Spatial and temporal patterns of growth and consumption by juvenile spring/summer Chinook salmon Oncorhynchus tshawytscha

Somatic growth is often used as a metric of habitat quality, but such an approach has limitations because growth results from complex interactions between abiotic and biotic factors. In this study, we derived estimates of weekly growth (based on otolith growth increments) across several months for four populations of threatened Chinook salmon, Oncorhynchus tshawytscha, from the Salmon River Basin, Idaho, USA. Although mean stream temperature varied by 2–5 °C across populations, growth across the season did not vary significantly by population. To investigate this further, we applied a bioenergetics model that produced estimates of consumption rates. We then examined how growth and consumption rates varied according to rearing stream and day in the season. Using generalized least squares models, somatic growth (g?day^?1) was best explained by stream and date, yet a model with only date had moderate support, and thus indicated limited support for stream effects. Specific consumption rate (g?g^?1?day^?1 and J?g^?1?day^?1) was best explained using a model that included main effects of stream and date. These findings are consistent with the hypothesis that higher temperatures confer higher metabolic costs that require greater consumption to produce similar growth rates in cooler streams. This highlights that similarity in growth rate among streams may mask changes in individual behavior and/or energetic acquisition associated with differences in temperatures among streams. Results of this study represent the first steps towards identifying factors that underlie important population level and habitat quality differences.     

Microbial processes of the carbon and sulfur cycles in the Chukchi Sea

The research performed in August 2004 within the framework of the Russian-American Long-term Census of the Arctic (RUSALCA) resulted in the first data concerning the rates of the key microbial processes in the water column and bottom sediments of the Bering strait and the Chukchi Sea. The total bacterial counts in the water column varied from 30 × 10³ cells ml^?1 in the northern and eastern parts to 245 × 10³ cells ml^?1 in the southern part. The methane content in the water column of the Chukchi sea varied from 8 nmol CH₄l^?1 in the eastern part of the sea to 31 nmol CH₄l^?1 in the northern part of the Herald Canyon. Microbial activity occurred in the upper 0–3 cm of the bottom sediments; the methane formation rate varied from 0.25 to 16 nmol CH₄dm^?3 day^?1. The rates of methane oxidation varied from 1.61 to 14.7 nmol CH₄dm^?3 day^?1. The rates of sulfate reduction varied from 1.35 to 16.2 μmol SO ₄ ^2? dm^?1 day^?1. The rate of methane formation in the sediments increased with depth, while sulfate reduction rates decreased (less than 1 μmol SO ₄ ^2? dm^?3 day^?1). These high concentrations of biogenic elements and high rates of microbial processes in the upper sediment layers suggest a specific type of trophic chain in the Chukchi Sea. The approximate calculated balance of methane emission from the water column into the atmosphere is from 5.4 to 57.3 μmol CH₄m^?2 day^?1.     

An approach to the assessment of risk from chronic radiation to populations of European lobster, Homarus gammarus (L.)

The basic principles underlying a four-discrete age group, logistic, growth model for the European lobster Homarus gammarus are presented and discussed at proof-of-concept level. The model considers reproduction, removal by predation, natural death, fishing, radiation and migration. Non-stochastic effects of chronic low linear energy transfer (LET) radiation are modelled with emphasis on ⁹⁹Tc, using three endpoints: repairable radiation damage, impairment of reproductive ability and, at higher dose rates, mortality. An allometric approach for the calculation of LD_50/30 as a function of the mass of each life stage is used in model calibration. The model predicts that at a dose rate of 1 Gy day⁻¹, lobster population reproduction and survival become severely compromised, leading eventually to population extinction. At 0.01 Gy day⁻¹, the survival rate of an isolated population is reduced by 10%, mainly through loss of fecundity, comparable to natural migration losses. Fishing is the main ecological stress and only dose rates in the range 0.03–0.1 Gy day⁻¹ can achieve discernible effects above it. On the balance of radiation and other ecological stresses, a benchmark value of 0.01 Gy day⁻¹ is proposed for the protection of lobster populations. This value appears consistent with available information on radiation effects in wildlife.     

OLISTHODISCUS LUTEUS (CHRYSOPHYCEAE) I. EFFECTS OF SALINITY AND TEMPERATURE ON GROWTH. MOTILITY AND SURVIVALS1, 2

The effect of salinity and temperature on Olisthodiscus luteus Carter has been examined to across the relative importance of these factory on dynamics of natural population. A salinity range 2–50% was observed with increased tolerance to low salinity (<5%.) at higher temperature (20–30°C). Slinities at 4–5%. Had densities of 10³ cells/ml^?1, and growth >0.5 division day^?1 at temperature of 15–30°C higher salinities (5–50%.) variable but distinct optima for density, growth and motility were observed 5, 10 and 30°C. Density and motility showed no clear optima from 10–10%.15–25°C where maximum growth rates >1.0 division/day^?1 were common. Temperature increased from (0.5–1.9 division. Day^?1) and increases of three orders of magnitude (10^2?10³) for maximum densities. Temperature optima 20°C for growth 5–35%. And 25°C for >40%. were observed. The implications of these findings to natural populations of O. luleus are discussed.     

Diversity, abundance, and activity of ammonia-oxidizing bacteria and archaea in Chongming eastern intertidal sediments

Ammonia oxidation plays a pivotal role in the cycling and removal of nitrogen in aquatic sediments. Certain bacterial groups and a novel group of archaea, which is affiliated with the novel phylum Thaumarchaeota, can perform this initial nitrification step. We examined the diversity and abundance of ammonia-oxidizing β-Proteobacteria (β-AOB) and ammonia-oxidizing archaea (AOA) in the sediments of Chongming eastern tidal flat using the ammonia monooxygenase-α subunit (amoA) gene as functional markers. Clone library analysis showed that AOA had a higher diversity of amoA gene than β-AOB. The β-Proteobacterial amoA community composition correlated significantly with water soluble salts in the sediments, whereas the archaeal amoA community composition was correlated more with nitrate concentrations. Quantitative PCR (qPCR) results indicated that the abundance of β-AOB amoA gene (9.11?×?10⁴–6.47?×?10⁵?copies?g^?1 sediment) was always greater than that of AOA amoA gene (7.98?×?10³–3.51?×?10⁵?copies?g^?1 sediment) in all the samples analyzed in this study. The β-Proteobacterial amoA gene abundance was closely related to organic carbon, while no significant correlations were observed between archaeal amoA gene abundance and the environmental factors. Potential nitrification rates were significantly greater in summer than in winter and correlated strongly with the abundance of amoA genes. Additionally, a greater contribution of single amoA gene to potential nitrification occurred in summer (1.03–5.39 pmol?N?copy^?1?day^?1) compared with winter (0.16–0.38 pmol?N?copy^?1?day^?1), suggesting a higher activity of ammonia-oxidizing prokaryotes in warm seasons.     

Sea ice microbial dynamics over an annual ice cycle in Prydz Bay, Antarctica

Microbial community dynamics within the fast sea ice of Prydz Bay (68°S?78°E) were investigated over an annual cycle at two sites (1 and 3?km offshore) between April and November 2008. There are few long-term sea ice studies, and few that cover the phase of winter darkness when autotrophic processes are curtailed. Mean chlorophyll a concentrations in the ice column ranged between 0.76 and 44.8?μg?L^?1 at the 1-km site (Site 1) and 3.11–144.6?μg?L^?1 at the 3-km site (Site 2). Highest chlorophyll a usually occurred at the base of the ice. Bacterial concentrations ranged between 0.30 and 2.08?×?10⁸?cells?L^?1, heterotrophic nanoflagellates (HNAN) between 0.21?×?10⁵ and 2.98?×?10⁵?cells?L^?1 and phototrophic nanoflagellates (PNAN) 0–1.06?×?10⁵?cells?L^?1. While HNAN occurred throughout the year, PNAN were largely absent in winter. Dinoflagellates were a conspicuous and occasionally an abundant element of the community (maximum 17,460?cells?L^?1), while ciliates were sparse. The bacterial community showed considerable morphological diversity with a dominance of filamentous forms. Bacterial production continued throughout the year ranging between 0 and 22.92?μg?C?L^?1?day^?1 throughout the ice column. Lowest rates occurred between late June and early August. The sea ice sustained an active and diverse microbial community through its annual extent. The data suggest that during winter darkness the microbial community is dominated by heterotrophic processes, sustained by a pool of dissolved organic carbon.     

Radiation effects in generic populations inhabiting a limiting environment

A generic population model is formulated for radiation risk assessment of natural biota. The model demonstrates that effects of radiation on the population survival do not follow directly the effects on individual organisms. Dose rates resulting in population extinction can be analytically calculated. Besides individual radiosensitivity, two key parameters were found to determine the survival potential of a population under chronic radiation stress: the ratio “biomass losses/biomass synthesis,” and the lump amount of limiting resource in the environment. A benchmark scenario “Population response to chronic irradiation” developed within the IAEA Programme EMRAS II was calculated for generic populations of mice, hare/rabbit, wolf/wild dog, and deer/goat chronically exposed to different levels of ionizing radiation. In the conditions of the benchmark scenario, model populations survived normally (>90% of the control value) at dose rates below the following levels: 3 mGy day⁻¹ for wolf/wild dog; 10 mGy day⁻¹ for deer/goat; 14 mGy day⁻¹ for hare/rabbit; and 20 mGy day⁻¹ for mice. The model predictions showed a relatively high survival potential of short-lived and productive species such as mice. At the same time, populations of long-lived animals with slow and radiosensitive reproduction such as wolf/wild dog were candidates to extinction at chronic exposures above 5 mGy day⁻¹. Recovery of short-lived and productive species took a much shorter time compared with long-lived and slow reproductive species.     

Mixotrophic algae in three ice-covered lakes of the Pocono Mountains, U.S.A.

1. The occurrence and grazing activity of mixotrophic (phagotrophic) algae in three icecovered freshwater lakes of different trophic status were examined (oligotrophic Lake Giles, mesotrophic Lake Lacawac, eutrophic Lake Waynewood), Microbial population densities were low (4.1–7.2 × 10⁵ bacteria ml^?1 and 1.2–2.4 × 10³ nanoplanktonic protists ml^?1). All three nanoplankton communities were dominated by chloroplast-bearing forms (60–96%). 2. Mixotrophs formed up to 48% of the phototrophic nanoplankton in Lake Lacawac and were responsible for up to ～90% of the observed uptake of bacteria-sized particles. The abundance of mixotrophic algae in Lakes Giles and Waynewood were extremely low (3 and 2% of the phototrophic algae, respectively), and heterotrophs dominated nanoplankton bacterivory. 3. The overall impact of nanoplankton feeding activity on the bacterial assemblage was low under the ice in Lakes Giles and Waynewood. Removal rates of bacteria based on our particle uptake experiments were 1.0 and 4.0% of the bacterial standing stock day^?1 in these lakes, respectively. Removal rates were higher in Lake Lacawac and ranged from 4.9 to 11% of the bacterial standing stock day^?1 on 2 successive sampling days.     

Non-parametric estimation of thresholds for radiation effects in vertebrate species under chronic low-LET exposures

Databases on effects of chronic low-LET radiation exposure were analyzed by non-parametric statistical methods, to estimate the threshold dose rates above which radiation effects can be expected in vertebrate organisms. Data were grouped under three umbrella endpoints: effects on morbidity, reproduction, and life shortening. The data sets were compiled on a simple ‘yes’ or ‘no’ basis. Each data set included dose rates at which effects were reported without further details about the size or peculiarity of the effects. In total, the data sets include 84 values for endpoint “morbidity”, 77 values for reproduction, and 41 values for life shortening. The dose rates in each set were ranked from low to higher values. The threshold TDR5 for radiation effects of a given umbrella type was estimated as a dose rate below which only a small percentage (5%) of data reported statistically significant radiation effects. The statistical treatment of the data sets was performed using non-parametric order statistics, and the bootstrap method. The resulting thresholds estimated by the order statistics are for morbidity effects 8.1 × 10⁻⁴ Gy day⁻¹ (2.0 × 10⁻⁴–1.0 × 10⁻³), reproduction effects 6.0 × 10⁻⁴ Gy day⁻¹ (4.0 × 10⁻⁴–1.5 × 10⁻³), and life shortening 3.0 × 10⁻³ Gy day⁻¹ (1.0 × 10⁻³–6.0 × 10⁻³), respectively. The bootstrap method gave slightly lower values: 2.1 × 10⁻⁴ Gy day⁻¹ (1.4 × 10⁻⁴–3.2 × 10⁻⁴) (morbidity), 4.1 × 10⁻⁴ Gy day⁻¹ (3.0 × 10⁻⁴–5.7 × 10⁻⁴) (reproduction), and 1.1 × 10⁻³ Gy day⁻¹ (7.9 × 10⁻⁴–1.3 × 10⁻³) (life shortening), respectively. The generic threshold dose rate (based on all umbrella types of effects) was estimated at 1.0 × 10⁻³ Gy day⁻¹.     

A microbiological study of an underground gas storage in the process of gas injection

The liquid phase of different units of an underground gas storage (UGS) in the period of gas injection was studied with respect to its hydrochemical composition and characterized microbiologically. The presence of viable aerobic and anaerobic bacteria was revealed in the UGS stratal and associated waters. An important source of microorganisms and biogenic elements in the ecosystem studied is water and various technogenic admixtures contained in trace amounts in the gas entering from the gas main in the period of gas injection into the storage. Owing to this fact, the bacterial functional diversity, number, and activity are maximal in the system of gas treatment and purification and considerably lower in the observation well zone. At the terminal stages, the anaerobic transformation of organic matter in the UGS aqueous media occurs via sulfate reduction and methanogenesis; exceptionally high rates of these processes (up to 4.9 × 10⁵ ng S^2? l^?1 day^?1 and 2.8 × 10⁶ nl CH₄ l^?1 day^?1, respectively) were recorded for above-ground technological equipment.     

Bone marrow dosimetry for mice: exposure from bone-seeking 89,90Sr

Studies of radiobiological effects in murine rodents exposed to internal radiation in the wild or in laboratory experiments require dosimetric support. The main problem of bone marrow (BM) dosimetry for bone-seeking β-emitters is dosimetric modeling, because the bone is a heterogeneous structure with complex microarchitecture. To date, there are several approaches to calculating the absorbed dose in BM, which mostly use rough geometric approximations. Recently, in the framework of studies of people exposed to ⁹⁰Sr in the Urals, a new approach (SPSD) has been developed. The aim of the current study was to test for the first time the possibility of extension of the SPSD approach elaborated for humans to mice. For this, computational phantoms of femur bones of laboratory animals (C57BL/6, C57BL/6 J, BALB/c, BALB/cJ) aged 5–8 weeks (growing) and?>?8 weeks (adults) were created. The dose factors DF_Sr-90(BM?←?TBV?+?CBV) to convert the Sr isotope activity concentration in a bone tissue into units of dose rate absorbed in the bone marrow were 1.75?±?0.42 and 2.57?±?0.93 μGy day^?1 per Bq g^?1 for growing and adult animals, respectively, while corresponding values for DF_Sr-89(BM?←?TBV?+?CBV) were 1.08?±?0.27 and 1.66?±?0.67 μGy day^?1 per Bq g^?1, respectively. These results are about 2.5 times lower than skeleton-average DFs calculated assuming homogenous bone, where source and target coincide. The results of the present study demonstrate the possibility of application of the SPSD approach elaborated for humans to non-human mammals. It is concluded that the study demonstrates the feasibility and appropriateness of application of the SPSD approach elaborated for humans to non-human mammals. This approach opens up new prospects for studying the radiobiological consequences of red bone marrow exposure for both laboratory and wildlife mammals.

     

Spatial distribution of phytoplankton productivity in the Amundsen Sea, Antarctica

To date, no direct measurements of primary production were taken in the Amundsen Sea, which is one of the highest primary productivity regions in the Antarctic. Phytoplankton carbon and nitrogen uptake experiments were conducted at 16 selected stations using a ¹³C–¹⁵N dual isotope tracer technique. We found no statistically significant depletions of major inorganic nutrients (nitrate?+?nitrite, ammonium, and silicate) although the concentrations of these nutrients were markedly reduced in the surface layer of the polynya stations where large celled phytoplankton (>20?μm) predominated (ca. 64?%). The average chl-a concentration was significantly higher at polynya stations than at non-polynya stations (p?<?0.01). Average daily carbon and nitrogen uptake rates by phytoplankton at polynya stations were 2.2?g?C?m^?2?day^?1 (SD?=?±1.4?g?C?m^?2?day^?1) and 0.9?g?N?m^?2?day^?1 (SD?=?±0.2?g?N?m^?2?day^?1), respectively, about 5–10 times higher than those at non-polynya stations. These ranges are as high as those in the Ross Sea, which has the highest productivity among polynyas in the Antarctic Ocean. The unique productivity patterns in the Amundsen Sea are likely due to differences in iron limitation, phytoplankton productivity, the timing of phytoplankton growing season, or a combination of these factors.     

Mutation analysis of 28 autosomal short tandem repeats in the Chinese Han population

Short tandem repeats (STRs) have been extensively used in forensic genetics. However, according to previous studies, the mutation rates of STRs are relatively high and are affected by many factors. Therefore, it is important to analyze STR mutations and determine the influence of underlying factors on STR mutation rates. Mutation rates of 28 autosomal STRs were determined from 8708 paternity testing cases in the Chinese Han population, and the relationships between STR mutation rates and population, sex, age, allele length and heterozygosity were investigated. A total of 279 mutations were observed at 27 loci in a total of 233,530 meiosis cases, including 273 (97.8%) one-step, 5 (1.8%) two-step and 1 (0.4%) three-step mutations. The overall average mutation rate was 1.19?×?10^–3 (95% CI 1.06?×?10^–3???1.34?×?10^–3) ranging from 0 (TPOX) to 2.79?×?10^–3 (D13S325). Mutation rate comparisons revealed statistically significant differences at several STRs among populations. Paternal mutations occurred more frequently than maternal mutations, at a ratio of 6.04:1, and the mutation rate tended to increase with paternal age. Moreover, our study revealed a bias towards contraction mutations for long alleles and expansion mutations for short alleles. No obvious bias was observed in the overall mutation direction. In addition, STR loci with higher expected heterozygosity (H_exp) tended to have higher mutation rates. This work revealed the relationships between STR mutation rates and several influencing factors, providing useful data and information for further research on STR mutations in forensic genetics.

     

Development of an experimental laboratory fertilization protocol for the South African abalone,Haliotis midae (Linnaeus 1758)

In this study, effective gamete concentrations, egg viability, and fertilization volumes were evaluated for Haliotis midae (L.). Sperm concentrations between 5?×?10³ and 5?×?10⁴?mL^?1 (p?>?0.05) consistently resulted in high hatch-out rates (96?±?1%). At concentrations higher than 5?×?10⁵?mL^?1, hatch-out rates decreased to 69?±?7% (p??1 resulted in high fertilization rates, with 50?eggs?mL^?1 being the ideal concentration for fertilization in H. midae. Egg viability was consistently high up to 100?min post-spawning, with a decrease in hatch-out success, when eggs were fertilized 120?min post-spawning. Fertilization volumes did not affect successful hatch-out. The results from this study can be implemented by South African abalone farms to increase hatch-out rates and subsequent culture. It can also be used as basis for the development of fertilization protocols in other marine invertebrate species.     

Dynamics of hybrid dysgenesis frequency in Drosophila melanogaster in controlled terms of protracted radiation exposure

The dynamics of hybrid dysgenesis frequency in F ₁ descendants of two lines of Drosophila melanogaster (lines Santon-s and radius incompletus (ri) brining P-mobile element), which was maintained for 20 generations were under the conditions of chronic radiation with three dose rate (1.2 × 10^?8; 0.3 × 10^?8; 0.12 × 10^?8 Gy/s), have been studied. Gradual changes have been shown in the dose dependences of the hybrid dysgenesis frequency for F ₁ descendants of every 20 generations from parents exposed to radiation. The complicated dynamics of the transitional process of the appearance of gonadal dysgenesis depending on the duration and dose rate of irradiation in ancestors, has been found. The cumulative effect of the prolonged irradiation appears in the form of adaptation at the lowest dose rate of irradiation and at exhaustion at the highest used dose rate. Problem of the transitional process peculiarities, including the hierarchy of protective and adaptive reactions under the conditions of the chronic irradiation has been discussed.     

Neonatal exposure to bisphenol A advances pubertal development in female rats

Neonatal exposure to bisphenol A (BPA) is hypothesized to advance pubertal development. However, the effects of neonatal BPA exposure on pubertal development has not been described. In this study, female Sprague‐Dawley rats were exposed to 0.05, 0.5, 5, or 10 mg·kg^?1·day^?1 BPA, or corn oil vehicle alone from postnatal day 1 (PND1) to PND10 via subcutaneous injection. We evaluated day of vaginal opening (DVO), ovarian morphology, serum hormone concentrations, and hypothalamic expression of Gnrh1 and Kiss1 in female rats at PND35. DVO was significantly advanced in rats exposed to 5 and 10 mg·kg^?1·day^?1 BPA. Serum hormone concentrations increased as BPA dose increased. Additionally, hypothalamic Gnrh1 and Kiss1 expression were increased with BPA exposure; rats exposed to 10 mg·kg^?1·day^?1 BPA had significantly upregulated hypothalamic Gnrh1 and Kiss1 expressions in terms of both messenger RNA and protein levels. Our results suggest that exposure to a 10 mg·kg^?1·day^?1 dose of BPA might advance pubertal development significantly. In addition, within the range of 0 to 10 mg·kg^?1·day^?1, neonatal exposure to BPA may affect pubertal development in a dose‐dependent manner.     

Zygote-derived seedling production of Sargassum thunbergii: focus on two frequently experienced constraints in tank culture of seaweed

Mass collection of germlings and growth of fouling algae are two main constraints for the seedling production of Sargassum thunbergii. In this study, 65% and 40% of reproductive output (allocation of biomass to sexual reproductive tissue) for farmed and natural populations respectively, were recorded during peak reproduction. In terms of germlings per kilogram wet weight of plants, the farmed population gave a higher yield than the natural population (3.2?×?10⁵ and 1.2?×?10⁵ germlings kg^-1, respectively). These results indicate that farmed populations could be used as parental plants for germling collection in seedling production. During the experiment, fouling was controlled by jet washing and high-density seeding. A germling detachment of less than 10% was observed when, after 48?h of attachment, collectors were jet-washed with an intensity of 1?kg cm^-2. High-density seeding had adverse effects on length mean, size equality, and occurrence of branches of germlings. However, 30–50 individuals cm^-2 are thought to be usable in the seedling production of S. thunbergii because of less density effects. Seedlings of?>?0.5?cm length could be achieved after 1?month of tank culture.     

Key parameters for outdoor biomass production of Scenedesmus obliquus in solar tracked photobioreactors

The biomass productivity of Scenedesmus obliquus was investigated outdoors during all seasons in solar tracked flat panel photobioreactors (PBR) to evaluate key parameters for process optimization. CO₂ was supplied by flue gas from an attached combined block heat and power plant. Waste heat from the power plant was used to heat the culture during winter. The parameters pH, CO₂, and inorganic salt concentrations were automatically adjusted to nonlimiting levels. The optimum biomass concentration increased directly with the photosynthetic active radiation (PAR) from 3 to 5 g dry weight (DW)?L^?1 for a low PAR of 10 mol photons m^?2 day^?1 and high PAR of 40–60 mol photons m^?2 day^?1, respectively. The annual average biomass yield (photosynthetic efficiency) was 0.4?±?0.5 g DW mol^?1 photons. However, biomass yields of 1.5 g DW mol^?1 photons close to the theoretical maximum were obtained at low PAR. The productivity (including the night biomass losses) ranged during all seasons from ?5 up to 30 g DW m^?2 day^?1 with a mean productivity of 9?±?7 g DW m^?2 day^?1. Low night temperatures of the culture medium and elevated day temperatures to the species-specific optimum increased the productivity. Thus, continuous regulation of the biomass concentration and the culture temperature with regard to the fluctuating weather conditions is essential for process optimization of outdoor microalgal production systems in temperate climates.     

Outdoor pilot-scale production of Botryococcus braunii in panel reactors

In this paper, the outdoor production of Botryococcus braunii in pilot-scale panel reactors (0.4?m³) is studied under uncontrolled conditions at a location close to the Atacama Desert (Chile). Discontinuous experiments were performed on different dates to determine the feasibility of the culture and the influence of environmental conditions on the system yield. Data showed that solar radiation is a major parameter in determining system yield, the average irradiance inside the culture determining both the growth rate and biomass productivity. A maximum specific growth rate of 0.09?day^?1 and biomass productivity of 0.02?g?L^?1?day^?1 (dry weight) were measured in discontinuous mode, at an average irradiance of 60?μE?m^?2?s^?1. With respect to lipids, a productivity of 2.5?mg?L^?1?day^?1 was obtained under favourable growth conditions; no accumulation of lipids at the stationary phase was observed. To confirm this behaviour, a semicontinuous culture was performed at 0.04?day^?1 in a larger reactor (1?m³). In this experiment, the biomass concentration and productivity was 0.3?g?L^?1 and 0.015?g?L^?1?day^?1, respectively. The lipid content and productivity was 15.6% and 2.4?mg?L^?1?day^?1, respectively, the mean average irradiance inside the reactor being 60?μmol photons?m^?2?s^?1. The light path of the reactor determines the light availability, thus determining also the biomass concentration and productivity of the reactor once the dilution rate is fixed. Experimentally, biomass productivity of 0.015?g?L^?1?day^?1 was determined for a light path of 0.15?m, but this can be increased by more than three times for a light path of 0.1?m. These data confirm that this alga can be produced outdoors in a secure form, the culture yield improving when optimal conditions are applied, the data reported here establishing the starting point for the development of the process.     

pH effects on growth and lipid accumulation of the biofuel microalgae Nannochloropsis salina and invading organisms

Biofuels derived from non-crop sources, such as microalgae, offer their own advantages and limitations. Despite high growth rates and lipid accumulation, microalgae cultivation still requires more energy than it produces. Furthermore, invading organisms can lower efficiency of algae production. Simple environmental changes might be able to increase algae productivity while minimizing undesired organisms like competitive algae or predatory algae grazers. Microalgae are susceptible to pH changes. In many production systems, pH is kept below 8 by CO₂ addition. Here, we uncouple the effects of pH and CO₂ input, by using chemical pH buffers and investigate how pH influences Nannochloropsis salina growth and lipid accumulation as well as invading organisms. We used a wide range of pH levels (5, 6, 7, 8, 9, and 10). N. salina showed highest growth rates at pH 8 and 9 (0.19?±?0.008 and 0.19?±?0.011, respectively; mean ± SD). Maximum cell densities in these treatments were reached around 21 days into the experiment (95.6?×?10⁶?±?9?×?10⁶ cells mL^?1 for pH 8 and 92.8?×?10⁶?±?24?×?10⁶ cells mL^?1 for pH 9). Lipid accumulation of unbuffered controls were 21.8?±?5.8 % fatty acid methyl esters content by mass, and we were unable to trigger additional significant lipid accumulation by manipulating pH levels at the beginning of stationary phase. Ciliates (grazing predators) occurred in significant higher densities at pH 6 (56.9?±?39.6?×?10⁴ organisms mL^?1) than higher pH treatments (0.1–6.8?×?10⁴ organisms mL^?1). Furthermore, the addition of buffers themselves seemed to negatively impact diatoms (algal competitors). They were more abundant in an unbuffered control (12.7?±?5.1?×?10⁴ organisms mL^?1) than any of the pH treatments (3.6–4.7?×?10⁴ organisms mL^?1). In general, pH values of 8 to 9 might be most conducive to increasing algae production and minimizing invading organisms. CO₂ addition seems more valuable to algae as an inorganic carbon source and not as an essential mechanism to reduce pH.