PIs.: L. Levin, W. Ziebis, R. Lee, K. Halanych

Project Summary
Millimolar H2S concentrations and the near absence of oxygen make methane seep sediments one of the most toxic environments on earth, yet metazoan assemblages persist in such settings. In microbial-mat covered seeps on the upper slopes of the Pacific Northwest, these assemblages are comprised nearly exclusively of dorvilleid polychaetes. At seeps located within the oxygen minimum zone off the Oregon and California margins we have identified up to 17 co-occurring dorvilleid species, including 10 in a single genus. We hypothesize that this annelid group, through exceptional tolerance to low oxygen and high sulfide concentrations, has found a suite of niches which it alone has been able to exploit, and as a result has experienced evolutionary release in the absence of predators and competitors. Here we propose to use this dorvilleid assemblage as a model system with which to investigate how metazoan communities evolve in and adapt to extreme sulfide conditions. Integrated studies of the geochemical environment with dorvilleid ecology and physiology will address mechanisms of niche partitioning and explore how communities are organized under conditions of extreme sulfide stress. Coordinated studies will be made of oxygen and sulfide concentration in sediments, dorvilleid species distributions, reproductive biology, and isotope- and molecular-based diet analyses. We will conduct species-level physiological tests of sulfide tolerance and thiotrophic bacterial activity, and in situ experiments to examine responses to sulfide gradients. Studies of seep dorvilleid phylogeny at several hierarchical levels will determine the evolutionary capabilities of these metazoans to adapt to an extreme environment. By mapping ecological features onto a phylogenetic framework, we will identify correlations among ecology, physiology, life history and evolutionary history that help elucidate the mechanisms of speciation under extreme stress. We anticipate that dorvilleid polychaetes will ultimately provide a superb metazoan model for integrated extremophile research.

Location of studied sites along the Northeast Pacific margin (click to enlarge)

Investigations will be carried out in regions of extensive seepage (~ 500 x 300 m) located at 515-525 m water depth on the northern California continental slope off shore of the Eel River mouth (40° 47.08' N 124° 35.68' W), and on the Oregon margin at Hydrate Ridge (44°40.1'N 125°05.8'W) at 590-800 m. Both areas are located within the eastern Pacific oxygen minimum zone (OMZ) (< 0.2-0.5 ml/l O2). Two cruises with the ALVIN aboard the Atlantis are scheduled off California and Oregon for 2006 to conduct research, deploy and recover colonization experiments. Nighttime operations will include cross-margin sampling of the OMZ via multicorer.