Population dynamics model of Copepoda (Neocalanus cristatus) in the northwestern subarctic Pacific

A population dynamics model (PDM) was developed for Neocalanus cristatus, which is the dominant large copepod in the northwestern subarctic Pacific, to simulate the increase of production with developmental stage and the transfer of production by vertical migration. The PDM was coupled with a lower trophic level ecosystem model, North Pacific Ecosystem Model Used for Regional Oceanography (NEMURO, developed by the North Pacific Marine Science Organization (PICES)), by replacing the large zooplankton component (ZooL) in NEMURO with the PDM. Ecological effects in the coupled model were compared to those in the original NEMURO. In the simulations, the annual cycle of copepodite stages begins during the spring bloom, followed by a decrease in biomass during summer, then migration of Neocalanus to the deep water where they diapause during autumn and winter, and finally the simulation ends with egg production in winter. The PDM successfully described the annual life cycle of Neocalanus. During early copepodite stages (during the spring bloom), they graze small phytoplankton (PhyS) without consuming large phytoplankton (PhyL). Therefore, PhyL biomass increases greatly in spring. In summer, during the last copepodite stage, they begin to prey mostly on PhyL, causing a decrease in the PhyL biomass, while the PhyS biomass increases. Production of PhyL remains higher than that of PhyS because predatory pressure by Neocalanus gradually weakens as the last copepodite stage, near the surface, approaches its end in summer. These simulations suggest that in addition to Neocalanus we should include PDMs for the other large copepods, which consume PhyL during the summer, in order to reproduce the lower trophic ecosystems of the northwestern subarctic Pacific.