Monthly HPLC measurements of pigment concentration from an intertidal muddy sediment of Marennes-Oléron Bay, France

Chloropigments and carotenoids were measured by HPLC in an intertidal muddy sediment of Marennes-Oleron Bay (France). Concentrations were determined as a function of s-ent depth at low tide. The analyses were carried out at monthly intervals over l yr. Pigment anal-indicated that the microphytobenthic community was dominated by diatoms throughout the sampling year. Chlorophyll b was not encountered at any time or depth, indicating that no input from macmphytic detritus had occurred at the sampling site. There was a large pool of phaeopigments a. d whlch phaeophorbides were the major forms (75%). A microphytobenthic bloom occurred between March and June during which phaeopigments significantly increased with a high proportion of phaeophorb ~d e s likely due to intense grazing activ~ty of benthic invertebrates. P~gment concentrat~ons were still high at 5 cm depth and changes occurred simultaneously in the aphotic (<5 mm sediment depLh] and photic (>5 mm sediment depth) layers of the sediment, reflecting an impact of bioturbation and physical mixing (resuspension/redeposition) of the upper sediment layer. There was a decrease of the pigment content of the sediment between June and July. It was attributed to grazing and to a resuspension event. Overall, the pigment analysis of this intertidal sediment indicates a predominance of t h e diatom community, a close coupling between the dynamics of microphytobenthos biomass and the grazing activity of benthic invertebrates, and the influence of sediment mixing.