Dynamics of particulate organic matter in a coastal system characterized by the occurrence of marine mucilage – A stable isotope study Camilla Liénart a,b, ⁎, Nicolas Susperregui c,d , Vanessa Rouaud c,e , Joana Cavalheiro c,e , Valérie David a,b , Yolanda Del Amo a,b , Robert Duran c,e , Béatrice Lauga c,e , Mathilde Monperrus c,e , Thierry Pigot c,e , Sabrina Bichon a,b , Karine Charlier a,b , Nicolas Savoye a,b a Univ. Bordeaux, Laboratoire d'Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), UMR 5805, Allée Geoffroy Saint-Hilaire, 33615 Pessac Cedex, France b CNRS, Laboratoire d'Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), UMR 5805, Allée Geoffroy Saint-Hilaire, 33615 Pessac Cedex, France c Univ. de Pau et des Pays de l'Adour, Institut des sciences analytiques et de Physicochimie Pour l'Environnement et les Matériaux (IPREM), UMR CNRS 5254, 2 Avenue du Président Pierre Angot, 64000 Pau, France d Institut des Milieux Aquatiques (IMA), 1 rue de Donzac, 64100 Bayonne, France e Univ. de Pau et des Pays de l'Adour, Fédération MIRA, FR4155, Allée du parc Montaury, 64600 Anglet, France abstract article info Article history: Received 28 January 2016 Received in revised form 22 July 2016 Accepted 3 August 2016 Available online xxxx In coastal systems, particulate organic matter (POM) originates from various autochthonous and allochthonous organic matter sources. Also, some coastal systems are characterized by the occurrence of large amounts of mu- cilaginous material of biologic origin (i.e. phytoplankton, bacteria), which aggregates and potentially traps other organisms and particles present in the water column. This study focuses on POM origin and spatio-temporal dy- namics in the South-East coast of the Bay of Biscay, an area subject to mucilage occurrence. In order to investigate POM quantitative and qualitative (C and N elemental and isotopic ratios) characteristics, sampling was per- formed over an annual cycle at two sites experiencing different mucilage occurrence and river influence. Contri- bution of phytoplankton, terrestrial POM and anthropogenic POM to coastal-POM composition was calculated using a three-sources mixing model. Overall, phytoplankton dominated the coastal-POM composition at all sea- sons, sites and most of the depths (71.6 ± 24.2%). Terrestrial-POM contribution was moderate (22.7 ± 21.8%) and anthropogenic-POM contribution was usually negligible (5.7 ± 7.4%). Both sites mainly exhibited similar vertical and temporal variations in terms of POM origin and dynamics: terrestrial-POM contribution increased with depth and was higher in winter at all depths and in autumn in bottom waters, compared to other seasons. The main differences between both sites were related to the vertical dynamics of the terrestrial contribution to the coastal POM. Horizontal, vertical and temporal variation of POM composition was linked to processes driving the sedimentary hydrodynamics: the river flow, the direction of the river plume and events of sediment resus- pension/deposition. During the study period, the mucilage occurred only as flocs (small aggregates). The muci- lage was of autochthonous origin and did not trap detectable amount of allochthonous material. © 2016 Elsevier B.V. All rights reserved. Keywords: Particulate organic matter Stable isotopes Marine mucilage Coastal systems Bay of Biscay 1. Introduction Coastal systems are defined as the portion of global ocean where physical, biological and biogeochemical processes are directly affected by land (Gattuso and Smith, 2007). Coastal zones are among the most productive ecosystems of the planet: although they cover only 5% of the surface area of the global ocean, they account for about 12% of oce- anic primary production, 71% of organic matter burial (Dunne et al., 2007) and offer 60 times more ecosystem services per surface area unit than the open ocean (de Groot et al., 2012). Especially, these sys- tems act as dynamical land/sea interfaces by regulating numerous fluxes of matter and energy. Coastal systems are under the influence of different sources of organic matter (OM) (Bode et al., 2006). Indeed, the pool of particulate organic matter (POM) in coastal systems is a mix- ture of organic particles as living organisms and/or detritus originating from autochthonous (in situ pelagic and benthic primary producers) as well as allochthonous (continental) reservoirs (Savoye et al., 2012; Tesi et al., 2007). All these POM sources potentially fuel the coastal Journal of Sea Research xxx (2016) xxx–xxx ⁎ Corresponding author at: Univ. Bordeaux, Laboratoire d'Environnements et Paléoenvironnements Océaniques et Continentaux (EPOC), UMR CNRS 5805, Station Marine d'Arcachon, 2 rue du Pr. Jolyet, 33120 Arcachon Cedex, France. E-mail addresses: camilla.lienart@u-bordeaux.fr (C. Liénart), ima.susperregui@wanadoo.fr (N. Susperregui), vanessa.rouaud@univ-pau.fr (V. Rouaud), joana.cavalheiro@univ-pau.fr (J. Cavalheiro), valerie.david@u-bordeaux.fr (V. David), yolanda.del-amo@u-bordeaux.fr (Y. Del Amo), robert.duran@univ-pau.fr (R. Duran), beatrice.lauga@univ-pau.fr (B. Lauga), mathilde.monperrus@univ-pau.fr (M. Monperrus), thierry.pigot@univ-pau.fr (T. Pigot), sabrina.bichon@u-bordeaux.fr (S. Bichon), karine.charlier@u-bordeaux.fr (K. Charlier), nicolas.savoye@u-bordeaux.fr (N. Savoye). SEARES-01467; No of Pages 11 http://dx.doi.org/10.1016/j.seares.2016.08.001 1385-1101/© 2016 Elsevier B.V. All rights reserved. Contents lists available at ScienceDirect Journal of Sea Research journal homepage: www.elsevier.com/locate/seares Please cite this article as: Liénart, C., et al., Dynamics of particulate organic matter in a coastal system characterized by the occurrence of marine mucilage – A stable isotope..., J. Sea Res. (2016), http://dx.doi.org/10.1016/j.seares.2016.08.001