Articles | Volume 15, issue 23
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 Savelli, Christine Dupuy, Laurent Barillé, Astrid Lerouxel, Katell Guizien, Anne Philippe, Pierrick Bocher, Pierre Polsenaere, and Vincent Le Fouest

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