Unexpected discovery of a serpentinite‐hosted chemosynthetic ecosystem on Asùt Tesoru Seamount, Mariana Forearc

Chemosynthetic ecosystems powered by microbial primary production are rare ‘hot spots’ of biological activity in the deep-sea characterized dense aggregations specially adapted animal species. Among settings where such systems have been found, serpentinite-hosted seep supported alkaline geofluid particularly understudied with just a few known sites worldwide. Mariana Forearc hosts world's only series active serpentinite mud volcanoes, but communities reported from South Chamorro Seamount large bathymodioline mussels dominate. Here, we report discovery on conical summit Asùt Tesoru Seamount, Forearc. Named ‘Big Blue Seep’, this field features white, likely carbonate crusts inhabited animals, under which fluid seepage could be seen. We confirm 16 species, including typical seep-associated fauna as Desbruyeresia gastropods and Acharax awning-clams. This is surprising previous research expeditions did not notice any sign chemosynthesis-based seamount, although community indeed difficult to spot due lack large-bodied epifauna mussels. The Big Seep adjacent three drill holes made International Ocean Discovery Program expedition 366 (Holes U1496A-C), may impact seepage. Our findings represent second ecosystem associated volcanism, suggestive further other volcanoes.