Biology of Moina mongolica (Moinidae,Cladocera) and perspective as live food for marine fish larvae: review

Moina mongolica, 1.0-1.4 mm long and 0.8 mm wide, is an Old World euryhaline species. This paper reviewed the recent advances on its autecology, reproductive biology, feeding ecology and perspective as live food for marine fish larviculture. Salinity tolerance of this species ranges from 0.4–1.4 to 65.2–75.4. Within 2–50 salinity, Moina mongolica can complete its life cycle through parthenogenesis. The optimum temperature is between 25 °C and 28 °C, while it tolerates high temperature between 34.4 °C and 36.0 °C and lower temperature between 3.2 °C and 5.4 °C. The non-toxic level of unionised ammonia (24 h LC₅₀) for M. mongolica is <2.6 mg NH₃–N l^–1. Juvenile individuals filter 2.37 ml d^–1 and feed 9.45×10⁶ algal cells d^–1, while mature individuals filter 9.45 ml d^–1 and consume 4.94×10⁶ algal cells d^–1. At 28 °C, M. mongolica reaches sex maturity in 4 d and gives birth once a day afterward; females carry 7.3 eggs brood^–1 and spawn 2.8 times during their lifetime. A variety of food can be used for M. mongolica culture including unicellular algae, yeast and manure, but the best feeding regime is the combination of Nannochloropsis oculata and horse manure. Moina mongolica reproduces parthenogenetically during most lifetime, but resting eggs can be induced at temperature (16 °C) combined with food density at 2000–5000 N. oculata ml^–1. The tolerance to low dissolved oxygen (0.14–0.93 mg l^–1) and high ammonia makes it suitable for mass production. Biochemical analyses showed that the content of eicospantanoic acid (20:53) in M. mongolica accounts for 12.7% of total fatty acids, which is higher than other live food such as Artemia nauplii and rotifers. This cladoceran has the characteristics of wide salinity adaptation, rapid reproduction and ease of mass culture. The review highlights its potential as live food for marine fish larvae.     

Observations on the distribution patterns,behaviour, diets and reproductive cycles of sand-dwelling clinids (Perciformes: Clinidae) from South Africa

Synopsis Twenty-two samples of sand-dwelling fishes were collected from sublittoral sandy substrata off the Cape Peninsula, South Africa using a novel quantitative technique in which the ichthyocide, rotenone, was introduced beneath 6.25 m² plastic sheets weighted around the perimeter with chain. A total of 94 fish of eight species and four families were recorded. Of these, four species of the family Clinidae made up 92% of the material. Fish densities varied from 0.10–2.96 fish m^–2 (0.17–1.14 g m^–2). Distribution patterns amongst the Clinidae were explained by sediment particle size, with all of the newly discovered species, Cancelloxus longior, inhabiting fine sand (median grain size 0.25–0.50 mm), and all Xenopoclinus leprosus, C. elongatus and Pavoclinus smalei occurring in gravel (> 1 mm). Xenopoclinus kochi was found in all sediment types, but was most abundant in coarse substrata. Diets of all four species were similar, consisting chiefly of amphipods and isopods. However, small differences in prey preference were evident. All four species reached sexual maturity at 25–30 mm standard length, were viviparous, exhibited superembryonation and gave birth to live young of approximately 14 mm. Breeding seasonality occurred in all species except P. smalei.     

The spring-time abundance and feeding ofEurytemora affinis (Poppe) in Volkerak-Zoommeer,a newly-created freshwater lake system in the Rhine delta (The Netherlands)

Eurytemora affinis, a calanoid copepod, has been encountered in Volkerak-Zoommeer (Rhine delta region, S.W. Netherlands) both before this lake system was isolated in 1987 from the estuarine influence, and after. It was the main particle-feeding crustacean at all the 3 sampling stations in March–April 1990 when it reached densities of up to 215 ind.l^–1. Its decline from mid April onwards, and low densities through summer, coincided with increase in cladocerans, especiallyDaphnia spp. (D. pulex andD. galeata), a decrease in seston (<33m) and chlorophyll concentrations and in primary production rates. The clearance rates (CR) ofEurytemora measured in the spring period varied enormously (0.6–24 ml.ind^–1.d^–1) depending mainly on size (0.44–1.06 mm), food concentration (0.8–2.2 mg C.l^–1), and the water temperature which varied only narrowly (8.0–9.0°C). Mean ingestion rates of the animals measuring 0.68±0.02 mm during the study was 6.7±3.2 gC.ind^–1.d^–1; and assimilation efficiency varied between 27 and 53% (mean: 41±9%). The weight specific CR (SCR) varied between 0.96 and 6.4 litre.mg^–1 body C.d^–1. Pooled regression of SCR on the animal's body weight at the 3 study stations revealed a significant inverse relationship. Also daily ration and specific assimilation ofE. affinis varied greatly and inversely with the body weight. This calanoid contributed from about 50 to 100% to the zooplankton community grazing rates and assimilation rates, the former often exceeding the phytoplankton primary production.     

Examining the relationship between bacteria and heterotrophic nanoflagellates in Funka Bay (Japan) using the size-fractionation method

The chemical and biological conditions, and the bacteria-heterotrophic nanoflagellate (HNF) relationship were investigated in the vicinity of Funka Bay, southwest of Hokkaido, Japan during early spring 1999. At the time of sampling, chlorophyll a concentration, bacteria, phycoerythrin rich-cyanobacteria, and HNF abundance were in the following ranges: 0.3–3.6 g l^–1, 2.5–5.6 × 10⁵ cells ml^–1, 0.6–1.2 × 10³ cells ml^–1, and 2.2–4.2 × 10³ cells ml^–1, respectively. Dissolved inorganic nitrogen, phosphate and silicate concentrations were in the ranges: 8.7–12.2 M, 0.9–2.0 M, and 21.6–25.5 M, respectively. Primary production ranged from 6.4 to 76.3 mg C m^–3 d^–1. Using water samples from regions of different productivity levels (in and outside bay), the bacteria - HNF relationship was uncoupled experimentally by the size-fractionation technique. Higher primary production (19.9 mg C m^–3 d^–1) in the bay supported higher bacterial growth rate (0.029 h^–1). However, outside the bay both primary production (6.4 mg C m^–3 d^–1) and bacterial growth rate (0.007 h^–1) were lower. The HNF growth rates and grazing rates were similar for both but by comparing both HNF grazing capacity and bacterial production, there was net decrease in bacterial abundance outside the bay and net increase inside the bay. The microbial parameters (rates and abundance) and the amount of carbon flow estimated through the phytoplankton – dissolved organic matter (DOM) – bacteria loop were different between the coastal station and the open ocean station. However HNF grazing and growth rates was similar for both stations.     

Effects of Zn2+ and Cu2+ on growth,lignin degradation and ligninolytic enzymes in Phanerochaete chrysosporium

The influence of Zn²⁺ (6.0 × 10^–3 –18.0 × 10^–3 M) and Cu²⁺ (4 × 10^–4 –1.2 × 10^–4 M) in the basal medium on mycelial growth (dry weight), activities of lignin peroxidase (Lip), manganese peroxidase (Mnp), solubilization, and mineralization (¹⁴CO₂ evolution) of lignin during a period of 3 weeks was studied in Phanerochaete chrysosporium strain MTCC-787. Highest mycelial growth was obtained at 0.6 M Zn²⁺ and 0.4 M Cu²⁺ levels. Enzyme activities were found to increase up to the highest levels of both the trace elements. However, Zn²⁺ had a relatively more stimulatory effect on Lip production and the reverse was true in case of Cu²⁺. [¹⁴C]Lignin solubilization was also promoted by higher levels of both trace elements. Mineralization of [¹⁴C]lignin was optimal at 6.0 M Zn²⁺ and 1.2 M Cu²⁺. The stimulatory effect of Zn²⁺ on Lip production was correlated with higher rates of [¹⁴C]lignin mineralization.     

Factors affecting the growth form of Aspergillus terreus NRRL 1960 in relation to itaconic acid fermentation

The effect of medium composition on the growth form of Aspergillus terreus NRRL 1960 in relation to itaconic acid fermentation has been studied. Four types of mycelial pellets were obtained under the conditions used and may be classified as (a) frayed and loose with 0.1–0.5 mm diameter (b) compact with 0.1–0.5 mm diameter (c) loose with 0.5–2.0 mm diameter and (d) compact with 0.5–2.0 mm diameter. Their respective maximum specific rates of formation and yields of itaconic acid, based on 100 g sucrose supplied, were (a) 1.25 mol mg^–1h^–1 and 55–59 g, (b) 0.27–0.43 mol mg^–1 h^–1 and 26–38 g, (c) 0.75–0.90 mol mg^–1 h^–1 and 45–51 g and (d) 0.12 mol mg^–1 h^–1 and 10 g. The presence of Ca²⁺, Zn²⁺ and Fe²⁺ in the basal medium at concentrations of 23.3 mg/100 ml, 0.01 mg/100 ml and 0.006 mg/100 ml respectively were found to be adequate and crucial in obtaining the desired outgrowth for both high production rates and consistent yields of itaconic acid. The further addition of either commercial plaster of Paris or analytical-reagent-grade CaSO₄, especially when activated by heating to 530°C and present in excess of solubility, results in small and frayed pellets, which lead to itaconic acid yields of 55–59 g acid/100 g sugar supplied.     

Swimming response of goldfish,Carassius auratus,and the tetra,Hemigrammus caudovittatus,larvae to individual food items and patches

Synopsis Swimming speed and swimming path of goldfish and tetra larvae were studied in aquaria containing food patches composed of decapsulated cysts and immobilized nauplii of Artemia salina or sparsely distributed prey. The mean swimming speed of starved larvae in the medium without food was about four times higher than the speed of larvae feeding in a patch. Satiated larvae swam about 1.5 times slower than hungry fish. Consumption of single prey items by starved larvae caused the following sequence of swimming responses: handling pause (cessation of swimming), slow swimming in a restricted area, and fast swimming (approximately twice as fast as hungry larvae before encountering food) accompanied by a widening of the area searched (area increased searching). Mean swimming speed was constant over a broad range (10¹–10³ ind·1^–1 of food density, although at extreme (high or low) values of food density it depended on swimming responses of the predator. Frequency of visits to the different parts of the aquarium strongly depended on encounters of hungry fish with food particles or patches.     

On the Population Ecology of the Zebra Seabream Diplodus cervinus cervinus (Lowe 1838) from the Coasts of the Canarian archipelago, North West Africa

Zebra seabream, Diplodus cervinus cervinus, caught off the Canary Islands is characterized by protogynous hermaphroditism. The male:female ratio is in favour of females (1:2.16). The reproductive season extends from spring to summer, with a peak in spawning activity in May–June. Males reach maturity at a larger total length, 327mm (5 years old) than females 273mm (4 years old). Recruitment occurs from late October to January in shallow waters of 0.5–8m depth along the coastal line. The recruits are located over rocky substrates with an important algae vegetation forming schools lower than 2m². During the spawning season, schools of adults from 3 to 8 fish are observed. The schools are formed by one large individual and a few moderate size individuals. Mating takes place in small groups formed by one dominant male and a group of several females (polygamy). Moderate size individuals are often observed mixed in large schools (up to 30 individuals) of Diplodus sargus cadenati. Subadults form groups of a few fish (<5 individuals) or more commonly mixed groups (>15 individuals) with individuals of species of similar size. Otoliths age readings indicate that the population consists of 18 age groups, including a very high proportion of individuals between 2 and 4 years old. The von Bertalanffy growth parameters for the whole population are: L = 603mm, k = 0.149 year^–1, and t₀ = –0.22 year. The mean rates of total, natural and fishing mortality are 0.551, 0.215 and 0.336 year^–1, respectively. The length at first capture is 183mm. The exploitation rate indicates that the stock is overfished. The direct effects of fishing on the population result in changes in the abundance, with a reduction to 85% of the unexploited equilibrium level. The length at first capture by the commercial fishery is less than the length at maturity. With 58% of the total catch below this length there is a danger of recruitment overfishing.     

Phytoplankton biomass and primary production in semi-enclosed reef lagoons of the central Great Barrier Reef,Australia

Phytoplankton biomass and primary production rates within semi-enclosed reef lagoons of the central Great Barrier Reef were compared with adjacent shelf waters. Chlorophyll concentrations and surface primary production rates were usually higher in lagoons although seasonal differences were only significant during the summer. Nitrate concentrations were higher in lagoons than in shelf waters year-round. Nano- (<20 m size fraction) or pico-phytoplankton (<2 m size fraction) dominated phytoplankton biomass and production within reef lagoons throughout the year. Net phytoplankton (>10–20 m size fraction), however, were relatively more important in both reef lagoons and open shelf waters during the summer. Biomass-specific production within lagoons (range 41–90 mg C mg chl^–1 day^–1) was high, regardless of season. Lagoonal phytoplankton production (range 0.2–1.6 g C m^–2 day^–1) was directly correlated with standing crop and inversely related to lagoon flushing rates. Phytoplankton blooms develop within GBR reef lagoons during intermittent calm periods when water residence times exceed phytoplankton generation times.     

Nitrous oxide production by nitrogen-fixing,fast-growing Rhizobia

Rhizobium trifolii, R. leguminosarum, andR. hedysarum, grownex planta under anoxic conditions in a chemically defined medium, evolve N₂O from NO₃ ^–, NO₂ ^–, and (NH₄)₂NO₃. The amount of nitrous oxide formed after 96 hours is about 0.2M×mg^–1 cells d.w. Large availability of organic matter enhances the production of N₂O from nitrate by free-livingR. trifolii in peat/sand mixtures. Denitrification of the above species andR. meliloti was detected also in planta. Nitrous oxide production increases almost linearly from 10–45M×mg^–1 nodules d.w. when nitrogen-fixing plants are exposed to increasing concentrations of nitrate (1–12M).     

Chromosome size and DNA content of species of anemone L. and related genera (Ranunculaceae)

Relative amounts of DNA were determined by Feulgen cytophotometry in 22 diploid species of Ranunculaceae (n=7, 8, 9) representing six genera, and exhibiting large differences in chromosome size, but no marked differences in karyotype pattern. Chemical determination of absolute amounts of DNA for six of these species, allowed conversion of all the photometric data into absolute units of DNA. The mean DNA content per nucleus varied from.13×10^–11gm in Aquilegia to 5.25×10^–11gm in species of Anemone in the section Homalocarpus. The DNA values obtained appeared to be quantized, and data for the majority of species fitted a non-geometrical series with the observed relative terms: 1—8—12—16—20—24—40. The magnitude of these variations in DNA content, the preservation of the karyotype and the tendency towards a simple numerical progression in DNA values, lead us to prefer an interpretation of the evolution of DNA content in terms of differential polynemy to one postulating changes in size of genetic units in an unchanging number of strands per chromosome.     

The effect of 2-chloro, 6-(trichloromethyl) pyridine on the chemoautotrophic metabolism of nitrifying bacteria

Studies were conducted to elucidate the mechanism of action of 2-chloro-6-(trichloromethyl)pyridine or Technical N-SERVE on the nitrification process brought about byNitrosomonas europaea. The growth ofNitrosomonas was completely inhibited in the presence of 0.2 ppm N-SERVE while 1.0 ppm of the chemical was effective in the complete inhibition of ammonia oxidation by fresh cell suspensions. Cells stored at 4 C for a period of three days required somewhat higher concentrations (1.5 ppm) of N-SERVE for the complete inhibition of their ammonia oxidizing ability while the cytochrome oxidase of these cells was inhibited to the extent of 65 to 70 percent in the presence of a corresponding amount of N-SERVE. A 45 – 70 percent reversal of the inhibition of ammonia oxidation caused by N-SERVE was obtained by the addition of 6×10^–4 M Cu⁺⁺. An equivalent concentration of Cu⁺⁺ was also effective for the complete reversal of the inhibition of cytochrome oxidase present in whole cells.Hydroxylamine oxidation by intactNitrosomonas cells was not affected by levels of N-SERVE ranging from 1 – 3 ppm. The cytochrome oxidase effective in hydroxylamine oxidation and present in cell-free extracts was not inhibited by even 100 ppm N-SERVE. Likewise, the hydroxylamine activating enzyme hydroxylamine cytochromec reductase was also not inhibited by such levels of the chemical. Raising the concentration to 170 ppm N-SERVE, however, caused a 90 percent inhibition of the enzyme.Although a 5×10^–6 M concentration of allylthiourea completely inhibited ammonia oxidation byNitrosomonas cells, concentrations up to 10^–3 M of this compound did not affect the cytochrome oxidase activity of whole cells or cell-free extracts. The inhibition of ammonia oxidation caused by 5×10^–6 M allythiourea, unlike the inhibition by N-SERVE, could not be reversed by the addition of 6×10^–4 M Cu⁺⁺.Evidence is presented that the action of N-SERVE is on that component of cytochrome oxidase which is involved in ammonia oxidation.     

Evolutionary temperature adaptation of fish sarcoplasmic reticulum

Summary Sarcoplasmic reticulum has been isolated from the white muscle of 15 species of teleost fish adapted to diverse thermal environments. Evidence has been obtained that the Ca²⁺-dependent ATPase of fish sarcoplasmic reticulum has undergone evolutionary modification for function at different temperatures. Compared with tropical fish, cold adapted species have higher rates of Ca²⁺ transport and Ca²⁺-ATPase activities at low temperatures. Most species have linear Arrhenius plots over the temperature range 0–30°C. Activation enthalpies (H ) of the ATPase ranged from 53–190 kJ mol^–1 and were positively correlated with environment temperature. Activation entropy (S ) varied from negative values in cold adapted species to positive values in tropical fish.In contrast to the Ca²⁺-ATPase, the basal ATPase of fish sarcoplasmic reticulum showed no relationship between either ATPase activity or thermodynamic activation parameters and environmental temperature.Only the Ca²⁺-dependent ATPase is coupled to Ca²⁺ transport. The percentage of total ATPase activity which is Ca²⁺ activated is higher at low temperatures in cold than in warm adapted species. For example, ratios of Ca²⁺-dependent/total ATPase at 2°C varied from 80–98% in Arctic, Antarctic and North Sea species to only 2–50% in various tropical fish. Above 20°C, similar ratios in the range 80–98% were obtained for all species. The nature of the basal ATPase and mechanisms of temperature adaptation of fish sarcoplasmic reticulum are discussed.Abbreviations ET environmental temperature - EGTA ethylene glycol-bis (-aminolethyl ether)-N, N-tetraacetic acid - HEPES N-2-hydroxylpiperazine-N-2-ethanesulfonic acid - SR sarcoplasmic reticulum     

Analysis of the Global Architecture of Hemoglobin A2 by Heme Binding Studies and Molecular Modeling

The kinetics of CNProto- and CNDeutero-hemin binding to apohemoglobin A₂ was investigated in a stopped-flow device in 0.05 M potassium phosphate buffer, pH 7, at 10°C. The overall kinetic profile exhibited multiple phases: Phases I–IV corresponding with heme insertion (8.5–13 × 10⁷ M^–1 s^–1), local structural rearrangement (0.21–0.23 s^–1), global structural event (0.071–0.098 s^–1), and formation of the Fe–His bond (0.009–0.012 s^–1), respectively. Kinetic differences observed between apohemoglobin A₂ and apohemoglobin A (previously studied) prompted an analysis of the structures of and chains through molecular modeling. This revealed a structural repositioning of the residues not only at, but also distant from the site of the amino acid substitutions, specifically those involved in the heme contact and subunit interface. A significant global change was observed in the structure of the exon-coded 3 region and provided additional evidence for the designation of this as the subunit assembly domain.     

Feeding rate inhibition in crowded Daphnia pulex

Feeding rates of Daphnia pulex fed a range of levels of the alga Chlamydomonas reinhardi of 15 °C are strongly density-dependent. At lower densities, Daphnia (30 1^–1) fed at higher rates than crowded (270 1^–1) Daphnia which manifest a relatively depressed saturation feeding response. At 30 individuals/liter, Daphnia consumed 8.5 – 15.7 × 10⁴ cells d^–1h^–1 (on a volume basis, 12.1 – 22.2 × 10⁶ m³), at 270 L^–1 3.7 – 3.9 × 10⁴ (5.2 – 5.5 = 10⁶ m³ cells d^–1h^–1 when feeding on algae at 80 000 cells ml^–1 (11.3 × 10⁶ m³ ml^–1). The feeding rate data best fit an Ivlev feeding function. An autoallelopath might be causing the repression. Water preconditioned with crowded Daphnia completely repressed feeding in uncrowded Daphnia after six hours.     

Characterization of a chloride channel reconstituted from cardiac sarcoplasmic reticulum

We have characterized a voltage-sensitive chloride channel from cardiac sarcoplasmic reticulum (SR) following reconstitution of porcine heart SR into planar lipid bilayers. In 250 mm KCl, the channel had a main conductance level of 130 pS and exhibited two substrates of 61 and 154 pS. The channel was very selective for Cl^– over K⁺ or Na⁺ ( and ). It was permeable to several anions and displayed the following sequence of anion permeability: SCN^– > I^– > NO ₃ ^– Br^– > Cl^– > f^– > HCOO^–. Single-channel conductance saturated with increasing Cl^– concentrations (K _m= 900 mm and _max = 488 pS). Channel activity was voltage dependent, with an open probability ranging from 1.0 around 0 mV to 0.5 at +80 mV. From –20 to +80 mV, channel gating was time-independent. However, at voltages below –40 mV the channel entered a long-lasting closed state. Mean open times varied with voltage, from 340 msec at –20 mV to 6 msec at +80 mV, whereas closed times were unaffected. The channel was not Ca²⁺-dependent. Channel activity was blocked by disulfonic stilbenes, arylaminobenzoates, zinc, and cadmium. Single-channel conductance was sensitive to trans pH, ranging from 190 pS at pH 5.5 to 60 pS at pH 9.0. These characteristics are different from those previously described for Cl^– channels from skeletal or cardiac muscle SR.We thank Dr. Barry Pallotta for help with open and closed intervals analysis and Dr. Gerhard Meissner for his suggestions for the preparation of cardiac sarcoplasmic reticulum membranes. This work was supported by a grant from the National Institutes of Health to R.L.R. and a Student Grant-in-Aid from the American Heart Association, North Carolina affiliate to C.T. R.L.R. is an Established Investigator of the American Heart Association.     

Photolithotrophy,photoheterotrophy and chemoheterotrophy during spring phytoplankton development (Lake Pavin)

In order to determine the relative importance of autotrophic and heterotrophic activities in both bacterial and phytoplanktonic communities in an oligomesotrophic lake, the size fractionation by differential filtration and the use of a bacterial inhibitor (gentamycin) were combined. The study was carried out at Lake Pavin during the spring planktonic bloom. Photosynthetic and photo- and chemoheterotrophic activities were measured from the assimilation of NaH¹⁴CO₃ and glucose-³H, using a double labeling technique. The bacterial community was at low cell concentration (0.6 to 7 × 10⁵ cells ml^–) and represented very low biomass values (0.9 to 11.5 gC liter^–1). The abundance of the phytoplankton varied between 0.5 and 1.8 × 10⁶ cells liter^–1, and biomass values ranged between 19 and 118 gC liter^–1. The diatom Melosira italica sp. subarctica (O. Mueller) was the largely dominant species in the meta- and hypolimnion. Inorganic fixation by photolithotrophy (mean value: 1.66 mg C m^–3 hour^–1) largely predominates over assimilation by photoheterotrophy (mean value: 0.93 g C m^–3 hour^–1) or chemoheterotrophy (mean value: 2.42 g C m^–3 hour^–1). However, because of the considerable underestimation of heterotrophic assimilation due to the experimental methods used, and because of the spatial and temporal separation of photolithotrophic and photo- and chemoheterotrophic activities, it is likely that the fixation of organic carbon by microalgae plays an important role in the survival of species and/or in competitive interactions, as the results with Monoraphidium contortum (Pasch. et Korschik.), the prevailing species in the epilimnion, would suggest. Send offprint requests to: C. Amblard.     

The relative importance of different ciliate taxa in the pelagic food web of lake constance

Abundance, biovolume, and species composition of pelagic ciliates in Lake Constance were recorded over two annual cycles (1987/88). Production was estimated from mean annual biovolumes and size-specific growth rates obtained from the literature. Cell concentrations and biovolumes ranged from 0.1 to 120 cells ml^–1 and from 3 to 1,200 mm³ m^–3, respectively. Mean annual values were, respectively, 6.8 cells ml^–1 and 94 mm³ m^–3 in 1987, and 12.0 cells ml^–1 and 130 mm³ m^–3 in 1988. In both years, prostome nanociliates (<20m) dominated numerically, while strobiliids in the size range 20–35m contributed most significantly to ciliate production. Ciliate community production, according to a crude calculation, yielded approximately 10–15 g C m^–2 year^–1.     

Distribution and activity of bacteria in the headwaters of the Rhode River Estuary,Maryland, USA

A transect along the axis of the headwaters of a tidal estuary was sampled for microbial, nutrient, and physical parameters. Chlorophylla averaged 42g 1^–1 and phytoplankton comprised an estimated 80% of the total microbial biomass as determined by adenosine triphosphate (ATP). Bacterial concentrations ranged from 0.3–53.9×10⁶ cells ml^–1 and comprised about 4% of the total living microbial biomass. Bacterial production, determined by³H-methyl-thymidine incorporation was about 0.05–2.09× 10⁹ cells 1^–1 h^–1, with specific growth rates of 0.26–1.69 d^–1. Most bacterial production was retained on 0.2m pore size filters, but passed through 1.0m filters. Significant positive correlations were found between all biomass measures and most nutrient measures with the exception of dissolved inorganic nitrogen nutrients where correlations were negative. Seasonal variability was evident in all parameters and variability among the stations was evident in most. The results suggest that bacterial production requires a significant carbon input, likely derived from autotrophic production, and that microbial trophic interactions are important.     

Continuous culture of the hyperthermophilic archaeum Pyrococcus furiosus

Summary A system for continuous culture of the hyperthermophilic archaeum Pyrococcus furiosus in the absence of elemental sulphur has been developed. An all-glass gas-lift bioreactor was used to provide high mass transfer at low shear forces, whilst eliminating the potential for corrosion. Steady-state cell densities of P. furiosus were found to increase with higher inert gas flow rates, reaching a maximum in this system with 0.5 vol. vol^–1 min^–1 of nitrogen (N₂). N₂ permitted higher cell densities than the other inert gases tested (argon, helium and sulphur hexafluoride) under equivalent conditions. At 0.5 vol. vol^–1 min^–1 of N₂ a cell density in excess of 3 × 10⁹ ml^–1 could be maintained indefinitely at a dilution rate of 0.2 h^–1. Higher dilution rates gave progressively lower steady-state cell densities. Teh biomass production was maximal, however, at a dilution rate of 0.4 h^–1. At this dilution rate the bioreactor was able to generate more than 1.5 g wet weight of cells h^–1 l^–1 culture volume.Correspondence to: N. Raven