Macrofauna and Nematode Abundance in the Abyssal and Hadal Zones of Interconnected Deep-Sea Ecosystems in the Kuril Basin (Sea of Okhotsk) and the Kuril-Kamchatka Trench (Pacific Ocean)

The Kuril Basin and the Kuril-Kamchatka Trench are two interconnected deep-sea ecosystems both located in one of most highly productive regions world’s oceans. main distinguishing features these low oxygen concentration near-bottom water Basin, high hydrostatic pressure trench. We investigated abundance meio- macrobenthic nematodes macrofauna on floor (depths 3,300–3,366 m) area 3,432–9,539 m), as well influence some environmental factors quantitative distribution bottom fauna. This was not studied so far. study also focused species composition Polychaeta Bivalvia, which were dominant among macrofaunal samples. influencing depth, concentration, structure sediments. communities characterized by a macrofauna, richness polychaetes, pronounced dominance small-sized probably more tolerant to concentrations. Compared (at depths 3,432–5,741 had diverse abundant very nematodes. In trench than 6,000 diversity decreased, while increased with increasing depth. On floor, highest due density populations several bivalve polychaete species, apparently adapted floor. Obviously, primary production surface waters supports fauna areas northwestern Pacific. Furthermore, large number animals chemosynthetic endosymbiotic bacteria found Trench. suggests significant contribution organic carbon functioning ecosystems.