A paradox resolved: Sulfide acquisition by roots of seep tubeworms sustains net chemoautotrophy

Vestimentiferan tubeworms, symbiotic with sulfur-oxidizing chemoautotrophic bacteria, dominate many cold-seep sites in the Gulf of Mexico. The most ab undant vestimentiferan species at these sites, Lamellibrachia cf. luymesi, grows quite slowly to lengths exceeding 2 meters and lives in excess of 170 -250 years. L. cf. luymesi can grow a posterior extension of its tube and t issue, termed a "root," down into sulfidic sediments below its point of ori ginal attachment. This extension can be longer than the anterior portion of the animal. Here we show, using methods optimized for detection of hydroge n sulfide down to 0.1 muM in seawater, that hydrogen sulfide was never dete cted around the plumes of large cold-seep vestimentiferans and rarely detec table only around the bases of mature aggregations. Respiration experiments , which exposed the root portions of L. cf. luymesi to sulfide concentratio ns between 51-561 muM, demonstrate that L. cf. luymesi use their roots as a respiratory surface to acquire sulfide at an average rate of 4.1 mu mol.g( -1).h(-1). Net dissolved inorganic carbon uptake across the plume of the tu beworms was shown to occur in response to exposure of the posterior (root) portion of the worms to sulfide, demonstrating that sulfide acquisition by roots of the seep vestimentiferan L. cf. luymesi can be sufficient to fuel net autotrophic total dissolved inorganic carbon uptake.