Research results

　The microplankton present at the site was 10.2 mg per cubic meter. The zooplankton was dominated by krill and copepods Metridia ochotensis, which are diurnal vertical migrants, and their feeding pressure was estimated to be 21% of the daily microplankton abundance. Zooplankton faecal pallets were abundant in the shallowest layer (0-100 m) during the daytime, reaching a maximum of 1,888 per cubic meter and 2.96 mg of carbon (Figure 2). There was a diurnal variation in faecal pallet size, with larger faecal pallets being observed only at night. This indicates that the larger faecal pallets settle faster, so that faecal pallets excreted during the night settle into the deep sea during the night and are not observed during the day. Observations of faecal pallets during rearing experiments revealed fluorescent phytoplankton cells in the faecal pallets (p.1, Figure). In addition, at depths of 500-1000 m, the mesopelagic copepod Gaetanus variabilis fed on feces excreted by zooplankton in the upper layer (Fig. 3), indicating that repacking is an important behavior for deep-sea organisms. This is a direct indication that organic matter in the form of faecal pallets is an important food resource for deep-sea organisms.