Macrofaunal morphospecies from hard-substrate methane seep samples collected on R/V Atlantis cruise AT50-12, Southern California Borderland from July 2023 (Methanosphere project)

This dataset documents macrofaunal communities associated with hard substrates (carbonate, phosphorite, and wood) collected from methane seeps in the Southern California Borderland. Samples were obtained with the HOV Alvin during R/V Atlantis cruise AT50-12 (July 16–28, 2023). The dataset provides morphospecies-level counts of macrofauna together with collection and sample metadata.