Modification of sediment geochemistry by the hydrocarbon seep tubeworm Lamellibrachia luymesi: A combined empirical and modeling approach

The sulfide-oxidizing symbiotic tubeworm Lamellibrachia luymesi is a dominant member of deep-sea hydrocarbon seep ecosystems on the Gulf of Mexico seafloor. This tubeworm forms large aggregations that can live for centuries and provide habitat for an assortment of associated fauna. Previous studies have suggested that persistence of these tubeworms for such long time periods is contingent upon their ability to supply sediments with sulfate. To examine this hypothesis, we characterized the tubeworm’s geochemical environment using pore water peepers and compared the measured depth profiles with those predicted by a sulfur diffusion–reaction–supply model. We found a large range of sulfide concentrations in the tubeworm habitat, indicating that this species can live under conditions of both high and low sulfide availability. In sediments rich in hydrocarbons, we found compelling evidence that tubeworms enhance microbial sulfide production, likely through a combination of sulfide uptake and sulfate release through their root-like structures buried in the sediment. Our in situ empirical data combined with the results of the geochemical model corroborate previous physiological studies that indicate that tubeworms release between 70% and 90% of the sulfate produced during sulfide oxidation by their symbionts across their roots into the surrounding sediment. In sediments low in hydrocarbon content, sulfide production is hydrocarbon-limited rather than sulfate-limited, and our model predicts that tubeworm growth could be limited by low sulfide availability.