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

Abstract

Chloropigments and carotenoids were measured by HPLC in an intertidal muddy sediment of Marennes-Oleron Bay (France). Concentrations were determined as a function of sediment depth at low tide. The analyses were carried out at monthly intervals over 1 yr. Pigment analysis 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 macrophytic detritus had occurred at the sampling site. There was a large pool of phaeopigments a, of which phaeophorbides were the major forms (75%). A microphytobenthic bloom occurred between March and June during which phaeopigments significantly increased with a high proportion of phaeophorbides likely due to intense grazing activity of benthic invertebrates. Pigment concentrations were still high at 5 cm depth and changes occurred simultaneously in the aphotic ( 5 mm sediment depth) 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 the diatom community, a close coupling between the dynamics of microphytobenthos biomass and the grazing activity of benthic invertebrates, and the influence of sediment mixing.