Benthic Fauna on Ridges and Abyssal Plains in the Central Arctic Ocean: Baseline Data for Future Management

Abstract

The benthos of the Central Arctic Ocean (CAO) abyss is an underworld yet to be thoroughly and systematically understood. Although 50% of the Arctic is deep sea, most research has been focused on the continental shelves and the water column. This is largely because research in the CAO is challenging, especially due to the ocean being ice-covered. Yet, today, anthropogenic pressures on the CAO are increasing with the ice cover declining, improving access for human activities. Since intense mining debates are occurring just south of this research area, it is urgent to compile information about benthic diversity also across the CAO. Existing data of benthic fauna of the CAO from decades of research provide valuable insights of benthic distribution and biodiversity in the Arctic deep-sea and substantial habitat diversity is now recognized, but spatial distribution and taxonomic knowledge gaps remain. Additional sampling and a pan-Arctic perspective are therefore essential for analyzing habitat-specific biodiversity, especially in areas that could be of interest for human use. This study is built on both a previously compiled dataset of benthic taxa records (depths >500 m), and new meiofauna samples to investigate patterns of benthic community composition and abundance compared between deep-sea ridges and deep-sea basins in the CAO from Fram Strait northwards. My findings reveal that ridges have generally higher benthic abundance for both macro- and meiofauna, yet differences were not statistically significant. In the meiofauna, nematodes contributed most to abundance in soft sediment habitats of both ridges and basins, with >74% of total abundance in both habitats. Additionally, the similarities in benthic community structure across the CAO rather resemble geographical proximity, suggesting that neighboring regions – whether ridges or basins – generally have more benthic biota in common than similar geomorphological features do. A large fraction of benthic taxa from soft sediments at both ridges and basins that currently have only been recorded from a given ridge or basin of the CAO do also occur in other deep-sea areas outside the CAO. However, local habitat variations within ridges are recognized as a source of benthic faunal dissimilarity. Specifically, the presence of a wide range of geomorphological features (e. g. hydrothermal vents and seamounts) caused largely non-overlapping species presence among different habitats within the Gakkel Ridge, suggesting that ridge regions potentially possess benthic fauna that are not found elsewhere. This is suspected because most seamounts and vents in the CAO remain unmapped, and perhaps house more undiscovered fauna. My study highlights the need for increased research efforts to develop baseline data of ridge and basin ecosystems in the CAO. Such research will critically improve the statistical power needed to assess to what extent ridge habitat heterogeneity creates unique benthic biodiversity. It is essential to attain sufficient understanding of the CAO deep-sea benthos before potential anthropogenic activities occur in these understudied ecosystems.