GRAZING OF BOSMINA LONGIROSTRIS ON TWO PLANKTONIC ALGAE: THE INFLUENCE OF SIZE AND TASTE.

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 ▲]

Feeding of Brachionus calyciflorus on Tetrahymena pyriformis using

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 ▲]

Grazing by large river zooplankton: a key to summer potamoplankton decline? The case of the Meuse and Moselle rivers in 1994 and 1995

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 ▲]

Relative importance of the trophic and direct pathways on PCB contamination in the rotifer species Brachionus calyciflorus (Pallas)

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 ▲]