Short-term variability of intertidal microphytobenthic production using an oxygen microprofiling system
Résumé
Despite their high productivity and their key role in coastal processes, intertidal areas remain poorly documented because alternating conditions of sediment-water and sediment-air interfaces result in inaccurate temporal estimations of interfacial carbon exchanges. This study describes the short-term variability of microphytobenthic production in an estuarine mudflat (the Canche estuary of the English Channel) by using an autonomous acquisition system for oxygen microprofiles. More than 240 profiles were measured at low and high tide during three deployments performed within a 3-week period (April-May 2007). Additional measurements characterised the surficial sediments (granulometry, porosity, chlorophyll a, temperature, salinity) and incident light. Depth-integrated gross production values were correlated with light intensity and reached up to 146 mg C m-2 h-1, while the turbidity of the overlying water prevented any primary production during immersion. Photosynthesis-irradiance curves were highly variable between field campaigns. Indeed, we have recorded a drastic reduction in microphytobenthic production, which might result from a pulse input of polychaete juveniles (Lanice conchilega). Ephemeral structures, such as invertebrate tubes, are seldom considered as factors that may influence the variability of benthic primary production. Monitoring oxygen microprofiles may be a useful tool for understanding and quantifying the impact of short-term temporal changes on the budgets of microphytobenthic production.