Macrozoobenthos of the Pechora Bay in 2020–2021 indicates a likely change of common bivalve molluscs in the Arctic estuary.

The Pechora Bay is a hydrologically and ecologically important area of the Barents Sea but there are still gaps in our knowledge of biodiversity of the area, including macrozoobenthos. In the first half of the twentieth century, the Pechora Bay was noted as a type locality for the bivalve mollusc Portlandia aestuariorum. Only a few surveys of macrozoobenthos have been conducted since and the last work from this area indicated the absence of P. aestuariorum. In this paper, we described macrozoobenthos and hydrological conditions of the bay based on the data collected in field campaigns in 2020–2021. All estuarine stations corresponded to a monodominant community of Macoma balthica poor in biomass (27.29 ± 20.82 g m⁻²) and species richness (33 species of macrozoobenthos recorded from 10 stations). The seaward most station was occupied by a marine assemblage of macrozoobenthos dominated by polychaetes Nephtys longosetosa and Cistenides hyperborea. Macrozoobenthos of the bay forms an ecocline from estuarine to marine species along the gradient of salinity. No significant differences in macrobenthic abundance, biomass and species richness were found between the 2 years of sampling and described fauna corresponds well to communities sampled in 1990s. Portlandia aestuariorum was absent in all our samples, which supports the hypothesis of disappearance of this previously common bivalve mollusc from the area, but the question of the driver of the change in macrozoobenthos remains open and requires further investigation. [ABSTRACT FROM AUTHOR]