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Craig R. Smith and Amy R. Baco
Department of Oceanography, University of Hawaii, 1000 Pope Road, Honolulu, HI, 96822, USA
Chemoautotrophic communities on lipid-rich whale skeletons are known from a total of 8 modern sites and 8 fossil sites (up to 30 million years old) in the deep Pacific Ocean. We are using natural and experimentally implanted whale skeletons to study community structure, succession, and vent-seep affinities of whale-fall communities in the northeast Pacific at water depths of 1000 - 2000 m. With ROVs and submersibles, we have thus far sampled whale carcasses of the following ages: 1 wk, 2 wk, 4.5 mo, 3.4 yr, > 4 yr, > 7 yr, and > 11 yr? since arrival at the seafloor. Because of the experimental difficulties of working with dead whales, these carcasses cover a broad range of sizes and occur in a variety of different habitats. Nonetheless, results are consistent with the following successional pattern. (1) An early stage dominated by large mobile scavengers, e.g., hagfish (Epatretus deani), macrourid fish, lithodid crabs and sleeper sharks (Somniosus pacificus?)during which soft tissue is stripped from the skeleton on time scales of months. (2) An intermediate stage lasting months to years(?) in which local sediments are organically enriched, and the infauna dominated by high densities of enrichment respondents such as dorvilleid polychaetes (up to10,000 m-2) and/or large gastropods (e.g., Bittium sp., up to 100 m-2). (3) An advanced sulfophilic stage in which chemoautotrophic bacterial mats, mussels, vesicomyd clams and vestimentiferans utilize sulfide released by anaerobic decay of bone lipids. This advanced stage can persist for > 11 yr on large skeletons. Stable isotope analyses using C-13 and N-15 suggest that this last stage can harbor a broad based food web, including macrofaunal species living solely on chemoautotrophic production (vesicomyid clams), mixotrophs utilizing both endosymbiont-based chemoautotrophy and heterotrophy to obtain carbon (e.g., the mussel Idas washingtonia), bacterial mat grazers (two limpets, an isopod, and possibly a snail) and direct feeders on bone organic material (two limpets).
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