Chemosynthetic environments support distinct benthic communities capable of utilizing reduced chemical compounds for nutrition. Hundreds of methane seeps have been documented along the U.S. Atlantic margin (USAM), and detailed investigations at a few seeps have revealed distinct environments containing mussels, microbial mats, authigenic carbonates, and soft sediments. The dominant mussel Bathymodiolus childressi contains methanotrophic endosymbionts but is also capable of filter feeding. We used SIA (δ13C, δ 5N, and δ34S) and an isotope mixing model (MixSIAR) to estimate resource contribution to B. childressi and characterize food webs at two seep sites (Baltimore Seep: 400 m and Norfolk Seep: 1500 m depths) along the USAM, and applied a linear mixed-effects model to explore the role of mussel population density and tissue type in influencing SIA variance.