Franz Josef Land's macrobenthos: Record-high wet biomass values on the Eurasian Arctic shelf

To address critical gaps in our understanding of benthic ecosystems in the Arctic, this study sampled macrobenthos across the Franz Josef Land archipelago during the 2020-2021 field campaign. In total, 65 benthic grab stations were analysed, and 29 stations assessed for macrofauna with ROV video recordings. The stations, located in shallow waters ranging from 11 to 176 metres depth, covered a substantial portion of the archipelago. This data set is by far the largest published on the area’s benthic biodiversity since the 1970s. From 143,577 specimens of macrobenthos analysed, a total of 333 taxa (257 species) were identified. Most stations were dominated by three overlapping macrobenthic assemblages: (1) S trongylocentrotus sp. – Ophiura robusta , (2) Hiatella arctica – O. robusta and (3) Astarte spp. Exceptionally high biomass of macrobenthos was noted, reaching 3.9 kg m -2 , possibly the highest documented for the Eurasian Arctic shelf. This finding suggests a greater potential for carbon sequestration in this region than previously understood. High spatial heterogeneity and high benthic biomass can be attributed to the complex hydrodynamic regime and abundance of hard substrates in these shallow waters, which also makes the area attractive for benthic predators, in particular the Atlantic walrus ( Odobenus rosmarus rosmarus ).