Variability in Taxonomic Composition, Standing Stock, and Productivity of the Plankton Community in the Kuroshio and its Neighboring Waters

Phytoplankton growth and consumption by microzooplankton stimulated by turbulent nitrate flux suggest rapid trophic transfer in the oligotrophic Kuroshio

“…Despite the large turbulent nitrate flux (O: 1 mmol m −2 d −1 ), the chlorophyll a concentrations in the area of the Tokara Strait impacted by the Kuroshio Current were as low as the values reported from nearby areas of the Kuroshio (Kobari et al, 2018(Kobari et al, , 2019 and oceanic sites in the North Pacific Ocean (Calbet and Landry, 2004). Based on the gradient-enrichment experiments, standing stocks and the growth rates of all size-fractionated phytoplankton increased at nitrate enrichments above 0.5 µmol L −1 , which were equivalent to the concentrations produced by the observed turbulent nitrate flux.…”

“…In global comparisons, microzooplankton grazing has a significant impact on phytoplankton, particularly at oceanic sites (Calbet and Landry, 2004). Microzooplankton standing stocks in the Kuroshio Current as it passes through the Tokara Strait are lower than those on the continental shelf of the ECS (Chen et al, 2003) and might be removed by mesozooplankton predation (Kobari et al, 2019). The low microzooplankton standing stocks in the Kuroshio Current imply Figure 5.…”

“…Phytoplankton standing stocks in the Kuroshio consist mainly of picoplankton and nanoplankton, and the predominant components are haptophytes, diatoms, and unicellular cyanobacteria like Prochlorococcus and Synechococcus (T. Endo and Suzuki, 2019). Heterotrophic bacteria and calanoid copepods contribute to heterotrophic biomass in the Kuroshio, whereas microzooplankton biomass is relatively small (Kobari et al, 2019). Based on a mass balance model, Kobari et al (2019) have concluded that mesozooplankton standing stocks in the Kuroshio are supported by microautotrophs and nanoautotrophs and microzooplankton.…”

“…Heterotrophic bacteria and calanoid copepods contribute to heterotrophic biomass in the Kuroshio, whereas microzooplankton biomass is relatively small (Kobari et al, 2019). Based on a mass balance model, Kobari et al (2019) have concluded that mesozooplankton standing stocks in the Kuroshio are supported by microautotrophs and nanoautotrophs and microzooplankton. However, we have little understanding of how biogeochemical processes and trophodynamics support the plankton community in the Kuroshio.…”

Phytoplankton productivity and rapid trophic transfer to microzooplankton stimulated by turbulent nitrate flux in oligotrophic Kuroshio Current

“…Otherwise, the coastal water mass is sometimes entrapped and transported into the Kuroshio and more pelagic sites (Nakamura et al, 2006;Kobari et al, 2019). Use of waters in the vicinity of the oligotrophic Kuroshio as a nursery and feeding ground would therefore appear to be a risky strategy unless there is a mechanism that enhance biological production in the Kuroshio.…”