The intra-annual variability of soft-bottom macrobenthos abundance patterns in the North Channel of the Seine estuary |
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Authors: | Nicolas Desroy Anne-Laure Janson Lionel Denis Gregory Charrier Sandric Lesourd Jean-Claude Dauvin |
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Institution: | 1.Station Marine de Wimereux,CNRS FRE,Wimereux,France;2.Ifremer,Laboratoire Environnement et Ressources,Saint Malo,France;3.Laboratoire de Morphodynamique Continentale et C?tière, UMR 6143,Université de Rouen,Mont-Saint-Aignan Cedex,France;4.Laboratoire de Ressources halieutiques,Institut Universitaire Européen de la Mer,Plouzane,France;5.Université du Littoral-C?te d’Opale, CNRS UMR ,Wimereux,France |
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Abstract: | Temporal and spatial variability of the Abra alba–Pectinaria koreni and Macoma balthica communities was examined in the northern part of the Seine estuary (North Channel) over different space and time scales in
order to assess the role that the hydrologic regime and/or anthropogenic influences play in defining benthic communities over
time. Sediment in the North Channel displayed strong spatial and temporal variability, sustained by intense sediment transport
episodes. Total macrobenthic abundances ranged widely on the course of the year and there was no evidence of a seasonal signal
for the density fluctuations, whatever the spatial scale considered. The bio-sedimentary dynamics can be divided into two
periods: the first corresponds to the high flow rate period (January–May) during which fauna is influenced by fine silt/clay
deposition, and the second to the low flow rate period (June–December) during which sandy deposits prevail. Despite the absence
of significant correlations between sediment composition and abundance, episodes of sediment transport seem to be an important
structuring mechanism in the Seine estuary. As a consequence, the faunal composition varied throughout the year. The winter
and spring fauna, characterised by species living on muddy fine-sands or muds, were enriched during the summer and autumn
by species living in clean fine sand, such as Donax vittatus, Nephtys cirrosa or Spio decoratus, mainly represented by adult individuals. Secondary settlement of drifters may explain the rapid structuration of assemblages
a few days after the sandy deposits. Our results suggest the importance of the bentho-pelagic coupling, primarily induced
by the sedimentary instability, on the macrobenthic fauna dynamics. The intra-annual variability of assemblages at the mouth
of the Seine river and the silted situation of the North Channel might simply be the result of the silting up and alteration
of the inner estuary, generated by several decades of man-made modifications and natural processes. |
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Keywords: | Temporal variability Bentho-pelagic coupling Sediment Abra alba community Anthropogenic impacts Port 2000 |
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