Biomass and mass balance isotope content of mussel seep populations

Abstract

Cold seep mussels, Bathymodiolus childressi, are common cold seep constituents that form large populations at upper continental slope (500-1000 m) cold seep sites in the Northern Gulf of Mexico. These mussels utilize methane present through symbiotic relationships with methanotrophic bacteria. This study uses a coupled isotope technique to determine the relative incorporation of respiratory carbon in the shell as a measure of the availability of methane between different seep sites. This method indicates a higher abundance of methane at the Brine Pool site than at the Bush Hill site which appears significantly more resource limited and that changes in methane availability can arise on both decadal and yearly time scales. The method has implications for determining long term methane abundances in both archived samples and disarticulated shells with a relative minimum of additional cost. Additionally, analysis of the means and standard deviations of & #948;15N, & #948;13C, and & #948;34S of mussel soft tissue can provide indications of the presence and variability of those resources across time and space. These analyses indicate the utilization of unique resources, specifically ammonium and thermogenic or biogenic methane, between the two sites. The difference in resources at each site can support further development of unique mixing models for each site that utilize the resources present and not a single blanket analysis using similar resource values for all cold seep sites.