Ecological properties of Lepidodinium chlorophorum blooms : from cellular ecophysiology to ecosystem impacts

• Main Author: Roux, Pauline
• Other Authors: Unité Littoral (LITTORAL), Institut Français de Recherche pour l'Exploitation de la Mer (IFREMER), Nantes Université, Raffaele Siano, Mathilde Schapira, Élodie Fleury
• Format: Doctoral or Postdoctoral Thesis
• Language: French
• Published: HAL CCSD 2022
• Subjects: Harmful algal blooms; Coastal ecology; Lepidodinium chlorophorum; Environmental DNA; Particules Exo-polymériques; Milieu marin côtier; [SDU.STU]Sciences of the Universe [physics]/Earth Sciences; Crassostrea gigas
• Online Access: https://theses.hal.science/tel-03851976; https://theses.hal.science/tel-03851976/document; https://theses.hal.science/tel-03851976/file/ROUX.pdf

Green Seawater Discolorations (GSD) caused by the proliferation of Lepidodinium chlorophorum in southern Brittany are associated with mass mortalities of bivalves. Few information is available regarding the biology and ecology of this dinoflagellate. This work provides a first ecological conceptual model of this species. L. chlorophorum is the main producer of Transparent Exopolymer Particles (TEP) and bacteria induce an overproduction of TEP. The genus Lepidodinium was detected at low abundances in the water column during the non productive period and bloom initiation may be induced by ammonium inputs. Any benthic cysts were observed in the sediment, questioning their existence. Freshwater inputs and stratification may trigger the development of a GSD. Remote sensing showed the importance of tidal currents in the spatial dynamics of the GSD. Bacterial remineralisation of TEP may sustain the bloom for more than one month. While TEP could confer an ecological benefit for L. chlorophorum, this organic matter could negatively impact the ecosystem. The physiological recovery of the oyster Crassostrea gigas exposed to GSD concentrations was studied under controlled conditions. The oyster is able to filter and ingest this dinoflagellate. However, the presence of acidic glycoconjugates within the digestive tubules, impaired filtration and disturbed assimilation have been observed, suggesting that long-term exposure could affect the cupped oyster. These first insights into the ecological properties of L. chlorophorum in southern Brittany constitute the baseline for further studies in other ecosystems impacted by this species. En Bretagne sud, les Eaux Colorées Vertes (ECV) engendrées par Lepidodinium chlorophorum sont associées à des mortalités de bivalves. Cependant, la biologie et l'écologie de ce dinoflagellé restent peu étudiées. Ce travail fournit un premier modèle conceptuel de son écologie. L. chlorophorum produit des Particules Exo-polymériques Transparentes (TEP) et les bactéries induisent une surproduction ...