Biomass Profiles Research Articles

Zooplankton and micronekton biomass off Somalia and in the southern Red Sea during the SW monsoon of 1992 and the NE monsoon of 1993

Spatial and seasonal variations in mesozooplankton, macrozooplankton and micronekton biomass distribution were studied in the Somali Basin and the southern Red Sea and Gulf of Aden. Cruises were made in May–June and July–August 1992 during the SW monsoon, and in January–February 1993 during the NE monsoon. Samples were taken in day and night series from stratified layers to depths of 600 or 1000 m, using an RMT1 + 8, combining two nets with mesh size of 0.34 mm and 4.5 mm, respectively. During the SW monsoon the mean zooplankton biomass from RMT1 samples (displacement volume 0–300 m, night) were low in the southern Red Sea and the Gulf of Aden, 14.0–17.5 ml m-2. At 11°N in the Somali Current, where coastal upwelling occurs, the maximum biomass value of 38.0 ml m −2 was recorded. Downstream from the upwelling in the Great Whirl, biomass values were lower, ranging from 21.0 to 35.9 ml m −2. In the Somali Basin south of 5°N the mesozooplankton biomass was lower than in the Somali Current and northern areas. During the NE monsoon large phytoplankton blooms occurred in the southern Red Sea and the Gulf of Aden, and the mean zooplankton biomass almost doubled to 23.9–40.2 ml m −2 compared with the SW monsoon. Primary production in the northern Somali Basin was much higher during the NE monsoon than recorded during earlier studies, and biomass values for the zooplankton therefore were not as low as might be expected. No statistical significant difference was found in the season's mean biomass values. This is remarkable because in the northern Somali Basin the mean phytoplankton carbon production during the NE monsoon was about two-thirds of the production during the SW monsoon. This seeming paradox is probably due to large mesh sizes that did not retain the small size (herbivorous) zooplankton fraction present during the SW monsoon. The mean macrozooplankton and micronekton biomass from RMT8 samples (0–300 m night) in the southern Red Sea, the Gulf of Aden and the Somali Basin showed no significant seasonal difference. However, biomasses of mesopelagic fish and large crustaceans were high in the southern Red Sea during the SW monsoon, and were high in the Somali Current during the NE monsoon, whereas in the northern Somali Basin biomasses remained about the same. Biomasses of large crustaceans in the Gulf of Aden were higher during the NE monsoon. The pelagic swimming crab Charybdis smithii was found during the SW monsoon in the equatorial and northern Somali Basin, attaining high displacements. The species was not found in the Somali upwelling area during this season, whereas during the NE monsoon the highest displacements for C. smithii were recorded. Vertical profiles of biomass from RMTI and RMT8 samples show that zooplankton and micronekton occur in the oxygen minimum zone and that the lowest oxygen concentrations in the sampled depth range (0.11 ml 1 −1) do not seem to hamper diurnal vertical migration.

Thermal stratification, nutrient dynamics, and phytoplankton productivity during the onset of spring phytoplankton growth in Lake Baikal, Russia

Lake Baikal, Russian Siberia, was sampled in July 1990 during the period of spring mixing and initiation of thermal stratification. Vertical profiles of temperature, dissolved nutrients (nitrate and soluble reactive phosphorus), phytoplankton biomass, and primary productivity were determined in an eleven-station transect encompassing the entire 636 km length of the lake. Pronounced horizontal variability in hydrodynamic conditions was observed, with the southern region of the lake being strongly thermally stratified while the middle and north basins were largely isothermal through July. The extent of depletion of surface water nutrients, and the magnitude of phytoplankton biomass and productivity, were found to be strongly correlated with the degree of thermal stratification. Horizontal differences likely reflected the contribution of two important factors: variation in the timing of ice-out in different parts of the lake (driving large-scale patterns of thermal stratification and other limnological properties) and localized effects of river inflows that may contribute to the preliminary stabilization of the water column in the face of intense turbulent spring mixing (driving meso-scale patterns). Examination of the relationships between surface water inorganic N and P depletion suggested that during the spring and early summer, phytoplankton growth in unstratified portions of the lake was largely unconstrained by nutrient supplies. As summer progressed, the importance of co-limitation by both N and P became more apparent. Uptake and regeneration rates, measured directly using the stable isotope 15N, revealed that phytoplankton in stratified portions of the lake relied primarily on NH4 as their N source. Rates of NH4 regeneration were in approximate equilibrium with uptake; both processes were dominated by organisms <2 µm. This pattern is similar to that observed for oligotrophic marine systems. Our study underscores the importance of hydrodynamic conditions in influencing patterns of biological productivity and nutrient dynamics that occur in Lake Baikal during its brief growing season.

Improved biomass distribution using pulsed injections of electron donor and acceptor

In situ bioremediation relies on the creation of contaminant-degrading biomass in subsurface soils. Pulsed injection of the electron donor and acceptor has been suggested as a method for evenly distributing biomass for more effective in situ bioremediation. Biofilms were developed in laboratory soil columns under both pulsed and continuous acetate and nitrate delivery using denitrifying conditions with acetate as the sole carbon and energy source. Separate experiments were conducted with either continuous or pulsed addition. Pulsing resulted in more evenly distributed biomass profiles as measured by both tryptic soy agar plate counts and total protein.

Influence of salad constituents on growth of Pseudomonas marginalis: a predictive microbiology approach

In order to describe the behaviour of Pseudomonas marginalis on ready‐to‐use vegetables, the effects of carbon and nitrogen sources on biomass profile were evaluated. First of all, experiments were carried out in synthetic medium with a multiwell analyser, using a factorial design. To establish a predictive model, a non‐linear equation was developed: cell density profile was described by two Gompertz functions including yeast extract, pectin and fructose influences. Starch had little or no effect on growth rate of Ps. marginalis. Finally, validation of the mathematical model was performed with cultures in 50 ml synthetic medium flasks and with endive juice assays. In each case, a good agreement between model prediction and experimental data was found.

The vertical distribution of below‐ground biomass in grassland communities in relation to grazing regime and habitat characteristics

Abstract. 40 sites, representing different pasture types in Northwest Spain, were sampled in respect of their floristic composition, distribution of above and below‐ground biomass and environmental and physical variables. Five plant community types were identified by classification techniques of plant species composition. These communities were then characterized in terms of the percentage of ground covered by herbaceous and shrub vegetation, stones, rocks and gaps as well as their topographic location and characteristics of the shallow soil (pH, organic matter, nitrogen and calcium content). Bio‐mass was assessed in terms of above‐ground structures, surface crowns and three below‐ground layers to a depth of 10 cm. Three types of grazing regime were distinguished: Concentrated Intense Grazing in early spring (CIG), Extended Intense Grazing throughout the spring (EIG), and Non‐Intense Grazing (NIG). Grazing regime showed the highest association with plant community type and three broad categories were identified: xeric stressed pastures, which nevertheless received CIG, mesic pastures with EIG, and three kinds of NIG mesic pastures.The xeric communities had the highest proportion of aboveground biomass, as a consequence of their greater proportion of woody perennials. These xeric communities displayed a more gradual reduction in below‐ground biomass with depth than mesic pastures, a likely consequence of the low water content in the upper soil layers. The mesic communities had a high concentration of below‐ground biomass in the upper layers when they were intensely grazed. However, when grazing was low (i.e. NIG situations), these communities had greater variability in biomass profiles than any of the other pasture types. Possible causes of the patterns in biomass distribution of the intensely grazed pastures are discussed.

Development of root biomass in an Eucalyptus globulus plantation under different water and nutrient regimes

The distribution along the soil profile of Eucalyptus globulus root biomass was followed in a plantation in central Portugal at 1, 2 and 6 years after planting, using an excavation technique. The experimental design consisted of a control (C) and 3 treatments: application of solid fertilizers twice a year (F), irrigation without the application of fertilizers (I) and irrigation combined with liquid fertilizers (IL). Below- and above-ground biomass decreased as follows: IL>I>F>C. So, water stress limited growth more severely than nutrient stress. The roots rapidly colonized the top soil volume (0–20 cm depth) during the first year after planting. Fine root biomass 6 years after planting was 2.2, 1.8 and 1.6 times higher in IL treatment than it was respectively in control, and in F and I treatments. The distribution of fine roots along the soil profile 6 years after planting was more even in IL compared to the other treatments. However, fine roots in the top soil were more concentrated along the tree rows in the irrigated treatments than in the others. The proportion of below-ground biomass relative to the total tree biomass and the root/shoot ratio were higher in C than in the treatments at early growth stages. This pattern was not so clear 6 years after planting, due to the increased proportion of the tap root relative to total biomass, especially in the IL treatment.

Multirate state and parameter estimation in an antibiotic fermentation with delayed measurements

This article discusses issues related to estimation and monitoring of fermentation processes that exhibit endogenous metabolism and time-varying maintenance activity. Such culture-related activities hamper the use of traditional, software sensor-based algorithms, such as the extended kalman filter (EKF). In the approach presented here, the individual effects of the endogenous decay and the true maintenance processes have been lumped to represent a modified maintenance coefficient, m(c). Model equations that relate measurable process outputs, such as the carbon dioxide evolution rate (CER) and biomass, to the observable process parameters (such as net specific growth rate and the modified maintenance coefficient) are proposed. These model equations are used in an estimator that can formally accommodate delayed, infrequent measurements of the culture states (such as the biomass) as well as frequent, culture-related secondary measurements (such as the CER). The resulting multirate software sensor-based estimation strategy is used to monitor biomass profiles as well as profiles of critical fermentation parameters, such as the specific growth for a fed-batch fermentation of Streptomyces clavuligerus.

Fluidized bed reactor operation for groundwater denitrification

Groundwater denitrification was carried out in a laboratory scale fluidized bed reactor using sand particles as the biomass carrier. This paper is concentrated on the fluidized bed reactor operation at very high nitrate loading rates (between 30 to 100 kg.NO3/m3 reactor/day) with corresponding short retention times (5 to 1.5 minutes). The effects of nitrate loading rate on nitrate and nitrite removal, as well as on reactor biomass profiles and biofilm characteristics, are presented in this article. The results of the present study indicate that this type of reactor can operate efficiently at retention times shorter than 3 minutes and at nitrate loading rates higher than 70 kg.NO3/m3/day. However, this system requires careful control of the biofilm thickness to achieve a reliable reactor operation.

Differential extracellular enzyme production in colonies of Coriolus versicolor, Phlebia radiata and Phlebia rufa: effect of gaseous regime

SUMMARY: The effects of different gaseous regimes on the growth rate and extracellular enzyme location in vitro of colonies of Phlebia radiata, Phlebia rufa and Coriolus versicolor are reported. The two Phlebia species showed similar growth, extracellular enzyme and pH responses to gaseous composition (N2, O2 and CO2), but the responses of C. versicolor differed. Whilst maximum extension rates were obtained for all species under atmospheric gaseous composition, maximum biomass production occurred at 5% (v/v) O2 with 20% (v/v) CO2 for the Phlebia species and at 5% O2 with 60% CO2 for C. versicolor. The Phlebia species had a coenocytic margin (5–6 mm width) under atmospheric conditions, which increased in width with increasing percentage of CO2. Laccase and peroxidase activity were present throughout the septate region, but not in the coenocytic zone. With C. versicolor laccase and peroxidase activities appeared throughout the colony, but were more intense in the peripheral region, under all gaseous regimes. A laser densitometer, normally used to visualize proteins on electrophoresis strips, was used to estimate profiles of biomass and laccase-α-naphthol activity within colonies. Surface pH changed little in colonies of C. versicolor but dropped by over 1 pH unit from the margin inwards with the Phlebia species. The significance of these results is discussed in terms of ecological strategy and developmental versatility.

Characterization and Comparison of Biomass from Mesophilic and Thermophilic Fixed Bed Anaerobic Digesters

Two lab-scale mesophilic (MAF) and thermophilic (TAF) anaerobic filters treating effluents from a mussel cooking factory were operated at their maximum organic load rate (OLR) for a long period of time. The biomass profiles and the distribution of occluded and attached biomass were determined. Biomass distribution in the MAF was more homogeneous along the filter. Most of the biomass in the TAF was attached while both attached and occluded biomass was observed in the MAF. The hydrolytic, acidogenic, acetogenic and methanogenic activities of sludges at different levels were determined. An attempt is made to explain the behaviour of both reactors as a function of these activities and other kinetic parameters.

Growth and substrate consumption of Nitrobacter agilis cells immobilized in carrageenan: Part 1. Dynamic modeling

The modeling of the growth of Nitrobacter agilis cell immobilized in kappa-carrageenan is presented. A detailed description is given of the modeling of internal diffusion and growth of cells in the support matrix in addition to external mass transfer resistance. The model predicts the substrate and biomass profiles in the support as well as the macroscopic oxygen consumption rate of the immobilized biocatalyst in time. The model is tested by experiments with continuously operated airlift loop reactors containing cells immobilized in kappa-carrageenan. The model describes experimental data very well. It is clearly shown that external mass transfer may not be neglected. Furthermore, a sensitivity analysis of the parameters at their values during the experiments revealed that apart from the radius of the spheres and the substrate bulk concentration, the external mass transfer resistance coefficient is the most sensitive parameter for our case.

Internal seiches in Lake Constance: influence on plankton abundance at a fixed sampling site

Dunng thermal stratification, pronounced internal seiches occur in Lake Constance with periods of 4-6 days The amplitudes reach 12 m at the sampling site in Uberhnger See (north- western part of Lake Constance). Seiches change the thickness of the warm and generally biologically rich epilimnion and, thus, also the areal abundance of planktonic organisms at a fixed sampling site. The potential impact of seiche-dnven changes of epilimnetic thickness on observed plankton abundance was calculated using continuously recorded temperature profiles and weekly vertical profiles of plankton biomass. Observed plankton biomass was recalculated by taking into account the effect of changing layer thickness in order to give a more realistic picture of biomass changes caused by waxing and waning of populations Our calculations imply that changes of strata thickness do not mask the general seasonal trend in population dynamics (e g. spring bloom and clear water phase), estimates of average yearly standing stock are not significantly affected if sampling is done at least weekly. However, changes of strata thickness can alter areal plankton abundance at the sampling site by a factor of 2 within 2 days During pronounced seiches, areal abundance of phytoplanklon , which generally exhibit a stronger vertical gradient than-most other plankton, may be changed by a factor of 3—4 within hours Hence, at our sampling site, the impact of changes in strata thickness cannot be ignored for detailed analysis of population dynamics of autotrophs involving comparisons between single observations

Subsurface chlorophyll maximum in the tropical and subtropical western Pacific Ocean: Vertical profiles of phytoplankton biomass and its relationship with chlorophylla and particulate organic carbon

Vertical distribution of phytoplankton biomass in terms of carbon content (PC) and its relationship with chlorophylla and particulate organic carbon (POC) were examined together with phytoplankton growth rates in the tropical and subtropical western Pacific in 1979, where a prominent subsurface chlorophyll maximum (SCM) developed between 65 and 150 m. Fluorescence microscopy combined with image analysis was used for measurement of cell volume which was converted to PC. The SCM coincided consistently with subsurface maximum of PC, and the SCM primarily reflected in situ accumulation of phytoplankton biomass. The PC:chlorophylla ratio decreased with depth; the ratio was 1.8 times, on average, higher in populations at the SCM compared to those near the surface. This increase in relative cellular chlorophylla along with depth accentuated the magnitude of the SCM. The PC:POC ratio was substantially lower near the surface, 0.17 on average, and increased sharply around the SCM, with a mean value of 0.53. Thus suspended particles around SCM were richer in phytoplankton than those in the upper layers. A major part of PC was contributed by autotrophic eukaryotes both near the surface and at the SCM, and prokaryotic picoplankton comprised a relatively small proportion (6.3 to 14.9%) of PC. The high phytoplankton biomass around the SCM was suggested to be ascribed to in-situ growth of phytoplankton.

Photosynthesis and Canopy Structure of a Submerged Plant, Potamogeton Pectinatus, in a Danish Lowland Stream

SUMMARY (1) The depth distributions of photosynthesis and respiration were examined in a Potamogeton pectinatus population in the River SusA. This examination was based on calculated vertical profiles of photon flux density (PFD) and biomass in the field and photosynthesis-light curves for different depth strata measured in the laboratory. (2) Potamogeton showed no sign of shade acclimatization with increasing depth in the canopy. On the contrary, basal leaves had lower chlorophyll content and lower photosynthetic efficiency than apical leaves in both low and high light. Potamogeton has an apical growth form leading to increasing age of the tissue with depth in the canopy. The reduced activity of basal leaves can be explained by light limitation and the beginning of senescence. (3) Potamogeton stands concentrated their biomass at the water surface during summer, and thereby compensated for high water attenuation. The calculated photosynthetic rate of the stand was strongly reduced if the biomass was assumed constant with depth. Simultaneously, the depth strata with highest photosynthetic and respiratory activity and the light compensation point in the canopy moved towards the surface. (4) Integrated photosynthesis of the stand showed a hyperbolic dependency on surface PFD. Photosaturation was usually not reached at maximum PFD, due to extensive selfshading. Gross 02 production was primarily regulated by PFD and biomass and showed a unimodal seasonal pattern with maximum in mid-August (7 5 g02 m-2 day- 1). Gross 02 production corresponded to total stream photosynthesis at maximum biomass during mid-summer. Dark respiration was a high proportion of gross photosynthesis, and this proportion increased with biomass and age of tissue during the growing season. Net 02 production increased linearly from early May to early August and was positive until late August. Changes in biomass followed the same seasonal pattern.

Surface pigments, algal biomass profiles, and potential production of the euphotic layer: Relationships reinvestigated in view of remote‐sensing applications

Maps of surface chlorophyllous pigment (Chl a + Pheo a) are currently produced from ocean color sensors. Transforming such maps into maps of primary production can be reliably done only by using light‐production models in conjunction with additional information about the column‐integrated pigment content and its vertical distribution.As a preliminary effort in this direction, ∼4,000 vertical profiles of pigment (Chl a + Pheo a) determined only in oceanic Case 1 waters have been statistically analyzed. They were scaled according to dimensionless depths (actual depth divided by the depth of the euphotic layer, Ze) and expressed as dimensionless concentrations (actual concentration divided by the mean concentration within the euphotic layer). The depth Ze, generally unknown, was computed with a previously developed bio‐optical model. Highly significant relationships were found allowing 〈C〉tot the pigment content of the euphotic layer, to be inferred from the surface concentration, C&amp;#x0304;pd, observed within the layer of one penetration depth. According to their C&amp;#x0304;d values (ranging from 0.01 to &gt;10 mg m−3), we categorized the profiles into seven trophic situations and computed a mean vertical profile for each. Between a quasi‐uniform profile in eutrophic waters and a profile with a strong deep maximum in oligotrophic waters, the shape evolves rather regularly. The well‐mixed cold waters, essentially in the Antarctic zone, have been separately examined. On average, their profiles are featureless, without deep maxima, whatever their trophic state. Averaged values of ρ, the ratio of Chl a to (Chl a + Pheo a), have also been obtained for each trophic category.The energy stored by photosynthesizing algae, once normalized with respect to the integrated chlorophyll biomass 〈C〉tot is proportional to the available photosynthetic energy at the surface via a parameter ψ*, which is the cross‐section for photosynthesis per unit of areal chlorophyll. By taking advantage of the relative stability of ψ*, we can compute primary production from ocean color data acquired from space. For such a computation, inputs are the irradiance field at the ocean surface, the “surface” pigment from which 〈C〉tot can be derived, the mean ρ value pertinent to the trophic situation as depicted by the C&amp;#x0304;pd or 〈C〉tot values, and the cross‐section ψ*. Instead of a constant ψ* value, the mean profiles can be used; they allow the climatological field of the ψ* parameter to be adjusted through the parallel use of a spectral light‐production model.

The biological pump: Profiles of plankton production and consumption in the upper ocean

The ‘biological pump’ mediates flux of carbon to the interior of the ocean by interctions between the components of the vertically-structured pelagic ecosystem of the photic zone. Chlorophyll profiles are not a simple indicator of autotrophic biomass or production, because of non-linearities in the physiology of cells and preferential vertical distribution of taxa. Profiles of numbers or biomass of heterotrophs do not correspond with profiles of consumption, because of depth-selection (taxa, seasons) for reasons unconnected with feeding. Depths of highest plant biomass, chlorophyll and growth rate coincide when these depths are shallow, but become progressively separated in profiles where they are deeper — so that highest growth rate lies progressively shallower than the chloropyll maximum. It is still uncertain how plant biomass is distributed in deep profiles. Depths of greatest heterotroph biomass (mesozooplankton) are usually close to depths of fastest plant growth rate, and thus lie shallower than the chlorophyll maximum in profiles where this itself is deep. This correlation is functional, and relates to the role of heterotrophs in excreting metabolic wastes (especially ammonia), which may fuel a significant component of integrated algal production, especially in the oligotrophic ocean. Some, but not all faecal material from mesozooplankton of the photic zone appears in vertical flux below the pycnocine, depending on the size of the source organisms, and the degree of vertical mixing above the pycnocline. Diel, but probably not seasonal, vertical migration is significant in the vertical flux of dissolved nitrogen. Regional generalisations of the vertical relations of the main components of the ‘biological pump’ now appear within reach, and an approach is suggested.

Bacterioplankton biomass and production during destratification in a monomictic eutrophic bay of a tropical lagoon

Vertical profiles of bacterial biomass (AODC method), production of biomass (thymidine method) and total ETS (Electron Transport System) activity were recorded on 14 dates during the destratification process in the monomictic eutrophic Bietri Bay (Ebrie Lagoon, Ivory Coast). Bacterial biomass and production were both very high, indicating the importance of heterotrophic processes in this system. Interpretation of ETS data suggests that bacteria or 'bacteria-associated organisms' are responsible for most of the oxygen consumed in the water column.'Integrated bacterial production of biomass represented ca 80 % of carbon produced by primary producers, thus showing that autotrophic production does not meet heterotrophic requirements of bacteria. Destratification appears to be of less importance than suggested by the physical and chemical characteristics, resulting in a decrease of bacterial biomass and production by a factor of 2 in the epilimnion. In the hypolimnion, the 'anaerobic community' characterized by low specific incorporation rates (3.4 X mol cell-i h-') and high mean cellular volume (0.203 pm3) during stratification is replaced by an 'aerobic community' with higher specific thymidine incorporation rates (6.6 X lo- mol cell-' h-') and lower mean cellular volumes (0.151 pm3). Interpretation of bacterial production of biomass in these newly oxygenated layers demonstrates that oxygen requirements in the aphotic zone are roughly equivalent to autotrophic production of oxygen in the euphotic zone, thus showing that oxygenation of the entire water column is necessarily transient and explaining the return to anoxic conditions before the establishment of a new density stratification.

Vertical profiles of pelagic communities in the vicinity of the Azores Front and their implications to deep ocean ecology

Three early wintertime and five early summertime stations were occupied in the vicinity of the Azores Front to the south-west of the islands. At each station the surface 1100–1400m of the water column were systematically sampled both by day and by night, using the Institute of Oceanographic Sciences' RMTI+8M system. The biological sampling was set in the context of an extensive study of the physical oceanography of the frontal region. It included one station in the core of an eddy which was seen to spawn from a meander during the course of the physical observations. The biological communities on either side of the front were almost indistinguishable in terms of their specific composition. However, there were substantial differences in the sizes of the standing-crops, the vertical distributions of the major taxonomic groups and the ranges of the diel vertical migrations being carried out by these groups. The waters on both sides of the front were oligotrophic. However, both phytoplankton standing-crop, as indicated by chlorophyll concentrations, and measures of productivity suggested that the water to the north (Eastern Atlantic Water), which was slightly cooler and with a shallower and steeper nutricline, was a little more productive than the water to the south (Western Atlantic Water). Associated with this trend in phytoplankton crop and productivity were quite sharp declines in the standing-crops of both plankton and micronekton across the front, moving from EAW to WAW. There was no evidence of enhanced productivity within the front itself, but there was an increase in the micronektonic standing-crop. Between the stations, there were consistent trends in the ratios of the standing-crops of plankton and micronekton, which were sampled simultaneously. By day, the planktonic biomasses exceeded the micronektonic biomasses by up to an order of magnitude in the wind-mixed layer. The ratios declined with depth, approaching unity at 200m during the wintertime, but remaining quite high to depths of 800m during the summer. At night, the ratios tended to be lower as a result of diel vertical migration, but except in one or two of the deepest samples the planktonic biomass always exceeded that of the micronekton. The total biomass profiles were very similar in shape between the stations, although there were quite large differences in the depths of the quartiles. There were substantial differences between the day and the night profiles. These could be attributed mostly to the effects of diel vertical migrations, but must also have included unquantifiable effects as a result of variations in net avoidance. The subdivision of the catches into the major taxonomic groups showed that the degree of avoidance varied substantially between them; euphausiids were the most effective daytime avoiders, but decapod crustaceans and fish showed a suprisingly small tendency to avoid. The ranges and the numbers of each group undertaking vertical migrations varied markedly between the stations, and these differences were expressed in the biomass estimates. Attempts have been made to quantify the movement of biomass in and out of the surface 200m and 500m resulting from these migrations. There were substantial changes in migratory behaviour across the front, even though there were no detectable changes in the light profiles. The data also imply that the micronektonic migrants play an important role in the active transport of organic substances down from the euphotic zone to mesopelagic depths (>500m), either in their gut contents or directly as a result of predation at depth. In addition, migrating plankton seem likely to be important in redistributing nutrients about the nutricline in these oligotrophic regions where the water column stability limits physical vertical mixing processes. Preliminary estimates suggest that their influence may be sufficiently large to alter the ratio between “new” and “old” production.

Midwater biomass profiles over the Madeira Abyssal Plain and the contribution of copepods

Midwater biomass profiles over the Madeira Abyssal Plain and the contribution of copepods

Computer modeling of antibiotic fermentation with on‐line product removal

The fermentation of Streptomyces griseus for the production of cycloheximide is similar to other antibiotic fermentations in that product synthesis is subject to feedback regulation and the desired product is degraded in the fermentation broth. The productivity of this fermentation can thus be dramatically increased by removing the antibiotic from the whole broth as it is produced. One means for effecting this on-line product removal is to contact the whole fermentation broth with neutral polymeric resin immobilized in hydrogel beads. The antibiotic adsorbs to the immobilized resin via hydrophobic interactions. In this work, the adsorption of the antibiotic onto the immobilized resin was characterized. A biochemical model of the fermentation was then used to describe the time profiles of biomass, substrate, and antibiotic in a fermentation system in which whole broth is circulated from the fermentor through a continuously stirred extractor containing the adsorbent beads. Various operating conditions were examined to optimize the productivity of the fermentation.