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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.dsr.2006.01.007 Byline: Christian Levesque (a)(b)(c), S. Kim Juniper (a)(b), Helene Limen (a) Keywords: Food web; Environmental variability; Hydrothermal vents; Stable isotopes; Northeast Pacific; Juan de Fuca Ridge; Axial Volcano Abstract: Deep-sea hydrothermal vents are characterized by steep spatial gradients and high temporal variability in habitat conditions. This leads to the organization of species distribution along spatial habitat gradients, which may constrain food resource utilization and food web structure. We conducted a stable-isotope-based study to test the hypothesis that food resource utilization is constrained by spatial habitat variability at diffuse hydrothermal vents on Axial Volcano, Northeast Pacific. Our study included the ten most biomass-prominent species and considered the temporal change in food web structure at recently created vent sites during three consecutive years. We related species average stable isotopic composition to their position between the center and the periphery of vent sites, using previously published data. Species spread widely along the [delta].sup.13C axis, and showed a small variability in [delta].sup.15N. This indicates that most species partition food resources between isotopically different carbon sources, and that they are not organized along predator-prey trophic chains. Particulate organic matter (POM) stable isotopic composition from a concomitant study corresponds to the signature of the expected diet for most organisms. Species average [delta].sup.13C was significantly correlated to their relative position between the center and the periphery of vent sites. We relate this spatial variability in species isotopic composition to variability in the isotopic signature of both dissolved inorganic carbon (DIC) and POM. This spatial isotopic signal of consumers reveals the spatial structuring of food (POM) production and its consumption by the fauna. Accrual of species during the development of diffuse sites increased the inter-specific spread in [delta].sup.13C, but did not increase the range in [delta].sup.15N. Our results show that the spatial organization of species distribution results in a fragmented food web where species partition POM food resources according to their position in space. Shaping of species distribution by habitat gradients therefore constrains food web structure and the occurrence of predator-prey and competitive interactions. Author Affiliation: (a) GEOTOP Centre, Universite du Quebec a Montreal, CP 8888, Succursale Centre-Ville, Montreal, Quebec Canada H3C 3P8 (b) Departement des sciences biologiques, Universite du Quebec a Montreal, CP 8888, Succursale Centre-Ville, Montreal, Quebec Canada H3C 3P8 (c) Monterey Bay Aquarium Research Institute, 7700 Sandholdt Road, Moss Landing, CA 95039, USA Article History: Received 24 March 2005; Revised 20 January 2006; Accepted 27 January 2006

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