Factors controlling benthic metabolism during low tide along a granulometric gradient in an intertidal bay (Roscoff Aber Bay, France)

In this study, benthic metabolism was measured during low tide, in a small intertidal bay. Gross primary production (GPP) and benthic community respiration (BCR) were calculated via in situ CO2 flux measurements at the air-sediment interface within a benthic chamber. These rates (GPP and BCR) were determined simultaneously with microphytobenthos (MPB), bacterial (BB), macrofaunal (MaB) and meiofaunal (MeB) biomasses, grain size analysis and nutrient standing stocks in sediment porewater (NO2-, NO3-, NH4+, SiO32- and PO43-). The aims of this study were to determine (1) the relative influence of environmental regulating factors on benthic metabolism under in situ conditions and (2) the relative contribution of benthic compartments to BCR. Among all the potential regulating factors measured (i.e. sediment temperature, dissolved inorganic nutrient concentrations in porewater), and the entire size range of benthic organisms sampled (i.e. from macro-fauna to bacteria), results showed that (1) granulometry strongly controlled the distribution of benthic compartments at the bay scale and (2) GPP and BCR were mostly influenced by temperature at the sampling site scale. Moreover, out of bacteria, macrofauna and meiofauna, bacterial activity contributed the most to BCR (bacterial > macrofaunal > meiofaunal respiration). Mean bacterial respiration was estimated to be 1.5 +/- 0.5 mg C m(-2) h(-1) and represented up to 88 % of BCR in fine-sand sediments.