Enriching Rotifers with “Premium” Microalgae. Nannochloropsis gaditana

The nutritive quality of Nannochloropsis gaditana cultured semicontinuously with different daily renewal rates was tested as a diet for short-term enrichment of the rotifer Brachionus plicatilis. After 24 h, dramatic differences in the survival, dry weight, and biochemical composition of the rotifers depending on the renewal rate of microalgal cultures were observed. Survival after the feeding period increased with increasing renewal rates. Rotifers fed microalgae from low renewal rate, nutrient-deficient cultures showed low dry weight and organic contents very similar to those of the initial rotifers that were starved for 12 h before the start of the feeding period. On the contrary, rotifers fed nutrient-sufficient microalgal cells underwent up to twofold increases of dry weight and protein, lipid, and carbohydrate contents with regard to rotifers fed nutrient-depleted N. gaditana. Consequently, feed conversion rate decreased in these conditions, indicating a better assimilation of the microalgal biomass obtained at high renewal rates. No single microalgal biochemical parameter among those studied can explain the response of the filter feeder. Similarly to gross composition, EPA and n-3 contents in rotifers fed microalgae from nutrient-sufficient cultures were double than the contents found in rotifers fed nutrient-limited microalgae. In addition, very high positive correlations between the contents of EPA and n-3 in N. gaditana and B. plicatilis were observed. These results demonstrate that selecting the appropriate conditions of semicontinuous culture can strongly enhance the nutritional value of microalgae that is reflected in the growth and biochemical composition of the filter-feeder even in short exposure periods.     

Stress-Induced Changes in Optical Properties,Pigment and Fatty Acid Content of <Emphasis Type="Italic">Nannochloropsis</Emphasis> sp.: Implications for Non-destructive Assay of Total Fatty Acids

In order to develop a practical approach for fast and non-destructive assay of total fatty acid (TFA) and pigments in the biomass of the marine microalga Nannochloropsis sp. changes in TFA, chlorophyll, and carotenoid contents were monitored in parallel with the cell suspension absorbance. The experiments were conducted with the cultures grown under normal (complete nutrient f/2 medium at 75 μmol PAR photons/(m² s)) or stressful (nitrogen-lacking media at 350 μmol PAR photons/(m² s)) conditions. The reliable measurement of the cell suspension absorbance using a spectrophotometer without integrating sphere was achieved by deposition of cells on glass–fiber filters in the chlorophyll content range of 3–13 mg/L. Under stressful conditions, a 30–50% decline in biomass and chlorophyll, retention of carotenoids and a build-up of TFA (15–45 % of dry weight) were recorded. Spectral regions sensitive to widely ranging changes in carotenoid-to-chlorophyll ratio and correlated changes of TFA content were revealed. Employing the tight inter-correlation of stress-induced changes in lipid metabolism and rearrangement of the pigment apparatus, the spectral indices were constructed for non-destructive assessment of carotenoid-to-chlorophyll ratio (range 0.3–0.6; root mean square error (RMSE) = 0.03; r ² = 0.93) as well as TFA content of Nannochloropsis sp. biomass (range 5.0–45%; RMSE = 3.23 %; r ² = 0.89) in the broad band 400–550 nm normalized to that in chlorophyll absorption band (centered at 678 nm). The findings are discussed in the context of real-time monitoring of the TFA accumulation by Nannochloropsis cultures under stressful conditions.     

Growth Rate of the Microalga Tetraselmis suecica Changes the Biochemical Composition of Artemia Species

The impact of different microalgal semicontinuous cultures on growth and biochemical composition in the next link of the food chain was tested using the filter feeder Artemia species as a model. The marine microalga Tetraselmis suecica was cultured semicontinuously with renewal rates between 10% and 50% and used to feed Artemia. Microalgal cultures maintained with a low renewal rate that had biochemical composition similar to that of the stationary-phase cultures commonly used in aquaculture produced poor growth and survival and low food-conversion efficiency compared to cultures maintained with a high renewal rate. Changes in the renewal rate in microalgal cultures also resulted in important changes in the gross biochemical composition of the filter feeder. The gross biochemical composition of the Artemia resembled that of the microalgae used as food except for total lipid content. The percentage of protein in the organic fraction of Artemia increased from 45% to 65% of the organic weight with increasing renewal rates in the microalgal cultures, while the carbohydrate percentage decreased under the same conditions. Higher renewal rates resulted in higher lipid percentages in the microalga, but in Artemia the percentage of lipids decreased from 19% of the organic weight with a renewal rate of 10%, to 13% with a renewal rate of 50%. The percentage of all polyunsaturated fatty acids in Artemia, including 20:5n-3, increased slightly with increasing renewal rates in the microalgal cultures. Results emphasize the importance of controlling microalgal nutritional value for the success of aquaculture food chains in which filter feeders are involved. Received October 15, 2000; accepted December 29, 2000.     

Evaluation of <Emphasis Type="Italic">Isochrysis galbana</Emphasis> (clone T-ISO) cell numbers by digital image analysis of color intensity

In microalgal cultivation, measuring cell numbers as a means to monitor growth rates is a long-standing problem. Many automated counting systems and schemes have been developed; among these are image analysis systems. However, such imaging systems have presented difficulties in dealing with the complexities of computer recognition of individual microscopic cells. It is known that the coloration of microalgae suspension is species specific and that color intensity increases are typically associated with increasing numbers. Using this qualitative insight, the present work describes the design, construction, and comparative performance of an inexpensive digital imaging system optimized for counting microalgal cells. The system circumvents the need to count individual cells and extracts cell numbers directly from the macroscopic color intensity of a microalgal suspension. The results suggest, using Isochrysis galbana (T-ISO) as an illustrative example, that this scheme is potentially useful for inexpensive and automated biomonitoring of microalgal cell numbers. Percentage difference comparisons with a standard Coulter Counter indicated that the three algorithms tested provided better than 10% accuracy over density thresholds of 1.52 × 10⁶ to 8.10 × 10⁶ cells mL⁻¹ with precision of 4% attainable at high density concentrations.     

Role of microorganisms in corrosion inhibition of metals in aquatic habitats

In acetate-limited chemostat cultures of Acinetobacter johnsonii 210A at a dilution rate of 0.1 h⁻¹ the polyphosphate content of the cells increased from 13% to 24% of the biomass dry weight by glucose (100 mM), which was only oxidized to gluconic acid. At this dilution rate, only about 17% of the energy from glucose oxidation was calculated to be used for polyphosphate synthesis, the remaining 83% being used for biomass formation. Suspensions of non-growing, phosphate-deficient cells had a six- to tenfold increased uptake rate of phosphate and accumulated polyphosphate aerobically up to 53% of the biomass dry weight when supplied with only orthophosphate and Mg²⁺. The initial polyphosphate synthesis rate was 98 ± 17 nmol phosphate min⁻¹ mg protein⁻¹. Intracellular poly-β-hydroxybutyrate and lipids served as energy sources for the active uptake of phosphate and its subsequent sequestration to polyphosphate. The H⁺-ATPase inhibitor N,N′-dicyclohexylcarbodiimide caused low ATP levels and a severe inhibition of polyphosphate formation, suggesting the involvement of polyphosphate kinase in polyphosphate synthesis. It is concluded that, in A. johnsonii 210A, (i) polyphosphate is accumulated as the energy supply is in excess of that required for biosynthesis, (ii) not only intracellular poly-β-hydroxybutyrate but also neutral lipids can serve as an energy source for polyphosphate-kinase-mediated polyphosphate formation, (iii) phosphate-deficient cells may accumulate as much polyphosphate as activated sludges and recombinants of Escherichia coli designed for polyphosphate accumulation. Received: 23 October 1998 / Received revision: 18 January 1999 / Accepted: 22 January 1999     

Reduction of biomass in a bioscrubber for waste gas treatment by limited supply of phosphate and potassium ions

  Elimination of n-butanol from the gas phase was examined with a mixed culture in a compact bioscrubber. The extent of the cell concentration was limited by the supply of n-butanol, phosphate or potassium, and the growth rate was determined by the dilution rate. With n-butanol as the limiting substrate the cellular yield was 0.53 g dry cell weight/g n-butanol. Phosphate limitation decreased this yield to 0.34 g and potassium limitation to 0.31 g dry cell weight/g n-butanol at a dilution rate of 0.1/h. Under these conditions n-butanol was eliminated from the gas phase by 84%–100%. In the same order of limitations the specific degradation rate ranged from 0.19 g to 0.32 g n-butanol g dry cell weight⁻¹ h⁻¹. The fraction of n-butanol required to satisfy the needs for maintenance energy increased significantly depending on the limiting nutrient. Limitation by n-butanol, phosphate or potassium caused a maintenance requirement of 0.07, 0.16 and 0.34 g n-butanol g dry cell weight⁻¹ h⁻¹, thus showing a fivefold increase. This high demand for the carbon source demonstrated the feasibility of operating a bioscrubber under mineral limitation to reduce biomass formation significantly, and to maintain a high degree of substrate elimination from the gas phase. Received: 22 May 1996 / Received revision: 23 July 1996 / Accepted: 5 August 1996     

Renewal rate and nutrient concentration as tools to modify productivity and biochemical composition of cyclostat cultures of the marine microalga Dunaliella tertiolecta

A factorial experimental design with two nutrient concentrations (2 and 4 mmol Nl^–1 in the form of NaNO₃) and five rates of daily renewal of the cultures (10%, 20%, 30%, 40% and 50%) was carried out in cyclostat, light/dark-synchronized cultures of the marine microalga Dunaliella tertiolecta Butcher. Steady-state cellular density was a linear function inversely proportional to renewal rate. Maximal cellular productivity, 3 × 10⁹ cells1^–1 day^–1, equivalent to 0.24 g1^–1 day^–1 dry weight and 0.17 g1^–1 day^–1 organic weight, was found with renewal rates of 20%–30% and 4mmol N1^–1, but maximal protein productivity, 0.066 g1^–1 day^–1, was obtained with a renewal rate of 40% for both nutrient concentrations. The protein content ranged between 30% and 70% of the organic fraction depending on the culture conditions. Carbohydrates were the only fraction accumulating in response to nutrient stress, ranging from 57% to 10% of the organic fraction, meanwhile the lipid content was increased by increase of nutrient availability. Under non-nitrogen-limited conditions the C:N ratio stabilized around 5.2–5.3 and the protein content of the organic fraction around 70%, but the cell nitrogen quota decreased under these conditions with increasing renewal rates, owing to the lower organic content of cells obtained with high growth rates. The high capacity for changing the biochemical composition, demonstrated for D. tertiolecta in the cyclostat system, has interesting implications for the management of continuous cultures of microalgae and its applications in biotechnological processes.     

Growth dynamics and the proximate biochemical composition and fatty acid profile of the heterotrophically grown diatom <Emphasis Type="Italic">Cyclotella cryptica</Emphasis>

To investigate the nutritional value of the diatom Cyclotella cryptica as an alternative feed for aquaculture, its heterotrophic growth characteristics were studied. First, the proximate biochemical composition and fatty acid profiles were studied under a controlled heterotrophic growth condition. The approximate total ash, carbohydrate, lipid, and protein content were 245 mg g⁻¹ (dry weight), 360 mg g⁻¹, 165 mg g⁻¹ and 260 mg g⁻¹, respectively. Polyunsaturated fatty acids accounted for 24.5, 31.3, 45.1 and 17.3% of the total lipids in the phospholipid, sterol, free fatty acid and triglyceride classes. Secondly, the effect of aeration and agitation rates on the specific growth rate of C. cryptica under heterotrophic conditions was studied. The maximum specific growth rate was not significantly affected (P > 0.05) by the rate of agitation within the range of 100 to 160 rpm, but it was significantly affected (P > 0.05) by the rate of aeration. Optimal growth occurred when the aeration rate was within the range of 0.44 to 1.07 v/v/min. Viability measurements throughout the growth period showed that the C. cryptica cells remained viable in spite of the varied cultivation conditions. Hydrodynamic forces are an important parameter within biological systems, and optimisation is crucial for the successful scale-up of microalgal cultivation systems. Whilst the investigation was preliminary in nature, the information gained in this study will be useful for the continual development of an alternative and cost-effective feed for bivalve spat rations.     

Production of lipids in 10 strains of Chlorella and Parachlorella, and enhanced lipid productivity in Chlorella vulgaris

We tested 10 different Chlorella and Parachlorella strains under lipid induction growth conditions in autotrophic laboratory cultures. Between tested strains, substantial differences in both biomass and lipid productivity as well as in the final content of lipids were found. The most productive strain (Chlorella vulgaris CCALA 256) was subsequently studied in detail. The availability of nitrates and/or phosphates strongly influenced growth and accumulation of lipids in cells by affecting cell division. Nutrient limitation substantially enhanced lipid productivity up to a maximal value of 1.5 g l⁻¹ day⁻¹. We also demonstrated the production of lipids through large-scale cultivation of C. vulgaris in a thin layer photobioreactor, even under suboptimal conditions. After 8 days of cultivation, maximal lipid productivity was 0.33 g l⁻¹ day⁻¹, biomass density was 5.7 g l⁻¹ dry weight and total lipid content was more than 30% dry weight. C. vulgaris lipids comprise fatty acids with a relatively high degree of saturation compared with canola oil offering a possible alternative to the use of higher plant oils.     

Poly-(3-hydroxybutyrate) production from whey by high-density cultivation of recombinant Escherichia coli

Recombinant Escherichia coli strain GCSC 6576, harboring a high-copy-number plasmid containing the Ralstonia eutropha genes for polyhydroxyalkanoate (PHA) synthesis and the E. coli ftsZ gene, was employed to produce poly-(3-hydroxybutyrate) (PHB) from whey. pH-stat fed-batch fermentation, using whey powder as the nutrient feed, produced cellular dry weight and PHB concentrations of 109 g l⁻¹ and 50 g l⁻¹ respectively in 47 h. When concentrated whey solution containing 210 g l⁻¹ lactose was used as the nutrient feed, cellular dry weight and PHB concentrations of 87 g l⁻¹ and 69 g l⁻¹ respectively could be obtained in 49 h by pH-stat fed-batch culture. The PHB content was as high as 80% of the cellular dry weight. These results suggest that cost-effective production of PHB is possible by fed-batch culture of recombinant E. coli using concentrated whey solution as a substrate. Received: 19 December 1997 / Received revision: 17 March 1998 / Accepted: 20 March 1998     

Pullulan production from deproteinized whey by Aureobasidium pullulans

Aureobasidium pullulans P56 was investigated using an adaptation technique and a mixed culture system. The adaptation of A. pullulans and the mixed cultures of A. pullulans and/or Lactobacillus brevisX20, Debaryomyces hansenii 194 and Aspergillus niger did not increase the production of polysaccharide. Enzymic hydrolysis of lactose in deproteinized whey gave a higher polysaccharide concentration and polysaccharide yield than acidic hydrolysed lactose. Maximum polysaccharide concentration (11.0 ± 0.5 g L⁻¹), biomass dry weight (10.5 ± 0.4 g L⁻¹), polysaccharide yield (47.2 ± 1.8%) and sugar utilization (93.2 ± 2.8%) were achieved using enzyme-hydrolysed whey (pH 6.5) containing 25 g L⁻¹ lactose and supplemented with K₂HPO₄ 0.5%, L-glutamic acid 1%, olive oil 2.5%, and Tween 80 0.5%. In this case the pullulan content of the crude polysaccharide was 40%. Received 16 December 1997/ Accepted in revised form 12 March 1999     

Treatment of dairy and swine manure effluents using freshwater algae: fatty acid content and composition of algal biomass at different manure loading rates

An alternative to land spreading of manure effluents is to mass-culture algae on the N and P present in the manure and convert manure N and P into algal biomass. The objective of this study was to determine how the fatty acid (FA) content and composition of algae respond to changes in the type of manure, manure loading rate, and to whether the algae was grown with supplemental carbon dioxide. Algal biomass was harvested weekly from indoor laboratory-scale algal turf scrubber (ATS) units using different loading rates of raw and anaerobically digested dairy manure effluents and raw swine manure effluent. Manure loading rates corresponded to N loading rates of 0.2 to 1.3 g TN m⁻² day⁻¹ for raw swine manure effluent and 0.3 to 2.3 g TN m⁻² day⁻¹ for dairy manure effluents. In addition, algal biomass was harvested from outdoor pilot-scale ATS units using different loading rates of raw and anaerobically digested dairy manure effluents. Both indoor and outdoor units were dominated by Rhizoclonium sp. FA content values of the algal biomass ranged from 0.6 to 1.5% of dry weight and showed no consistent relationship to loading rate, type of manure, or to whether supplemental carbon dioxide was added to the systems. FA composition was remarkably consistent among samples and >90% of the FA content consisted of 14:0, 16:0, 16:1ω7, 16:1ω9, 18:0, 18:1ω9, 18:2 ω6, and 18:3ω3.     

Carbon-limited fed-batch production of medium-chain-length polyhydroxyalkanoates from nonanoic acid by <Emphasis Type="Italic">Pseudomonas putida</Emphasis> KT2440

Pseudomonas putida KT2440 grew on glucose at a specific rate of 0.48 h⁻¹ but accumulated almost no poly-3-hydroxyalkanoates (PHA). Subsequent nitrogen limitation on nonanoic acid resulted in the accumulation of only 27% medium-chain-length PHA (MCL-PHA). In contrast, exponential nonanoic acid-limited growth (μ = 0.15 h⁻¹) produced 70 g l⁻¹ biomass containing 75% PHA. At a higher exponential feed rate (μ = 0.25 h⁻¹), the overall productivity was increased but less biomass (56 g l⁻¹) was produced due to higher oxygen demand, and the biomass contained less PHA (67%). It was concluded that carbon-limited exponential feeding of nonanoic acid or related substrates to cultures of P. putida KT2440 is a simple and highly effective method of producing MCL-PHA. Nitrogen limitation is unnecessary.     

Potential of the seaweed Gracilaria lemaneiformis for integrated multi-trophic aquaculture with scallop Chlamys farreri in North China

In this study the red alga, Gracilaria lemaneiformis, was cultivated with the scallop Chlamys farreri in an integrated multi-trophic aquaculture (IMTA) system for 3 weeks at the Marine Aquaculture Laboratory of the Institute of Oceanology, Chinese Academy of Sciences (IOCAS) in Qingdao, Shandong Province, North China. The nutrient uptake rate and nutrient reduction efficiency of ammonium and phosphorus from scallop excretion were determined. The experiment included four treatments each with three replicates, and three scallop monoculture systems served as the control. Scallop density (407.9 ± 2.84 g m⁻³) remained the same in all treatments while seaweed density differed. The seaweed density was set at four levels (treatments 1, 2, 3, 4) with thallus wet weight of 69.3 ± 3.21, 139.1 ± 3.80, 263.5 ± 6.83, and 347.6 ± 6.30 g m⁻³, respectively. There were no significant differences in the initial nitrogen and phosphorus concentration between each treatment and the control group (ANOVA, p > 0.05). The results showed that at the end of the experiment, the nitrogen concentration in the control group and treatment 1 was significantly higher than in the other treatments. There was also a significant difference in phosphorus concentration between the control group and the IMTA treatments (ANOVA, p < 0.05). Growth rate, C and N content of the thallus, and mortality of scallop was different between the IMTA treatments. The nutrient uptake rate and nutrient reduction efficiency of ammonium and phosphorus changed with different cultivation density and time. The maximum reduction efficiency of ammonium and phosphorus was 83.7% and 70.4%, respectively. The maximum uptake rate of ammonium and phosphorus was 6.3 and 3.3 μmol g⁻¹ DW h⁻¹. A bivalve/seaweed biomass ratio from 1:0.33 to 1:0.80 (treatments 2, 3, and 4) was preferable for efficient nutrient uptake and for maintaining lower nutrient levels. Results indicate that G. lemaneiformis can efficiently absorb the ammonium and phosphorus from scallop excretion and is a suitable candidate for IMTA.     

Comparison of Nitrogen Fixation for North- and South-facing <Emphasis Type="Italic">Robinia pseudoacacia</Emphasis> Stands in Central Korea

The nitrogenase activity, root nodule biomass, and rates of nitrogen (N) fixation were measured in 25-year-old pure north- and south-facing Robinia pseudoacacia stands in an urban forest of Seoul (Kkachisan Mountain) in central Korea. The nitrogenase activity was estimated using an acetylene reduction (AR) assay, which showed an increasing trend during the early growing season, with sustained high rates from June through to September with a decrease thereafter. July had the highest nitrogenase activity rate (micromoles C₂H₄ per gram dry nodule per hour), averaging 95.8 and 115.1 for the north- and south-facing stands, respectively. The maximum root nodule biomass (kilograms per hectare) was 45.7 and 9.1 for the north- and south-facing stands in July, respectively. The AR rate appeared to be strongly correlated to the soil temperature (r ² = 0.68, P < 0.001) and soil pH (r ² = 0.59, P < 0.001) while root nodule biomass was correlated to the soil temperature (r ² = 0.36, P < 0.01) and water content (r ² = 0.35, P < 0.05). The soil temperature showed clear differences between seasons, while there was a significant difference in soil pH, organic matter, total N concentrations, and available phosphorus between the north- and south-facing stands. The N₂ fixation rates during the growing season varied from 0.1 to 37.5 kg N ha⁻¹ month⁻¹ depending on the sampling location and time. The annual N₂ fixation rate (kg N per hectare per year) was 112.3 and 23.2 for the north- and south-facing stands, respectively. The differences in N₂ fixation rate between the two stands were due mainly to the differences in total nodule biomass.     

Microalgal growth enhancement by levoglucosan isolated from the green seaweed <Emphasis Type="Italic">Monostroma nitidum</Emphasis>

Microalgal growth was enhanced by the addition of levoglucosan to the culture medium. The growth-enhancing compound levoglucosan was isolated from the green seaweed Monostroma nitidum using water extraction, molecular fractionation, DEAE-cellulose column chromatography, and high-performance liquid chromatography. Yield of the compound from seaweed powder was 5 × 10⁻³% (w/w). At 10 mM concentration, levoglucosan enhanced cell growth and the specific growth rate of all feed microalgal species tested (Chaetoceros gracilis, Chlorella ellipsoidea, Dunaliella salina, Isochrysis galbana, Nannochloris oculata, Navicula incerta, Pavlova lutheri, Tetraselmis suecica) in most culture media by approximately 150%. Cellular fatty acid profiles and cell size differed marginally between cultures with and without levoglucosan.     

Determination of the kinetic parameters during continuous cultivation of the lipase-producing thermophile Bacillus sp. IHI-91 on olive oil

A thermostable lipase was produced in continuous cultivation of a newly isolated thermophilic Bacillus sp. strain IHI-91 growing optimally at 65 °C. Lipase activity decreased with increasing dilution rate while lipase productivity showed a maximum of 340 U l⁻¹ h⁻¹ at a dilution rate of 0.4 h⁻¹. Lipase productivity was increased by 50% compared to data from batch fermentations. Up to 70% of the total lipase activity measured was associated to cells and by-products or residual substrate. Kinetic and stoichiometric parameters for the utilisation of olive oil were determined. The maximal biomass output method led to a saturation constant K _S of 0.88 g/l. Both batch growth data and a washout experiment yielded a maximal specific growth rate, μ_max, of 1.0 h⁻¹. Oxygen uptake rates of up to 2.9 g l⁻¹h⁻¹ were calculated and the yield coefficient, Y _X/O, was determined to be 0.29 g dry cell weight/g O₂. From an overall material balance the yield coefficient, Y _X/S, was estimated to be 0.60 g dry cell weight/g olive oil. Received: 8 January 1997 / Received revision: 30 April 1997 / Accepted: 4 May 1997     

Biomass Expansion Factors of Natural Japanese Red Pine (<Emphasis Type="Italic">Pinus densiflora</Emphasis>) Forests in Korea

Biomass expansion factors, which convert the timber volume (or dry weight) to biomass, are used to estimate the forest biomass and account for the carbon budget at the national or regional level. This study estimated the biomass conversion and expansion factors (BCEF), root to shoot ratio (R), biomass expansion factors (BEF) of natural Japanese Red Pine (Pinus densiflora Sieb. et Zucc.) forests based on direct field measurements and publications in Korea. This study attempted to fit the non-linear relationships between the biomass expansion factors (BCEF and BEF) and main stand factors [stand age, tree height, and diameter at breast height (DBH)]. The relationship between BEF and each main stand factor was expressed as a simple logarithmical equation. The BCEF was also expressed as a logarithmical equation of the tree height, DBH, and stand volume, whereas there was no significant relationship between BCEF and stand age. The mean value for BCEF, BEF, and R was 0.5821 Mg m⁻³ (n = 22, SD = 0.1196), 1.4465 (n = 22, SD = 0.2905), and 0.2220 (n = 17, SD = 0.0687), respectively. The values of the biomass expansion factors in this study may indicate much representativeness to estimate forest biomass in natural Japanese Red Pine forests of Korea than the default values given by the IPCC (2003, 2006).     

Dependence of temperature on loss rates of rotifers,lipids, and ω3 fatty acids in starved Brachionus plicatilis cultures

Rotifer cultures of Brachionus plicatilis (SINTEF-strain, length 250 m) rich in 3 fatty acids were starved for > 5 days at variable temperature (0–18 °C). The net specific loss rate of rotifer numbers were 0.04 day^–1 (range 0–0.08 day^–1) at 5–18 °C, but reached values up to 0.25 day^–1 at 0–3 °C. The loss rate was independent on culture density (range 40–1000 ind ml^–1), but was to some extent dependent on the initial physiological state of the rotifers (i.e., egg ratio).The loss rate of lipids was 0.02–0.05 day^–1 below 10 °C, where the potential growth rate of the rotifer is low (0–0.09 day^–1). The loss rate of lipids increased rapidly for higher temperatures where the rotifer can maintain positive growth, and reached 0.19 day^–1 at 18 °C. The Q₁₀ for the lipid loss rate versus temperature was higher than the Q₁₀ for respiration found in other strains. This may suggest that other processes than respiration were involved in lipid catabolism. The content of 3 fatty acids became reduced somewhat faster than the lipids (i.e. in particular 22:6 3), but the fatty acid per cent distribution remained remarkably unaffected by the temperature during starvation.The results showed that rotifer cultures could be starved for up to 4 days at 5–8 °C without essential quantitative losses of lipids, 3 fatty acids, and rotifers. The rotifers exhausted their endogenous lipids through reproduction (anabolism) and respiration (including enhanced locomotion) at higher temperatures. At lower temperatures, the mortality rate became very high.     

Fish and nutrient enrichment effects on rotifers in a Mediterranean shallow lake: a mesocosm experiment

A mesocosm experiment was conducted “in situ” in a Chara dominated shallow lake near Valencia (Spain) to study top–down and bottom–up effects on rotifers by means of nutrient and fish additions. Both processes were important in determining rotifer abundance, biomass and diversity. A total of 36 mesocoms were established with triplicate treatment combinations of three fish levels (from no fish to 45 individuals of Gambusia holbrooki males) and four nutrient enrichment levels (from no additions to 10 mg l⁻¹ nitrate-N and 1 mg l⁻¹ phosphate-P). The main effect was a notable increase of planktonic and plant associated rotifers densities with fish. Rotifers benefited from mosquitofish predation on microcrustaceans and chironomids. The results showed a marked negative relationship between rotifer and cyclopoid abundances, indicating the importance of the predatory pressure of cyclopoids on rotifers. Effects on rotifer diversity were also evident, in general rotifer diversity decreased with nutrients and increased with fish. The effects of nutrients analysed at species level showed two contrasting density responses: an increase or a decrease with nutrients, which levelled off at high nutrient concentrations. High-level nutrient additions (from 5 mg l⁻¹ nitrate-N and 0.5 mg l⁻¹ phosphate-P) induced a switch to a turbid state with macrophyte disappearance. Most planktonic rotifer species, as well as plant associated ones, diminished when the turbid state was well established, especially in the mesocosms without fish. In the turbid mesocosms, relative abundance of plant-associated rotifers (as a whole) was higher than that of planktonic rotifers. The changes in rotifer species composition after the switch from a clear to a turbid water state are also described. Species of the genus Anuraeopsis, Trichocerca and Hexarthra, dominant in the clear water state, practically disappeared in the turbid water state, in which Proalides tentaculatus and Lecane nana were the main species. Guest editors: S. S. S. Sarma, R. D. Gulati, R. L. Wallace, S. Nandini, H. J. Dumont & R. Rico-Martínez Advances in Rotifer Research