Ocean Floor Observation and Bathymetry System image analyses of Vestnesa Ridge methane seepage collected during expeditions MSM108, PS136 and PS143/1 in 2022-2024

The Vestnesa Ridge at 79 degree_north in the Arctic Fram Strait is known for sub-surface methane hydrate reservoirs and numerous gas emitting pockmarks, with associated microbial and faunal communities on its eastern flank. Over three consecutive years three expeditions to the LTER (Long-Term Ecological Research) observatory HAUSGARTEN took place: MSM108 (2022), PS136 (2023) and PS143/1 (2024). During these expeditions, the towed Ocean Floor Observation and Bathymetry System (OFOBS) was used to investigate active methane seepage on the north-western flank of the Vestnesa Ridge in water depths of 1200 to 1375 m. In-situ images were collected by the OFOBS at methane seep sites by Autun Purser.
Here we report the first faunal abundance description of the discovered active methane seep field. In-situ image analyses of the methane seep field and its active and inactive areas showed a regional community comprising 47 megafaunal taxa. The presence of obligate seep-associated faunal taxa, such as the tube-building siboglinid polychaetes and oligochaetes were interpreted as indicative of active methane seepage in the area. The most frequent taxon observed, ophiuroids in the genus Ophiocten Lutken, 1855, occurred in high densities with up to 80 ind. per m2 in inactive areas but was absent from the seafloor closer than a few meters from bacterial mat or tubeworm forests.
Katrin Linse analysed the in-situ images for seafloor cover and faunal abundances. Maximilian Schrade supported data analyses in Excel. Katrin Linse identified faunal morphotaxa and assigned labels to new seen taxa following the taxon codes established by Hemmateenejad et al. (2025b).

The contribution of KL was supported by the BIOPOLE National Capability Multicentre Round 2 funding from the Natural Environment Research Council (grant no. NE/W004933/1). MS is funded by the Biodiverse Anthropocene Progamme (ANTS) and the Finnish Cultural Foundation. AP was supported by grant no. AWI_PS136_01 and AWI_PS143/1_1.