References of "Joaquim-Justo, Célia"
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See detailTrophic links in the lowland river Meuse (Belgium): importance of the predation exerted by rotifers on bacterio- and protozooplankton.
Joaquim-Justo, Célia ULg; Pirlot, S; Viroux, Laurent et al

Conference (2003, June 07)

Trophic interactions within the plankton of the lowland river Meuse (Belgium) were measured in Spring and Summer (2001). Consumption of bacteria by protozoa was measured by monitoring the radioactivity ... [more ▼]

Trophic interactions within the plankton of the lowland river Meuse (Belgium) were measured in Spring and Summer (2001). Consumption of bacteria by protozoa was measured by monitoring the radioactivity disappearance of 3H-thymidine labelled bacteria. The proportion of protozoan bacterivory attributable to flagellates and ciliates was determined with fluorescently labelled bacteria (FLB). Metazooplankton bacterivory was assessed with 0.5 µm fluorescent microparticles (FMPs) and predation of metazooplankton on ciliates was measured by using natural ciliate assemblages labelled with FMPs as tracer food. Grazing of metazooplankton on flagellates was determined through in situ incubations with manipulated metazooplankton densities. flagellates were the main bacterial consumers their grazing being 91  10 % of total bacterial grazing. Metazooplankton, essentially rotifers, grazing on bacteria was negligible compared to grazing by protozoa and to bacterial production. Protozoa grazing balanced bacterial production in early samplings but was lower in July. Predation of rotifers on heterotrophic flagellates (HF) was generally low (1.765 3.432 mg C m-3 d-1 ), the higher contribution of HF in the diet of rotifers being observed when Keratella cochlearis was the dominant metazooplankter. Predation of rotifers on ciliates was low in the first samples (0.557  0.004 mg C m-3 d-1) in contrast to measurements performed in July (8.722  1.363 mg C m-3d-1). The proportion of protozoa in the diet of rotifers was generally low compared to phytoplankton (< 30% of total carbon ingestion) except when phytoplankton biomass decreased below the incipient limiting level (ILL) of the main metazooplantonic species. In such conditions, protozoa (mainly ciliates) constituted ca. 50% of total rotifer food. These results give evidence that microbial organisms play an important role within the plankton of the river Meuse, ciliates providing an alternative food for metazooplankton when phytoplankton becomes scarce. [less ▲]

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See detailPCB trends and patterns in the plankton of the river Meuse (Belgium).
Joaquim-Justo, Célia ULg; Schockert, Vincianne ULg; Deguée, N et al

Poster (2002, May 12)

PCB concentrations were monitored in the river Meuse (Belgium) from 1993 to 1998; compartments sampled were water, suspended matter (mainly phytoplankton), zooplankton and sediment. The PCB patterns were ... [more ▼]

PCB concentrations were monitored in the river Meuse (Belgium) from 1993 to 1998; compartments sampled were water, suspended matter (mainly phytoplankton), zooplankton and sediment. The PCB patterns were compared to those of Aroclors and found to best match a mixture of 30 to 40% of Aroclor 1254 and 60 to 70% of Aroclor 1260 for all compartments with the exception of suspended matter where the proportions were of 50% of both Aroclor 1254 and 1260. These patterns together with the average total concentrations did not show any trends throughout the monitoring period nor did they show any particular seasonal pattern variations. Mean total PCBs concentrations were of 0.029 ng/g in the water, 3408 ng/g D.W. in suspended matter, 862 ng/g D.W. in zooplankton and 387 ng/g D.W. in the sediment. Bioconcentration factors for phytoplankton (suspended matter) and zooplankton were respectively of 118 000 and 30 000 indicating there is no biomagnification between these two trophic levels. These results will be commented on the basis of in vitro contamination experiments with planktonic organisms. [less ▲]

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See detailIN SITU MEASUREMENTS OF METAZOOPLANKTON PREDATION ON PROTOZOOPLANKTON: USE OF FLUORESCENTLY LABELLED PROTISTS.
Joaquim-Justo, Célia ULg; Caufman, F; Thomé, Jean-Pierre ULg

Poster (2001, February 04)

The importance of trophic relationships between metazooplankton and protozoans in rivers are not yet well known, but as some authors have shown during the last decade, the predation exerted by ... [more ▼]

The importance of trophic relationships between metazooplankton and protozoans in rivers are not yet well known, but as some authors have shown during the last decade, the predation exerted by metazooplankton on these organisms might be of importance in the transfer of energy from the pico- and nanoplankton to the metazooplankton. Fluorescent carboxylate microspheres of 0.5 µm in diameter were used to label natural protozooplankton. Different combinations of labelling times and concentrations of microspheres were tested to achieve an optimal labelling of the protists (i.e. a maximal proportion of individuals labelled with an identical number of microspheres); the most appropriate labelling conditions were with short incubations (10 minutes) and relatively low microsphere concentrations (1.105 FMP/ml). Live labelled protozooplankton was used to determine ingestion rates of the natural metazooplankton of the river Meuse (Belgium). It could be showed for all abundant species (i.e. the rotifers Brachionus calyciflorus, Brachionus angularis and Keratella cochlearis) that the predation exerted on protozooplankton was high (from 34 to 182 protists.rotifer-1.h-1) in in situ conditions. [less ▲]

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See detailA note on the use of fluorescently labelled algae for the determination of gut passage time in Bosmina and Daphnia
Cauchie, Henry-Michel ULg; Deguée, N.; Joaquim-Justo, Célia ULg et al

in Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie = Proceedings of the International Association of Theoretical and Applied Limnology (2001), 27

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See detailUSE OF FLUORESCENTLY LABELLED PROTOZOANS TO INVESTIGATE THE PREDATION OF ROTIFERS ON PROTOZOOPLANKTON
Joaquim-Justo, Célia ULg; Detry, Cédric ULg; Thomé, Jean-Pierre ULg

Conference (2000, January 16)

The importance of trophic relationships between rotifers and protozoans in rivers are not yet well known, but as some authors have shown during the last decade, the predation exerted by rotifers on these ... [more ▼]

The importance of trophic relationships between rotifers and protozoans in rivers are not yet well known, but as some authors have shown during the last decade, the predation exerted by rotifers on these organisms might be of importance in the transfer of energy from the pico- and nanoplankton to the metazooplankton. Fluorescent polycarbonate beads of 0.45 µm in diameter were used to label the ciliate Tetrahymena pyriformis. Different combinations of labelling times and concentrations of microspheres were tested to achieve an optimal labelling of the ciliates (i.e. a maximal proportion of individuals having ingested the same number of microspheres). Live labelled Tetrahymena pyriformis were used to determine both the gut passage time and the ingestion rate of the rotifer Brachionus calyciflorus. The ingestion rates measured with relatively high densities of ciliates (from 30 to 500 cells.ml-1) were on average of 30 cells.ind-1.day-1. The ingestion rates yielded by this method were compared with ingestion rates measured by assessing the disappearance of the ciliates in experimental media during 5-6 hour incubations. Results from both methods were comparable but the use of fluorescently labelled prey items produced less variable results. [less ▲]

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See detailTrophics relationships between planktonic micro-organisms in the river Meuse (Belgium): a carbon budget
Servais, Pierre; Gosselain, Véronique; Joaquim-Justo, Célia ULg et al

in Arch. Hydrobiol (2000)

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See detailGRAZING OF BOSMINA LONGIROSTRIS ON TWO PLANKTONIC ALGAE: THE INFLUENCE OF SIZE AND TASTE.
Joaquim-Justo, Célia ULg; Gosselain, V; Descy, Jean-Pierra et al

Poster (1998, August 09)

The cladoceran Bosmina longirostris is a dominant species in the River Meuse (Belgium) especially during summer. Grazing of this small-sized cosmopolitan cladoceran on algae has been stated to be related ... [more ▼]

The cladoceran Bosmina longirostris is a dominant species in the River Meuse (Belgium) especially during summer. Grazing of this small-sized cosmopolitan cladoceran on algae has been stated to be related to the size of the grazed cells by some authors while other studies emphasised on the ability of bosminids to actively capture 'good tasting' particles. Grazing experiments were carried out in the laboratory with B. longirostris feeding on two algal species (Dictyosphaerium ehrenbergianum, 3-4 µm of diameter, and Chlamydomonas reinhardtii, 9-10 µm of diameter). Gut passage times and ingestion rates of the bosminids were determined with radioactively and fluorescently labelled algae. Although both algae have sizes reported to be actively grazed by B. longirostris, they were ingested at very different rates. The relative influence of cell size and cell 'taste' will be discussed. [less ▲]

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See detailSome technical problems of feeding rate measurements in rotifers with fluorescently labelled algae.
Joaquim-Justo, Célia ULg; Detry, C; Thomé, Jean-Pierre ULg

Poster (1998, June 22)

Grazing of metazooplankton on phytoplankton and protozooplankton has been widely studied using the radiotracer technique. An interesting alternative to radioactive label is the use of fluorescent dies ... [more ▼]

Grazing of metazooplankton on phytoplankton and protozooplankton has been widely studied using the radiotracer technique. An interesting alternative to radioactive label is the use of fluorescent dies. Indeed, the use of fluorescently labelled algae (FLA) or protozoans does not imply particular security measures or equipment; moreover they allow the visualisation of the labelled prey in the predator sometimes providing useful informations on the variability between individuals and on the mechanism of feeding processes. Prior to the use of this method in ingestion rate measurements with Brachionus calyciflorus discrimination experiments were performed. The FLAs were Chlorella-like algae (Dictyosphaerium ehrenbergianum) labelled with DTAF (5-(4,6-dichlorotriazin-2-yl) aminofluorescein). The ingestion rate of the rotifer on the FLAs was 3 to 15 times lower than the ingestion rate on non labelled. Evidence was gathered that the staining procedure (heat-killing of the algae) was mainly responsible for the discrimination of the rotifer rather than the dye itself. Other technical considerations will be discussed like the occurrence of crashed algae in the rotifers gut and the inter-individual variability. [less ▲]

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See detailFeeding of Brachionus calyciflorus on Tetrahymena pyriformis using
Joaquim-Justo, Célia ULg; Detry, C; Thomé, Jean-Pierre ULg

Poster (1998, June 22)

This study was carried out in the wider frame of the quatitative evaluation of trophic transfers occurring in large rivers between metozooplankton and protozooplankton. Since the rotifer B. calyciflorus ... [more ▼]

This study was carried out in the wider frame of the quatitative evaluation of trophic transfers occurring in large rivers between metozooplankton and protozooplankton. Since the rotifer B. calyciflorus is dominant in the river Meuse (Belgium) its feeding on the widespread ciliate T. pyriformis was studied. Grazing rates were either determined through monitoring of cell number variations in experimental media or through use of fluorescently labeled ciliates. The labeling procedure consisted in allowing the ciliates to ingest fluorescent microspheres (0.5 µm in diameter) for short period of time; since number of ingested fluorescent spheres are very stable [less ▲]

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See detailQuantification of the trophic pathway in the PCB contamination of two zooplanktonic species: Daphnia magna Straus and Brachionus calyciflorus Pallas
Joaquim-Justo, Célia ULg; Thomé, Jean-Pierre ULg

in Verhandlungen der Internationalen Vereinigung für Theoretische und Angewandte Limnologie = Proceedings of the International Association of Theoretical and Applied Limnology (1998), 26

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See detailGrazing by large river zooplankton: a key to summer potamoplankton decline? The case of the Meuse and Moselle rivers in 1994 and 1995
Gosselain, Véronique; Descy, Jean-Pierre; Viroux, Laurent et al

in Hydrobiologia (1998)

To explain summer declines in phytoplankton biomass in large rivers, we compared the effect of zooplankton grazing on the planktonic algae of two large European rivers, the Meuse and the Moselle. In situ ... [more ▼]

To explain summer declines in phytoplankton biomass in large rivers, we compared the effect of zooplankton grazing on the planktonic algae of two large European rivers, the Meuse and the Moselle. In situ grazing was measured during two years (1994 and 1995), using the Haney method. Total zooplankton community filtration rates recorded in the river Meuse ranged between 1 and 32% of the water volume filtered per day. A drastic algal decline was observed early July both years and may be explained by high densities of a rotiferdominated zooplankton community (500–700 ind. l􀀀1) with more than 75%of Brachionus calyciflorus. During the summer period in 1994, when grazingwas over 20%, edible algal biomasswas controlled by a diversified rotifer community (up to 2500 ind.l􀀀1), while a nonedible algal assemblage developed. In contrast, phytoplankton biomass remained comparatively lowin the Moselle throughout the lowflowperiod, as did zooplankton numbers duringmost of this time (fewer than 200 ind. l􀀀1 during the summer period). The proportion of crustaceans in this zooplanktonwas rather higher than in the Meuse, and they dominated at times, in biomass as well as in numbers. Nevertheless, measured in situ grazing rates (1–15%) could not explain the low summer algal biomass, even if low filtration rates may at times represent a significant carbon loss for phytoplankton, when and where net algal production was low. As a conclusion, the role of phytoplankton – zooplankton interactions in controlling algal biomass in large rivers is discussed. [less ▲]

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See detailLaboratory and in situ grazing rates of freshwater rotifers and their contribution to community grazing rates
Gosselain, V.; Joaquim-Justo, Célia ULg; Viroux, L. et al

in Archiv für Hydrobiologie. Supplementband, Large rivers (1996), 13(1-4), 353-361

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See detailRelative importance of the trophic and direct pathways on PCB contamination in the rotifer species Brachionus calyciflorus (Pallas)
Joaquim-Justo, Célia ULg; Gosselain, V; Descy, Jean-Pierre et al

in Hydrobiologia (1995)

To determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used 14 C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ... [more ▼]

To determine the contribution of food ingestion (trophic pathway) to PCB contamination of zooplankton in the river Meuse (Belgium), we used 14 C-labelled algae (Dictyosphaerium ehrenbergianum) to measure ingestion and assimilation rates in the rotifer species Brachionus calyciflorus . When the concentration of algae in the culture medium varied from 20 103 to 200 103 algal cells ml -1 (0.12 to 1 .18 mg C 1 - '), the Brachionus calyciflorus ingestion rate varied from 0 .25 ± 0 .12 to 1 .52 ± 0 .43 ng C ind -1 h-1 at 15 °C and from 0 .74 ± 0 .17 to 5 .93 ± 0.61 ng Cind-' h-1 at 20 °C . The assimilation efficiency (ratio of the assimilation rate to the ingestion rate) measured in a culture medium containing 200 103 algal cells ml`' was 55 .7 ± 5.8%. Since the PCB concentration measured in the phytoplankton of the river Meuse is about 3 pg PCBs g -1 D.W., the estimated PCB contamination of zooplankton ascribable to the trophic pathway ranges from 0 .22 ± 0 .17 to 1 .31 ± 0.77 jag PCBs g -1 D.W. at 15 °C and from 0.64 ± 0 .34 to 5 .10 ± 2 .10 pg PCBs g -1 D. W. at 20'C . The lower figure based on measurements effected at 20 ° C is comparable to the actual level measured in zooplankton samples collected in the river Meuse (0 .69 ± 0.20 pg PCBs g`' D.W.) . The applicability of the formula used in our estimate was checked in a 48-hour in vitro experiment in which the rotifers were fed contaminated algae . The PCB accumulation measured in the rotifers was found to coincide with the calculated PCB contamination . Additional experiments were carried out to determine the contribution of the direct pathway to PCB contamination of zooplankton living in the river Meuse (0.02 pg PCBs 1-1 of water; average dissolved organic matter : 3 mg C 1 -1 ). The PCB concentration in zooplankton resulting from direct uptake of PCBs from the water was estimated at 0 .19 ± 0.05 jug PCBs g -1 D.W. These results show that in zooplankton living in polluted ecosystems, PCBs are likely to accumulate via the trophic pathway to concentrations up to 30 times higher than by direct contamination . Furthermore, our estimates of PCB contamination via the trophic pathway coincide quite well with actual concentrations measured in situ . [less ▲]

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