Methane seep community of the Hakon Mosby mud volcano (the Norwegian Sea): composition and trophic aspects

The H (a) over circle kon Mosby mud volcano (the Norwegian Sea, depth c. 1250 m) was studied in July 1998 by a joint Russian-Gennan-USA-Norwegian expedition on the 40th cruise of the RV Akademik Mstislav Keldysh using the two Mir submersibles. The benthic community is dominated by two species of symbiotrophic pogonophores, Sclerolinum contortum (more abundant) and Oligobrachia haakonmosbiensis. The biomass of S. contortum reaches at least 435 g m(-2); for O. haakonmosbiensis the value is 350 g m(-2). Different benthic organisms form associations with each species of pogonophore. The total list of known benthic fauna includes 46 species. A zoareid fish, Lycodes squamiventer, is a common member of the benthic, community. Bacterial mats are found over an extensive part of the crater. The background benthic community is much poorer and is dominated by ophiuroids (Ophiocten gracilis, Ophiopleura borealis). Pycnogonids (Collossendeis proboscidea), buccinid gastropods and asteroids are also present. Stable carbon isotope data showed significant depletion of C-13 in both species of pogonophores: in S. contortuin delta(13)C was up to -48.3parts per thousand, in O. haakonmosbiensis the value varied from -51.1 to -56.1parts per thousand. It can be suggested that the methane carbon contributes to the nutrition of the pogonophoran O. haakonmosbisensis. Carbon isotopes also revealed incorporation of non-photosynthetic carbon into local trophic webs: delta(13)C in Metacaprella horrida (amphipod) showed -44.9parts per thousand, in the tube-dwelling polychaete (Amphinomidae) -40.6parts per thousand. In the bacterial mat delta(13)C varied from -17.6 to -53.0.