On the radiocarbon method: filtration or the acidification and bubbling method?

It has recently been claimed that ¹⁴C fixation measured by theacidification and bubbling method gives considerably highervalues than using the filtration method. The observed discrepancyis probably due to a particle fraction (<0.8 >0.2 µm)not included in those results. The size fraction <1.0 >0.2µm can be a significant fraction of the ¹⁴C-fixation especiallyin oligotrophic water. The ¹⁴C-activity in that size fractionis probably due to bacteria assimilating labelled extracellularproducts.     

Measurements of phytoplankton primary production by means of the acidification and bubbling method

We examined the possibility of using the acidification and bubblingmethod (ABM) to determine phytoplankton primary production incoastal marine environments. Our results from a number of laboratoryand field experiments, suggested that (i) incubations of samplescan be carried out in glass vials instead of using the normalincubation bottles, and (ii) storage of samples fixed with formalinor glutaraldehyde can be carried out for at least 8 weeks withouta change in radioactivity. In the course of our work, we designeda new manifold removing excess ¹⁴C via ABM. A linear correlationbetween the G_24-max values obtained by the two techniques (r=0.93)was found On average the ABM gave values 1.8 times higher thanthose yielded by the particulate filtration procedure On a squaremetre basis, the ABM gave values 1.4 times higher than thoseyielded by the particulate filtration procedure. The annualproduction at six marine locations was 57% higher when usingthe ABM. The ABM is superior to the traditional filtration procedure,because filtration artefacts are avoided, precision is improved,the dissolved primary production is included in the measurement,and the immediate amount of field work is considerably reduced.     

Automated counting of phytoplankton by pattern recognition: a comparison with a manual counting method

Computer-based image analysis and pattern recognition methodswere used to construct a system able automatically to identify,count and measure selected groups of phytoplankton. An imageanalysis algorithm was employed to isolate and measure objectsfrom digitized images of a phytoplankton sample. The measurementsobtained were used to identify selected groups of phytoplanktonby a combination of artificial neural networks and simple rule-basedprocedures. The system was trained and tested using samplesof lake water covering an annual growth cycle from Lough Neaghin Northern Ireland. Total volume estimates were obtained forthe four major phytoplankton species, using both the automatedsystem and a manual counting method. Estimates of total cellvolume obtained from the automated system were within 10% ofthose derived by manual analysis of the same cells. The automatedsystem produced total cell volume estimates close to those obtainedfrom manual analysis of different aliquots of the same watersample. Variation between successive counts of the same watersample was higher with the automated system than with the manualcounting method. Limitations and possible improvements to thetechnology are discussed.     

Ultrasonic singing by the blue-throated hummingbird: a comparison between production and perception

Blue-throated hummingbirds produce elaborate songs extending into the ultrasonic frequency range, up to 30 kHz. Ultrasonic song elements include harmonics and extensions of audible notes, non-harmonic components of audible syllables, and sounds produced at frequencies above 20 kHz without corresponding hearing range sound. To determine whether ultrasonic song elements function in intraspecific communication, we tested the hearing range of male and female blue-throated hummingbirds. We measured auditory thresholds for tone pips ranging from 1 kHz to 50 kHz using auditory brainstem responses. Neither male nor female blue-throated hummingbirds appear to be able to hear above 7 kHz. No auditory brainstem responses could be detected between 8 and 50 kHz at 90 dB. This high-frequency cutoff is well within the range reported for other species of birds. These results suggest that high-frequency song elements are not used in intraspecific communication. We propose that the restricted hummingbird hearing range may exemplify a phylogenetic constraint.     

Photosynthetic carbon uptake by marine phytoplankton: comparison of the stable (13C) and radioactive (14C) isotope methods

The ¹⁴C and the ¹³C methods are routinely used for measuringphytoplankton production. However, few systematic comparisonsof estimates using the two approaches have been conducted. Thepresent comparison is based on 257 pairs of samples, representing1 year of monthly sampling at 10 depths in the euphotic zone.Data, obtained by the same operators following a standard protocol,were collected at three different stations on the Scotian Shelf(Northwestern Atlantic Ocean). Overall agreement between thetwo methods was good (r=0.827). However, relative differencesbetween the two sets of estimates were not randomly distributedin time and space. Three factors (photic depth, station andsampling date), identified to explain the observed differences,were included in a three-way analysis of variance (ANOVA) usingrelative differences as the covariate. Following this ANOVA,the whole set was split into three subsets. For the two subsetswhere the above identified factors did not have any significanteffect, the distribution of relative differences was narrowerthan these for the whole data set. Significant effects of thethree factors persisted for the third subset and relative differencesexhibited wide variations. Possible explanations for the observeddifferences include (i) the volume of incubation bottles, (ii)the incubation temperature and (iii) the absence of measurementsof dark uptake.     

Growth-regulated peptide-alpha (GRO-alpha) production by oral keratinocytes: a comparison with skin keratinocytes

Growth regulated peptide (GRO-alpha) is chemotactic for neutrophils. It also stimulates keratinocyte proliferation and migration, and angiogenesis in cutaneous wound healing. We compared GRO-alpha production by normal human skin and oral keratinocytes, and the effects of cytokine stimulation. Resting keratinocytes produced little, if any, GRO-alpha. TNF-alpha induced a large increase in GRO-alpha mRNA and protein production in both cell types (P<0.001). However, the response of oral keratinocytes was significantly higher (P<0.01). Oral, but not skin, keratinocytes also produced significant amounts of GRO-alpha in response to IL-1 alpha (P<0.005) and IL-4 (P<0.01) stimulation. Indeed, there was an additive effect on GRO-alpha production when oral keratinocytes were stimulated with combinations of TNF-alpha and IL-1 alpha or TNF-alpha and IL-4. Neither cell type responded to interferon gamma. Keratinocyte GRO-alpha production may help selectively recruit neutrophils in mucocutaneous inflammatory diseases, and differences in production by skin and oral keratinocyte could explain the different presentation of these diseases at the two sites. The increased GRO-alpha responsiveness of oral keratinocytes may also help explain the excellent wound healing properties of oral mucosa.     

Primary production of phytoplankton estimated by means of the dilution method in coastal waters

The development and application of a dilution method for measuringprimary production in coastal waters is described.     

Development of an Agent-Based Model (ABM) to Simulate the Immune System and Integration of a Regression Method to Estimate the Key ABM Parameters by Fitting the Experimental Data

Agent-based models (ABM) and differential equations (DE) are two commonly used methods for immune system simulation. However, it is difficult for ABM to estimate key parameters of the model by incorporating experimental data, whereas the differential equation model is incapable of describing the complicated immune system in detail. To overcome these problems, we developed an integrated ABM regression model (IABMR). It can combine the advantages of ABM and DE by employing ABM to mimic the multi-scale immune system with various phenotypes and types of cells as well as using the input and output of ABM to build up the Loess regression for key parameter estimation. Next, we employed the greedy algorithm to estimate the key parameters of the ABM with respect to the same experimental data set and used ABM to describe a 3D immune system similar to previous studies that employed the DE model. These results indicate that IABMR not only has the potential to simulate the immune system at various scales, phenotypes and cell types, but can also accurately infer the key parameters like DE model. Therefore, this study innovatively developed a complex system development mechanism that could simulate the complicated immune system in detail like ABM and validate the reliability and efficiency of model like DE by fitting the experimental data.     

Bacterioplankton and phytoplankton production in a large patagonian reservoir (República Argentina)

Relationships between the secondary production of bacterioplankton and the primary production of phytoplankton in the Ezequiel Ramos Mexia Reservoir were examined. Monthly surveys, parallel measurements on consecutive days, and measurements at different times during the same day were undertaken to determine factors that might influence the relationships between the two sets of productivity measurements.The vertical and seasonal distribution of bacterial production appeared to be strongly related to primary production, with temperature as an important component of this trend. The bacterial production in the water column was equivalent to between 2 and 45% of the phytoplankton production over a period of one year.In a diel study, bacterial secondary production rates fluctuated, with maximum values during the night and early morning. There was no temporal coincidence between algal primary production and bacterial secondary production in daily surveys. It was therefore concluded that isolated measurements of productivity reflect events only at the particular time at which they are obtained. The relationship between algae and bacteria is extremely complex and must be carefully evaluated. The nature of the relationship could be underevaluated if the only measurements taken into consideration were made during the daylight period.     

Energetics of offspring production: a comparison of a marsupial (Monodelphis domestica) and a eutherian (Mesocricetus auratus)

This study compares the energetic cost of reproduction during gestation and lactation of a eutherian, the golden hamster (Mesocricetus auratus), and a similar-sized (60–120 g) marsupial, the gray short-tailed opossum (Monodelphis domestica). Food consumption was monitored in 20 reproductively active (RA) opossums and 16 RA hamsters from conception to weaning and at equivalent intervals in 19 non-reproductive (NR) opossums and 21 NR hamsters, all maintained within their zone of thermoneutrality (30 °C). Total energy assimilated from conception to weaning [opossums: 1261.3 ± 28.0 Kcal (1 Kcal = 4.1868 J) and hamsters: 1647.5 ± 60.6 Kcal] was positively correlated with litter size and mass per young in both species. Maternal mass-specific assimilated energy was significantly greater in hamsters than in opossums during gestation (P < 0.001), but not during lactation or from conception to weaning (P > 0.05). Efficiency of offspring production (energy stored in young/incremental energy in RA females) was higher in hamsters than in opossums and, in both species, it was higher during lactation than in gestation. The energetic cost of reproduction (per young per day) was higher in hamsters than in opossums. The marsupial mode of reproduction, as seen in opossums, yields young at lower cost but requires a longer reproductive period than is the case for a similar-sized eutherian. Accepted: 8 September 1998     

The effect of soil acidification on atmospheric methane uptake by a Maine forest soil(1)

Soil from the zone of maximal methanotrophic activity (approximately 5-8 cm depth) in a mixed coniferous-hardwood forest consumed atmospheric methane over a wide pH range (3.5-7.5) with a broad optimum between 4.8 and 6.0. Methane uptake at native soil pH values (4.4-4.8) was only slightly less rapid than rates at optimal pH values. Addition of mineral acids to intact soil cores in pulsed applications decreased atmospheric methane consumption. The extent of inhibition varied with the type, concentration and volume of acid added: nitric acid was more inhibitory than sulfuric acid at an equivalent soil pH, and methane uptake decreased with increasing volumes and concentrations of added acid. Although ammonium chloride at 1 μmol g fresh weight (gfw) soil(-1) inhibited methane uptake, the extent of inhibition did not vary significantly with decreasing soil pH below values of 4.4.     

Distribution and production of macrophytes and phytoplankton in the lagoon of Venice: comparison of actual and past situation

This paper aims at comparing inedited maps of macrophytes and phytoplankton distribution in the lagoon of Venice in 1980 and 2003. The macrophyte distribution is displayed with reference to different biomass intervals which allow the calculation of the occupied surface, standing crop (SC), net (NPP) and gross (GPP) production. In 1980 the total macroalgal SC was ca. 841 ktonnes whereas the annual NPP and GPP were estimated to be ca. 2912 and 18498 ktonnes, respectively. In 2003 macroalgae displayed a marked regression and the SC, NPP and GPP decreased to ca. 89, 471 and 2336 ktonnes. Maps of the seagrass distribution date back to 1990 but their biomass and production have been quantified only in 2003. On the whole, in 2003, on a surface of ca. 56 km2 the three species living in the lagoon accounted for a SC and a NPP of ca. 209 and 821 ktonnes, whereas the GPP estimated according to literature was about twice as high as the NPP. Cymodocea nodosa was the most abundant phanerogam in the lagoon. Its SC was higher than the total of the macroalgae, although the latter were more productive. Zostera marina covered the highest surface in the lagoon but its biomass and production were a little lower than that of C. nodosa. Nanozostera noltii, which was common and widespread in the past, displayed an evident regression trend which was mainly due to the increase of the water turbidity and the disruptions of its habitat. Similarly, phytoplankton, underwent a descending trend, although data quoted in the present paper display its distribution only in the summer period.     

Relationship between extracellular and cellular production in the sulphuric green bactreium Chlorobium limicola Nads. (Chlorobacteriaceae) as compared to primary production of phytoplankton

1. The authors examined the relationship between extracellular production of green hydrosulphuric bacteria (Chlorobium limicola Nads) and extracellular production of phytoplankton using radioactive carbon. Dark assimilation of carbon was also taken into consideration.
2. Mean values of extracellular production of phytoplankton were 58.40% (stand II) and 65.2% (stand I) of cellular production, and for extracellular production of Chlorobium limicola the values were respectively 44.7% (stand II) and 70.7% (stand I). On average 70.8% of carbon assimilated in the dark filtered outside the cell in case of phytoplankton, and 31.0%-in case of Chlorobium limicola.
3. Extracellular and cellular production in case of phytoplankton and Clorobium limicola was calculated for 1 square metre of the water column.

     

Changes in phytoplankton biomass and primary production between 1991 and 2001 in the Westerschelde estuary (Belgium/The Netherlands)

The Westerschelde estuary is a very polluted and turbid estuary, but the last decade the waterquality improved. Dredging activity also increased in 1997 to allow bigger ships to enter the port of Antwerpen. This could potentially decrease the light conditions for the phytoplankton. Because of all these recent changes in the estuary we studied primary productivity in 2001 and compared it to values in 1991. The results show that due to a decrease in discharge in particulate and dissolved organic carbon the oxygen concentrations in general have increased in the upstream region, although in spring and summer low oxygen concentrations (10–30% saturation) can still be found. Phosphate and ammonia concentrations have decreased and the zone of nitrification which was very large in 1991 has become very small and is now located in the uppermost upstream region of the estuary. Si-concentrations have remained the same. All nutrient concentrations are still high enough not to limit phytoplankton growth. Turbidity remained unaltered as a result of the dredging works, and as a result phytoplankton biomass in most of the estuary did not show a decrease, although there were signs that in the upstream region phytoplankton biomass decreased, possible caused by increased grazing pressure. The relationship between phytoplankton biomass and primary productivity did not change, and from the data it can be concluded that the dredging activity will not influence the gross and net primary productivity of the phytoplankton.     

Abundance and production of bacteria, and relationship to phytoplankton production, in a large tropical lake (Lake Tanganyika)

1. Abundance and bacterial production (BP) of heterotrophic bacteria (HBact) were measured in the north and south basins of Lake Tanganyika, East Africa, during seasonal sampling series between 2002 and 2007. The major objective of the study was to assess whether BP can supplement phytoplankton particulate primary production (particulate PP) in the pelagic waters, and whether BP and particulate PP are related in this large lake. HBact were enumerated in the 0–100 m surface layer by epifluorescence microscopy and flow cytometry; BP was quantified using ³H‐thymidine incorporation, usually in three mixolimnion layers (0–40, 40–60 and 60–100 m). 2. Flow cytometry allowed three subpopulations to be distinguished: low nucleic acid content bacteria (LNA), high nucleic acid content bacteria (HNA) and Synechococcus‐like picocyanobacteria (PCya). The proportion of HNA was on average 67% of total bacterial abundance, and tended to increase with depth. HBact abundance was between 1.2 × 10⁵ and 4.8 × 10⁶ cells mL⁻¹, and was maximal in the 0–40 m layer (i.e. roughly, the euphotic layer). Using a single conversion factor of 15 fg C cell⁻¹, estimated from biovolume measurements, average HBact biomass (integrated over a 100‐m water column depth) was 1.89 ± 1.05 g C m⁻². 3. Significant differences in BP appeared between seasons, especially in the south basin. The range of BP integrated over the 0–100 m layer was 93–735 mg C m⁻² day⁻¹, and overlapped with the range of particulate PP (150–1687 mg C m⁻² day⁻¹) measured in the same period of time at the same sites. 4. Depth‐integrated BP was significantly correlated to particulate PP and chlorophyll‐a, and BP in the euphotic layer was on average 25% of PP. 5. These results suggest that HBact contribute substantially to the particulate organic carbon available to consumers in Lake Tanganyika, and that BP may be sustained by phytoplankton‐derived organic carbon in the pelagic waters.     

Freeze-drying of Streptococcus thermophilus: a comparison between the vacuum and the atmospheric method

Frozen suspensions of Streptococcus thermophilus were freeze-dried in a vacuum or a fluidized adsorbent bed at atmospheric pressure. Optimum operating conditions for each process were defined. For the duration of processing and survival rate of bacteria, in each case vacuum freeze-drying seemed more satisfactory than atmospheric pressure freeze-drying. The use of reconstituted skimmed milk as a suspension medium provides good protection for S. thermophilus.     

Determination of tissue content of catecholamines in Atlantic salmon (Salmo salar): a comparison of HPLC-EC and the trihydroxyindol fluoremetric method.

1. The catecholamine (CA) content in tissues of the Atlantic salmon (Salmo salar) was determined by HPLC-electrochemical detection (EC) and the fluoremetric trihydroxyindol (THI) method after sorbent purification on phenyl boronic acid-bonded silica or aluminum oxide. 2. Bonded silica proved more efficient and reliable for CA purification than aluminum oxide. 3. The THI method was inadequate for determination of noradrenaline in samples low in CA and in samples rich in CA but predominated by adrenaline. 4. The CA content in the head kidney, the atrium, the ventricle and skeletal muscle measured by HPLC-EC was 15, 1.8, 1.1 and 0.1 nmol/g wet weight, respectively. 5. Adrenaline dominated in the head kidney (approximately 80%) while adrenaline and noradrenaline occurred in a ratio approximately 1:1 in both cardiac and skeletal muscle.     

红眼寄居蟹在实验室和野外条件下对贝壳的利用

占据适宜的贝壳对于寄居蟹的发育、繁殖和存活至关重要。尽管很多研究探讨了蟹类对贝壳的选择,但寄居蟹选择多大的贝壳仍不清楚。在实验条件下,本文作者用巴西Anchieta岛上野生红眼寄居蟹( Pagurusbrevidactylus)最常利用的黑衣蟹守螺( Cerithium atratum)和节桑椹螺( Morula nodulosa)进行了贝壳选择实验,通过回归分析确定目标贝类及其大小。观察到寄居蟹对一种独特贝类的选择具有性别意义,从而验证了野外观察结果。雄性明显地倾向选择黑衣蟹守螺的贝壳,而产卵和非产卵的雌性个体对腹足类贝壳的选择差异不显著。尽管两性之间对适宜贝壳的选择存在差异,贝壳适宜度指数(SAI)表明,种群占据那些足够大的贝壳(SAI =1·20±0·23)。红眼寄居蟹对贝壳利用的这种模式可能是为了避免与体型相似同域物种的竞争,从而在后来的生长中减少频繁地更换贝壳。根据目前的数据可以得到以下结论:红眼寄居蟹对贝壳的选择不仅取决于贝壳的参数,而且还与寄居蟹的个体和性选择有关[动物学报51 (5) : 813 -820 , 2005]。     

Nutrients and phytoplankton primary production in the marine tidal Oosterschelde estuary (The Netherlands)

In a shallow marine tidal area, the eastern part of Oosterschelde estuary in the S.W. Netherlands, phytoplankton primary production amounted to 176–338 g C.m^?2.y^?1 during the period 1981–1985. The influence of nutrient concentrations on the phytoplankton primary production is discussed. Phosphate and inorganic nitrogen generally were amply available. Import of inorganic nitrogen into the basin was shown and an intense delivery of ammonia by zoobenthos was suggested. Nitrate was considered to be slightly influenced by phytoplankton consumption and mainly by nitrate reduction at the bottom. Silicate may have played a limiting role in phytoplankton primary production. The first phytoplankton bloom in spring (diatom bloom) always terminated when silicate concentration decreased below K_s values. Further on in 1983 and 1984 both primary production and chlorophyll curves showed a dip when silicate was not available. The influence of available light on the primary production was demonstrated during situations with a low extinction coefficient when primary production reached maximum values. Further on during 1985 the spring bloom occurred already in March when winter extinction coefficients were lower than during preceding winters. Long term production studies are necessary to understand the extreme fluctuations of annual production patterns in relation to the prevailing environmental conditions.