Correlation of the siboglinid (Annelida: Siboglinidae) distribution to higher concentrations of hydrocarbons in the Sea of Okhotsk

Abstract Siboglinids are a characteristic feature of reducing environments. More than 75% of all siboglinids were found in the Sea of Okhotsk at a depth of less than 400 m, while some species are known to inhabit the abyssal depth in other regions. Among the six species of siboglinids encountered in the Sea of Okhotsk, only two are widespread: Siboglinum caulleryi and Oligobrachia dogieli. A significant number of all findings belong to the area where, according to geological data, the methane concentration varies between 0.22 and 4.46*109 nmol/kg. There is a vast territory in the central part of the Sea of Okhotsk that is not inhabited by siboglinids and is characterized by minimum methane concentration values. Thus, data on the Sea of Okhotsk indicate that siboglinids are related to sites of methane seepage.