Vertical distributions of megafauna on inactive vent sulfide features correspond to their feeding modes

Abstract

The discovery of inactive hydrothermal vent sulfide features located off the ridge axis in the 9°50'N region of the East Pacific Rise provides an opportunity to investigate knowledge gaps in the distribution and feeding ecology of communities inhabiting this type of deep-sea habitat. Previous seafloor imaging studies indicate that megafaunal taxa on inactive sulfides are not endemic to these features, but their assemblages differ from other deep-sea habitats. I investigated the influence of environmental conditions on megafaunal distributions using highresolution imagery of two inactive sulfide features, Lucky's Mound and Sentry Spire, to determine how taxonomic composition and feeding traits vary with vertical position on the features. A total of 51 morphotypes, each categorized to feeding mode, was identified from three levels of the features (spire, apron, and base) and a section of the surrounding flat oceanic rise. Quantitative image analysis showed that passive suspension feeders were more abundant on the spires of the sulfide features than the base or surrounding rise. Deposit feeders were more abundant on the base of Lucky’s mound and the oceanic rise, than on the spire or apron, but were unexpectedly abundant on the spire of Sentry Spire. These distributions correspond generally to the expected availability of suspended organic particles and detritus on the seafloor that serve, respectively, as food for these two feeding modes, and indicate a potential role for physical attributes of the sulfide feature to influence their faunal assemblages. Distinct differences in community composition between the two inactive sulfide features, however, suggest that other, feature-specific processes, perhaps including local chemoautotrophic production, may also play a role.