Filling knowledge gaps in Arctic marine biodiversity: Environment, plankton, and benthos of Franz Josef Land, Barents Sea.

Franz Josef Land (FJL) is a remote archipelago that has become more accessible for large-scale studies due to recent warming. This paper summarizes recent survey findings on oceanography, climate, plankton, and benthic communities conducted in FJL. Cold Arctic waters predominantly affect FJL, but an increased inflow of warmer Atlantic water has been observed in recent decades. The bacterioplankton in FJL is mainly comprised of ultra-small bacterial cells, which make up to 60% of the biomass. Phytoplankton are predominantly composed of cells smaller than 20 μm, with the greatest concentrations found above the pycnocline. The population of larger microalgae ranges from 4.5 to 1250 thousand cells L⁻¹, with dinoflagellates occupying the euphotic zone, Dinobryon being the most abundant species in the thermocline, and spore-bearing cells of Chaetoceros diatoms dominating in the deepest region. Summer zooplankton comprise large Calanus copepods, smaller copepods, and meroplankton, with an average dry biomass of 114–391 mg m⁻³. The community structure varies mainly based on water temperature and phytoplankton density, with greater biomasses found in colder offshore waters. August represents the breeding season for plankton populations. The local benthic fauna is diverse and displays high species abundance (3370 ind. m⁻²) and wet biomass (428 g m⁻²). There is a distinct vertical stratification in the benthic community structure, evidenced by a consistent decline in both abundance and biomass with increasing depth. The trophic structure is predominantly influenced by food availability, sediments, and currents. The trend of borealization in the Barents Sea biota is supported by recent distribution records of certain boreal benthic species and increased abundances of typical Atlantic zooplankton species. The results of our study establish a foundational dataset to aid in ongoing scientific inquiry, preservation efforts, and strategic decision-making with regards to the natural resources of the FJL region. • The area has a complex oceanography and is influenced mainly by Arctic Water. • Clear spatial and vertical patterns are common in the local biota. • Plankton abundance and biomass peak in August. • Benthic fauna shows high species diversity, abundance, and biomass. • Warming has led to increased taxa abundances and borealization of the fauna. [ABSTRACT FROM AUTHOR]