Articles | Volume 15, issue 23
Biogeosciences, 15, 7243–7271, 2018
Biogeosciences, 15, 7243–7271, 2018

Research article 06 Dec 2018

Research article | 06 Dec 2018

On biotic and abiotic drivers of the microphytobenthos seasonal cycle in a temperate intertidal mudflat: a modelling study

Raphaël Savelli1, Christine Dupuy1, Laurent Barillé2, Astrid Lerouxel2, Katell Guizien3, Anne Philippe1, Pierrick Bocher1, Pierre Polsenaere4, and Vincent Le Fouest1 Raphaël Savelli et al.
  • 1LIttoral, ENvironnement et SociétéS (LIENSs), Université de La Rochelle, UMR 7266, CNRS-ULR, 2 rue Olympe de Gouges, 17000 La Rochelle, France
  • 2Mer Molécules Santé (MMS) – EA 21 60, Université de Nantes, Laboratoire Mer Molécules Santé, 2 rue de la Houssinière, 44322 Nantes CEDEX, France
  • 3CNRS-Université Pierre et Marie Curie, UMR 8222 Laboratoire d'Ecogéochimie des Environnements Benthiques, Observatoire Océanologique de Banyuls-sur-Mer, UMR8222, rue du Fontaulé, 66650 Banyuls-sur-Mer, France
  • 4IFREMER, Laboratoire Environnement Ressources des Pertuis Charentais (LER/PC), BP7, 17137 L'Houmeau, France

Abstract. Microphytobenthos (MPB) from intertidal mudflats are key primary producers at the land–ocean interface. MPB can be more productive than phytoplankton and sustain both benthic and pelagic higher trophic levels. The objective of this study is to assess the contribution of light, mud temperature, and gastropod Peringia ulvae grazing pressure in shaping the seasonal MPB dynamics on the Brouage mudflat (NW France). We use a physical–biological coupled model applied to the sediment first centimetre for the year 2008. The simulated data compare to observations, including time-coincident remotely sensed and in situ data. The model suggests an MPB annual cycle characterised by a main spring bloom, a biomass depression in summer, and a moderate fall bloom. In early spring, simulated photosynthetic rates are high due to mud surface temperature (MST) values close to the MPB temperature optimum for photosynthesis and because increasing solar irradiance triggers the onset of the MPB spring bloom. Simulated peaks of high P. ulvae grazing (11 days during which ingestion rates exceed the primary production rate) mostly contribute to the decline of the MPB bloom along with the temperature limitation for MPB growth. In late spring–summer, the MPB biomass depression is due to the combined effect of thermo-inhibition and a moderate but sustained grazing pressure. The model ability to infer biotic and abiotic mechanisms driving the seasonal MPB dynamics could open the door to a new assessment of the export flux of biogenic matter from the coast to the open ocean and, more generally, of the contribution of productive intertidal biofilms to the coastal carbon cycle.

Short summary
We simulate the benthic microalgae seasonal cycle on a temperate intertidal mudflat by combining a physical–biological coupled model with remotely sensed and in situ data. While optimal light and temperature conditions lead to a spring bloom, thermo-inhibition and grazing result in a summer depression of biomass. The model ability to infer mechanisms driving the seasonal cycle could open the door to the contribution of productive intertidal biofilms to the coastal carbon cycle.
Final-revised paper