data_PlosOne_Meleder_2017.txt

These data are those used in the paper PlosOne Meleder et al. 2017 " Microphytobenthos primary production estimated by hyperspectral reflectance

Étude de la structure des peuplements intertidaux du microphytobenthos (apport de la télédétection visible - infrarouge)

L'objectif de cette étude est d'évaluer l'intérêt de la télédétection multispectrale (SPOT ; bandes spectrales larges et peu nombreuses) et hyperspectrale (DAIS ; bandes spectrales étroites et nombreuses) dans le domaine visible-infrarouge (entre 400 et 1000 nm), pour l'étude des peuplements du microphytobenthos d'un écosystème intertidal. La zone d'étude choisie est une baie à caractère conchylicole de la façade atlantique, la baie de Bourgneuf (47ʿN ; 2ʿW). Le microphytobenthos est composé d'organismes unicellulaires photosynthétiques vivant dans les premiers millimètres de sédiments et largement dominés en baie de Bourgneuf par les Diatomées. La télédétection visible-infrarouge permet l'étude de ces peuplements à partir de leurs caractéristiques spectrales liées à la présence de pigments et mesurées par des radiomètres de terrain et aéroportés. Toutefois, l'interprétation de ces données radiométriques nécessite une connaissance du terrain. Une étude descriptive de la structure du microphytobenthos basée sur un suivi spatial et temporel, a été mise en place durant 15 mois en baie de Bourgneuf. Il apparaît une structuration spatiale des peuplements liée à la granulométrie et à une absence de variabilité saisonnière de la biomasse. Des mesures radiométriques sont réalisées in situ et en laboratoire (cultures monospécifiques) afin d'établir un lien avec les analyses pigmentaires des organismes mesurées en Chromatographie Liquide Haute Pression (CLHP). La biomasse du microphytobenthos est alors estimée à partir des réflectances mesurées à 632 nm (bande d'absorption de la chlorophylle c) dans une gamme de valeurs allant jusqu'à 200 mg Chl a.m-2. Une cartographie du microphytobenthos a été réalisée par les calibrations de six images multispectrales (SPOT) et d'une image hyperspectrale (DAIS) à partir de ces mêmes mesures radiométriques. Ainsi, il apparaît que les peuplements du microphytobenthos se développent le long d'une bande orientée nord-sud en bas d'estran, au niveau de l'isobathe +2 m et pouvant occuper jusqu'à 25 % de la surface étudiée. La calibration de l'image DAIS permet de bien différentier les microalgues des macroalgues. Les plus fortes biomasses microphytobenthiques cartographiées à partir de cette image sont de l'ordre de 60 mg Chl a.m-2 pour des pixels de 5x5 m.The aim of this work is to assess the use of multispectral (SPOT ; few large spectral bands) and hyperspectral (DAIS ; many thin spectral bands) visible infrared remote sensing (between 400 and 1000 nm) to study microphytobenthos assemblages in intertidal ecosystems. The study area is a shellfish ecosystem located south of the Loire river, the Bourgneuf bay (47ʿN ; 2ʿW). Microphytobenthos, which is composed of photosynthetic unicellular organisms inhabiting the upper millimetres of intertidal sediments, is dominated by Diatom in Bourgneuf bay. Each pigment of these organisms exhibit absorbance signature allowing the detection of benthic diatom biofilms by field or satellite/airborne swas around 60 mg Chl a.m-2 for a pixel of 5 x 5 m...NANTES-BU Sciences (441092104) / SudocSudocFranceF

Physiological and photophysiological responses of the benthic diatom Entomoneis paludosa (Bacillariophyceae) to dissolved inorganic and organic nitrogen in culture

International audienceBenthic diatoms are dominant primary producers in intertidal flats. This study investigated the effect of different nitrogen sources and concentrations on Entomoneis paludosa growth and physiological responses. Six nitrogen sources either inorganic (nitrate and ammonium) or organic (urea, arginine, glutamine and glycine) supplied at two concentrations (40 and 400 mu M-N) induced significant effects on growth, carbon, nitrogen, pigment content and maximum PSII quantum efficiency (F-v/F-m). Entomoneis paludosa grew under all nitrogen sources albeit showing differences in lag phase, growth rate and cell yield. Inorganic nitrogen, urea and arginine induced higher growth, whereas glycine did not support high biomass. F-v/F-m showed variability dependent on nitrogen source and C/N ratio. F-v/F-m varied between 0.55 and 0.65 at 400 mu M-N with the highest values observed in glycine, glutamine and urea, whereas nitrate, ammonium and arginine induced lower F-v/F-m. All cellular components decreased in the 40 mu M-N treatments, with nitrogen and pigments being lower than carbon content. Light-harvesting pigment ratios Chl c/Chl a and photoprotective pigment ratios (diatoxanthin + diadinoxanthin)/Chl a increased, while fucoxanthin/Chl a ratios were unaffected by N-limitations. Entomoneis paludosa was capable of quickly adapting and using a wide variety of nitrogen sources. This adaptability may contribute to microphytobenthos diatom ecological success in mudflat ecosystems

Identification of microbial exopolymer producers in sandy and muddy intertidal sediments by compound-specific isotope analysis

Extracellular polymeric substances (EPS) refer to a wide variety of high molecular weight molecules secreted outside the cell membrane by biofilm microorganisms. In the present study, EPS from marine microphytobenthic biofilms were extracted and their isotope ratios were analysed. A comparison of these ratios with the carbon isotope ratios of fatty acid biomarkers allowed the identification of the main EPS producers of two contrasting types of intertidal marine sediments. Our study reveals that EPS production and degradation are supported by very different communities in muddy and sandy sediments and that EPS sources are more diverse in the sand. In mud, bound EPS are mainly derived from diatoms, while colloidal EPS are the result of degradation of bound exopolymers by certain specialised bacteria. In sand, bound EPS are rather of bacterial or cyanobacterial origin and diatoms contribute mainly to colloidal EPS. These differences are thought to be related to differences in the functioning of the epipelic and epipsammic communities and in particular to the use of EPS either for motility or for cell attachment purposes

Extensive spatial impacts of oyster reefs on an intertidal mudflat community via predator facilitation

Habitat engineers make strong and far-reaching imprints on ecosystem processes. In intertidal mudflats, the dominant primary producer, microphytobenthos (MPB), often forms high biomass patches around oyster reefs. We evaluate multiple hypotheses linking MPB with oyster reefs, including oyster biodeposition, meiofaunal grazing, and abiotic factors, aiming to help predict effects of reef removal or proliferation. We quantify spatial patterns of an Atlantic mudflat community and its environment around two large Crassostrea reefs before experimentally sacrificing one reef via burning. MPB biomass was enriched surrounding living oyster reefs although infaunal biomass and individual sizes were low. Structural equation modelling best supported the hypothesis that crab predation intensity, which decayed with distance from the reefs, locally freed MPB from grazing. Our results suggest that Crassostrea reef expansion may enrich local MPB patches and redirect trophic energy flows away from mudflat infauna, with potential implications for the sustainability of local fisheries and bird conservation