A Three Years' Study of Life Cycle,Population Dynamics and Production of Asellus aquaticus L. in a Macrophyte Rich Stream

Populations of A. aquaticus were sampled quantitatively in 1979–82 at two localities in the river Suså which has a slope of <1 m km⁻¹ and large variations in macrophyte biomass, discharge and stream velocity. The latter two differed significantly between years. A. aquaticus had (1)−2 life cycles per year and summer and winter cohort production intervals of 85 and 290 days. Populations of A. aquaticus varied between 0 and 28,000 ind. m⁻² with an exponential increase in the spring and an exponential decrease in the autumn-winter. The A. aquaticus rate of decrease varied between 0.62 and 5.61 % d⁻¹ and increased with increasing rate of elimination of the macrophyte biomass Differences between the two localities were due to differences in physical heterogeneity. Production varied between 2.8 and 9.1 g DW m⁻² yr⁻¹ and between 12.9 and 55 g DW m⁻² yr⁻¹ at the two localities and P/B ratios were 7.4–9.9 yr⁻¹. Physical limitations are thought to be most important for the populations of A. aquaticus in the Suså, and the macrophyte biomass played an important role in modifying the physical environment. Differences between streams and lake populations are discussed.     

Transformation of the offshore benthic community in Lake Michigan: recent shift from the native amphipod Diporeia spp. to the invasive mussel Dreissena rostriformis bugensis

1. The native amphipod Diporeia spp. was once the dominant benthic organism in Lake Michigan and served as an important pathway of energy flow from lower to upper trophic levels. Lake‐wide surveys were conducted in 1994/1995, 2000 and 2005, and abundances of Diporeia and the invasive bivalves Dreissena polymorpha (zebra mussel) and Dreissena rostriformis bugensis (quagga mussel) were assessed. In addition, more frequent surveys were conducted in the southern region of the lake between 1980 and 2007 to augment trend interpretation. 2. Between 1994/1995 and 2005, lake‐wide density of Diporeia declined from 5365 to 329 m⁻², and biomass (dry weight, DW) declined from 3.9 to 0.4 g DW m⁻². The percentage of all sites with no Diporeia increased over time: 1.1% in 1994/1995, 21.7% in 2000 and 66.9% in 2005. On the other hand, total dreissenid density increased from 173 to 8816 m⁻², and total biomass increased from 0.4 to 28.6 g DW m⁻². Over this 10‐year time period, D. r. bugensis displaced D. polymorpha as the dominant dreissenid, comprising 97.7% of the total population in 2005. In 2007, Diporeia was rarely found at depths shallower than 90 m and continued to decline at greater depths, whereas densities of D. r. bugensis continued to increase at depths greater than 50 m. 3. The decline in Diporeia occurred progressively from shallow to deep regions, and was temporally coincident with the expansion of D. polymorpha in nearshore waters followed by the expansion of D. r. bugensis in offshore waters. In addition, Diporeia density was negatively related to dreissenid density within and across depth intervals; the latter result indicated that dreissenids in shallow waters remotely influenced Diporeia in deep waters. 4. With the loss of Diporeia and increase in D. r. bugensis, the benthic community has become a major energy sink rather that a pathway to upper trophic levels. With this replacement of dominant taxa, we estimate that the relative benthic energy pool increased from 17 to 109 kcal m⁻² between 1994/1995 and 2005, and to 342 kcal m⁻² by 2007. We project that previously observed impacts on fish populations will continue and become more pronounced as the D. r. bugensis population continues to expand in deeper waters.     

Sedimentation of Nodularia spumigena and distribution of nodularin in the food web during transport of a cyanobacterial bloom from the Baltic Sea to the Kattegat

Nodularia spumigena is a toxic cyanobacteria that blooms in the Baltic Sea every year. In the brackish water of the Baltic Sea, its toxin, nodularin, mainly affects the biota in the surface water due to the natural buoyancy of this species. However, the fate of the toxin is unknown, once the cyanobacteria bloom enters the more saline waters of the Kattegat. In order to investigate this knowledge gap, a bloom of N. spumigena was followed during its passage, carried by surface currents, from the Baltic Sea into the Kattegat area, through the Öresund strait. N. spumigena cells showed an increased cell concentration through the water column during the passage of the bloom (up to 130 10³ cells ml⁻¹), and cells (4.2 10³ cells ml⁻¹) could be found down to 20 m depth, below a pycnocline. Sedimentation trap samples from below the pycnocline (10–12 m depth) also showed an increased sedimentation of N. spumigena filaments during the passage of the bloom. The toxin nodularin was detected both in water samples (0.3–6.0 μg l⁻¹), samples of sedimenting material (a toxin accumulation rate of 20 μg m^-2 day⁻¹), zooplankton (up to 0.1 ng ind.⁻¹ in copepods), blue mussels (70–230 μg kg⁻¹ DW), pelagic and benthic fish (herring (1.0–3.4 μg kg⁻¹ DW in herring muscle or liver) and flounder (1.3-6.2 μg kg⁻¹ DW in muscle, and 11.7-26.3 μg kg⁻¹ DW in liver). A laboratory experiment showed that N. spumigena filaments developed a decreased buoyancy at increased salinities and that they were even sinking with a rate of up to 1,7 m day⁻¹ at the highest salinity (32 PSU). This has implications for the fate of brackish water cyanobacterial blooms, when these reach more saline waters. It can be speculated that a significant part of the blooms content of nodularin will reach benthic organisms in this situation, compared to blooms decaying in brackish water, where most of the bloom is considered to be decomposed in the surface waters.     

Annual Changes of Abundance and Biomass of Planktonic Ciliates in the Gdańsk Basin,Southern Baltic

Seasonal changes in the species composition, abundance and biomass of planktonic ciliates were determined every 2–3 weeks at two sites of 30 m depth and one location of 105 m depth in the southwestern Gdańsk Basin between January 1987 and January 1988. A total of 40 ciliate taxa were observed during this period. Autotrophic Mesodinium rubrum dominated ciliate abundance and biomass: maximal values of 50 · 10⁻¹ ind. ^1-1 and 65 μg C 1⁻¹ were recorded. The annual mean biomass of M. rubrum comprised 6 to 9% of the annual mean phytoplankton biomass. The highest abundances and biomasses of heterotrophic ciliates were noted at all stations in the spring and summer in the euphotic zone with maximum values of 28 · 10³ ind. 1⁻¹ and 23 μg C 1⁻¹. Three ciliates assemblages were distinguished in the epipelagic layer: large and medium-size non-predatory ciliates, achieving peak abundance in spring and autumn; small-size microphagous ciliates and epibiotic ciliates which were abundant in summer, and large-size predacious ciliates dominating in spring. Below 60 m, a separate deep-water ciliate community composed of Prorodon-like ciliates and Metacystis spp. was found. The ciliate biomass in the 60–105 m layer was similar to the ciliate biomass in the euphotic zone. The heterotrophic ciliate community contributed 10 to 13% to the annual mean zooplankton biomass. The potential annual production of M. rubrum comprised 6 to 9% of the total primary production. Carbon demand of non-predatory ciliates, calculated on the basis of their potential production, was estimated to be equivalent to 12–15% of the gross primary production.     

Population Dynamics,Reproductive Biology and Productivity of Streblospio shrubsolii (Polychaeta: Spionidae) in Different Sediments at Low Salinities in a Mediterranean Lagoon (Monolimni Lagoon,Northern Aegean)

Monthly samples of Streblospio shrubsolii were collected from February 1998 to February 1999 at both parts of Monolimni Lagoon (0.3 psu < Sal. < 6 psu). Streblospio shrubsolii displayed a life cycle of about one year. Reproductive activity occurred from February to October. The worms showed a mean of 14 or 16 gametogenic segments. Reproductive activity, growth and density increased during spring despite the low salinities (∼0.3 psu). Streblospio shrubsolii showed faster growth, larger body size during autumn–winter, more reproductive peaks, a relatively higher mean annual density, mean anual biomass (B) and annual production (P) at the innermost part of the lagoon, in organically richer very fine sand, than those at the outer part in fine sand. Mean annual density was 1,320 individuals m^–2 at the outer part and 1,745 individuals m^–2 at the innermost. Production calculated by Hynes' s method gave a B of 0.20 g DW m^–2 y^–1 and P of 0.45 g DW m^–2 y^–1 at the outer part; the respective values at the innermost part were 0.29 g DW m^–2 y^–1 and 0.61 g DW m^–2 y^–1. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Life History,Reproduction, Growth,Population Dynamics and Production of Gammarus aequicauda (Crustacea: Amphipoda) at Extremely Low Salinities in a Mediterranean Lagoon

Aspects of the biology of Gammarus aequicauda were studied at extremely low salinities (0.3–5.7 psu) in Monolimni Lagoon, N. Aegean Sea. Samples were collected monthly from February 1998 to February 1999. Breeding occurred continuously but peaked in late spring, late summer and autumn and three cohorts were produced. The spring and summer cohorts showed fast growth (0.15 mm d^–1), accelerated maturity and life span of about three and seven months respectively, while the overwintering cohort showed a life span of about nine months. The largest individual had a body length of 23.6 mm. Mean brood size was 54.5 early embryos, while the intramarsupial loss was 46%. Population density sharply increased in late spring, summer and autumn. Secondary production calculated by Hynes' method gave a mean annual density of 1077.4 ind. m^–2, a mean annual crop (B) of 2.93 g DW m^–2, an annual production (P) of 35.03 g DW m^–2 and a P: B ratio of 11.96. Gammarus aequicauda showed a life‐history pattern similar to those previously reported for this species at higher salinity environments with comparatively large final body length and high growth rate during summer, brood size and P: B ratio, but with high embryo loss as well. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Reproductive potential in Ruppia cirrhosa (Petagna) Grande in response to water permanence

We compared the reproductive effort of perennial and annual Ruppia cirrhosa (Petagna) Grande in a mediterranean coastal lagoon where the species develops in permanent waters as well as in shallow areas which dry up during some months. In permanently flooded areas, Ruppia cirrhosa was perennial with biomass maxima up to 800 g DW m⁻². Here, the reproductive period lasted 8–10 weeks (between April and June), the reproductive effort was low (with 4–8 fl g⁻¹ DW) and mature fruit development was practically absent. In temporarily flooded areas, in contrast, Ruppia cirrhosa developed in an annual cycle which was completed in less than 8 weeks (maximum biomass of 137 g DW m⁻²); reproductive activity began later in the year (June) and lasted 3–4 weeks, but led to more flowers (17 fl g⁻¹ DW) and a high fruit production (up to 590 fr m⁻²). We conclude that reproductive effort in Ruppia cirrhosa is highly plastic and interpret this as an adaptation to temporay flooding.     

Distribution and production ofChironomus salinarius (Diptera: Chironomidae) in a shallow coastal lagoon in the Bay of Cádiz

The abundance, generation time and production ofChironomus salinarius larvae in a lagoon fish-pond system in the Bay of Cádiz were studied by taking monthly samples at 3 sites during 1991 and 1992. Numerical abundance and biomass of larvae showed considerable spatial, seasonal and interannual variation (ANCOVAs,P<0.001). The maximum mean annual density was 7048 larvae m^–2, and corresponded to a biomass of 3.08 g dry weight (DW) m^–2. It was recorded at the site with the lowest rate of water renewal. Seasonal patterns were similar at all sites, with main annual peaks of abundance and biomass in autumn-early winter. Chironomid density was positively related to the biomass of benthic macroalgae (P<0.001). The population studied was multivoltine with a probable average of five generations per year, with overlapping cohorts and a predominance of third- and fourth-instar larvae. Estimates of annual production ranged between 72.2 g DW m^–2 yr^–1 at the site with the lowest rate of water renewal in 1991 and 0.1 g DW m^–2 yr^–1 at the site with the highest rate of water renewal in 1992. Mean annual production and the production/biomass ratio for the system was estimated to be 16.8 g DW m^–2 yr^–1 and 12.7, respectively. Possible factors leading to the observed density fluctuations are discussed, as well as possible sources of error in production estimates.     

Annual productivity of Spirulina (Arthrospira) and nutrient removal in a pig wastewater recycling process under tropical conditions

An evaluation was made of the annual productivity of Spirulina (Arthrospira) and its ability to remove nutrients in outdoor raceways treating anaerobic effluents from pig wastewater under tropical conditions. The study was based at a pilot plant at La Mancha beach, State of Veracruz, Mexico. Batch or semi-continuous cultures were established at different seasons during four consecutive years. The protein content of the harvested biomass and the N and P removal from the ponds were also evaluated. Anaerobic effluents from digested pig waste were added in a proportion of 2% (v/v) to untreated sea-water diluted 1:4 with fresh water supplemented with 2 g L^–1 sodium bicarbonate, at days 0, 3 and 5. A straight filament strain of Spirulina adapted to grow in this complex medium was utilized. A pH value 9.5 ± 0.2 was maintained. The productivity of batch cultures during summer 1998 was significantly more with a pond depth of 0.10 m than with a depth 0.065 m. The average productivity of semi-continuous cultures during summer 1999 was 14.4 g m^–2 d^–1 with a pond depth of 0.15 m and 15.1 g m^–2 d^–1 with a depth of 0.20 m. The average annual productivity for semi-continuous cultures operating with depths of 0.10 m for winter and 0.15 and 0.25 m for the rest of the year, was 11.8 g m^–2 d^–1. This is the highest value reported for a Spirulina cultivation system utilising sea-water. The average protein content of the semi-continuous cultures was 48.9% ash-free dry weight. NH₄-N removal was in the range 84–96% and P removal in the range of 72–87%, depending on the depth of the culture and the season.     

Life history, aspects of reproductive biology and production of Corophium orientale (Crustacea: Amphipoda) in Monolimni lagoon (Evros Delta, North Aegean Sea)

Monthly samples of Corophium orientale were collected during February 1998–February 1999 in both parts of Monolimni lagoon (0.3 < Sal. < 6 psu, 2 < Temp. < 28.5 °C). Corophium orientaleshowed a semiannual life cycle. In the southern part, breeding occurred from early spring to mid autumn having three peaks, in early spring, early summer and early autumn, and three cohorts were produced, a spring cohort, a summer cohort and an overwintering one. In the shallower innermost northern part of Monolimni lagoon, breeding peaked in mid-spring and, also, in early autumn, and two discrete cohorts, a spring and an overwintering one, were produced. A lack of large individuals, attributed to a temporary size – selective predation by migrating shorebirds, was observed during summer. That lack possibly contributed to the hiatus in reproduction. Photoperiod seemed to be a more important cue than temperature in the initiation of the reproductive cycle, while extremely low salinities (<1 psu) did not deter breeding. Females attained maturity at a smaller size in late spring and, especially, in summer than in early spring at lower temperatures. Brood size was a function of females body size. Females, matured during summer at high temperatures, showed the lowest brood size, body length ratio. Mean brood size was small (12–13 early embryos) and embryo loss during development high (54%), possibly due to a negative effect of low salinities. A 1:1 sex ratio existed in the small body length classes, but females preponderated in the large ones. The spring cohort in the southern part, which developed at moderate temperatures, showed the highest growth rate (40 m day^–1). Secondary production of C. orientalecalculated by Hyness method gave a mean annual density of 4562.5 and 9327.6 ind. m^–2, a mean annual crop (B) of 1.03 and 2.67 g DW m^–2, an annual production (P) of 6.91 and 22.54 g DW m^–2 and a P/B ratio of 6.7 and 8.4 in the northern and southern part of the lagoon, respectively.     

Qualitative and quantitative aspects of the epiphytic component in a mixed seagrass meadow from Papua New Guinea

During 1982, structural and functional aspects of the epiphytic component in a tropical mixed seagrass meadow, have been investigated for each seagrass species separately. This meadow consisted of the seagrasses Thalassia hemprichii (Ehrenb.) Aschers., Cymodocea serrulata (R.Br.) Aschers. et Magnus, C. rotundata Ehrenb. et Hempr. ex Aschers., Halodule uninervis (Forssk.) Aschers. and Syringodium isoetifolium (Aschers.) Dandy.No significant differences were observed in floristic composition, number of algal species, abundance and diversity of the epiphytic component. On an area basis, annual mean above-ground biomass (seagrass leaves and epiphytes), amounted to 82 g ADW, of which 18% could be ascribed to the epiphytic component. The contribution of the epiphytic component to the annual mean above-ground production ranged from 16% on leaves of Thalassia hemprichii to 33% on leaves of Cymodocea serrulata. Total annual mean epiphyte production was 4.6 g ADW m⁻² sediment surface day⁻¹ (19%).When including the macroalgal component of this mixed seagrass meadow, total annual mean above-ground plant biomass amounted to 93 g ADW (212 g DW) on an area basis, of which the epiphytes contributed 15.5% (28.5% DW), the macroalgal component 12% (32.5% DW) and the seagrass leaves 72.5% (39.5% DW). Aspects of the epiphytic component (e.g., floristic composition, abundance, biomass and production) in monospecific and mixed seagrass communities are discussed.     

Lichenochemical Screening and Antioxidant Capacity of Four Tunisian Lichen Species

The phenolic composition and antioxidant capacity of four Tunisian lichen species, Cladonia rangiformis, Flavoparmelia caperata, Squamarina cartilaginea and Xanthoria parietina, were determined in order to provide a better understanding of their lichenochemical composition. Powdered material of F. caperata was the richest in total phenolic content (956.68 μg GAE g⁻¹ DW) and S. cartilaginea in proanthocyanidin content (77.31 μg CE g⁻¹ DW), while the acetone extract of X. parietina showed the highest flavonoid content (9.56 μg CE g⁻¹ DW). The antioxidant capacity of all lichen extracts and crude material was evaluated by DPPH^. scavenging, iron-chelating, and iron-reducing powers. Results showed that methanol extracts of S. cartilaginea had the highest DPPH^. antioxidant capacity (IC₅₀=0.9 μg mL⁻¹) and the highest iron-reducing power was attributed to the acetone extract of this species. All extracts of all species were further screened by Fourier-transform infrared spectroscopy (FT-IR) and nuclear resonance spectroscopy (NMR); results showed an abundance of phenols, aromatic compounds, and fatty acids. Overall, our results showed that the investigated species are a rich source of potentially bioactive compounds with valuable properties.     

Organic Carbon Flux to a Large Salt Lake: Pyramid Lake,Nevada, USA

Energy flux to a large, deep, salt lake from phytoplankton, periphyton and macrophyte primary production as well as fluvial transport and wind-transported terrestrial vegetation and dust were quantified. Average areal phytoplankton net photosynthesis was 511 mg C m⁻² d⁻¹. Highest rates were during water-blooms of the bluegreen alga, Nodularia spumigena. Although areal daily net photosynthesis by periphyton in Pyramid Lake was comparable to other salt lakes, annual carbon influx by periphyton was small due to the lake's graben morphology and moderate euphotic depth (mean, 11.9 m). Macrophytes were uncommon and, therefore a minor source of energy. Truckee River is the only major fluvial discharge to Pyramid Lake and dissolved organic carbon was the principal organic carbon fraction in river water. Large upstream water diversions coupled with several drought years resulted in an average fluvial organic carbon load of only 7.3 g Cm⁻²y⁻¹ or 4% of median phytoplankton net photosynthesis. Tumbleweeds were the most common terrestrial plant material observed in Pyramid Lake comprising a maximum projected importance of 6% of total annual carbon input. Windborne dust represented < .1% of annual carbon input. Phytoplankton primary production is the predominant energy source to Pyramid Lake, accounting for over 80% of annual carbon influx. The relative magnitude of autochthonous and allochthonous vectors to the annual carbon budget of this desert salt lake are comparable to those of the few other large lakes for which detailed energy input budgets have been calculated.     

Investigation of Microorganisms in Bentonite Deposits

Microbiological characteristics of bentonite deposits were investigated as a natural analogue of microbial behavior in the buffer material for geological disposal of radioactive waste. Distributions of microorganisms in bentonite were examined at four sites in two different bentonite deposits in Japan. The sites included pond bottom, wetland, and wet mine gallery environments where bentonite layers have been left undisturbed for 2 to 30 years. Excavation was performed without using drilling water and the center parts of the cores were used for microbial examination. Plate counts with R2A medium of aerobic and anaerobic bacteria at the drilling mouth ranged from 10⁵ to 10⁷/g DW (dry weight) and from 10³ to 10⁶/g DW, respectively. The CFDA-AM (Carboxyfluorescein diacetate acetoxymethyl ester) cell counts ranged from 10⁶ to 10⁹/g DW. Bacterial numbers in the bentonite layers declined with distance from the drilling mouth; both aerobes and anaerobes were less than 10²/g DW and CFDA-AM cell counts less than 10⁶/g DW for core samples taken from approximately 1 m depth, except at the pond bottom. These results suggest that microbial activity in natural bentonite is lower than in typical soils and aquatic sediments and does not spread easily.     

Ulva rigida (Ulvales,Chlorophyta) tank culture as biofilters for dissolved inorganic nitrogen from fishpond effluents

Ulva rigida was cultivated in 7501 tanks at different densities with direct and continuous inflow (at 2, 4, 8 and 12 volumes d^–1) of the effluents from a commercial marine fishpond (40 metric tonnes, Tm, of Sparus aurata, water exchange rate of 16 m³ Tm^–1) in order to assess the maximum and optimum dissolved inorganic nitrogen (DIN) uptake rate and the annual stability of the Ulva tank biofiltering system. Maximum yields (40 g DW m^–2 d^–1) were obtained at a density of 2.5 g FW 1^–1 and at a DIN inflow rate of 1.7 g DIN m^–2 d^–1. Maximum DIN uptake rates were obtained during summer (2.2 g DIN M^–2 d^–1), and minimum in winter (1.1 g DIN m^–2 d^–1) with a yearly average DIN uptake rate of 1.77 g DIN m^–2 d^–1 At yearly average DIN removal efficiency (2.0 g DIN m^–2 d^–1, if winter period is excluded), 153 m² of Ulva tank surface would be needed to recover 100% of the DIN produced by 1 Tm of fish.Abbreviations DIN= dissolved inorganic nitrogen (NH _inf4 ^sup+ + NO _inf3 ^sup– + NO _inf2 ^sup– ); - FW= fresh weight; - DW= dry weight; - PFD= photon flux density; - V= DIN uptake rate     

The energy budget of two sympatric Daphnia species in Lake Constance: productivity and energy residence times

Summary Two Daphnia species, D. hyalina and D. galeata, are living in Lake Constance. Both populations show logistic growth, with the phase of exponential increase in May and the phase of steady state during the summer. In spring, food is not limited and both daphnids reveal an exploitative strategy: females mature early, primiparae are small, egg weights are small, but clutch sizes are large. From June on, when food limiting conditions prevail, D. hyalina starts to migrate vertically with a diurnal rhythm whereas D. galeata keeps on living in the epilimnion over the whole season. The differing thermal environments of the populations lead to short generation times (age of first reproduction) of 11 days for D. galeata in mid-summer, and to 47 days (July) for D. hyalina. The annual production (P) of D. hyalina and D. galeata were 18 and 24 g DW/m², respectively. The average standing stocks (B) were 1.6 and 0.9 g DW/m². This corresponds to turnover rates of 11 x and 27 x per season (200 days), and to turnover times of 18 days and 7.5 days, respectively. From 1980 to 1982 the cumulative annual primary production (PPR) varied between 260 and 330 g C/m². The common productivity (P) of the functional component Daphnia (=sum of both Daphnia species) followed the PPR, but the Daphnia stading stock was constant at 2.5 g DW/m². The increase of secondary production (P) was a consequence of a shift in abundance between the two Daphnia species: at low PPR, D. hyalina was 4 x more abundant, but at high PPR, the two species were equally abundant. Such internal regulatory mechanism within a system component is in accordance with the hypothesis of Cheslak and Lamarra (1981): increase of energy residence time (B/R) with declining nutrients and increasing strength of competitive interrelationships within a given functional component of an ecosystem.This research was supported by the Deutsche Forschungsgemeinschaft within Sonderforschungsbereich Stoffhaushalt des Bodensees (SFB 248)     

Composition and Productivity of the Benthic Macroinvertebrate Community of a Subtropical Reservoir

Physical-chemical conditions, phytoplankton productivity, community structure and productivity of the macroinvertebrate benthic community were determined during 1976–77 in a subtropical reservoir. Physical-chemical results revealed high nitrate and phosphate concentrations with highest values in the riverine segment. Large phytoplankton populations were present during most of the year. Phytoplankton productivity was high, producing an annual mean of 87 mg C · m⁻³ · h⁻¹ (12 hours light day). High turbidity in the riverine segment limited phytoplankton productivity during winter and spring. Macrobenthos was dominated by chironomids (Chironomus, Procladius, Coelotanypus and Tanypus) and oligochaetes (Limnodrilus). The annual mean benthic population was estimated at 1,626 · m⁻² with a mean dry weight of 0.66 g · m⁻². Mean benthic species diversity was 1.80. A lacustrine-riverine community gradient was revealed. Benthic productivity was 6.8 g · m⁻² · yr⁻¹ (dry weight) with a P: B ratio of 10. A low correlation was observed between benthic and phytoplankton productivity, and between phytoplankton standing crop and benthic macroinvertebrate numbers throughout the reservoir. Algal food supplies had little impact on the benthic community which was composed predominately of species which fed mostly on organic detritus. Stressful conditions caused by low dissolved oxygen concentrations probably inhibited development of the benthic community throughout the reservoir during summer months, while high sedimentation rates limited development in the head waters.     

Abundance,population dynamics and production of Chironomidae (Diptera) in an ul traoligotrophic lake in South Greenland

Macrozoobenthos of the ultraoligotrophic Lake 95 (61°N, 46°W, 8 ha, z_max=18 m, ) is composed of about 14 taxa dominated by 12 Chironomidae species. Abundance, life cycle, biomass and production were estimated for the six dominant taxa. Abundance declined fromca. 4150 at 2.5 m depth toca. 1400 ind m^–2 at 16 m depth and averagedca. 3200 ind m^–2 on a lakewide basis. By numbers,Heterotrissocladius changi andH. oliveri dominated the average fauna.H. changi was common at the 2.5 m and 5 m depth stations, whereasH. oliveri dominated from 5 m depth downwards. Chironomids showed mainly a 1-yr life cycle, but apparently bothHeterotrissocladius species had two contemporary cohorts with emergence in midsummer and late autumn/early spring, respectively. Average annual ratio was 4.2 and 4.6 forH. oliveri andH. changi, respectively. Annual production varied from 0.3 g ash-free dry weight (AFDW) m^–2 y^–1 at 16 m depth to 1.6 g AFDW m^–2 y^–1 at 2.5 m depthH. changi contributed 45%, fiveMicropsectra spp. 17% andH. oliveri 15% to total average production, which on a lakewide basis wasca. 1.1 g AFDW or 25 kJ m^–2 y^–1. Lake 95 thus belongs at the very low end of measured lake zoobenthic productions, which range from 10 kJ m^–2 y^–1 in Arctic lakes toca. 1600 kJ m^–2 y^–1 in highly eutrophic shallow lakes.     

Bioproduction of phenylethanoid glycosides by plant cell culture of Scrophularia striata Boiss.: from shake-flasks to bioreactor

Phenylethanoid glycosides (PeG) are a class of polyphenols found in some plants that have pharmaceutical effects as anti-inflammatories and anti-oxidants. The presence of PeG (acteoside) in the aerial parts of Scrophularia striata Boiss. has been demonstrated. Considerable progress has been made using plant cell cultures to stimulate formation and accumulation of secondary metabolites. The present study optimized phenylethanoid production from shake flasks to bioreactor using a cell culture of S. striata. The optimal conditions for production of cell biomass by scale-up to a bioreactor were determined to be a pH of 4.8, air flow rate of 0.5–1.5 l min⁻¹, and mixing speed of 110–170 rpm at 25 ± 1 °C in darkness. Growth parameters and PeG production were measured and compared with the results from the shake flasks. The results showed that cell biomass was high in the bioreactor (15.64 g l⁻¹ DW) and in the shake flasks (14.16 g l⁻¹ DW). The acteoside content in the bioreactor was 1404.20 μg g⁻¹ DW, which is threefold higher than in the shake flasks (459.71 μg g⁻¹ DW). The echinacoside concentration in the bioreactor was 1449.39 μg g⁻¹, 1.36-fold lower than in the shake flasks (1973.03 μg g⁻¹ DW). This study established an efficient way for production of acteoside, the major PeG, in a bioreactor.

     

Seasonal variation in the phytomass,chemical composition and nutritional value of Azolla filiculoides Lam. along the water courses in the Nile Delta,Egypt

The present study aims to assess phenological behaviour, phytomass production, chemical composition and nutritional value of Azolla filiculoides in the water courses of the Nile Delta, Egypt. The sampling process was carried out seasonally using twenty‐five plots (each of 1 × 1 m) distributed along 15 irrigation canals and 10 drainage canals in the study area. Sprouting of A. filiculoides had its maximum activity during winter, vegetative growth during spring and summer and withering during autumn. Maximum seasonal phytomass (285.2 g DW m^‐2) was found during spring. The annual mean was significantly higher in drainage canals (278.3 g DW m^‐2) than in irrigation canals (144.4 g DW m^‐2). The concentrations of Ca, Mg and Na in A. filiculoides from drainage canals were significantly higher than in those from irrigation canals. Regarding the type of water courses, there were no significant differences in organic contents and nutritive values between the irrigation and drainage canals. The analysis of growth characteristics indicated that A. filiculoides can grow quite well in drainage canals; its macronutrient (N, Ca, Mg, Na and Fe) contents are high enough to allow it to be used as a bio‐fertilizer. On the other hand, A. filiculoides could be considered as a ‘nutrients and heavy metals remover’ especially in drainage canals for wastewater treatment if the plant is harvested during its maximum phytomass. As feed supplement for animals, this plant could be considered as excellent forage because its high levels of carbohydrate, protein, crude fat, total digestible nutrients and the lower crude fiber contents (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)