Fatty Acids in Tubeworm-Associated Sediments in the Gulf of Mexico

Vestimentiferan tubeworms in the Gulf of Mexico are a visible and unique component of the macrofaunal community. Tubeworm distribution is controlled by microbially produced sulfide. Sulfide is absorbed by tubeworms from sediments through posterior extensions of their bodies, euphemistically called "roots." Diffusion of seawater sulfate into the sediments may, on its own, provide insufficient sulfate for sulfate-reducing bacteria to supply the sulfide required by a large, mature tubeworm aggregation. Tubeworms potentially overcome this shortfall by actively facilitating sulfate migration into anoxic sediments, possibly by excreting sulfate through their roots. Microbial biomass production would be stimulated by increased sulfate availability. In the summer of 2000, ten push cores were collected in close proximity to tubeworm aggregations using the submersible Johnson Sea-Link. Pore waters were analyzed for sulfur stable isotopes, and fatty acids from residual sediments were used to characterize the sediment microbial community. Lipid analysis shows a quantitive correlation between known bacterial biomarkers and the general biomass markers, hexadecanoate (16:0) and tetradecanoate (14:0). This correlation suggests that the extracted material is largely bacterial. Additionally, good correlations between biomarkers for sulfate-reducing bacteria, 13-methyltetradecanoate (ai-15:0) and 15-methylhexadecanoate (i-17:0), with hexadecanoate suggests microbial community composition does not change with respect to proximity of the tubeworm aggregation. Finally, microbial activity is largely controlled by labile organic matter inputs. Lipid distributions do not suggest tubeworms irrigate sediments with sulfate; however, this may be indicative of the small scale of sulfate diffusion from tubeworm roots rather than an absence of irrigation.