Short-term variability of intertidal benthic community production during emersion and the implication in annual budget calculation

Short-term variability in benthic community primary production was studied during the course of emersion on a study site located in the Bay of Somme (eastern English Channel, France). Primary production was estimated at the community level through in situ measurements of carbon dioxide fluxes (infra-red analysis) in benthic chambers. Throughout the emersion period, gross community production (GCP) exhibited strong variations that were strongly correlated with natural variations in light. Light response curves explained the variations in GCP during the greater part of the emersion period, and vertical migrations of the microphytobenthos were suggested to explain the remaining variations (i.e. just before or just after immersion of the study site). A time lag was observed between the start of emersion and the maximum GCP, which was positively correlated with the time lag between emersion and local noon. The introduction of this time lag within the annual budget calculation enhanced production variability at a 2 wk time scale (i.e. tidal cycle), but light variability at the small time scale (i.e. cloudiness) remained the major factor inducing production variability. Results highlighted that omitting the time lag between emersion time and the maximum GCP within annual budget calculations led to large overestimations of annual GCP, since the annual budget for the study site was recalculated as being 67 g C m–2 yr–1 compared to 110 g C m–2 yr–1 when the short-term variability was not taken into account.