2 weeks after the initial bloom. The vertical distributions of chlorophyll- a are presented for nine different stations in the Marginal Ice Zone (MIZ) of the northern Barents Sea and discussed in terms of simultaneously measured temperature–salinity CTD profiles. Water mass properties and sea ice history have a significant impact on the vertical distribution of phytoplankton. The surface chlorophyll- a concentration was about 60% higher (±70% S.D.) than the total column average. The correlation coefficient was 0.87, indicating that surface values are good predictors for relative levels of total phytoplankton biomass during spring conditions. We propose a method to identify the stage of the phytoplankton bloom based on satellite observations of chlorophyll- a, temperature, salinity and sea ice history. Based on an extensive set of field measurements at different times from many locations in the Barents Sea, we have produced empirical formulae to estimate the integrated chlorophyll- a content for the water column from surface (satellite) measurements during early spring (homogeneous water masses) and bloom conditions.

Seasonal changes in nutrients, chlorophyll a and the phytoplankton assemblage of the western subarctic gyre in the Pacific Ocean

The standing stock and species composition of phytoplankton (>10 μm) were studied using monthly water samples collected at Stn KNOT (Kyodo North Pacific Ocean Time Series; 44°N, 155°E) in the western subarctic gyre in the Pacific Ocean through June 1998 to June 1999 (except for January–April 1999) and January–February 2000. One-liter water samples were preserved in 1% neutrally buffered formalin. Identification and enumeration of phytoplankton were made with an inverted microscope. Nutrients did not appear to be depleted for phytoplakton growth during any season. The vertical distribution of phytoplankton was primarily restricted by the pycnocline, and the bulk of phytoplankton assemblage existed within the surface mixed layer. In July, however, some senescent cells were observed at 200 m. Phytoplankton abundance clearly showed a spring maximum (i.e. spring bloom) in May. The seasonal change in cell numbers, however, did not coincide closely with the change in chlorophyll a concentration. Centric diatoms, which were composed of Thalassiosira, Chaetoceros, and Coscinodiscus, dominated all year round, and showed temporal succession. Pennate diatoms (mostly Neodenticula seminae and Fragilariopsis) increased only during the spring bloom. Dinoflagellates (mostly Gymnodinium and Prorocentrum) were low in abundance, although they increased in summer when the phytoplankton standing stock was low. Silicoflagellate abundance was extremely low. Comparing the annual species composition of phytoplankton between Stn KNOT and Stn P (50°N, 145°W) in the Alaskan Gyre, there was a remarkable difference between the two sites. The phytoplankton assemblage at Stn P is characterized by a high abundance of Rhizosolenia alata and low abundance of Thalassiosira. In contrast, Thalassiosira dominates at Stn KNOT during most seasons.

レーザ光を用いた植物プランクトン鉛直分布観測手法

レーザ光を用いた植物プランクトン鉛直分布観測手法

Regularities of seasonal dynamics of the vertical distribution of phytoplankton in a pond

Regularities of seasonal dynamics of the vertical distribution of phytoplankton in a pond

Algal games: The vertical distribution of phytoplankton in poorly mixed water columns

Phytoplankton often face the dilemma of living in contrasting gradients of two essential resources: light that is supplied from above and nutrients that are often supplied from below. In poorly mixed water columns, algae can be heterogeneously distributed, with thin layers of biomass found on the surface, at depth, or on the sediment surface. Here, we show that these patterns can result from intraspecific competition for light and nutrients. First, we present numerical solutions of a reaction‐diffusion‐taxis model of phytoplankton, nutrients, and light. We argue that motile phytoplankton can form a thin layer under poorly mixed conditions. We then analyze a related game theoretical model that treats the depth of a thin layer of phytoplankton as the strategy. The evolutionarily stable strategy is the depth at which the phytoplankton are equally limited by both resources, as long as the layer is restricted to the water column. The layer becomes shallower with an increase in the nutrient supply and deeper with an increase in the light supply. For low nutrient levels, low background attenuation, and shallow water columns a benthic layer occurs; for intermediate nutrient levels in deep water columns, a deep chlorophyll maximum occurs; and for high nutrient levels, a surface scum occurs. These general patterns are in agreement with field observations. Thus, this model can explain many patterns of algal distribution found in poorly mixed aquatic ecosystems.

Factors influencing the time scale of vertical phytoplankton distribution in a mountain lake (Lake Waegital, Switzerland)

Factors influencing the time scale of vertical phytoplankton distribution in a mountain lake (Lake Waegital, Switzerland)

Vertical Distribution of Phytoplankton in Salt Lake Shira

Vertical Distribution of Phytoplankton in Salt Lake Shira

Ecological monitoring of phytoplankton in Lake Baikal

The results of the long-term investigations of phytoplankton of the whole of Lake Baikal summarizing almost 40years of systematic observations are given in this paper. These studies draw attention to spatial heterogeneity of planktonic biomass across the basin during the spring maximal bloom. The research of vertical distribution of phytoplankton during different years allows us to specify the role of phytoplankton in the cycle of organic substances and in biological productivity of Lake Baikal. For the first time, Baikal picophytoplankton, peculiarities of its production, seasonal and inter-annual dynamics, biocoenotic interrelations and its role in the ecosystem of Lake Baikal have been described. Changes occurring in Baikal pelagial phytocoenoses during the 1970–1990s in comparison with those of 1950–1960s have been revealed.

Ecological monitoring of phytoplankton in Lake Baikal

Abstract The results of the long-term investigations of phytoplankton of the whole of Lake Baikal summarizing almost 40 years of systematic observations are given in this paper. These studies draw attention to spatial heterogeneity of planktonic biomass across the basin during the spring maximal bloom. The research of vertical distribution of phytoplankton during different years allows us to specify the role of phytoplankton in the cycle of organic substances and in biological productivity of Lake Baikal. For the first time, Baikal picophytoplankton, peculiarities of its production, seasonal and inter-annual dynamics, biocoenotic interrelations and its role in the ecosystem of Lake Baikal have been described. Changes occurring in Baikal pelagial phytocoenoses during the 1970–1990s in comparison with those of 1950–1960s have been revealed.

Is buoyancy regulation in cyanobacteria an adaptation to exploit separation of light and nutrients?

Fogg and Walsby’s (1971) hypothesis that buoyancy regulation in cyanobacteria might be an adaptation to exploit the separation of light and nutrients has since become a paradigm. The evidence of its veracity is examined within observations of algal abundance and chlorophyll distributions in several Australian freshwater systems and is also reviewed from the literature. It is clear from both laboratory experiments and field measurements that filamentous genera such as Anabaena and colony-forming genera such as Microcystis are capable of changing their buoyancy within a diurnal cycle. However, evidence for population migration to exploit separation of light and nutrient availability is tenuous, with most field observations of the vertical distribution of phytoplankton populations showing no evidence of vertical migration to sufficient depth to reach nutrients in stratified systems. Instead, changes in the vertical distribution of phytoplankton suggest a response either to the dynamics of the surface mixed layer or to lateral advection. In natural systems, algal buoyancy appears to be dependent much more on light than on nutrients, this being consistent with the carbohydrate ballast mechanism. Physical mechanisms can provide sufficient replenishment of epilimnetic nutrients to explain the observed net growth rates of phytoplankton populations in situ.

Detailed observations of the phytoplankton spring bloom in the stratifying central North Sea

Analysis of detailed time series of bio-optical and temperature data from the North Sea supports the view that a minimum level of turbulence is a prerequisite for the onset and maintenance of the phytoplankton spring bloom in shelf seas, which distinguishes these seas from the open ocean. The start of the spring bloom, primarily diatoms, is controlled by the light regime, while its progress is predominantly dependent upon episodic turbulence input following short periods of stratie cation, which allow the resuspension of a fast sinking (50‐ 200 m day 2 1 ) phytoplankton community from the bottom mixing layer. A relationship between turbulence and the vertical distribution of phytoplankton is proposed which is found at synoptic time scales and on time scales of a day and less. Throughout the spring bloom, algal biomass is either equally distributed through the water column or concentrated in the bottom mixing layer. Growth can only be sustained in the near-surface layer during periods of substantial turbulence input. The establishment of semi-permanent seasonal stratie cation causes an almost complete reduction in near-surface biomass and a concomitant increase in biomass in the bottom mixing layer which subsequently acts as a source for occasional increased near-surface biomass until early summer.

Limnological Characteristics and Vertical Distribution of Phytoplankton in Oligotrophic Lake Akan-Panke.

The limnological characteristics and vertical distribution of phytoplankton in Lake Akan-Panke were surveyed to clarify the metabolism in an oligotrophic lake. Maximum water temperature was 19.6°C in August 1992, and the concentration of dissolved oxygen was always over 4.8 mg 1-1 in the hypolimnion. Transparency ranged from 7.1 to 17.6 m, and was relatively high in July and August. Standing stocks of nitrogen, phosphorus, and chlorophyll-a (chl-a) were 8.20, 0.33, and 0.114 g m-2, respectively. In particular, that of phosphorus was at a low level in July and August. Therefore, phosphorus may be the limiting factor in this lake. These data suggest the theory that Lake Akan-Panke is in an oligotrophic state. However, this lake had a relatively high concentration of chl-a at a deeper layer (30-45 m) during the early thawing season in May 1992 and July 1993, and large size phytoplankton (>20μm) dominated at those times. When thermal stratification was developing in the lake in July and August, the phytoplankton population and chl-a concentration decreased in the surface layer and formed a sub-surface maximum in the metalimnion, mainly dominated by large size phytoplankton (> 20 μm) . In contrast, relatively small size phytoplankton (< 20 μm) dominated the hypolimnion in August and October. Since most of the chl-a was trapped in the 45 m layer rather than in the 20 m layer by the sediment trap method in May 1992 and August 1993, the high chl-a concentration observed in the deeper layer might be due to the growth of phytoplankton in the layer and/or to sinking of the phytoplankton from the upper layer which increased in May (spring bloom). This suggests that the high biomass of phytoplankton in the deeper layer derived from sinking.