This study investigates the macrofaunal communities associated with authigenic carbonates at methane seeps on the Costa Rica margin, focusing on the role of these substrates in promoting biodiversity. The research highlights the significant contribution of carbonate rocks to macrofaunal diversity and trophic diversity, which are influenced by seepage activity, hydrographic conditions, and habitat type. The macrofauna, dominated by grazing gastropods, polychaetes, crustaceans, cnidarians, and echinoderms, exhibit distinct assemblages on active and inactive carbonates, with higher densities and diversity on active sites. The stable isotope signatures of the fauna and carbonates reveal trophic linkages and resource partitioning among species. The study also compares the macrofaunal communities on carbonates to those in nearby soft-sediment habitats, finding that substrate type exerts a greater influence on macrofaunal composition and diversity than habitat or location. Overall, the research underscores the importance of authigenic carbonates in supporting diverse and adapted macrofaunal assemblages in chemosynthetic ecosystems.This study investigates the macrofaunal communities associated with authigenic carbonates at methane seeps on the Costa Rica margin, focusing on the role of these substrates in promoting biodiversity. The research highlights the significant contribution of carbonate rocks to macrofaunal diversity and trophic diversity, which are influenced by seepage activity, hydrographic conditions, and habitat type. The macrofauna, dominated by grazing gastropods, polychaetes, crustaceans, cnidarians, and echinoderms, exhibit distinct assemblages on active and inactive carbonates, with higher densities and diversity on active sites. The stable isotope signatures of the fauna and carbonates reveal trophic linkages and resource partitioning among species. The study also compares the macrofaunal communities on carbonates to those in nearby soft-sediment habitats, finding that substrate type exerts a greater influence on macrofaunal composition and diversity than habitat or location. Overall, the research underscores the importance of authigenic carbonates in supporting diverse and adapted macrofaunal assemblages in chemosynthetic ecosystems.