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      Spatial Variability of Benthic-Pelagic Coupling in an Estuary Ecosystem: Consequences for Microphytobenthos Resuspension Phenomenon

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          Abstract

          The high degree of physical factors in intertidal estuarine ecosystem increases material processing between benthic and pelagic compartments. In these ecosystems, microphytobenthos resuspension is a major phenomenon since its contribution to higher trophic levels can be highly significant. Understanding the sediment and associated microphytobenthos resuspension and its fate in the water column is indispensable for measuring the food available to benthic and pelagic food webs. To identify and hierarchize the physical/biological factors potentially involved in MPB resuspension, the entire intertidal area and surrounding water column of an estuarine ecosystem, the Bay des Veys, was sampled during ebb tide. A wide range of physical parameters (hydrodynamic regime, grain size of the sediment, and suspended matter) and biological parameters (flora and fauna assemblages, chlorophyll) were analyzed to characterize benthic-pelagic coupling at the bay scale. Samples were collected in two contrasted periods, spring and late summer, to assess the impact of forcing variables on benthic-pelagic coupling. A mapping approach using kriging interpolation enabled us to overlay benthic and pelagic maps of physical and biological variables, for both hydrological conditions and trophic indicators. Pelagic Chl a concentration was the best predictor explaining the suspension-feeders spatial distribution. Our results also suggest a perennial spatio-temporal structure of both benthic and pelagic compartments in the ecosystem, at least when the system is not imposed to intense wind, with MPB distribution controlled by both grain size and bathymetry. The benthic component appeared to control the pelagic one via resuspension phenomena at the scale of the bay. Co-inertia analysis showed closer benthic-pelagic coupling between the variables in spring. The higher MPB biomass observed in summer suggests a higher contribution to filter-feeders diets, indicating a higher resuspension effect in summer than in spring, in turn suggesting an important role of macrofauna bioturbation and filter feeding ( Cerastoderma edule).

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          Responses of benthic macrofauna and biogeochemical fluxes to various levels of mussel biodeposition: an in situ "benthocosm" experiment.

          An in situ experiment was done to evaluate the dose-dependent response of mussel biodeposition on benthic communities and biogeochemical fluxes. Natural benthic communities were exposed to 7 different levels of mussel biodeposition (equivalent to that produced by 0-764 mussels m(-2)) over 50 days. Benthic communities responded as predicted from the Pearson, T.H., Rosenberg, R., 1978. Macrobenthic succession in relation to organic enrichment and pollution of the marine environment. Oceanogr. Mar. Biol. Annu. Rev. 16, 229-311 model of organic enrichment. Total abundance and species richness decreased with increasing biodeposition. The abundance and biomass of opportunistic species (Capitella spp.) increased in the mesocosms subject to the greatest biodeposition. Sensitive species Tellina agilis and Pherusa plumosa tended to decrease in abundance and biomass with increasing biodeposition. The biotic index M-AMBI responded clearly to increased biodeposition and may be a useful tool for assessing the effect of mussel biodeposition on the benthic environment. These results are important for the construction of predictive models for determining environmental carrying capacity for bivalve aquaculture.
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            Monitoring Migration and Measuring Biomass in Benthic Biofilms: The Effects of Dark/far-red Adaptation and Vertical Migration on Fluorescence Measurements.

            Pulse modulated fluorescence has increasingly been used as an ecological tool to examine changes in the vertical distribution of microphytobenthic cells within the upper layers of estuarine sediments (most often using the minimum fluorescence yield F(o)) as well as to indicate the health of the community (using the maximum PS II quantum efficiency F(v)/F(m)). However, the practicalities of in situ measurements, often dictates that short dark adaptation periods must be used ( approximately 15 min). The use of far-red light as an alternative to dark adaptation was investigated in natural migratory microphytobenthic biofilms and artificial non-migratory biofilms. Prolonged periods of darkness ( approximately 24 h) were not adequate to achieve 'true' measurements of F(o) and F(v)/F(m), which require complete oxidation of Q(A) and full reversal of non-photochemical quenching (NPQ). In some instances, stable values were only achieved using far-red light. Prolonged exposure to dark/far-red light led to a downwards migration of cells in natural assemblages, as seen by a reduction in both F(o) and the maximum fluorescence yield (F(m)). In non-migratory biofilms, F(m) increased in the dark and far-red treatments, indicating a reversal of NPQ, whereas F(o) decreased in far-red light but increased in the dark. It is suggested that far-red light and darkness differentially affected the balance between NPQ reversal and Q(A) oxidation that lead to the measured F(o) yield. The use of far-red light as an alternative to dark adaptation is discussed and the implications of short (e.g., 15 min) dark adaptation times used in situ are discussed with reference to the vertical migration of cells within sediment biofilms.
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              Author and article information

              Contributors
              Role: Editor
              Journal
              PLoS One
              PLoS ONE
              plos
              plosone
              PLoS ONE
              Public Library of Science (San Francisco, USA )
              1932-6203
              2012
              29 August 2012
              : 7
              : 8
              : e44155
              Affiliations
              [1 ]Université de Caen Basse-Normandie, FRE3484 BioMEA, Caen, France
              [2 ]CNRS INEE, FRE3484 BioMEA, Caen, France
              [3 ]IFREMER, LERN, Port en Bessin, France
              [4 ]Université de Lille1, UMR CNRS 8187 LOG “Laboratoire d’océanologie et geosciences”, Station Marine de Wimereux, Wimereux, France
              [5 ]CNRS, UMR 7208 BOREA, Muséum d’histoire naturelle, CRESCO, Dinard, France
              National Institute of Water & Atmospheric Research, New Zealand
              Author notes

              Competing Interests: The authors have declared that no competing interests exist.

              Conceived and designed the experiments: MU FO SL. Performed the experiments: MU FO AG KG. Analyzed the data: MU FO SL. Contributed reagents/materials/analysis tools: MU AG FO RL. Wrote the paper: MU.

              Article
              PONE-D-12-09682
              10.1371/journal.pone.0044155
              3430628
              22952910
              728eea4d-cc82-4056-88e0-37af9626c8b2
              Copyright @ 2012

              This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.

              History
              : 5 April 2012
              : 30 July 2012
              Page count
              Pages: 17
              Funding
              This work was funded by the Regional council of Basse-Normandie. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.
              Categories
              Research Article
              Biology
              Ecology
              Biota
              Coastal Ecology
              Ecological Environments
              Ecosystems
              Marine Ecology
              Plant Ecology
              Spatial and Landscape Ecology
              Marine Biology
              Marine Ecology
              Phycology
              Zoology
              Malacology
              Earth Sciences
              Environmental Sciences
              Marine and Aquatic Sciences
              Coastal Ecology
              Marine Ecology
              Marine Geology
              Oceanography

              Uncategorized
              Uncategorized

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