Influence of seep emission on the non-symbiont-bearing fauna and vagrant species at an active giant pockmark in the Gulf of Guinea (Congo-Angola margin)
|Author(s)||Olu Karine1, Caprais Jean-Claude1, Galeron Joelle1, Causse R.2, Von Cosel R.3, Budzinski H.4, Le Menach K.4, Le Roux C.5, Levache D.6, Khripounoff Alexis1, Sibuet Myriam1|
|Affiliation(s)||1 : IFREMER, Ctr Brest, Dept Etud Ecosyst Profonds, F-29280 Plouzane, France.
2 : Museum Natl Hist Nat, BOME DMPA, UMR 5178, F-75231 Paris 05, France.
3 : Museum Natl Hist Nat, USM Taxon & Collect 602, F-75231 Paris 05, France.
4 : Univ Bordeaux, CNRS, ISM LPTC, UMR 5255, F-33405 Talence, France.
5 : UPMC, Stn Biol Roscoff, CNRS, UMR 7144, F-29682 Roscoff, France.
6 : TOTAL Explorat Prod, F-64018 Pau, France.
|Source||Deep Sea Research Part II: Topical Studies in Oceanography (0967-0645) (Elsevier), 2009-11 , Vol. 56 , N. 23 , P. 2380-2393|
|WOS© Times Cited||40|
|Keyword(s)||Congo Angola margin, Atlantic Equatorial African margin, Vagrant species, Isotopic signature, Megafauna, Cold seep|
|Abstract||Detailed surveying with an ROV found that a dense and diverse cold-seep community colonises a giant pockmark located at 3200 m depth, 8 km north from the deep Congo channel. Several types of assemblages, either dominated by Mytilidae and Vesicomyidae bivalves or Siboglinidae polychaetes, are distributed on the 800-m diameter active area. The site is characterised by a most active central zone in a depression with abundant carbonate concretions and high methane fluxes where high-density clusters of mussels and siboglinids dominate. In contrast, the peripheral zones display large fields of dead and live vesicomyids on soft sediment, with a lower mean density and lower methane concentration in seawater. The associated megafauna includes Alvinocarididae shrimps, echinoids, holothurians of the family Synaptidae, several species of gastropods, two species of galatheids, and Zoarcidae and Ophidiidae fishes. Multivariate analyses of video transect data show that the distribution of these major megafauna species at the pockmark scale is influenced by the habitat heterogeneity due to fluid or gas emission, occurrence of hydrates, substratum variability and by the presence of large symbiont-bearing species. Several assemblages dominated either by mytilids, vesicomyids, or siboglinids have been sampled for megafauna densities and biomass estimations and stable isotope measurements (delta C-13 and delta N-15) of dominant species and food sources. The highest estimates of megafauna densities have been obtained in mytilid beds. According to their stable isotopes values, non-symbiont-bearing species mainly rely on chemosynthesis-originated carbon, either as primary consumers of chemoautotrophic microorganisms, or at higher trophic level recycling organic matter, or relying on bivalve and tubeworm production. Most of them likely feed on different sources like shrimps, but differences according to habitat have been evidenced. Carbon and nitrogen isotope ratios of galatheids and benthic or benthopelagic fishes captured by trawls at increasing distances from the pockmark provide evidence of the high variability in the proportion of chemosynthesis-originated carbon in their diet, from 15% to 38%, according to the species captured as far as 4 km to the site.|