Harpacticoida (Copepoda) from the pelagic zone of the Sea of Okhotsk: diversity, spatiotemporal distribution, and role in benthopelagic coupling

Abstract

ABSTRACT We analysed the pattern of spatiotemporal distribution of harpacticoid assemblages of 106 plankton samples collected in May–August of 2013–2015 in Prostor Bay, South Kuril Islands (Sea of Okhotsk). Taxonomically and ecologically diverse harpacticoid assemblages were found in the water column. Among the 49 species identified, only one was truly planktonic, while the others were typically benthic, mainly phytal-dwelling forms. The most abundant and rich (42 species) assemblage occupied the shallow (10 m depth) area in the western, stone-bottomed part of the bay with a well-developed phytal zone. In deeper areas, the abundance and diversity of harpacticoids in plankton samples decreased steeply. There was a clear seasonal pattern of abundance, diversity and composition, with a peak in spring and then a decrease. On average, the total abundance was low (64 ind/m2). Neither interannual variations contributed significantly to the harpacticoid distribution. The analysis of the gut contents suggests that the harpacticoids feed on planktonic diatoms in the water column, but their residence time in the water column was short, and their feeding rate was low. In turn, the harpacticoids constituted a permanent but relatively minor fraction of the salmon fry diet. Thus, in quantitative terms, harpacticoids contribute relatively little to benthopelagic coupling in the Prostor Bay ecosystem.