Comparative study of sediment particle mixing in a Zostera noltei meadow and a bare sediment mudflat

Seasonal changes in sediment particle mixing, surface sediment and seagrass charac teristics, and benthic infaunal composition were measured in Arcachon Bay (France), within both a well-developed Zostera noltei meadow and a bare sediment mudflat. Sediment par- ticle mixing intensities (measured by the normal biodiffusion coefficient Db N ) were obtained by fitting a continuous time random walk model to in situ measured vertical luminophore profiles. Db N values (mean ± SD) were between 2.99 ± 2.75 and 22.45 ± 43.73 cm 2 yr −1 within the bare mud- flat and between 0.39 ± 0.30 and 18.07 ± 18.14 cm 2 yr −1 within the Zostera meadow. Spatiotempo- ral changes in infauna and Db N were lower within the Zostera meadow, which supports the buffer- ing effects of seagrass meadows on biological sedimentary processes. Within the Zostera meadow, root biomass declined during the survey, in correlation with increases in (1) the mean value and the variability of Db N and (2) the spatial variability of infaunal composition with a decrease in the dominant polychaete Melinna palmata. At this station, similarity matrices of mean Db N and abun- dances of a set of 3 infaunal species (including M. palmata) correlated significantly, which further supports the key role of this species in controlling sediment particle mixing through sediment stabilization. When considering the whole data set, the similarity matrices of the coefficients of variation of Db N and of the abundances of a set of 5 species (Abra segmentum, Glycera convoluta, Tubificoides benedii, Heteromastus filiformis, Ruditapes phillipinarum) correlated significantly, which supports the suspected role of these species in controlling sediment particle mixing.