The hidden diversity of the endemic Arctic sponges (Porifera)

The biogeographical analysis of the Barents Sea sponge fauna was undertaken on the basis of their modern distribution. Samples of sponges were collected in the Barents Sea during four annual multispecies trawl surveys (2003–2006) by the Knipovich Polar Research Institute of Marine Fisheries and Oceanography (PINRO) research vessels F. Nansen, Smolensk and Muklevich. Also, in 2019 fresh samples were collected during the benthic trawl survey by the PINRO research vessel F. Nansen. A total of 64 sponge species were studied. Among them, there was a large group of 24 (37.5% of the total number) boreal species–invaders from the North Atlantic, and their distribution in the Arctic Ocean is confined to the western Barents Sea. Since these species do not spread deep into the Arctic Ocean, they do not really affect the characteristics of the modern Arctic fauna. The second major component (24 species; 37.5%) of the Barents Sea sponge fauna (and the primary component of the modern Arctic fauna as a whole) is represented by Arctic endemics. A characteristic feature of some arctic sponges (endemics) is that there are pairs of morphologically and genetically close species inhabiting the North Atlantic. Their distributional ranges do not overlap significantly but are immediately adjacent to each other (vicariant species). The origin of vicariant species pairs among sponges inhabiting the Arctic and the adjoining North Atlantic was associated with glacial/interglacial cycles of the Quaternary, which drastically reorganised the boreal North Atlantic faunal elements that inhabited the Arctic Ocean in the Pliocene epoch. However, if we take a closer look not only at these species pairs but also at their close relatives inhabiting the North Atlantic, Arctic and North Pacific oceans, we see that they share the same roots as the North Pacific ones, and probably have evolved from the latter. The last species group, the arctic-boreal (16 species; 25%), is rather arbitrary and unified species of uncertain origin