Variations in seep mussel bed communities along physical and chemical environmental gradients

This study examined the faunal communities associated with beds of the hydrocarbon seep mussel Bathymodiolus childressi in the Gulf of Mexico and the relationships between these communities and local environmental characteristics. Mussels, their associated fauna and accompanying water chemistry parameters were collected at 17 locations across 4 hydrocarbon seep sites. A total of 19 species, mostly seep endemics, were identified. Species richness and fauna density were significantly and negatively correlated with methane concentration and were significantly and positively correlated with oxygen concentration. Canonical Correspondence Analysis (CCA) separated polychaetes, alvinocarid shrimp and gastropods along gradients of methane and oxygen concentrations. Polychaetes and alvinocarid shrimp tended towards lower oxygen and higher methane concentrations and gastropods tended towards higher oxygen and lower methane. The larger-sized predaceous gastropods and decapods were associated with lower sulfide and higher oxygen concentrations. The proportion of the community comprising of endemic species was significantly and positively correlated with mussel biomass and shell surface area. Other measures of habitat complexity (mussel density, shell surface area and biomass) explained little of the variation in the associated faunal communities. The results suggest that oxygen and methane availabilities play a substantial role in structuring these communities with several dominant seep heterotrophs partitioning resources among different microenvironments.