Journal of Oceanography, Vol. 53 (No. 4), pp. 383-396, 1997
Koji Suzuki1, Nobuhiko Handa2, Hiroshi Kiyosawa3 and Joji Ishizaka4
1Institute for Hydrospheric-Atomspheric Sciences, Nagoya University, Chikusa-ku, Nagoya 464-01, Japan
2Aichi Prefectural University, Misuho-ku, Nagoya 467, Japan
3Marine Biological Research Institute, Shinagawa-ku, Tokyo 142, Japan
4National Institute for Resources and Environment, Tsukuba, Ibaraki 305, Japan
(Received 7 January 1997; in revised form 13 March 1997; accepted 20 March 1997)
Abstract: The long meridional (175°E, 48°N-8°S) distribution of phytoplankton pigments was investigated in the central Pacific Ocean during the boreal summers of 1992 and 1993 by using high-performance liquid chromatography (HPLC). The sampling periods were under El Niño conditions. The distribution patterns of the chemotaxonomical pigments for eukaryotic phytoplankton were characterised: 19´-hexanoyloxyfucoxanthin (a prymnesiophyte marker) and 19´-butanoyloxyfucoxanthin (a pelagophyte marker) were detected throughout the whole study area, fucoxanthin (a diatom marker) was observed north of Kuroshio Extension, and peridinin (a dinoflagellate marker) was found at the stations both north of the Kuroshio Extension and the equatorial area, and the abundance of these pigments detected was not significantly changed (non-parametric one-way ANOVA, P >0.05) in the whole study area during the two sampling periods. However, the abundance of prokaryotic photoautotrophs (prochlorophytes and cyanobacteria) at the North Pacific subtropical gyre and the equatorial region during the horeal summers of 1993 was significantly higher (P < 0.001) than that during the boreal summer of 1992 as estimated by their chemotaxonomical marker, zeaxanthin. The high prokaryotic phytoplankton biomass during the boreal summer of 1993 was also calculated by using the algorithm of Letelier et al. (1993) for pardoning total chlorophyll abiomass into contributions by major phytoplankton taxa. The North Pacific subtropical gyre has generally been thought to support a homogeneous, stable biological community, but our result suggests that the abundance of prokaryotic phytoplankton in this gyre may be spatially and temporally variable, and these change can affect primary production and zooplankton biomass.