Seasonal changes in mesozooplankton swimmers collected by sediment trap moored at a single station on the Northwind Abyssal Plain in the western Arctic Ocean

To examine seasonal changes in the mesozooplankton community, analyses were made on the swimmer samples (>1 mm) collected by a sediment trap mooring at 184 m depth on the Northwind Abyssal Plain in the western Arctic Ocean during October 2010–September 2011. The zooplankton swimmer flux ranged from 5 to 44 ind. m−2 day−1 and was greater during July to October; copepods were the dominant taxon. Based on the zooplankton swimmer flux, cluster analysis classified samples into three groups (A, B-1 and B-2). The occurrence of each group showed clear seasonality; group A was observed during July to October, group B-1 was seen in November to January and group B-2 during March to June. The seasonal variability in population structures of four dominant copepod swimmers was clearly different between the species. Most Calanus hyperboreus were copepodid stage 6 female (C6F) throughout the year. For Metridia longa and Paraeuchaeta glacialis, C6Fs dominated during January to May, and early copepodid stages increased during June to October. Heterorhabdus norvegicus was dominated by stage C5 during November to February, and C6F/M during March to May. Since Pacific copepods (Neocalanus cristatus) occurred in significant number during August–September, possible causes are discussed.