Chemoautotrophic food availability influences copepod assemblage composition at deep hydrothermal vent sites within sea knoll calderas in the northwestern Pacific

Meiofaunal taxonomic compositions between adjacent hydrothermal vents located in deep-sea volcanic calderas are predicted to differ more than between vents on mid-ocean ridges, as caldera walls are expected to act as barriers to dispersal. However, taxonomic information on hydrothermal vent meiofauna in volcanic calderas is limited. Here, we investigated the spatial variation in benthic copepod taxonomic composition and its association with selected environmental parameters, including food resources, on chimney structures of vent sites in the calderas of 3 neighboring sea knolls (Bayonnaise Knoll, Myojin Knoll, and Myojin-sho Caldera) on the Izu-Ogasawara Arc, northwestern Pacific Ocean. Spatial differences in order-level copepod taxonomic composition were significantly correlated with differences in stable carbon isotopic signatures (delta C-13) of organic matter in the detritus of vent sites; these values reflected the relative contribution of carbon substrates in the vent fluid. The availability of vent chemoautotrophic carbon may have been the primary and a common factor controlling copepod assemblage composition at high taxonomic levels around the hydrothermal vents on these 3 knolls. We also found a bathymetric pattern in the abundance of Stygiopontius senokuchiae, a species of copepod in Dirivultidae specific to vents. While this species dominated Bayonnaise Knoll and Myojin-sho Caldera (depth of 740-800 m), their densities were lower in the deeper Myojin Knoll (depth 1250-1320 m). Our results suggest that the caldera wall may not be a significant dispersal barrier for vent copepods; instead, water depth and chemoautotrophic food resource availability are likely the key factors controlling vent copepod distributions.