Zooplankton distribution across the brackish and freshwater zone of the Scheldt estuary

Zooplankton diversity and distribution in the brackish and freshwater zone of the Scheldt is studied, as a continuation of preceeding studies carried out in the periods 1967-1669 and 1995-1997. We report on species diversity and abundancy of the zooplankters, collected on a monthly basis, in 20 sampling sites along the salinity gradient. Calanoids occur mainly in the brackish part, with Eurytemora affinis, Acartia tonsa and Eudiaptomus gracilis as the dominant species. In the freshwater region, rotifers (i.e. Brachionus calyciflorus, Keratella quadrata, among others), cyclopids (i.e. Acanthocyclops robustus, Cyclops vicinus) and cladocerans (Daphnia longispina, Bosmina longirostris...) are the dominant zooplankters. In addition, we report the presence of several species which were not detected in the former studies, such as the rotifers Brachionus leydigi var. quadratus, Notholca labis, Platyias quadricornis, Euchlanis dilatata, Gastropus hyptopus, Testudinella patina, Polyarthra dolichoptera and Trichotria sp. ; the cladocerans Acroperus harpae and Biapertura affinis, and the harparticoid Bryocamptus (Bryocamptus) minutus

New occurrence of <i>Lecane decipiens</i> (Murray, 1913) and some other alien rotifers in the Schelde estuary (Belgium)

Three alien rotifers were found in the Schelde estuary in spring and summer 2002-2003. Lecane decipiens and Brachionus variabilis, with a maximum of respectively 6 and 4 ind L-1, were rare and quite localized in the freshwater tidal reach, corresponding to the stage III (non invasive species) in Colautti and Mac Isaac’s invasion terminology. This record of L. decipiens is the first confirmed one in Europe. Keratella tropica was generally present in the freshwater reach but, more tolerant to salinity, it was also found in brackish water. With its maximum abundance of 18 ind L-1,K. tropica appeared to be invasive, with a stage Iva (widespread but rare) at the scale of the Schelde estuary. A description with illustrations of these introduced species is given with some information about their ecology

Rotifers in the Niger River, Niger: diversity and abundance in relation to environmental parameters

A first study of the rotifers of the Niger River in Niger is reported here. Two surveys took place under contrasting hydrological conditions: low-water level (16 April to 8 May 2018) and high-water level (1 to 15 February 2019). Zooplankton and physico-chemical parameters were sampled at eight stations spread over 520 km from Ayorou to Gaya. In total, 32 taxa were identified, including 26 at species level. During the low-water sampling, Polyarthra sp. (31%), Brachionus caudatus (23%), Synchaeta longipes (11%), Keratella tropica (7%) and Filinia longiseta (5%) were the most abundant, whereas Brachionus quadridentatu s (26%), Lecane hastata (25%), Keratella cochlearis (9%), Keratella lunaris (5%), Hexarthra sp. (3%) were dominant during the high-water sampling. The mean abundance of rotifers ranged between 14 × 103 ind. m−3 during the high-water sampling and 244 × 103 ind. m−3 during the low-water sampling. The highest diversity was observed in the three stations located upstream from the city of Niamey. The results reflect the difference in environmental parameters between the downstream and upstream Niamey stations. RDA analyses showed that the main environmental factors explaining the distribution of rotifers were dissolved oxygen, orthophosphate and nitrate concentrations

An Old World leaf‐cutting, fungus‐growing ant: A case of convergent evolution

International audienceThe African myrmicine ant Crematogaster clariventris is a territorially dominant arboreal species that constructs very hard carton nests. Noting that workers cut off leaves from different plant species while building or repairing their nests, we asked ourselves if there was a correlation. We conducted scanning electron microscopic observations of nest walls that revealed the presence of fungal mycelia. As the presence of filamentous Ascomycota has been shown on arboreal ant nests worldwide, we used a metabarcoding approach and, indeed, noted the presence of Operational Taxonomi

Zooplankton in the Schelde estuary, Belgium and the Netherlands: long-term trends in spring populations

A compilation of available data in between 1967 and 2002 on spring zooplankton abundance was made for the brackish and the freshwater zone of the Schelde estuary. The general picture is a significant increase of 1–2 orders of magnitude in abundance for Rotifera, Copepoda and Branchiopoda (mainly Cladocera) in the freshwater zone, while zooplankton abundance in the brackishwater zone remained more constant. Possible natural and management related causes for this increase in zooplankton abundance are briefly discussed. [KEYWORDS: Schelde estuary ; zooplankton ; long-term]

Spatial spring distribution of the copepod <i>Eurytemora affinis</i> (Copepoda, Calanoida) in a restoring estuary, the Scheldt (Belgium)

The spatial spring distribution of Eurytemora affinis (adults and C5) in the Scheldt estuary (Belgium) brackish and freshwater reaches was studied in between 1996 and 2007. The bulk of the E. affinis population being generally situated in the brackish water reach (salinity > 0.5); we studied which environmental factors are responsible for its recent sporadic occurrence in the freshwater estuarine reach. Using PLS analysis, it is shown that its presence upstream is limited by a sufficient oxygen concentration (>4 mg l-1) that is associated with temperature. Not only are the environmental conditions in the upstream zone important, but also the frequent presence of an O2 minimum zone in the mid-estuary (O2 min -1) seems to block the movement of the downstream E. affinis population in an upstream direction. Occasionally, the bulk of the population is however situated upstream. During these periods, high E. affinis abundance was also observed in the Durme tributary. Our findings suggest the possibility to use E. affinis as an “indicator” species of water quality, but also lead us to stress the necessity to consider conditions over the entire estuary when studying restoration effects, not exclusively in the zone of interest

Test of some ecological concepts on the longitudinal distribution of zooplankton along a lowland water course

The distribution of zooplankton communities from the source to the mouth of a lowland water course, the Scheldt, was used to test some concepts on the longitudinal distribution of organisms along both estuarine (Remane’s diversity concept) and riverine reaches (River Continuum Concept (RCC), Riverine Ecosystem Synthesis (RES)). Substantial zooplankton densities were found in both April and June samples all along the water course, and not only in the lower reaches as suggested by the RCC. Based on the zooplankton communities, and using hierarchical classifications and Generalized Linear Model, several successive zones influenced by different physical and chemical variables and trophic conditions could be distinguished along the Scheldt, in agreement with the RES model: the non-tidal riverine, the tidal freshwater, the tidal salinity gradient, and the marine zones. Over the entire freshwater reach, rotifers were numerically dominant during both samplings; crustaceans became more abundant in June than in April, specifically in the downstream reaches. Highest total zooplankton abundance and diversity were found in the tidal freshwater reach, lowest in the brackish water reach, in accordance with Remane’s concept. An influence of the tributaries on zooplankton communities is suggested, directly by import or dilution of zooplankton communities or through changing environmental conditions

Closing Moulinex: thoughts on the visibility and invisibility of industrial labour in contemporary France

This article explores some of the ways in which deindustrialisation and factory closures are figured in contemporary French cultural production. In doing so, it reflects on the visibility and invisibility of industrial workers and their work in representations of the social world. Having noted a significant preoccupation with these issues in French cultural production since the 1990s, the discussion focuses particularly on the closure of the well-known domestic appliance company, Moulinex, in September 2001. It contrasts the dominant media discourse on industrial closures with the literary narrative offered by Franck Magloire (son of a Moulinex worker) in Ouvrière (2003).Cet article considère certains aspects de la représentation de la désindustrialisation et des fermetures d'usine dans la production culturelle française contemporaine. Il présente ainsi une réflexion sur la visibilité et l'invisibilité des ouvriers et du travail industriel dans la représentation du monde social. Partant du constat que ces questions constituent une préoccupation importante dans la production culturelle française depuis les années 1990, l'analyse est centrée plus particulièrement sur le cas de la fermeture du célèbre fabricant du petit électroménager, Moulinex, en Septembre 2001. Elle fait ressortir le contraste entre le discours médiatique dominant sur les fermetures industrielles et le récit littéraire proposé par Franck Magloire (fils d'une ouvrière de Moulinex) dans Ouvrière (2003)