Unique gastropods dominate the fauna on inactive vent sulfide features in the eastern Pacific

Understanding the extent of habitat adaptation and endemism is essential for assessing resilience to natural and human disturbances. In the deep sea, a habitat of heightened interest is inactive vent sulfide features that form when hydrothermal vent activity ceases, changing the physical and chemical environment and shifting the microbial and animal community. Limited sampling of macrofauna (<1 cm) living on these features has suggested that some invertebrate species may be endemic and uniquely adapted to inactive sulfides. Here, we characterize the macrofaunal community composition across different sulfide rock surface types from two inactive sulfide features near the 9°47-50’N vent field of the East Pacific Rise (EPR). Using macrofauna identification, and image analysis of faunal density, we found a dense macrofaunal community dominated by gastropods. Most of the gastropod species appear uniquely associated with inactive sulfide features on the EPR. Further, the composition, diversity, and density of gastropods varied with rock surface characteristics, suggesting a trophic web driven by rock-based microbial chemosynthesis. As metal-rich inactive sulfide deposits are a target for seafloor mining, this discovery of a unique community highlights the need to better understand this type of fauna and its contribution to functional and taxonomic biodiversity in the world’s oceans. • Unique gastropods dominate a community tightly associated with inactive sulfide features on the East Pacific Rise • Sulfide features are distributed globally, making this ecosystem potentially an important contributor to global biodiversity, taxonomic and functional • This unique fauna is at risk from seafloor mining of metal-rich inactive sulfides