Stable carbon, nitrogen, and sulfur isotope composition of Oligobrachia haakonmosbiensis Smirnov, 2000 (Annelida: Siboglinidae) from the shallow-water Laptev Sea shelf

Cold methane seeps create suitable habitat conditions for chemosymbiotic frenulate tubeworms, one of the groups of the family Siboglinidae Caullery, 1914 that can form extensive aggregations at seeps at the shelf of the Arctic seas. The present study provides the first data on the ratio of natural stable C, N, and S isotopes in tissues of the siboglinid tubeworm Oligobrachia haakonmosbiensis found in methane seep fields on the Laptev Sea shelf. Values of delta 13C, delta 15N, and delta 34S for various body parts, such as cephalic and abdominal regions, tissues, whole worms with their tubes, and also worms and tubes separated, fixed in 96% ethanol, have been obtained for O. haakonmosbiensis. The lowest isotopic composition values were recorded from bodies of O. haakonmosbiensis with their tubes collected in the coastal zone at a depth of 25 m (delta 13C = -72.7 +/- 1.9%o; delta 15N = -10.9 +/- 1.2%o; and delta 34S = -28.1 +/- 1.9%o). Such low values are suggested to be associated mainly with large amounts of dissolved organic matter near the Lena River estuary. Our analysis of stable C, N, and S isotopes of O. haakonmosbiensis from the Laptev Sea has shown that the major energy source for symbiotic bacteria of this tubeworm species is hydrogen sulfide.