Blooms of the marine dinoflagellate Lepidodinium chlorophorum may cause green seawater discolorations, impacting marine biota and human activities in coastal zones. Hypoxic conditions associated with algal biomass recycling are suspected to cause fauna mortalities. This study aims at developing a better understanding of bloom dynamics using in situ and satellite data. Field monitoring was performed to characterize L. chlorophorum seasonal variability and discoloration events in southern Brittany (Atlantic, France) in 2019. The dinoflagellate was observed from May to Nov, with maximal abundance in summer, during water column stratification. The bloom lasted one month, during which L. chlorophorum dominated microphytoplankton. High loads of phosphate, ammonium, and transparent exopolymer particles (TEP) were recorded within the patches of discolored seawater. Bacterial stimulation is suggested to sustain bloom development. TEP production might provide an ecological advantage for the species, conversely causing hypoxia below a dense surface layer. Complementary to field data, high resolution satellite observation made it possible to detect patches of green seawater, measure their areal extent, and study their short-scale changes. Tidal currents were observed as being a primary driver of the bloom surface distribution. By demonstrating how the synergy between in situ monitoring and satellite remote sensing could improve the study of bloom phenology in coastal zones, our results constitute a baseline for future studies of marine ecosystems impacted by seawater discolorations.

Primary Presenter: Pauline ROUX, ISOMer, Nantes University (pauline.roux1@univ-nantes.fr)

Authors:

Pauline Roux, Nantes Université, Institut des Substances et Organismes de la Mer, ISOMer, UR 2160, F-44000, Nantes, France  (pauline.roux1@univ-nantes.fr)

Mathilde Schapira, Ifremer, LITTORAL, F-44300, Nantes, France  (mathilde.schapira@ifremer.fr)

Raffaele Siano, Ifremer, DYNECO, F-29280, Plouzané, France  (raffaele.siano@ifremer.fr)

Philippe Souchu, Ifremer, LITTORAL, F-44300, Nantes, France  (philippe.souchu@ifremer.fr)

Karine Collin, Ifremer, LITTORAL, F-44300, Nantes, France  (karine.collin@ifremer.fr)

Anne Schmitt, Ifremer, LITTORAL, F-44300, Nantes, France  (anne.schmitt@ifremer.fr)

Soazig Manach, Ifremer, LITTORAL, F-44300, Nantes, France  (soazig.manach@ifremer.fr)

Michael Retho, Ifremer, LITTORAL, F-44300, Nantes, France  (michael.retho@ifremer.fr)

Olivier Pierre-Duplessix, Ifremer, LITTORAL, F-44300, Nantes, France  (Olivier.Pierre.Duplessix@ifremer.fr)

Laetitia Marchand, Ifremer, BRM, F-44300, Nantes, France  (laetitia.marchand@ifremer.fr)

Sylvia Colliec-Jouault, Ifremer, BRM, F-44300, Nantes, France  (Sylvia.Colliec.Jouault@ifremer.fr)

Victor Pochic, Nantes Université, Institut des Substances et Organismes de la Mer, ISOMer, UR 2160, F-44000, Nantes, France  (victor.pochic@univ-nantes.fr)

Maria Laura Zoffoli, Consiglio Nazionale delle Ricerche, Istituto di Scienze Marine (CNR-ISMAR), 00133, Rome, Italy  (laura.zoffoli@artov.ismar.cnr.it)

Pierre Gernez, Nantes Université, Institut des Substances et Organismes de la Mer, ISOMer, UR 2160, F-44000, Nantes, France  (pierre.gernez@univ-nantes.fr)