Influence of the hydrodynamics on the dynamics of nearshore benthic communities and their geochemical environment
Influence de l'hydrodynamisme sur la dynamique des communautés benthiques pré-littorales et leur environnement géochimique
Résumé
Benthic sedimentary environments host micro- and macro-organisms which are the main agents of early diagenesis, a key step to sustain a recycled primary production in coastal areas. Nearshore soft-bottom habitats undergo intense but highly variable hydrodynamical stresses due to the dissipation of the energy accumulated by the ocean and brought by the rivers. Thus, elements recycling at the water-sediment interface is controlled by hydrodynamical conditions which regulate vertical fluxes across the interface as well as horizontal redistribution of particulate, including living organisms, and dissolved matter. Moreover, hydrodynamical conditions may also affect the diversity and abundance of benthic macrofauna assemblages depending on their reproductive behaviour. Indeed, while most micro-organisms have a direct reproductive cycle in the sediment, most macrofauna species have a complex life cycle with a pelagic larval stage enabling distant colonisation possibilities as a result of larval dispersal by the circulation. Herein, I present mechanistic models that I developped to describe the influence of hydrodynamical forcings on the dynamics of nearshore benthic invertebrates communities and their geochemical environment. Chapter 1 describes my contribution to the description of the main hydrodynamical processes of the microtidal nearshore area, focussing on its boundary layer dissipative role at fixed and mobile interfaces (shoreline, sea bottom, river mouth). Chapter 2 presents my investigations on the role of hydrodynamics on benthic macrofauna communities structuring, including larval dispersal, recruitment failures and benthic stages spatial redistribution. Chapter 3 presents my investigations on the role of hydrodynamics on the geochemical dynamics at the water-sediment interface, including sediment dynamics and dissolved fluxes in the wave-current-organisms interaction. Chapter 4 presents on future investigations aiming at coupling explicitly biogeochemical cycles with species life cycles in integrated ecosystem models for the nearshore area.
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