A threefold perspective on the role of a pockmark in benthic faunal communities and biodiversity patterns.

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Publisher: Elsevier B.V.
Document Type: Report
Length: 518 words

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Keywords Pockmark; Meiofauna; Macrofauna; Foraminifera; Nematoda; Polychaeta Highlights * Environmental conditions of pockmarks affect benthic community composition. * Meiofaunal taxa are able to take advantage of pockmark activity, i.g Desmodora. * Desmodora nematode could be a benthic indicator of fluid emission. * Benthic community compositions are largely dissimilar between the two sites. Abstract Pockmarks are circular-shaped depressions that increase seabed heterogeneity and are characterized by discontinuous fluid emissions. To understand how environmental conditions of pockmarks affect the structure of macro- and meiofauna, we investigated two sites in a pockmark field in the northwestern Madagascar margin. In a comparative approach, we explored the community structure of the dominant taxa (Polychaeta, Nematoda and hyaline foraminifera) in each component (macro-, metazoan meiofauna and foraminifera, respectively). The investigated active pockmark showed approximately two times higher meiofauna abundance compared to in a site away from another pockmark field, but macrofauna showed the opposite trend, with almost half density at the pockmark site. However, at both sites, macro- and meiofauna showed higher richness and abundance values in the top well-oxygenated layers of the sediment than in the underlaying ones. Polychaeta and Nematoda showed lower richness in the pockmark, opposed to hyaline foraminiferans, but lower evenness in the pockmark was found for the three groups. The detection of gas flares in the water column attests of the recent activity within the pockmark. High amount of sulfur-bearing minerals (mainly pyrite) evidences a production of dissolved free sulfides (not detected at the time of sampling) by sulfate reduction process driven by organic matter degradation and anaerobic oxidation of methane. Furthermore, recent increase in sedimentation rates in the past 70 years and organic matter inputs could have led to higher organic matter degradation rates resulting in reduced conditions and a high oxygen consumption. All this together seem to act as key factors in the determination of variation in richness, abundance and community composition of macrofauna and meiofauna. Additionally, some taxa seem to be more tolerant to these extreme conditions, such as species belonging to the Nematoda genus Desmodora and the phylum Kinorhyncha, which are highly abundant in the pockmark, and hence, may be considered as potential bioindicators of pockmark activity in this area. Further studies are required for a better assessment. Author Affiliation: (a) Institut Français de Recherche pour l'Exploitation de la MER (IFREMER), Laboratoire Environnement Profond, France (b) Marine Biology, Ghent University, Belgium (c) School of Environment Sciences Earth, Ocean & Ecology Sciences Department, University of Liverpool, UK (d) Institut Français de Recherche pour l'Exploitation de la MER (IFREMER), Unité Géosciences Marines, France * Corresponding author., Article History: Received 18 May 2020; Revised 23 October 2020; Accepted 23 October 2020 (footnote)1 Departamento de Biodiversidad, Ecología y Evolución, Facultad de Ciencias Biológicas, Universidad Complutense de Madrid, Spain. (footnote)2 CNR-IRBIM: National Council of Researches - Institute for Biological Resources and Marine Biotechnology, Italy. (footnote)3 Institut Halieutiques et des Sciences Marines (IH.SM), Toliara, Madagascar. Byline: Nuria Sánchez [Nuria.Sanchez.Santos@ifremer.fr] (a,1,*), Daniela Zeppilli (a), Elisa Baldrighi (a,2), Ann Vanreusel (b), Max Gasimandova Lahitsiresy (a,3), Christophe Brandily (a), Lucie Pastor (a), Lara Macheriotou (b), Guillermo García-Gómez (c), Stéphanie Dupré (d), Karine Olu (a)

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Gale Document Number: GALE|A648410969