Background Methane seeps support unique benthic ecosystems in the deep sea existing due to chemosynthetic organic matter. In contrast, in shallow waters there is little or no effect of methane seeps on macrofauna. In the present study we focused on the recently described methane discharge area at the northern Laptev Sea shelf. The aim of this work was to describe the shallow-water methane seep macrofauna and to understand whether there are differences in macrobenthic community structure between the methane seep and background areas. Methods Samples of macrofauna were taken during three expeditions of RV Akademik Mstislav Keldysh in 2015, 2017 and 2018 using 0.1 m2 grabs and the Sigsbee trawl. 21 grabs and two trawls in total were taken at two methane seep sites named Oden and C15, located at depths of 60–70 m. For control, three 0.1 m2 grabs were taken in area without methane seepage. Results The abundance of macrofauna was higher at methane seep stations compared to non-seep sites. Cluster analysis revealed five station groups corresponding to control area, Oden site and C15 site (the latter represented by three groups). Taxa responsible for differences among the station groups were mostly widespread Arctic species that were more abundant in samples from methane seep sites. However, high densities of symbiotrophic siboglinids Oligobrachia sp. were found exclusively at methane seep stations. In addition, several species possibly new to science were found at several methane seep stations, including the gastropod Frigidalvania sp. and the polychaete Ophryotrocha sp. The fauna at control stations was represented only by well-known and widespread Arctic taxa. Higher habitat heterogeneity of the C15 site compared to Oden was indicated by the higher number of station groups revealed by cluster analysis and higher species richness in C15 trawl sample. The development of the described communities at the shallow-water methane seeps can be related to pronounced oligotrophic environment on the northern Siberian shelf.
Macrozoobenthic communities provide vital ecosystem services including habitats and foraging resources for other species in all marine ecosystems. Although macrozoobenthos of deeper parts of the �echora �ea ��� �ar� macrozoobenthos of deeper parts of the �echora �ea ��� �ar� ents �ea) have been studied in more detail, there is a lack of research in shallow waters of the �echora �ay. The study area lies within the Nenetsky �tate Nature Reserve, established in 1997, to protect important breeding and moulting grounds of waterfowl. Macrozoobenthos provide key foraging resources for waterfowl in the nature reserve, however, there is a mismatch between ornithological and macrobenthic data. �ight stations were studied along the Russky Zavorot �eninsula in the �echora �ay on a depth of 1.1-1.8 m within the near�shore zone of the Nenetsky �tate Nature Reserve in August 2016. A monodominant community of Limecola balthica with a biomass of 21.31 ± 0.32 g/m 2 and 14 species in total was recorded across the area. The dominant species of the community correspond to those in the community of L. balthica recently described from the central estuarine part of the �echora estuary. A low biomass and poor species richness in the L. balthica community support the earlier published results for the northern part of the bay and indicate the dependence of the community charac� teristics on environmental factors. The paucity of macrozoobenthos in the area is likely attributed to extreme environmental conditions including the following: �1) the water column freezes to the bottom during winter in the shallows of the Pechora estuary or (2) the freshwater flow spreads under the ice, severely impacting salinity. Hence the community is comprised of eurythermal and euryhaline forms and is reduced in biomass. It is unlikely that the shallows of the Russky Zavorot �eninsula play an important role as feeding grounds for benthic preda� tors since a low in biomass barren community of a burrowing mollusc L. balthica does not provide enough forag� ing resources to feed stocks of waterfowl. The L. balthica�community could be used as an indicator of climate changes in the future-it is predicted that a reduction in sea ice volume will improve conditions for growth of L. balthica and may therefore lead to an increased body size and biomass of bivalves in the shallows.
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