Distribution patterns of deep-sea molluscs from the Bering Sea and Aleutian Trench

Abstract

The Aleutian Trench, a canyon-like structure in the deep sea floor that parallels the southern fringe of the Aleutian Islands off Alaska, has only been studied by a few previous expeditions. The trench itself and the adjacent island archipelago both present potential dispersal barriers to marine species, which may shape the regional biogeography. We report new findings on the molluscan fauna of the trench and adjacent regions, from the recent “AleutBio” expedition in summer 2022 on the German research vessel Sonne. We recovered over 4300 individual mollusc specimens representing 212 identified taxa in 7 classes (all living taxonomic classes except Polyplacophora), of which 180 could be assigned to a species-level morphospecies. Highlights from our new material include: one monoplacophoran, the dumbo octopus Grimpoteuthis imperator re-collected for the first time since its description, the deepest record for the large-bodied solenogaster family Neomeniidae at 6612 m, the very rare columbariid gastropod Tropidofusus aequilonius, and new hadal records for several bivalves: Rengea murrayi, Limatula cf. vancouverensis, Neilonella abyssopacifica, Neilonella politissima, Catillopecten squamiformis, Parvamussium pacificum, and Setigloma japonica and the bivalve family Sareptidae. Comparing records from the Bering Sea (3490–3655 m), the north rim of the trench (4220–4641 m), the hadal depths of the trench bottom (6181–7287 m), and the southern rim (4790–5330 m), provides a test of potential barriers to the distributions of species across these regions. Of the species found in the Bering Sea, 63 % are also found in the broader Aleutian Trench region. Similarly, of the mollusc species found on the south rim of the trench, 68 % cross the Aleutian Trench and are found on the north rim and/or in the Bering Sea. The dispersal potential of most mollusc species is apparently not restricted by deep-sea trenches or island chains in the North Pacific.