Introduction : Ecological studies at hydrothermal vents often emphasize the importance of spatio-temporal heterogeneity in organism distribution within individual sites (Sarrazin et al., 1997) but the relative roles of environmental conditions, biological interactions and/or random processes in structuring hydrothermal communities remain poorly understood (Sarrazin & Juniper, 1999). A model of community succession developed by Sarrazin et al. (1997, 1999) proposed that a series of faunal assemblages form a mosaic community that colonizes hydrothermal edifices of the northeast Pacific vents. This paper further develops the succession model by incorporating new observations. At the core of the model is the recognition of distinct faunal assemblages that characterize each of 6 (occasionally 3, see below) successional stages. Assemblage I is the first to colonize newly-formed chimney surfaces and is principally composed of the alvinellid polychaete Paralvinella sulfincola Desbruyeres & Laubier, 1993 and the copepod Stygiopontius quadrispinosus Humes, 1987. The formation of a marcasite (FeS2) crust beneath P. sulfincola tubes facilitates colonization of the substratum by the less tolerant alvinellid Paralvinella palmiformis Desbruyeres & Laubier, 1986, forming Assemblage II. As the substratum stabilizes and flow intensity decreases, other macrofaunal species progressively appear. Assemblage HI is dominated by P. palmiformis, high gastropod densities (Lepetodrilus fucensis McLean, 1988, Provanna variabilis Waren & Bouchet, 1986 and Depressigyra globulus War6n & Bouchet, 1989), and a few polynoid polychaetes. These species are joined by the vestimentifera Ridgeia piscesae Jones, 1985 in Assemblage IV, and the growth of R. piscesae leads to the complex and diverse Assemblage V (low-flow). Assemblage VI represents a senescent phase where R. piscesae gradually die and associated species disappear. The presence of scavengers and detritivores in Assemblage VI may be related to decreased hydrothermal flux and to the accumulation of detrital organic matter. Occasionally, another mature vestimentiferan assemblage (Assemblage V high-flow) can develop directly from Assemblage I or II under intense fluid flow rates. As in Assemblage V low-flow, Assemblage V high-flow is dominated by Ridgeia piscesae but gastropods and polynoids are rare and species diversity is considerably lower (Sarrazin & Juniper, 1999). These assemblages are typical of hydrothermal edifices throughout the northeast Pacific spreading ridges. Changes from Assemblages II through IV are mostly driven by reduction in hydrothermal fluid flow, while between Assemblage IV and V low-flow, biological processes such as tube worm growth initiate succession. The influence of environmental factors, such as H2S concentrations, fluid flow intensity and substratum type, on species distribution was confirmed from in situ measurements on two Juan de Fuca Ridge sulphide edifices by Sarrazin et al. (1999). Their data also indicated a relationship between flow intensity and mineralization of the substratum, suggesting that different areas of the edifice are progressively mineralized in parallel with faunal succession. Other habitat factors such as dissolved oxygen concentration and nutritional resources were also proposed to influence species distribution. Here we build upon the Sarrazin et al. (1999) model by incorporating preliminary analyses of substratum mineralogy and porosity, and temperature time series within different faunal assemblages. We also include a first consideration of food availability for deposit and suspension feeding invertebrates by biochemical characterization of particulate organic matter sampled from two early successional assemblages (II and V high-flow).