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Growth of Chlorella miniata, a green microalga was investigated during this study under various temperature and light intensity values with the purpose of determining growth rate changes of the microalgae with cultivation parameters, experiments were carried out using airlift photobioreactors with a study volume of 6 L. Culturing conditions were between 66 and 385 mu mol photon m(-2) s(-1) and between 14 and 30 degrees C for light intensity and ambient temperature, respectively. Acquired data were then used to test various mathematical models for coherency with experimental results. Aiba Model for light intensity and Skewed Normal Distribution Model for temperature parameters performed superior compared to the rest of the mathematical models used during the study. Utilizing both mathematical models a novel model was deduced to express effects of both light intensity and temperature parameters in combination on algal growth. Then the developed model was used to calculate the optimum growth condition of the species. The proposed mathematical model showed good coherency with experimental data and an average relative error of 1.97% for both temperature and light intensity effects on algal growth. The theoretical optimum temperature and light intensity for the maximum specific growth rate were calculated to be 22.43 degrees C and 291.5 mu mol photon m(-2) s(-1) respectively.

International audience; An integrated screening approach was developed to assess the potential of the Botryococcus genus for the production of lipids for biofuel application (hydrocarbons and triacylglycerols). The strategy developed in this study permitted to rigorously measure mandatory parameters for the determination of strain performance – i.e. growth rate and oil content. For that purpose, mini-photobioreactors run in parallel were used together with an exhaustive lipid class analysis. The quantitative productivity measurements indicated that the ten screened strains presented very different patterns in the conditions of PBR culture, firstly run in batch, and secondly in continuous mode. Indeed, with the applied setup, only four strains presented biomass productivities close to that previously measured for the reference strain 807/1 (between 74 and 307 mg L−1 day−1 of biomass for the tested strains). HC productivity obtained under continuous light (∼14 mg L−1 day−1) was close to that measured for the strain 807/1 (∼20 mg L−1 day−1), confirming B. braunii tested strains potential for biofuel application. The analysis of the lipid chemodiversity revealed moreover that this genus should be further investigated for its polar lipids, as it suggests potential pharmaceutical applications such as production of antitumorals or immunosuppressors.

The ecophysiology and competitive behavior of the prochlorophyte Prochlorothrix hollandica Burger-Wiersma, Stal et Mur, and the cyanobacterium Planktothrix agardhii Anagn. et Kom. were investigated in phosphorus-limited continuous cultures. When the species we-re exposed to successive saturating-pulses of P, the maximal P uptake rate decreased linearly with an increase in the P cell quota. Prochlorothrix had a higher maximal P uptake rate, a lower half-saturation constant for P uptake, higher maximal cell quota for P, and slightly lower minimal cell quota for P than Planktothrix. These data indicate that Prochlorothrix is an affinity and storage strategist, at least when compared to Planktothrix. On the other hand, Prochlorothrix had a lower maximal growth rate than Planktothrix. On the basis of these ecophysiological parameters, we developed a Droop model to predict the time course and outcome of competition under various P regimes. The model predictions were in line with the results of competition experiments under three different P-limited conditions (continuous P supply, 4-day pulse period, 12-day pulse period). Prochlorothrix competitively displaced Planktothrix under both a constant and a pulsed P supply, and competitive displacement of Planktothrix was slowest in the experiment with a 12-day pulse period. In the pulsed experiments, the mean filament lengths and chl a fluorescence of the species oscillated at the same frequency as the pulse additions. In contrast to the Droop model, the predictions of the Monod model were not in line with the outcome of the competition experiments. Our results demonstrate that Prochlorothrix is a very good competitor for P and that the time course and outcome of competition for P in a variable environment can be predicted on the basis of the P uptake and storage characteristics of the species.

The elemental ratios of marine phytoplankton emerge from complex interactions between the biotic and abiotic components of the ocean, and reflect the plastic response of individuals to changes in their environment. The stoichiometry of phytoplankton is, thus, dynamic and dependent on the physiological state of the cell. We present a theoretical model for the dynamics of the carbon, nitrogen and phosphorus contents of a phytoplankton population. By representing the regulatory processes controlling nutrient uptake, and focusing on the relation between nutrient content and protein synthesis, our model qualitatively replicates existing experimental observations for nutrient content and ratios. The population described by our model takes up nutrients in proportions that match the input ratios for a broad range of growth conditions. In addition, there are two zones of single-nutrient limitation separated by a wide zone of co-limitation. Within the co-limitation zone, a single point can be identified where nutrients are supplied in an optimal ratio. When different species compete, the existence of a wide co-limitation zone implies a more complex pattern of coexistence and exclusion compared to previous model predictions. However, additional comprehensive laboratory experiments are needed to test our predictions. Our model contributes to the understanding of the global cycles of oceanic nitrogen and phosphorus, as well as the elemental ratios of these nutrients in phytoplankton populations.

A facultatively oligotrophic ultramicrobacterium (strain RB2256) isolated from an Alaskan fjord by extinction dilution in seawater, was grown in batch culture and under single- and dual-substrate-limitation of alanine and glucose in a chemostat. The nature of the uptake systems, and the uptake kinetics and utilization patterns of alanine and glucose were investigated. Glucose uptake was inducible, the system exhibited a narrow substrate specificity, and part of the uptake system was osmotic-shock-sensitive. Half-saturation constants for glucose were between 7 and 74 mu M during glucose limitation. The initial step in glucose metabolism was the synthesis of sugar polymers, even during glucose-limited growth. The alanine uptake system was constitutively expressed and was binding-protein-dependent. In addition to L-alanine, nine other amino acids inhibited accumulation of [C-14]L-alanine, indicating broad substrate specificity of the alanine transporter. Half-saturation constants between 1.3 and 1.8 mu M were determined for alanine uptake during alanine limitation, Simultaneous utilization of glucose and alanine occurred during substrate-limited growth in the chemostat, and during growth in batch culture at relatively high (mM) substrate concentrations. However, the half-saturation constant for alanine transport during dual-substrate-limitation, i.e. in the presence of glucose, increased almost fivefold. We conclude that mixed substrate utilization is an inherent property of this organism.

Resource competition theory predicts that the outcome of competition for two nutrients depends on the ratio at which these nutrients are supplied. Yet there is considerable debate whether nutrientratios or absolute nutrient loads determine the species composition of phytoplankton and plant communities. Here we extend the classical resource competition model for two nutrients by includinglight as additional resource. Our results suggest the nutrientload hypothesis, which predicts that nutrient ratios determine the species composition in oligotrophic environments, whereas nutrientloads are decisive in eutrophic environments. The underlying mechanism is that nutrient enrichment shifts the species interactions from competition for nutrients to competition for light, which favors the dominance of superior light competitors overshadowing all other species. Intermediate nutrient loads can generate high biodiversity through a fine-grained patchwork of two-species and three-species coexistence equilibria. Depending on the species traits, however, competition for nutrients and light may also produce multiple alternative stable states, suppressing the predictability of the species composition. The nutrient-load hypothesis offers a solution for several discrepancies between classical resource competition theory and field observations, explains why eutrophication often leads to diversity loss, and provides a simple conceptual framework for patterns of biodiversity and community structure observed in nature.

The spelling of the words _eco-logy and _eco-nomics in the title is intended to emphasize that both words originated from the Greek word oikos, which means household, house, or family. Despite their common origin, never have two disciplines diverged so dramatically. Economic growth, aided by economic globalization, has markedly diminished natural capital, from which all other forms of capital are derived. Economic growth (without protecting the biospheric life support system) seems to be the primary goal of human society. In reality, the human economy is a subset of the biospheric life support system, which regenerates the resources that are the raw materials of the economic system. Yet political leaders continually state that the biospheric life support system cannot be protected if the possibility of doing so would adversely affect economic growth. However, growth of material goods and population cannot continue indefinitely without severe consequences. At present, many ecologists delay discussing biotic impoverishments with economists, fearing that such candor will _turn them off. The contextual framework of economists and ecologists is far from congruent, although the survival of human society, and even of the human species, depends on it.

Marine invertebrate recruitment may be affected by food limitation during the pelagic larval life stages. In the present study, field data on abundance of bivalve larvae along with their prey (small phytoplankton) were examined to see whether they were consistent with predictions made by an energetic model of larval requirements. Bivalve larvae were monitored during 2000 at ten different study sites in four different areas (Limfjorden, Sylt-Rømø bight, Western Wadden Sea and Delta area) along the coast of north-western Europe. Calculation of the energetic requirements of the larvae at 15°C indicated maintenance costs of a 200-μm bivalve larva to be 1.9 × 10 - 5 J larva- 1 d- 1, while the maximum assimilation rate, resulting in maximum growth, would amount to 6.2 × 10- 3 J larva- 1 d- 1. Calculation of potential assimilation rates of larvae in the field resulted in estimates between 10 - 5 and 10- 3 J larva- 1 d- 1. Maximum larval concentrations in the field occurred from May to September and ranged between 17 and 392 larvae dm- 3. Most larvae were able to cover their maintenance costs, but not to attain maximum growth rates. Between April and September, the potential assimilation rate averaged 7-26% of the maximum assimilation rate. Under the assumptions made for the present study, it is suggested that growth of larvae in north-west European waters is often food-limited. © 2005 Elsevier B.V. All rights reserved.

We investigate biological mechanisms that generate oscillations and chaos in multispecies competition models. For this purpose, we use a competition model concerned with competition for abiotic essential resources. Because phytoplankton and plants consume quite a number of abiotic essential resources, the model is particularly relevant for phytoplankton communities and terrestrial vegetation. We show that the predicted dynamics depend crucially on the relationship between the resource requirements and the resource consumption characteristics of the species. More specifically, the model predicts that competition generates (1) stable coexistence if species consume most of the resources for which they have high requirements, (2) oscillations and chaos if species consume most of the resources for which they have intermediate requirements, and (3) competitive exclusion with a winner that depends on the initial conditions if species consume most of the resources for which they have low requirements. The theoretical predictions are compared with available data on resource utilization patterns of phytoplankton species.

With the eutrophication of many freshwaters and coastal environments, phytoplankton blooms have become a common phenomenon. This article uses a reaction-diffusion model to investigate the implications of mixing processes for the dynamics and species composition of phytoplankton blooms. The model identifies four key parameters for bloom development: incident light intensity, background turbidity, water column depth, and turbulent mixing rates. The model predicts that the turbulent mixing rate is a major determinant of the species composition of phytoplankton blooms. In well-mixed environments, the species with lowest "critical light intensity" should become dominant. But at low mixing rates, the species with lowest critical light intensity is displaced if other species obtain a better position in the light gradient. Instead of a gradual change in species composition, the model predicts steep transitions between the dominance regions of the various species. The model predicts a low species diversity: phytoplankton blooms in eutrophic environments should be dominated by one or a few species only. The model predictions are consistent with laboratory competition experiments and many existing field data. We recommend examining competition in phytoplankton blooms under well-controlled laboratory conditions, and we derive scaling rules that facilitate translation from the laboratory to the field. [KEYWORDS: competition model; critical depth; critical turbulence reaction-diffusion equation; population dynamics; resource competition Deep chlorophyll maximum; agardhii-var-isothrix; hypertrophic lake; vertical migration; cyanobacterium microcystis; environmental-factors; resource competition; narragansett bay; limited growth; water column]

Biodiversity has both fascinated and puzzled biologists(1). In aquatic ecosystems, the biodiversity puzzle is particularly troublesome, and known as the 'paradox of the plankton'(2). Competition theory predicts that, at equilibrium, the number of coexisting species cannot exceed the number of limiting resources(3-6). For phytoplankton, only a few resources are potentially limiting: nitrogen, phosphorus, silicon, iron, light, inorganic carbon, and sometimes a few trace metals or vitamins. However, in natural waters dozens of phytoplankton species coexist(2). Here we offer a solution to the plankton paradox. First, we show that resource competition models(6-10) can generate oscillations and chaos when species compete for three or more resources. Second we show that these oscillations and chaotic fluctuations in species abundances allow the coexistence of many species on a handful of resources. This model of planktonic biodiversity may be broadly applicable to the biodiversity of many ecosystems. [KEYWORDS: Limited growth; competition; phytoplankton; communities limitation; hypothesis]

The ecophysiology and competitive behavior of the prochlorophyte Prochlorothrix hollandica Burger-Wiersma, Stal et Mur, and the cyanobacterium Planktothrix agardhii Anagn. et Kom. were investigated in phosphorus-limited continuous cultures. When the species we-re exposed to successive saturating-pulses of P, the maximal P uptake rate decreased linearly with an increase in the P cell quota. Prochlorothrix had a higher maximal P uptake rate, a lower half-saturation constant for P uptake, higher maximal cell quota for P, and slightly lower minimal cell quota for P than Planktothrix. These data indicate that Prochlorothrix is an affinity and storage strategist, at least when compared to Planktothrix. On the other hand, Prochlorothrix had a lower maximal growth rate than Planktothrix. On the basis of these ecophysiological parameters, we developed a Droop model to predict the time course and outcome of competition under various P regimes. The model predictions were in line with the results of competition experiments under three different P-limited conditions (continuous P supply, 4-day pulse period, 12-day pulse period). Prochlorothrix competitively displaced Planktothrix under both a constant and a pulsed P supply, and competitive displacement of Planktothrix was slowest in the experiment with a 12-day pulse period. In the pulsed experiments, the mean filament lengths and chl a fluorescence of the species oscillated at the same frequency as the pulse additions. In contrast to the Droop model, the predictions of the Monod model were not in line with the outcome of the competition experiments. Our results demonstrate that Prochlorothrix is a very good competitor for P and that the time course and outcome of competition for P in a variable environment can be predicted on the basis of the P uptake and storage characteristics of the species.

SUMMARY: A facultatively oligotrophic ultramicrobacterium (strain RB2256) isolated from an Alaskan fjord by extinction dilution in seawater, was grown in batch culture and under single- and dual-substrate-limitation of alanine and glucose in a chemostat. The nature of the uptake systems, and the uptake kinetics and utilization patterns of alanine and glucose were investigated. Glucose uptake was inducible, the system exhibited a narrow substrate specificity, and part of the uptake system was osmotic-shock-sensitive. Half-saturation constants for glucose were between 7 and 74 μM during glucose limitation. The initial step in glucose metabolism was the synthesis of sugar polymers, even during glucose-limited growth. The alanine uptake system was constitutively expressed and was binding-protein-dependent. In addition to L-alanine, nine other amino acids inhibited accumulation of [14C]L-alanine, indicating broad substrate specificity of the alanine transporter. Half-saturation constants between 1-3 and 1-8 μM were determined for alanine uptake during alanine limitation. Simultaneous utilization of glucose and alanine occurred during substrate-limited growth in the chemostat, and during growth in batch culture at relatively high (mM) substrate concentrations. However, the half-saturation constant for alanine transport during dual-substrate-limitation, i.e. in the presence of glucose, increased almost fivefold. We conclude that mixed substrate utilization is an inherent property of this organism.

At least in Western cultures, it seems that we are taught from childhood that growth in all things is inherently good. This thought is so ingrained in our make-ups that we rarely pay it any mind but subconsciously accept it as a truism to live by. The purpose of this paper is to explore the extent to which we should continue to subscribe to this view, or whether we need to change our mindset for the long-term benefit of humanity on this planet. If the questioning of this idea is too foreign for us to even contemplate, we should at least try to educate our emotions about this controversial subject to better understand why we continue to resist reason in favor of our gut or knee-jerk reaction that inhibits taking action to improve the sustainability of human life on Earth. This paper is written as a dialogue among fictitious interested parties in an attempt to provide a more balanced treatment while enlivening the debate in showcasing some passionate viewpoints. Complex systems engineering principles and research ideas are infused.