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International audience; Several species of marine polychaetes reside in individual protective tubes. These tubes may be agglomerated in patches of varied sizes with very high densities, or form massive reef-like mounds which can be stretch over several kilometers. These polychaetes can thus be considered as the most important building organisms after corals in coastal environments. We especially focused on several species belonging to the families of Sabellariidae, Terrebeliidae and Pectinariidae. Tubes grains are glued together with biomineralized cement secreted from a building organ connected to specialized glands. Different methods of micro-analysis were used to analyze the biomineral components of these cements for four varyingly gregarious tube-building polychaetes: Lanice conchilega, Pectinaria koreni, Sabellaria alveolata and Phragmatopoma caudata. The aim of this study is to describe and compare the inter- and the intraspecific variability in the main biomineral components of cement at local, regional and continental scales. Scanning Electron Microscopy confirms an identical structure of the cement within species of Sabellariidae in Europe and America. Electron Probe Micro-Analysis (EPMA) confirms the presence of calcium, phosphorus, and magnesium plus traces of manganese in all cements, with varying concentrations of these elements at different locations for the same species or for different species at the same location. Finally, our dataset is compared with previous studies from literature.

International audience; According to a recent demographic survey, the population structure of Pectinaria koreni might fit a source-sink metapopulation model at least at a regional scale. Spatial and temporal genetic structure of the populations present in the Baie de Seine (eastern Baie de Seine and Baie des Veys) was assessed using four highly polymorphic microsatellite loci which have revealed strong intra-locality genetic diversity. In the eastern Baie de Seine, both temporal (1994-1996) and spatial (1994) genetic differentiation were relatively low but significantly different from zero despite a 15-day dispersing larval stage. Such structures may be explained by the settlement of larvae from different gene pools and differing recruitment histories among sites within the eastern Baie de Seine. At a larger scale, similar levels of spatial differentiation were observed in 1999 between the eastern Baie de Seine and the Baie des Veys. The lack of any significant differences in gene diversity and allelic richness rules out a source-sink functioning at the scale of our study. The present paper provides further knowledge on the population dynamics of a univoltine species and its persistence in a highly dispersive environment via a shifting spatial mosaic.