Algal Specific Growth Rate Research Articles

A sequential electrochemical oxidation – algal photobioreactor system for the treatment of distillery wastewater

A sequential electrochemical oxidation (EO) and algal bubble column photobioreactor (BPBR) system was proposed to treat distillery wastewater (DWW). EO was carried out in a 2 L reactor with Ti-RuO2 anodes. Electrochemically oxidised DWW (EO-DWW) was then supplied to the microalgae Asterarcys quadricellulare. The EO operating current, treatment time and post-treatment dilution were optimised with a central composite design (CCD) with algal specific growth rate, lipid accumulation and photosynthetic quantum yield (Fv/Fm) as dependent variables. The optimal treatment conditions for the growth of A. quadricellulare were 27 A for 26 h and a post-treatment dilution of 8. Under optimal conditions, A. quadricellulare grew at a specific growth rate of 1.06 d−1 with a lipid accumulation of 12.7% and an Fv/Fm of 0.7. The optimal conditions were validated, and a 1.6 L bubble column photobioreactor was designed to treat the EO-DWW sequentially. The sequential EO-BPBR system removed 92% COD, 76% TOC and 82% TN from DWW. The algal biomass productivity was 0.96 g/L/d with a carbon sequestration of 550–700 mg/L/d and an aqueous carbon capture of 240–280 mg C/L/d. Additionally, the flue gas evolved from the EO reactor was analysed and contained 68% H2, 18% O2 and 12.5% CO2. The H2 in the flue gas can compensate for 26.5% of the energy spent for the EO process. The algal biomass produced in the sequential process can compensate for 6% of the total energy consumed for EO. Therefore, 32% of the energy spent on EO can be reclaimed by sequential EO-BPBR treatment.

Cu, Ni, and Zn effects on basic physiological and stress parameters of Raphidocelis subcapitata algae.

The submitted work observed Cu, Ni, and Zn effects on selected physiological and stress parameters of the alga Raphidocelis (Pseudokirchneriella) subcapitata. In 96-h experiments, EC50 values for algal specific growth rates (SGR) inhibition in Cu, Ni, and Zn presence were estimated as 0.15, 0.50, and 0.20 mg l-1. In addition to growth inhibition, the effect of metals at various concentrations on algal SGR was also monitored. While these experiments confirmed approximately the same toxicity of Zn and Cu on SGR, Ni toxicity on this parameter was observed as the lowest. In terms of the effect of metals on the level of selected photosynthetic pigments, chlorophyll a, chlorophyll b, and carotenoids, the following inhibition orders can be established: Zn > Cu > Ni, Ni > Cu > Zn, and Ni > Cu ≥ Zn, respectively. As a novelty of our research, we included monitoring and evaluation of the intensity of stress, which was the response of algal cells to the presence of Cu, Ni, and Zn, and its correlation with respect to production factors and metal accumulation in algal cells. As stress factors, thiol (-SH) group and TBARS (thiobarbituric acid reactive substances) as significant indicators of lipid level peroxidation were determined. The content of -SH groups depended on the concentration of metal, and its level was the most stimulated by Zn, less by Cu and Ni. The TBARS content was 2 to 5 times higher in Cu than in Zn or Ni presence. In the presence of Zn and Ni, TBARS content reached approximately the same levels. For this parameter, the following rank order can be arranged: Cu >> Ni ≥ Zn. While Cu and Ni accumulation in R. subcapitata was confirmed, Zn accumulation was not determined or was below the detectable limit. Regression analyses revealed significant positive correlation between Cu accumulation and TBARS while carotenoids as possible antioxidants confirmed with TBARS mostly negative correlations.

The joint effect of ammonium and pH on the growth of Chlorella vulgaris and ammonium removal in artificial liquid digestate

Although ammonium containing digestate is an ideal alternative medium for microalgae cultivation, high ammonium or unfavorable pH may inhibit microalgal growth. In this study, the joint effect of ammonium and pH on the growth of C. vulgaris and nutrient removal in artificial digestate was investigated. Our results show that ammonium and pH both affected algal growth, but free ammonia (FA) was the main actual inhibitory factor. Algal specific growth rate presented a negative correlation with FA and their relationship was well fitted by a linear regression model. Microalgal growth was little affected below 36.8 mg L−1 FA, while the obvious inhibition occurred at 184 mg L−1 FA (EC50), indicating a high tolerance to FA. Ammonium removal was well described by a first-order kinetics model. FA stress stimulated the production of extracellular organic matters (EOMs), which was good for microalgae adaptation but adverse to pollutant removal.

Optimization of Combined Submerged Macrophyte Planting Conditions for Inhibiting Algae by Response Surface Methodology

Combined planting of submerged macrophytes could be an effective way of controlling algal blooms in landscape waters. In this study, the algal inhibition of single and combined planting of Hydrilla verticillata (A) and Myriophyllum spicatum (B) were explored. The optimized combined planting conditions were investigated using the central composite design. The results showed that the combined planting had a synergistic algal-inhibiting effect. Its inhibition (I (K)) is about 10.8% higher than that of single planting with the same density. The synergism of the combined planting may be due to the different ways in which the two plants inhibit the algal growth. H. verticillata inhibited the algal biomass and M. spicatum inhibited the algal specific growth rate. When the density of H. verticillata and M. spicatum were 7.2 g/L and 6.7 g/L, the value of I (K) reached a maximum 92.2%. Although increasing planting density would improve the algal inhibition, high planting density was not beneficial for the growth of plants. Moreover, no further significant improvement was shown with the increasing planting density when the value of I(K) was higher than 90%. Therefore, the cost-effective combined macrophyte density was 11.6 g/L and the value of A/B ranged from 1.05 to 1.07, where the value of I (K) could achieve 90%. This study can provide a practical basis for using macrophytes to control algal blooms.

DETERMINATION OF GROWTH KINETICS AND BIOCHEMICAL COMPOSITION OF Nitzschia palea (Kützing) W. Smith ISOLATED FROM FRESHWATER SOURCES IN TURKEY

This study was performed in order to bring out a detailed information on growth dynamics and biochemical determination of the diatom species Nitzschia palea (Kützing) W. Smith under batch culture conditions in order to pave the way for further studies. The study material was isolated from a fresh water sample collected from Ankara, Turkey. The diatoms were cultured in Allen medium for 168 hours and the growth dynamics were determined by cell density and dry weight analyses. Specific growth rate, duplication time of the culture and biochemical compositions were also investigated. Molecular characterization of the N. palea strain was performed by applying Fourier Transform Infrared Spectroscopy. The cell density and the dry biomass of the culture at the end of the 168 hours incubation period was determined as 2.0x106±1.0x105cells/mL and 0.212±0.041 g L-1, respectively. The algal specific growth rate was found as 0.010 h-1 at 96-h and the doubling time was calculated as 68 h-1. The protein content was measured as 41.21%, carbohydrate content as 21.74%, lipid content as 16.84% and ash content as 19.88%. These results indicated that N. palea may be used in different fields of industries, especially in biodiesel production.

Multiobjective optimization of microalgae (Chlorella sp.) growth in a photobioreactor using Box‐Behnken design approach

AbstractThis study investigates a parameter optimization approach to maximize the specific growth rate of the Chlorella vulgaris microalgae species, its biomass productivity, and CO2 capture rate. For this purpose, the Box‐Behnken experimental design technique is applied with temperature, nitrogen to phosphorus ratio, and light‐dark cycle per day, as the growth controlling parameters. For each response, a quadratic model is developed separately describing the algal specific growth rate, biomass productivity, and CO2 capture rate, respectively. The maximum specific growth rate of 0.84 d−1 is obtained at 25 °C, with a nitrogen to phosphorus ratio of 3.4:1, and light‐dark cycles of 24/0 h. Maximum biomass productivity of 147.3 mg L−1 d−1 is found at 30 °C, with a nitrogen to phosphorus ratio of 3:1, and light‐dark cycles of 12/12 h. In addition, the maximum CO2 capture rate of 159.5 mg L−1 d−1 is also obtained at 30 °C, with a nitrogen to phosphorus ratio of 4:1, and light‐dark cycles of 23/1 h. Finally, a multi‐response optimization method is applied to maximize the specific growth rate, biomass productivity, and CO2 capture rate, simultaneously. The optimal set of 30 °C, a nitrogen to phosphorus ratio 3:1, and light‐dark cycles 16/8 h, provide the maximum specific growth rate of 0.66 per day, biomass productivity of 147.6 mg L−1 d−1, and CO2 capture rate of 141.7 mg L−1 d−1.

Enhancement of bioelectricity generation and algal productivity in microbial carbon-capture cell using low cost coconut shell as membrane separator

Proton exchange membranes (PEMs) are the most prominently used separator in microbial fuel cell (MFC) and microbial carbon capture cell (MCC). This study aims at evaluating the characteristics of coconut shell (CS) to explore its potential as a PEM. The CS exhibited superior water absorption (32%), which can stimulate the proton transmission through water molecules to the cathodic chamber. The proton conductivity of CS separator was comparable to Nafion 117; however, the oxygen mass transfer coefficient of CS separator was lower than Nafion 117, indicating it as superior separator. These separators were used in MCC with Chlorella sorokiniana grown in cathodic chamber. The maximum power density (MPD) and coulombic efficiency (CE) of MCC with CS separator were 3.2 W/m3 and 16.53%, respectively, whereas the MCC with Nafion 117 membrane showed a MPD of 1.8 W/m3 and CE of 8.42%. Although the COD removal efficiency in the anodic chamber of Nafion-MCC (72.14 ± 0.15%) was superior to CS-MCC (65.97 ± 0.83%), the algal specific growth rate at cathode was found better in CS-MCC (2.64 day−1) than Nafion-MCC (2.16 day−1). This study reveals the feasibility of using CS as low cost as well as energy efficient membrane separator for the application in MCC.

A comparative study of photosynthetic unit models for algal growth rate and fluorescence prediction under light/dark cycles

Accurate description of light-limited algal growth, especially under short light/dark (L/D) cycles, is crucial for prediction of photobioreactor performance and for optimization of operating conditions. Here, a variety of widely used photosynthetic unit (PSU)-based models are evaluated to determine their ability to predict algal specific growth rate and photochemical efficiency under a range of light/dark cycle conditions. Six models were fit to previously published experimental data for algal specific growth rate and photochemical efficiency. Subsequently the weighted sum of squared error (SSE) values, normalized sensitivities to parameter change, and corrected Akaike Information Criterion (AICc) scores were compared. The quality of the fits and the model sensitivities were used to evaluate the assumptions and relative merits of the models considered. For the available data under light/dark cycling conditions, the Bernardi Model scored significantly better on the AICc measure and shows good potential for future use in predicting algal behavior under L/D cycles.

An Algal Specific Growth Rate Relation Model to Assess Dynamical Brown Tide Disasters

This paper considers the coupling effect of nutrient and temperature on algal growth. We propose an algal specific growth rate relation model to assess dynamical brown tide disasters caused by Aureococcus Anophagefferens. To verify the model, we processed data from coastal waters along Qinhuangdao, China, during January 2014 to December 2014, where GIS spatial analysis tools were used to process satellite data on nutrient, chlorophyll a, and temperature, and then calculated the hazard degree of Aureococcus Anophagefferens brown tide. The results show that (1) the suggested model is in accordance with Shelford’s law of tolerance, which states that each species thrives best at a particular value of an environmental variable (the optimum) and cannot survive when the value is either too low or too high; (2) the coastal water along Qinhuangdao was more likely prone to brown tide blooms from May to July than the other months of the year in 2014; (3) the hazard degree of Aureococcus Anophagefferens in areas near the shore was higher than that in areas far from the shore in the same months. These findings would provide a technical basis to effective response to brown tide disasters in Qinhuangdao coastal waters.

Bioprospecting of microalgae for integrated biomass production and phytoremediation of unsterilized wastewater and anaerobic digestion centrate.

Eighteen microalgae, including two local isolates, were evaluated for their ability to grow and remove nutrients from unsterilized primary or secondary wastewater effluents as well as wastewater supplemented with nutrient-rich anaerobic digester centrate (ADC). Most of the tested species except several phylogenetically clustered Chlorella sorokiniana including local isolates and Scenedesmus strains were unable to grow efficiently. This may reflect the presence of certain genetic traits important for robust growth in the unsterilized wastewater. The maximum algal-specific growth rates and biomass density obtained in these bacterial-contaminated cultures were in the range of 0.8-1 day(-1) and 250-350 mg L(-1), respectively. ADC supplementation was especially helpful to biologically treated secondary effluent with its lower initial macronutrient and micronutrient content. As a result of algal growth, total nitrogen and orthophosphate levels were reduced by as much as 90 and 70 %, respectively. Biological assimilation was estimated to be the main mechanism of nitrogen removal in primary and secondary effluents with ammonia volatilization and bacterial nitrification-denitrification contributing for cultures supplemented with ADC. Assimilation by algae served as the principal mechanism of orthophosphate remediation in secondary wastewater cultures, while chemical precipitation appeared also to be important for orthophosphate removal in primary wastewater. Overall, cultivation of microalgae in primary and primary + 5 % ADC may be more favorable from an economical and sustainability perspective due to elimination of the costly and energy-intensive biological treatment step. These findings demonstrate that unsterilized wastewater and ADC can serve as critical nutrient sources for biomass generation and that robust microalgae can be potent players in wastewater phytoremediation.

Positive feedbacks between bottom-up and top-down controls promote the formation and toxicity of ecosystem disruptive algal blooms: A modeling study

Harmful algal blooms that disrupt and degrade ecosystems (ecosystem disruptive algal blooms, EDABs) are occurring with greater frequency and severity with eutrophication and other adverse anthropogenic alterations of coastal systems. EDAB events have been hypothesized to be caused by positive feedback interactions involving differential growth of competing algal species, low grazing mortality rates on EDAB species, and resulting decreases in nutrient inputs from grazer-mediated nutrient cycling as the EDAB event progresses. Here we develop a stoichiometric nutrient–phytoplankton–zooplankton (NPZ) model to test a conceptual positive feedback mechanism linked to increased cell toxicity and resultant decreases in grazing mortality rates in EDAB species under nutrient limitation of growth rate. As our model EDAB alga, we chose the slow-growing, toxic dinoflagellate Karenia brevis, whose toxin levels have been shown to increase with nutrient (nitrogen) limitation of specific growth rate. This species was competed with two high-nutrient adapted, faster-growing diatoms (Thalassiosira pseudonana and Thalassiosira weissflogii) using recently published data for relationships among nutrient (ammonium) concentration, carbon normalized ammonium uptake rates, cellular nitrogen:carbon (N:C) ratios, and specific growth rate. The model results support the proposed positive feedback mechanism for EDAB formation and toxicity. In all cases the toxic bloom was preceded by one or more pre-blooms of fast-growing diatoms, which drew dissolved nutrients to low growth rate-limiting levels, and stimulated the population growth of zooplankton grazers. Low specific grazing rates on the toxic, nutrient-limited EDAB species then promoted the population growth of this species, which further decreased grazing rates, grazing-linked nutrient recycling, nutrient concentrations, and algal specific growth rates. The nutrient limitation of growth rate further increased toxin concentrations in the EDAB algae, which further decreased grazing-linked nutrient recycling rates and nutrient concentrations, and caused an even greater nutrient limitation of growth rate and even higher toxin levels in the EDAB algae. This chain of interactions represented a positive feedback that resulted in the formation of a high-biomass toxic bloom, with low, nutrient-limited specific growth rates and associated high cellular C:N and toxin:C ratios. Together the elevated C:N and toxin:C ratios in the EDAB algae resulted in very high bloom toxicity. The positive feedbacks and resulting bloom formation and toxicity were increased by long water residence times, which increased the relative importance of grazing-linked nutrient recycling to the overall supply of limiting nutrient (N).

Utilisation of organic compounds by osmotrophic algae in an acidic lake of Patagonia (Argentina)

We investigated whether algal osmotrophy in naturally acidic Lake Caviahue is an important process for acquisition of organic carbon and organic nitrogen. To accomplish this, we quantified algal assimilation of organic compounds, measured the specific growth rate and biomass yield, and documented incorporation of organic compounds by phytoplankton in situ using microautoradiography. Substrate uptake quantification and microautoradiographic investigations were performed using 3H-leucine, 3H-glucose, 3H-thymidine, 14C-aspartic acid, 14C-acetic acid and 14C-bicarbonates. The results showed that the most important species of the phytoplankton community, Keratococcus rhaphidioides and Watanabea sp., took up various sources of organic carbon and nitrogen under both light and dark conditions. They were also able to assimilate leucine, thymidine, aspartic acid and acetate under high levels of inorganic nitrogen and phosphorus, while they could use leucine, arginine, glutamine and glucose under low levels of nitrogen and phosphorus. The assimilation rates were higher in light than in darkness, and the algal specific growth rates increased when organic sources were added. We proposed that osmotrophy complements the main photosynthetic process of the phytoplankton in Lake Caviahue, which helps to overcome the scarcity of light and inorganic nitrogen and carbon in the water column.

The partitioned aquaculture system: impact of design and environmental parameters on algal productivity and photosynthetic oxygen production

Fish production in pond culture systems is often limited by the dissolved oxygen (DO) concentration. Algal productivity greatly impacts the DO concentration but is difficult to control in traditional pond systems. The partitioned aquaculture system (PAS) was designed to increase fish production in pond systems by increasing net oxygen production through management of algal productivity and biomass concentration. This initial research was conducted to establish algal productivity and biomass levels in the PAS as a function of algal cell retention time, nutrient addition rate, water depth, and mixing and to characterize the photosynthetic oxygen production rate as a function of solar radiation. In order to focus on algal productivity, an inorganically fertilized PAS without fish was operated for this study. Algal productivity in the PAS was greater for the cell retention time of 1.2 days than 2.5 days, greater for external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day than for 0 mmol/l per day addition rate, greater for the water depth of 34 cm than 66 cm, and greater for the water velocity of 12.5 cm/s than 3.1 and 6.2 cm/s. Algal productivity rates of 5–10 g C/m 2 per day were achieved. Algal culture composition was impacted by inorganic carbon addition. Over a 2-year period, the algal culture was composed primarily of blue–green algae (Cyanophyta) when no external inorganic carbon was added, and green algae (Chlorophyta) at external inorganic carbon addition rates of 0.6 and 1.2 mmol/l per day. The maximum gross photosynthetic oxygen production rate at 20°C was found to be 0.096 mg O 2/mg TSS per hour for predominantly blue–green algal cultures and 0.14 mg O 2/mg TSS per hour for green algal cultures. Corresponding maximum algal specific growth rates, calculated using a literature value for algal cell composition, were 0.077 and 0.12/h for blue–green and green algae, respectively.

Pelagic ecosystem structure and functioning in the subtropical front region east of New Zealand in austral winter and spring 1993

Data are synthesized on biomass and fluxes of components of the pelagic food web, downward particulate flux, and associated physical and chemical oceanographic parameters in austral winter and spring in the Subtropical Front (STF) region east of New Zealand. All four food web types (sensu Legendre and Rassoulzadegan, Ophelia, 41, 153-172, 1995) are represented in this region. The STF food web is classified as 'multivorous' in spring and 'herbivorous'/'multivorous' in winter, even though grazing was dominated by microzooplankton. Based on relatively few data over each season, STF community biomass was dominated by large phytoplankton cells (>20 µm) in both seasons. Post- bloom conditions were sampled in spring and highest fucoxanthin vertical fluxes were recorded at this time. A phytoplankton sedimentation event may have occurred just after our mid-October sampling. Subtropical (ST) waters exhibited pronounced seasonality in all plankton compartments. The ST food web is classified as 'multivorous' in both winter and spring. Organic flux in sediment traps was highest in ST water relative to subantarctic (SA) and STF waters. Although the ST data coverage was limited, high spring algal specific growth rates, the large change in total community biomass between winter and spring, and small seasonal differences in early winter and spring macronutrient concentrations suggest that the structure and functioning of this ecosystem depended on the macronutrients entrained during deep winter mixing. Algal populations in SA high-nitrate-low-chlorophyll waters (HNLC) were dominated by small cells. Heterotrophic bacteria dominated community biomass in SA waters in winter and equalled phytoplankton biomass in spring. In contrast to Legendre and Rassoulzadegan's classification of the subarctic Pacific HNLC food web as 'multivorous', the SA food web is classified as 'microbial' tending towards 'microbial loop' in winter (i.e. there was greater carbon uptake by bacteria than phytoplankton) and 'microbial' in spring. Chlorophyll (Chl) a levels in spring were similar to those in winter, but because of a doubling of the C:Chl ratio, algal biomass (as carbon) was 2-fold higher in SA waters in spring, compared with winter. This seasonal increase in algal carbon biomass in spring occurred in spite of a >5-fold increase from winter to spring in microzooplankton biomass, challenging the notion of grazer control of algal biomass. Our findings are compared with Russian data collected in the South Pacific STF region in summer 1985. Aspects of ecosystem func- tioning in the STF region east of New Zealand may hold for other longitudes in the Southern Ocean, although it is likely that some characteristics are regional in nature.

Microalgal production using a hydraulically integrated serial turbidostat algal reactor (HISTAR): a conceptual model

A hydraulically integrated, serial turbidostat algal reactor (HISTAR) was mathematically modeled and developed for the mass production of microalgae. HISTAR, which hydraulically links precisely controlled turbidostats with continuous-flow stirred-tank reactors (CFSTRs) into a single production technology, was conceptualized emphasizing contaminant mitigation at the design stage to maintain system stability. This paper discusses the conceptual basis for the development of HISTAR and presents a theoretical overview of the CFSTRs. Mathematical modeling, using first-order algal growth kinetics combined with CFSTR reactor kinetics, was used to investigate the effects of system dilution rate, D s; net algal specific growth rate, U a; number of reactors, N; input algal biomass, X i; and contaminant concentration, C n , on algal productivity, as well as local dilution rate, D n , on suspended contaminant washout. The simulation results allowed the determination of preliminary design ranges for prototype development.

Carbon budget studies of symbiotic cnidarian anemones-evidence in support of some assumptions

Current models of carbon flux in symbiotic cnidarians are based on a number of parameters which are particularly difficult to measure directly. One of these is the duration of cytokinesis ( t d ), which in turn affects calculations of the algal-specific growth rate ( μ z ) and the carbon used for growth of the whole algal population ( C μ ). Conventionally a single t d value of 11 h, published from work on symbiotic algae in a tropical jellyfish, has been used even for the algae in Anthopleura elegantissima (Brandt), a temperate zone intertidal anemone. A model testing the effect of varying t d on carbon budget calculations reveals the significance of the choice of t d . Additionally we present evidence for the equivalence of nighttime and daytime respiration rates in A. elegantissima. Finally, the metabolic activity of the insoluble mesogleal matrix of the anemone is shown to be insignificant, and can be ignored without compromising carbon budget calculations.

Role of light, carbon dioxide and nitrogen in regulation of buoyancy, growth and bloom formation of Anabaena flos-aquae

The availability of light, CO 2 and NH 4 -N interacted to control buoyancy and growth of the gas vacuolate blue-green alga, Anabaena flos-aquae . At high light intensities algal growth rates were high; however, the alga was non-buoyant regardless of the availability of CO 2 or NH 4 -N. The mechanism for buoyancy loss involved increased cell turgor pressures at higher light intensities which resulted in collapse of gas vacuoles. At lower light intensities algal growth rates and cell turgor pressures were reduced and buoyancy was controlled by the availability of CO 2 and inorganic nitrogen. Carbon dioxide limitation increased buoyancy, while reduced inorganic nitrogen availability reduced buoyancy. Mechanisms for buoyancy regulation at low light intensities involved changes in cellular C/N ratios which appeared to affect the rate of synthesis and accumulation of protein-rich gas vacuoles. Algal specific growth rates were combined with buoyancy data to form a single index (μ bloom ) to the rate of surface bloom formation of A.flos-aquae as a function of the availability of light, CO 2 and NH 4 -N. The bloom formation index was enhanced with decreased availability of light and CO 2 , and increased availability of NH 4 -N.

Role of herbivory in controlling phytoplankton abundance: annual pigment budget for a temperate marine fjord

An annual pigment budget was constructed for Dabob Bay, Washington (USA) by comparing the downward vertical loss of phytoplankton pigments (chlorophyll and pheopigments) to the production of chlorophyll within the euphotic zone. The vertical flux of pigments was measured with sediment traps deployed at intervals of 1 to 6 wk over a 2.5 yr period yielding 763 d of trap exposure (28 November 1978–16 June 1981). The production rate of chlorophyll was calculated from measurements of algal specific growth rates, chlorophyll (chl) crops, primary production (as carbon) and appropriate C: chl ratios. Sixty one to 77% of the annual chlorophyll production was accounted for by the vertical flux of pheopigments resulting from herbivorous zooplankton grazing (macrozooplankton). Algal sinking, represented by downward chlorophyll flux, accounted for only 5 to 6% of the annual chlorophyll production. The remaining fraction of chlorophyll production was estimated to be consumed by small herbivores (microzooplankton), whose fecal material contributes to the suspended pool of pheopigments found in the euphotic zone. The suspended pheopigments are continuously removed by photodegradation. In Dabob Bay, the major process controlling phytoplankton abundance is zooplankton grazing and it appears that the ultimate fate of most phytoplankton is to be consumed by herbivores.

Interactions between an alga and three bacterial species in a consortium selected for photosynthetic biomass and starch production

AbstractA four‐membered consortium (MA003) of an algal species and bacteria was selected from a natural source for its ability to grow at 37°C and produce starch photosynthetically from carbon dioxide. The photosynthetic culture consisted of a Chlorella‐like green alga (A003) and three heterotrophic bacteria, Alcaligenes sp. (B001), Flavobacter sp. (B002) and Serratia sp. (B003). The substrates for the bacterial growth were probably organic nitrogen and carbon compounds excreted by the alga at specific rates which were independent of the algal specific growth rate. The maximum specific growth rate of the alga was decreased by an inhibitor produced by bacterium B002. Bacterium B001 removed the inhibitor of algal growth released by bacterium B002, and bacterium B003 decreased the growth of bacterium B002 and consequently the production of algal growth inhibitor. The growth of bacterium B003 was greatly suppressed in the four‐member consortium MA003. The coexisting bacteria in toto, did not affect the growth rate, yield and starch production of the algal member, but did help to establish a stable ecosystem and increase the biomass available. A culture density up to 36 g dry weight dm−3 was achieved without significant variation in the ratio of the species in the culture.

Effect of oxygen on the growth (yield) of Chlorella vulgaris

The growth yield of Chlorella vulgaris, Y kJ defined as g cells harvested per kJ of light energy absorbed by the cells, was assessed in a turbidostat culture by varying CO2 and O2 partial pressures ( $$p_{{\text{CO}}_{\text{2}} }$$ and $$p_{{\text{O}}_{\text{2}} }$$ ). The value of Y kJ ranged from 3.1×10-3 to 5.0×10-3 g cells/kJ under light-limited conditions [ $$p_{{\text{CO}}_{\text{2}} }$$ = 1.0∼2.4%, $$p_{{\text{O}}_{\text{2}} }$$ = 0∼65%; total pressure of gas (composed of CO2, O2 and N2)=1 atm]. In the light-limited environment, the algal specific growth rate μ deteriorated appreciably with the increase of $$p_{{\text{O}}_{\text{2}} }$$ . The deterioration accounts for the above range of Y kJ observed. The growth inhibition due to oxygen that was defined by subtracting from 1.0 the ratio of μ at given values of $$p_{{\text{O}}_{\text{2}} }$$ to that at $$p_{{\text{O}}_{\text{2}} }$$ = 0% extended from 0.07–0.30 (7–30%). However, glycolate could not be detected in the turbidostat culture. Isotopic experiments on the specific rate of 14CO2 uptake also revealed that the inhibition due to oxygen was from 22–38% when $$p_{{\text{O}}_{\text{2}} }$$ was varied from 0 to nearly 100%. These effects of oxygen were discussed, referring to the activity of ribulose-1,5-bisphosphate carboxylase that is inhibited competitively by oxygen.