Vesicomyid Clams Alter Biogeochemical Processes at Pacific Methane Seeps
Abstract
There exists a close relationship between fluid flow, biogeochemistry, and biota in seep sediments. Upwelling of methane and sulfide-rich fluids supports abundant macrofauna species harboring thiotrophic or methanotrophic symbionts. Variations in fluid flow, thus supply of methane and sulfide, are considered key factors controlling benthic communities. Vesicomyid clams harbor thiotrophic symbionts in their gills, which are supplied with oxygen from the surrounding water and hydrogen sulfide from the sediment. The clams are capable of extending their foot into the sediment to tap sulfide sources in deeper layers, consequently affecting water-sediment solute exchange. Because seep fluids are generally depleted in sulfate compared to seawater, this bioturbation activity may enhance the supply of sulfate to otherwise sulfate-limited sediments, thus boosting microbial activity of sulfate reduction (SR) coupled to anaerobic oxidation of methane (AOM). The goal of this study was to investigate the activity of three species of vesicomyid clams ( Calyptogena pacifica, C. kilmeri, C. gigas) from three methane seep habitats (Eel River Basin, Hydrate Ridge, Monterey Bay Canyon) and to evaluate its effect on biogeochemical processes. Sediment cores and clams were collected using the submersible Alvin or the ROV Jason, during three cruises with the R/V Atlantis in July and October 2006 and July 2007 (AT 15-7, AT 15-11, and AT 15-20). We performed high-resolution measurements of geochemical gradients in intact sediment cores using microsensors (O2, H2S, pH, redox potential). The cores were then sliced (1 cm intervals) for detailed chemical and microbiological analyses. Parallel cores were used to determine microbial activity (AOM, SR) with radioactive tracers. For detailed laboratory investigations, clams were kept in narrow aquaria (15 cm x 20 cm x 5 cm) in the ship's cold room. The front of the aquaria was perforated with holes at 1 cm resolution. These silicone-filled holes served as sampling ports or for direct microsensor measurements. Vertical and horizontal microprofiles were measured, pore water samples were extracted, and small sediment cores were taken along the length of the aquaria for microbial rate measurements and chemical and microbiological analyses. We documented different bioturbation activity for the three species of vesicomyid clam that related to distinct geochemical gradients and differences in microbial activity. Sulfate reduction, thus sulfide production, was significantly enhanced in the presence of clams compared to the control.
- Publication:
-
AGU Fall Meeting Abstracts
- Pub Date:
- December 2007
- Bibcode:
- 2007AGUFM.B43E1649B
- Keywords:
-
- 0456 Life in extreme environments;
- 0465 Microbiology: ecology;
- physiology and genomics (4840);
- 0471 Oxidation/reduction reactions (4851);
- 0488 Sulfur cycling;
- 4804 Benthic processes;
- benthos (0408)