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|Habitat heterogeneity influences cold-seep macrofaunal communities within and among seeps along the Norwegian margin – Part 2: contribution of chemosynthesis and nutritional patterns|Decker, C.; Olu, K. (2012). Habitat heterogeneity influences cold-seep macrofaunal communities within and among seeps along the Norwegian margin – Part 2: contribution of chemosynthesis and nutritional patterns. Mar. Ecol. (Berl.) 33(2): 231-245. http://dx.doi.org/10.1111/j.1439-0485.2011.00486.x
In: Marine Ecology (Berlin). Blackwell: Berlin. ISSN 0173-9565; e-ISSN 1439-0485, meer
Cold-seep; macrofaunal nutrition; methanederived carbon; Norwegian margin; stable isotope analysis
The relative contribution of chemosynthesis in heterotrophic fauna at seeps is known to be influenced by depth and by habitat. Using stable isotopes of carbon and nitrogen, we investigated macro- and megafaunal nutritional patterns in Norwegian margin cold seeps by comparing food webs both among habitats within a seep site and between different sites. The very active Håkon Mosby mud volcano (HMMV) is characterized by geochemical gradients, microbial activity and faunal zonation from the centre to the periphery. The Storegga Slide (600–900 m depth) has pockmarks with patchy less active seeps, and also shows concentric zonation of habitats but at much smaller spatial scale. The dominant carbon source for macrofaunal nutrition in both areas was chemosynthetically fixed and the bulk of organic carbon was derived from sulphur-oxidizing bacteria. In HMMV, food chains were clearly separated according to habitats, with significantly lighter d13C signatures on microbial mats and adjacent sediment (-33.06 to -50.62‰) than in siboglinid fields (-19.83 to -35.03‰). Mixing model outputs revealed that the contribution of methane-derived carbon was small in siboglinid fields (0–17%) but significant (39–61%) in the microbial mats. Moreover, the variability of macrofauna signatures within this later habitat suggests the co-occurrence of two food chains, one based on primary production via methanotrophy and the other via sulphide oxidation. The length of the food chains also varied among habitats, with at least one more trophic level in the siboglinid fields located at the periphery of the volcano. Conversely, in Storrega pockmarks, faunal d13C signatures did not vary among habitats but among species, although separate food chains seem to co-occur. The small size of the seepage areas and their lower fluxes compared to HMMV allow more background species to penetrate the seep area, increasing the range of d15N and the trophic level number. Probably due to the higher flux of photosynthetic particulate organic carbon, the overall chemosynthesis-based carbon contribution in invertebrate nutrition was lower than that in HMMV.
- Macrofauna of the Nordic Margin collected during the Vicking Cruise 2006 and ARK XXII Cruise 2007 and processed by IFREMER