|Ecology of whale falls at the deep-sea floor|
Smith, C.R.; Baco, A.R. (2003). Ecology of whale falls at the deep-sea floor. Oceanogr. Mar. Biol. Ann. Rev. 41: 311-354
In: Oceanography and Marine Biology: An Annual Review. Aberdeen University Press/Allen & Unwin: London. ISSN 0078-3218, more
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The falls of large whales (30-160t adult body weight) yield massive pulses of labile organic matter to the deep-sea floor. While scientists have long speculated on the ecological roles of such concentrated food inputs, observations have accumulated since the 1850s to suggest that deep-sea whale falls support a widespread, characteristic fauna. Interest in whalefall ecology heightened with the discovery in 1989 of a chemoautotrophic assemblage on a whale skeleton in the northeast Pacific; related communities were soon reported from whale falls in other bathyal and abyssal Pacific and Atlantic sites, and from 30 my a (million years ago) in the northeast Pacific fossil record. Recent time-series studies of natural and implanted deepsea whale falls off California, USA indicate that bathyal carcasses pass through at least three successional stages: 1) a mobile-scavenger stage lasting months to years, during which aggregations of sleeper sharks, hagfish, rat-tails and invertebrate scavengers remove whale soft tissue at high rates (40-60kgd-1); 2) an enrichment opportunist stage (duration of months to years) during which organically enriched sediments and exposed bones are colonised by dense assemblages (up to 40000m-2) of opportunistic polychaetes and crustaceans; 3) a sulphophilic ("or sulphur-loving") stage lasting for decades, during which a large, species-rich, trophically complex assemblage lives on the skeleton as it emits sulphide from anaerobic breakdown of bone lipids; this stage includes a chemoautotrophic component deriving nutrition from sulphur-oxidising bacteria. Local species diversity on large whale skeletons during the sulphophilic stage (mean of 185 macrofaunal species) is higher than in any other deep-sea hard substratum community. Global species richness on whale falls (407 species) is also high compared with cold seeps and rivals that of hydrothermal vents, even though whale-fall habitats are very poorly sampled. Population-level calculations suggest that whale falls are relatively common on the deep-sea floor, potentially allowing macrofaunal species to specialise on these habitat islands; to date, 21 macrofaunal species are known only from whale falls and may be whale-fall specialists. Nonetheless, whale falls also share 11 species with hydrothermal vents and 20 species with cold seeps, and thus may provide dispersal stepping stones for a subset of the vent and seep faunas. Molecular evidence also suggests that whale falls provided evolutionary stepping stones for the bathymodiolin mussel lineage to move down the continental slope and into deep-sea vent and seep habitats. Finally, whale-fall bacteria have proven to be a novel source of cold-adapted enzymes of potential utility in cold-water detergents. Despite these scientific advantages, major gaps persist in our understanding of the microbial processes, reproductive strategies, population genetics, and biogeography of whale-fall communities.