Seasonal, regional, and diel changes in the abundance of five large, dominant copepods in the western subarctic Pacific : Insights from Continuous Plankton Recorder surveys

In the marine ecosystem, mesozooplankton, especially large copepods, have an important role both in the mediation of primary production to higher trophic levels and in the transportation of organic materials from the surface to the deep ocean, termed the biological pump. Continuous Plankton Recorder (CPR) surveys have been used as a long-term monitoring method for mesozooplankton over wide geographical areas, including the North Pacific, where a CPR survey began in 2000. In this study, we used CPR samples collected in the western subarctic Pacific during 2001-2015 to investigate the abundance and population structure of five large, dominant copepods (Neocalanus cristatus, N. flemingeri, N. plumchrus, Eucalanus bungii and Metridia pacifica) and evaluate the differences in season, region, and diel scales between species. Significant seasonal changes in abundance and population structure were detected, and these changes were considered to reflect the life history of each species. Regional differences were detected for the three Necalanus species and were considered to be related to sea surface temperature and food availability. Diel changes in abundance were observed for N. cristatus and M. pacifica, with both species more abundant near the surface at night suggesting diel vertical migration