A review of the genus Muusoctopus (Cephalopoda: Octopoda) from Arctic waters.

We report two Arctic species of incirrate octopods new to science. One is formally described here as Muusoctopus aegir Golikov, Gudmundsson & Sabirov sp. nov. while the other, Muusoctopus sp. 1, is not formally described due to a limited number of samples (all are immature individuals). These two species differ from each other, and from other Muusoctopus, especially in: 1) absence of stylets (in M. aegir sp. nov.); 2) proportions of mantle and head; 3) funnel organ morphology (W-shaped with medial and marginal limbs of equal length in M. aegir sp. nov., or medial are slightly longer; V V-shaped with medial limbs slightly longer and broader than marginal in Muusoctopus sp. 1); 4) sucker and gill lamellae counts; 5) relative arm length and sucker diameter; and 6) male reproductive system relative size and morphology. Species of Muusoctopus now comprise four of 12 known Arctic cephalopods. Additionally, this study provides: a) new data on the morphology and reproductive biology of M. johnsonianus and M. sibiricus, and a diagnosis of M. sibiricus; b) the equations to estimate mantle length and body mass from beak measurements of M. aegir sp. nov. and M. johnsonianus; c) a cytochrome c oxidase subunit I gene barcode for M. sibiricus; d) new data on the ecology and distribution of all studied species; and e) a data table for the identification of northern North Atlantic and Arctic species of Muusoctopus.

The Impact of Sea Ice Loss on Benthic Communities of the Makarov Strait (Northeastern Barents Sea).

The continental shelf of the northeastern Barents Sea is presently experiencing a weak influx of Atlantic water from the west. In recent times, warming in Arctic regions has led to an increase in extended ice-free periods in this area, instead of significantly elevating water temperatures. The implications of this phenomenon on the structure and functioning of benthic communities were investigated during the autumn of 2019 within the Makarov Strait, located in the southwestern part of the St. Anna Trough. The macrozoobenthic communities exhibited a clear connection with the duration of ice-free periods. This variable influenced a vertical carbon flux, which subsequently served as the primary predictor for faunal abundance and diversity, as demonstrated by redundancy and correlation analyses. Two faunal groups were identified, corresponding to short and long open-water periods. Both groups had similar alpha diversity (65 ± 6 and 61 ± 9 species per station) and biomasses (39 ± 13 and 47 ± 13 g m-2) but displayed differing abundances (1140 ± 100 vs. 4070 ± 790 ind. m-2) and other diversity indices. We observed a decline in the proportion of polychaetes, accompanied by an increase in the proportion and diversity of bivalves, as well as a rise in the abundance of infaunal species, sub-surface deposit feeders, and mobile suspension feeders, in response to the increasing vertical carbon flux. The potential increase in anthropogenic pressures related to oil development in the northeastern Barents Sea highlights the importance of our study for conservation and monitoring efforts in the region.

Combining data from different sampling methods to study the development of an alien crab Chionoecetes opilio invasion in the remote and pristine Arctic Kara Sea.

Data obtained using three different types of sampling gear is compared and combined to assess the size composition and density of a non-indigenous snow crab population Chionoecetes opilio in the previously free of alien species Kara Sea benthos. The Sigsbee trawl has small mesh and catches even recently settled crabs. The large bottom trawl is able to catch large crabs, but does not retain younger crabs, due to its large mesh. Video sampling allows the observation of larger crabs, although some smaller crabs can also be spotted. The combined use of such gear could provide full scope data of the existing size groups in a population. The density of the crabs was calculated from the video footage. The highest figures were in Blagopoluchiya Bay at 0.87 crabs/m2, where the settlement seems to be reaching its first peak of population growth after the introduction. High density in the Kara Gates Strait at 0.55 crabs/m2, could be due to the close proximity of the Barents Sea from where the crabs can enter by both larval dispersal and active adult migration. All size groups have been present in most sampled areas, which suggest successful settlement and growth of crabs over a number of years. Again, this was not the case in Blagopoluchiya Bay with high density of small crabs (<30 mm CW), which confirms its recent population growth. Male to female ratio was strikingly different between the bays of the Novaya Zemlya Archipelago and west of the Yamal Peninsula (0.8 and 3.8 respectively). Seventy five ovigerous females were caught in 2016, which confirms the presence of a reproducing population in the Kara Sea. The spatial structure of the snow crab population in the Kara Sea is still in the process of formation. The presented data indicates that this process may lead to a complex system, which is based on local recruitment and transport of larvae from the Barents Sea and across the western Kara shelf; formation of nursery grounds; active migration of adults and their concentration in the areas of the shelf with appropriate feeding conditions.