Natural patches in Posidonia oceanica meadows: the seasonal biogeochemical pore water characteristics of two edge types
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Seagrass meadows can be assimilated to seascape matrixes encompassing a mosaic of natural and anthropogenic patches. Natural patches within the Mediterranean Posidonia oceanica meadows show a structural particularity which consist in a duality of their edge types. One edge is eroded by bottom currents, while the adjacent meadow colonizes the bare sediments. This study aims to study the dynamics of these two edges through the investigation of the biogeochemistry (pH, total alkalinity, dissolved inorganic carbon, CO2, CH4, N2O, H2S, dissolved inorganic nitrogen, PO4 3−) within vegetated and unvegetated sediments. These observations are compared with the adjacent meadow to have a better understanding of the colonization processes. Our results reveal that the P. oceanica matrix shows differences from the vegetated edges of sand patches, especially with regard to nutrient availability, which is generally more important at the colonized edge (dissolved inorganic nitrogen up to 65.39 μM in June). A clear disparity also occurs between the eroded and colonized edge with both a seasonal and bathymetrical variation of leaf biomass with higher disparities at 10 m in June (colonized edge 1415 gDW m−2; eroded edge 1133 gDW m−2). The most important contrasts during this study were assessed in June, suggesting that the warm period of the year is more suitable for sampling to highlight disparate characteristics in temperate seagrass meadows. These findings put into light the potential importance of biogeochemical processes in the dynamics of natural patch edges. We hypothesize that they may influence the structural dynamics of P. oceanica seascapes.
We thank Marc-Vincent Commarieu for TA analysis, and Renzo Biondo for nutrient analysis. We also thank Jonathan Richir, Nicolas Cimiterra and Michèle Leduc for their support during the scuba diving sampling and the acquisition of the temperature and light data. This study is part of the STARE-CAPMED (STAtion of Reference and rEsearch on Change of local and global Anthropogenic Pressures on Mediterranean Ecosystems Drifts) program funded by the Territorial Collectivity of Corsica and by the French Water Agency (PACA-Corsica). The GC was acquired with funds from the Fonds National de la Recherche Scientifique (FNRS) (Contract No. 2.4.598.07). Alberto V. Borges is a senior research associate at the FNRS. Arnaud Abadie acknowledges a CIFRE Ph.D. Grant (2013/0470) of the French ANRT (Association Nationale Recherche Technologie). We thank the two anonymous referees who contributed to improve the manuscript with constructive comments.
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Conflict of interest
The authors declare that they have no conflict of interest.
This article does not contain any studies with animals performed by any of the authors.
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