Arthrospira platensis biomass with high protein content cultivated in continuous process using urea as nitrogen source

Aims: Arthrospira platensis has been studied for single‐cell protein production because of its biomass composition and its ability of growing in alternative media. This work evaluated the effects of different dilution rates (D) and urea concentrations (N₀) on A. platensis continuous culture, in terms of growth, kinetic parameters, biomass composition and nitrogen removal. Methods and results: Arthrospira platensis was continuously cultivated in a glass‐made vertical column photobioreactor agitated with Rushton turbines. There were used different dilution rates (0·04–0·44 day^?1) and urea concentrations (0·5 and 5 mmol l^?1). With N₀ = 5 mmol l^?1, the maximum steady‐state biomass concentration was1415 mg l^?1, achieved with D = 0·04 day^?1, but the highest protein content (71·9%) was obtained by applying D = 0·12 day^?1, attaining a protein productivity of 106·41 mg l^?1 day^?1. Nitrogen removal reached 99% on steady‐state conditions. Conclusions: The best results were achieved by applying N₀ = 5 mmol l^?1; however, urea led to inhibitory conditions at D ≥ 0·16 day^?1, inducing the system wash‐out. The agitation afforded satisfactory mixture and did not harm the trichomes structure. Significance and Impact of the Study: These results can enhance the basis for the continuous removal of nitrogenous wastewater pollutants using cyanobacteria, with an easily assembled photobioreactor.     

Biomass and Lipid Production of Dinoflagellates and Raphidophytes in Indoor and Outdoor Photobioreactors

The principal fatty acids from the lipid profiles of two autochthonous dinoflagellates (Alexandrium minutum and Karlodinium veneficum) and one raphidophyte (Heterosigma akashiwo) maintained in bubble column photobioreactors under outdoor culture conditions are described for the first time. The biomass production, lipid content and lipid productivity of these three species were determined and the results compared to those obtained when the strains were cultured indoors. Under the latter condition, the biotic values did not significantly differ among species, whereas under outdoor conditions, differences in both duplication time and fatty acids content were observed. Specifically, A. minutum had higher biomass productivity (0.35 g·L^?1 day^?1), lipid productivity (80.7 mg lipid·L^?1 day^?1) and lipid concentration (252 mg lipid·L^?1) at harvest time (stationary phase) in outdoor conditions. In all three strains, the growth rate and physiological response to the light and temperature fluctuations of outdoor conditions greatly impacted the production parameters. Nonetheless, the species could be successfully grown in an outdoor photobioreactor and were of sufficient robustness to enable the establishment of long-term cultures yielding consistent biomass and lipid production.     

The use of outdoor phytoplankton continuous cultures to analyse factors influencing species selection

Natural phytoplankton populations have been grown in outdoor continuous cultures at three dilution rates (D = 0.5, 0.25, and 0.1 · day^?1) under nitrogen (N) or silicon (Si) limitation and two light intensities. At a high specific nutrient flux (high dilution rate) under N limitation an assemblage of primarily small, fast growing centric diatoms such as Skeletonema costatum (Grev.) Cleve and Chaetoceros spp. dominated with a low percentage of flagellates. At a low specific nutrient flux, a mixture of larger, slower growing centric diatoms, small flagellates, and pennate diatoms was obtained. Similar trends were observed under silicate limitation. Decreasing the light intensity at the lowest dilution rate selected for an assemblage similar to that observed at the high dilution rate and high light intensity.The results of these competition experiments suggest that specific nutrient flux (dilution rate) is an important factor in determining between group dominance (e.g., centric and pennate diatoms and small flagellates). Successful competitors representing broad phytoplankton groups can be arranged along a resource gradient of specific nutrient flux (dilution rate), with groups such as centric and pennate diatoms, represented as high and medium flux species, respectively.     

Effects of diurnal fluctuations in light intensity on the efficiency of growth of Skeletonema costatum (Grev.) Cleve (Bacillariophyceae) in a cyclostat

The effects of diurnal variations in light intensity on the biomass characteristics and the efficiency of daily growth of Skeletonema costatum (Grev.) Cleve were evaluated. The relative importance of changes in carbon specific rates of respiration and organic release to the efficiency of growth was determined. Light intensity was either constant at 130 μE · m^?2 · s^?1 during the light period or fluctuated throughout the light period from 500 to 10 μE · m^?2 · s^?1 at rates of either 1 or 12 cycles · day^?1. Total daily light was equivalent for all light regimes at 5.6 E · m^?2 · day^?1.Daily rates of growth remained comparable at ≈ 1 · day^?1 under constant and fluctuating light regimes. Cell size as daily mean carbon · cell^?1, nitrogen · cell^?1 and cellular volume was decreased under diurnally varying light whereas daily mean chlorophyll a · cell^?1 was unaffected.Rates of respiration, organic release and gross production were elevated several fold under diurnally varying light in comparison to constant light. Net growth efficiency decreased from 0.69 under constant light to values of 0.50 and 0.38 under 1 and 12 cycles · day^?1, respectively. Decreased efficiency of growth under diurnally fluctuating light resulted mostly from greater respiratory activity while organic release remained < 10% of gross production. Increased rates of gross production reflected enhancement in the efficiency of carbon fixation with fluctuating light.     

Egg production of the marine,planktonic copepod,Calanus pacificus Brodsky: Laboratory observations

When acclimated to a continuous, superabundant food supply and constant temperature, Calanus pacificus Brodsky females produce eggs at a weight-specific rate ranging from 0.13 · day^?1 at 8°C to 0.21 · day^?1 at 15°C. Maximum weight-specific egg production rates do not change with seasonal changes in female body size. The relationship between egg production rate and food concentration is hyperbolic, with threshold and critical concentrations that are high relative to other species for which data are available. Food concentration and temperature influence spawning frequency (i.e., the time required for oocytes to mature) much more than the number of eggs in a single spawning event (i.e., clutch size). Clutch size is significantly related to female body size.     

The feeding rates and efficiencies of a marine ciliate, Strombidium sp., grown under chemostat steady-state conditions

A marine ciliate of the genus Strombidium isolated from a marine rock-pool, was grown bacteriafree in a chemostat continuous culture system and fed on the alga Pavlova (Monochrysis) lutheri Droop, which was also grown in continuous culture. The growth rate of the ciliate was maintained constant whilst the growth rate of the alga was varied, the latter producing little change in its energy content.The specific filtration and ingestion rates of Strombidium were measured and found, in both cases, to vary inversely as a function of the concentration of available algae. The filtration rate showed a range from 2 to 35 μl · ciliate^?1 · day^?1 whilst the ingestion rate varied from 0.8 to 3.4 J · ciliate^?1 · day^?1. The efficiency of ingestion remained constant throughout the experiment with a mean of > 91%, the overall growth efficiency also remained constant but with a mean of only 6.5%.The rates and efficiencies are compared with the results obtained by other workers.     

The membraneless bioelectrochemical reactor stimulates hydrogen fermentation by inhibiting methanogenic archaea

The membraneless bioelectrochemical reactor (Ml-BER) is useful for dark hydrogen fermentation. The effect of the electrochemical reaction on microorganisms in the Ml-BER was investigated using glucose as the substrate and compared with organisms in a membraneless non-bioelectrochemical reactor (Ml-NBER) and bioelectrochemical reactor (BER) with a proton exchange membrane. The potentials on the working electrode of the Ml-BER and BER with membrane were regulated to ?0.9 V (versus Ag/AgCl) to avoid water electrolysis with a carbon electrode. The Ml-BER showed suppressed methane production (19.8?±?9.1 mg-C·L^?1·day^?1) and increased hydrogen production (12.6?±?3.1 mg-H·L^?1·day^?1) at pH_out 6.2?±?0.1, and the major intermediate was butyrate (24.9?±?2.4 mM), suggesting efficient hydrogen fermentation. In contrast, the Ml-NBER showed high methane production (239.3?±?17.9 mg-C·L^?1·day^?1) and low hydrogen production (0.2?±?0.0 mg-H·L^?1·day^?1) at pH_out 6.3?±?0.1. In the cathodic chamber of the BER with membrane, methane production was high (276.3?±?20.4 mg-C·L^?1·day^?1) (pH_out, 7.2?±?0.1). In the anodic chamber of the BER with membrane (anode-BER), gas production was low because of high lactate production (43.6?±?1.7 mM) at pH_out 5.0?±?0.1. Methanogenic archaea were not detected in the Ml-BER and anode-BER. However, Methanosarcina sp. and Methanobacterium sp. were found in Ml-NBER. Prokaryotic copy numbers in the Ml-BER and Ml-NBER were similar, as were the bacterial community structures. Thus, the electrochemical reaction in the Ml-BER affected hydrogenotrophic and acetoclastic methanogens, but not the bacterial community.     

Skeletal growth in the echinoderm Asterias rubens L. (Asteroidea,Echinodermata) estimated by 45Ca-labelling

The skeletal dry weight of the 4.4 ± 0.2 cm size class of Asterias rubens L. from Kiel Bay in the western Baltic is 0.34 ± 0.08 g. The sum of calcium and magnesium carbonates in the skeleton amounts to 94.0 ± 1.3% while the individual concentrations are 86.9 ± 1.3% CaCO₃ and 7.1 ± 0.7% MgCO₃. The MgCO₃ is 4% lower than expected for a magnesium calcite precipitated under Baltic temperature conditions (8°C). Strontium was not determined but strontium carbonate is known to be in the region of 0.4%. The remainder is organic matter and this gives rise to 2.9 ± 1.3% organic carbon.Animals studied were at the ‘waiting stage’ and their actual growth was minimal. Uptake of ⁴⁵Ca in the skeleton consists of a fast step followed by a slow step. The fast step is attributed to saturation of exchangeable skeletal pools while the slow step is due to net deposition of CaCO₃. Skeletal growth at the waiting stage calculated from the second rate constant was found to be 0.76 μg CaCO₃j-mg skeleton^?1 · day^?1 or 0.09% · day^?1 compared with 9.3 μg CaCO₃ · mg skeleton^t1&#x0304; · day^?1 or 1.1% · day^?1 at log phase. The isotope method is considered superior to size-frequency analysis in that it is capable of detecting differences in growth rate in individuals of the same size class and thus provides an insight into asteroid population structure.     

Effect of detritus supply on trophic relationships within experimental benthic food webs. I. Meiofauna-polychaete (capitella capitata (Type I) Fabricius) interactions

In a long-term (40–55 wk) microcosm experiment, the presence of the polychaete Capitella capitata (Type I) Fabricius reduced population densities and trophic transfer efficiencies (detritivore production per amount of detritus supplied) of the nematode Diplolaimella chitwoodi Gerlach at high (150 mg N · m^?2 · day^?1) detritus ration and of the harpacticoid copepod Tisbe holothuriae Humes at low (50 mg N · m^?2 · day^?1) detritus supply. The rarer nematodes Theristus ostentator Wieser & Hopper and Paracyatholaimus pesavis Wieser & Hopper fed at depth on fungal hyphae attached to polychaete fecal pellets thereby minimizing contact with the other metazoa.In a series of short-term (4-day) growth experiments, the presence of either Diplolaimella chitwoodi or Tisbe holothuriae reduced daily weight-specific growth (g increase · g worm^?1 · day^?1) of Capitella capitata on separate diets of mixed cereal and red seaweed, Gracilaria foliifera (Harvey) Taylor, detritus.Both sets of experiments suggest that Capitella capitata competes for food with Diplolaimella chitwoodi and Tisbe holothuriae. Meiofauna-polychaete interactions were dependent, in part, upon the degree of similarity among species in food requirements and habitat preferences, and may incorporate a variety of regulatory mechanisms other than competition or predation.     

Nutrient uptake and growth kinetics in brown seaweeds: Response to continuous and single additions of ammonium

The brown seaweeds Fucus distichus Linnaeus subsp. edentatus (de la Pylaie) Powell, a perennial, and Chordaria flagelliformis (O.F. Mueller) C. Agardh, a summer annual, were grown in continuous-flow greenhouse cultures. In winter, the growth of Fucus distichus ( μ = 0.01 · day^?1 ) in culture was not stimulated by added ammonium. Nitrogen in excess of the growth requirement was accumulated in the thallus ( 1.34–2.18 % N by dry wt, depending on the N-loading). In summer, the growth of both species in continuous cultures was stimulated by added ammonium. Chordaria flagelliformis showed higher rates of both growth (μ_max = 0.109 · day^?1) and ammonium uptake $\text{(V}{}_{\max }\text{= 23.2 μmol NH}{}_4{}^{\mathrm{+}}\text{· h}{}^{\mathrm{?1}}\text{· g dry wt}{}^{\mathrm{?1}}\text{)}$ than Fucus distichus (μ_max = 0.074 · day^?1, V_max = 13.9 μmolNH₄⁺ · h^?1 · gdrywt^?1). Calculated nitrogen subsistence quotas were similar in the two species (0.7% N in Chordaria, 0.6% N in Fucus). In those continuous cultures which did not receive added ammonium, Chordaria stored less nitrogen in excess of the subsistence quota than Fucus, although both species accumulated nitrogen at increased N-loading. Transient uptake rates were measured in response to single additions of ammonium. At any given initial concentration, short-term (30 min) uptake rates were a decreasing function of the thallus nitrogen quota and were higher for Chordaria than for Fucus. In N-depleted plants, short-term ammonium uptake rates exceeded both the uptake rates predicted from continuous cultures and the nitrogen requirements for growth. Chordaria flagelliformis, in particular, is able to scavenge efficiently low ambient N-nutrient concentrations and to sequester rapidly transient ammonium pulses. In comparison with Fucus distichus, Chordaria flagelliformis appears to be better adapted to short-term fluctuations in nutrient availability (on a scale of minutes to hours). Their N-storage capability allows both of these seaweeds to buffer the effect of fluctuations in external N-nutrient concentrations on their growth rates over periods of days to several weeks.     

Degradation Rates for Petroleum Hydrocarbons Undergoing Bioventing at the Meso-Scale

ABSTRACT

Bioventing can be effective for the remediation of soil contaminated with petroleum hydrocarbons. However, implementing laboratory results in field scenarios is difficult due to the lack of scale-up factors. Accordingly, laboratory bioventing experiments were undertaken at the meso-scale and then compared with previously completed micro-scale tests to evaluate the important scale-up factor. The developed meso-scale system holds 4 kg of soil, with bioventing conditions controlled from a nutrient, airflow, and water content perspective. Three soils were tested, and categorized as loamy sand, silt loam, and a mixture. Results over a 30-day period showed a two-stage degradation pattern that encompassed first-order degradation rates as compared with the single-stage first-order degradation rate determined in the micro-scale study. For the first stage (0–8 days), the degradation rate for loamy soil was 0.598 day^?1, with the silty soil at 0.460 day^?1, and mixed soil at 0.477 day^?1. After 8 days, the degradation rate constant for the loamy soil dropped to 0.123 day^?1, with the silty soil dropping to 0.075 day^?1, and the degradation rate for the mixed soil dropping to 0.093 day^?1. Comparison of the measured degradation rate values with the results from the micro-scale experiments gave scale-up factors varying from 1.9 to 2.7 for the types of soil considered in the current study. These differences in degradation rates between the two scales show the importance of scale-up factors when transferring feasibility study results to the field.     

Chemical composition and alkaline phosphatase activity of nutrient-saturated and P-deficient cells of four marine dinoflagellates

Four marine dinoflagellates, Amphidinium carterae Hulburt, Ceratium tripos (O.F. Müll.) Nitzsch, Prorocentrum minimum (Pav.) J. Schiller, and Scrippsiella trochoidea (Stein) Loeblich III were grown as dilution cultures at 18°C, S = 29%. and 30 μE·m^?2·s^?1 at L:D = 14:10 h. In nutrient-saturated cultures, the growth rates (doubl·day^?1) ranged from 0.38 for Scrippsiella to 0.80 for Prorocentrum, and carbon content (pg·cell^?1) from 83 for Amphidinium to 6900 for Ceratium. The atomic $\text{N}\text{C}$ ratio was 0.13–0.15, but for Ceratium it was 0.088, because of its thick, cellulose theca. The atomic $\text{N}\text{P}$ ratio ranged from 12–13 for Ceratium and Scrippsiella to 15–17 for Prorocentrum and Amphidinium. Under P-deficient conditions (growth rate 39–70% of the maximum), cellular P decreased considerably, but so did N, so that the $\text{N}\text{P}$ ratio was only slightly affected. There was a concomitant increase in carbon content per cell of 1.2- to 1.7-fold. Alkaline phosphatase activity was virtually nil in nutrient-saturated cells, but was readily demonstrable in all species when P-deficient.     

Kinetics of intracellular carbon allocation in a marine diatom

To test models of intracellular carbon flow we measured the labelling kinetics (from ¹⁴CO₂) of major classes of cell polymers (carbohydrate, protein, lipid) and of dissolved organic carbon produced by the marine diatom Thalassiosira pseudonana Hustedt, grown at rates of 0.2 to 2.0·day^?1 under nitrogen or light limitation. Compartmental analysis indicated that tracer carbon quickly entered respiratory and excretory streams, accumulating in the cells at the rate of net production after only 25–50% of cell generation (doubling) time. Respiration rates were low (≤ 0.1 · day^?1) and suggested that illuminated cells in steady-state growth made only minor use of oxidative respiration to support cell synthesis. The tracer was quick to enter all polymers; compartmental analysis indicated that polymer labelling rates were close to the rates of mass synthesis after several hours of incubation with ¹⁴C. Polymer labelling also showed a reallocation of photosynthate from protein to carbohydrate within a few hours of perturbation (shift-down) of nutrient supply in a N-limited chemostat. In steady-state growth, the protein: carbohydrate ratio increased directly with N-limited growth rate but attained its maximum under extreme light-limitation. Carbon flow into the metabolic processes of respiration, excretion and polymer synthesis appeared to be mediated by a small and rapidly cycled pool of substrates under all steady-state growth conditions.     

Seasonal variation in light- and temperature-dependent growth of marine planktonic diatoms in in situ dialysis cultures in the Trondheimsfjord,norway (63°N)

Three species of diatoms, Skeletonema costatum (Grev.) Cleve, Thalassiosira gravida Cleve, and T. pseudonana (Hustedt) Hasle et Heimdal, were grown in in situ dialysis culture in the Trondheimsfjord at depths of 0.5 and 4 m. The rates of growth and the chemical composition of exponentially growing cells were monitored and related to seasonal changes in illumination and temperature. Functions correlating growth rate with temperature were deduced. Growth took place from February to November. During this period temperature ranged from ?1 to 16°C, the average photon flux density (ifI) (per 24 h) from 9 to 570 μE · m^?2 · s^?1 (0.5 m depth), and the length of the days (I > 1 μE · m^?2 · s^?1) from 6 to 24 h. Light-limited growth was evident when the product of the average daily light and the chlorophyll/N ratio was < 10; this occurred mostly in early spring and late autumn. Peak densities (> 800 for the Thalassiosira spp. and > 1300–1400 μE · m^?2 · s^?1 for Skeletonema) seem to inhibit growth. The highest rates recorded were ≈1.6 doubl. · day^?1 (July, 15–16°C).The three species exhibit different ecological behaviour. Skeletonema is eurythermal (Q₁₀ = 1.8), whereas Thalassiosira pseudonana favours high temperatures, and T. gravida temperatures < 10°C. Moreover, Skeletonema has generally less chlorophyll and more phosphorus and ATP (≈ 1.4 ×) than the other two species. In Skeletonema, the ATP level seems related to the light-governed growth rate, and independent of temperature. In Thalassiosira no such correlation was found.     

A CARBON BUDGET FOR THE AUTOTROPHIC CILIATE MESODINIUM RUBRUM1

Extensive blooms of the autotrophic ciliate Mesodinium rubrum (Lohmann) occurred in the Peru coastal upwelling region at 15°S latitude in March through May 1977 and contributed significantly to the organic productivity of the region. From observations made during the JOINT-II oceanographic expedition, a budget of the carbon flux of these unusual photosynthetic organisms can be constructed. The light dependent C fixation was determined with short (1 h) incubations because of the organisms' sensitivity to confinement and rapid nutrient exhaustion. Maximum photosynthesis occurred at 50% of incident light with a maximum rate of particulate C synthesis of 2187 mg C · m^?3· h^?1. The specific carbon uptake rates were also high with a maximum light saturated value of 16.8 mg C ·(mg chl a)^?1· h^?1. The rate of excretion of dissolved organic C at the productivity maximum ranged from 16.1 to 181.1 mg C · m^?3· h^?1. The range of percent excretion was 1.8–12.5% the total C fixed, similar to the range found in both motile and nonmotile phytoplankton assemblages. Respiration, determined by the decrease in particulate C in the dark, averaged 4.6% of the previously fixed photosynthetic C · h^?1. M. rubrum actively took up amino acids and naturally occurring dissolved organic carbon. The C budget for this ciliate indicates that the daily contribution to the particulate food chain is large, although not as great as is indicated by short incubations. The contribution of M. rubrum to the productivity and elemental fluxes of upwelling and coastal ecosystems has been seriously underestimated.     

Optimisation of biomass and lipid production by adjusting the interspecific competition mode of Dunaliella salina and Nannochloropsis gaditana in mixed culture

The high cost of algal cultivation has been a barrier associated with the commercialisation of algal biodiesel. Therefore, this study aimed to enhance lipid production by optimising the nutrient supply to benefit the coexistence of Dunaliella salina and Nannochloropsis gaditana. The effects on biomass and lipid production of using different proportions of D. salina and N. gaditana, urea and NaHCO₃ were optimised by response surface method with a 17-run Box–Behnken design. The optimal conditions for the algal growth are 58 % of D. salina in the mixture at OD₆₈₀, 150 μL day^?1 urea (0.0044 g day^?1) and no addition of NaHCO₃. The biomass concentration and lipid production reached 1.00 and 0.383 g L^?1, respectively, which are exceeded by the amount before optimisation, indicating the efficiency of the model obtained by response surface method.     

Clearance rates of sessile rotifers: In situ determinations

Clearance rates of three sessile and four free-swimming rotifer species from a small acid bog-pond were measured using in situ techniques. Three radioactively labeled cell types, an alga (Chlamydomonas), a bacterium (Enterobacter = Aerobacter), and a yeast (Rhodotorula) were used as tracers. Clearance rates (using yeast) ranged from <1.0 to >250 µl · animal^?1 · h^?1 depending on species. Ptygura crystallina, Ptygura pilula, Floscularia conifera, and an unidentified bdelloid ingested all three foods with substantial variation in clearance rates among species and cell type. There was an insignificant error (<0.3%) in clearance rate associated with non-ingestive uptake of radioactivity. Among the free-swimming taxa, Lecane sp. had a clearance rate of <0.5 µl · animal^?1 · h^?1 on yeast, while another Lecane sp. and Trichotria tetractis did not ingest that cell type.     

Assessment of Human Health Risks of Consumption of Cadmium Contaminated Cultured Oysters

With farmed British Columbia (BC) oysters containing higher cadmium concentrations than wild oysters, long-term exposure to cadmium through consumption of oysters has the potential to cause health risks. This study reports on a risk assessment for cadmium intake resulting from the consumption of BC-cultured oyster. The study concludes that Health Canada's current recommended BC-cultured oyster consumption rate for Canadians of 12 oysters per month exceeds the Agency for Toxic Substances and Disease Registry chronic oral minimal risk levels (MRL) of 0.2 μ g·kg^{? 1}·day^{? 1} by approximately 4-to 5-fold and reaches the Food and Agriculture Organization/World Health Organization (FAP/WHO) reference dose of 1 μg·kg^?1·day^?1 for cadmium consumption for Canadians. This suggests that although the current recommended maximum oyster consumption rates is consistent with the FAO/WHO and U.S. Environmental Protection Agency limits for acceptable risk, it leaves little or no room for error or uncertainty. This is noteworthy as recent studies demonstrate toxicological effects at cadmium intakes of 0.43 to 0.71 μ gCd·kg^?1·day^?1. This study indicates that a lower maximum BC-cultured oyster rate should be considered, particularly for high risk groups, including women with low iron stores, people with renal impairment, smokers, children, and indigenous people who consume organ meats of games and wildlife other than shellfish.     

Density and ecological importance of bacteria on kelp fronds in an upwelling region

Bacteria on the surfaces of fronds of two co-occurring species of kelp have been sampled at monthly intervals for a year in the Benguela upwelling region. Counts of viable bacteria were obtained by the spread plate technique. Bacterial counts at frond bases of both kelps followed a seasonal pattern with minima of 10³ cells·cm^?2 in winter and maxima of 10⁶ cells·cm^?2 in late summer, similar to the bacterio-plankton cycle. At frond tips bacterial densities remained high (≈ 10⁷ cells·cm²) throughout the year and were significantly denser than on other parts of the frond. There was no significant difference between kelp species. Rate of frond erosion does not vary significantly at different seasons, and a minimal estimate of average daily contribution of bacteria eroding off frond tips with the tissue is 2.6 × 10⁹ cells·m^?2·day^?1. The large standing stock of benthic suspension-feeding animals probably utilizes this nitrogen-rich resource.     

A quantitative study of eicosapentaenoic acid (EPA) production by Nannochloropsis gaditana for aquaculture as a function of dilution rate,temperature and average irradiance

Different pilot-scale outdoor photobioreactors using medium recycling were operated in a greenhouse under different environmental conditions and the growth rates (0.1 to 0.5 day^?1) obtained evaluated in order to compare them with traditional systems used in aquaculture. The annualized volumetric growth rate for Nannochloropsis gaditana was 0.26 g l^?1 day^?1 (peak 0.4 g l^?1 day^?1) at 0.4 day^?1 in a 5-cm wide flat-panel bioreactor (FP-PBR). The biomass productivity achieved in this reactor was 10-fold higher than in traditional reactors, reaching values of 28 % and 45 % dry weight (d.w.) of lipids and proteins, respectively, with a 4.3 % (d.w.) content of eicosapentaenoic acid (EPA). A model for predicting EPA productivity from N. gaditana cultures that takes into account the existence of photolimitation and photoinhibition of growth under outdoor conditions is presented. The effect of temperature and average irradiance on EPA content is also studied. The maximum EPA productivity attained is 30 mg l^?1 day^?1.