[AOS09-P18] Island-mass effect on the phytoplankton and zooplankton community in south of Japan
Keywords:zooplankton, island-mass effect
The Sea surface chlorophyll concentration (SSChl, MODIS-Aqua) in the area bounded by 135.5-142.0 E and 30.0-37.0 N was examined for the grids with depths of > 500 m. Zooplankton samples were collected by vertical tow (0-150 m) of the NORPAC net with 0.335 mm mesh in the area south of Honshu in February to March of 1963-2017. Samples were fixed in 5% formalin-sea water and copepod biomass was estimated in the laboratory by Bench-top Video Plankton Recorder. The relationships between plankton biomass and distance to the Honshu coast and to the Izu Ridge were examined.
The SSChl declined as distance to the Honshu coast increased. But high SSChl was observed in several areas 150-250 km away to the coast. These areas were mainly located around the Izu Ridge, 32-33.5N, and interpreted as caused by island-mass effect when the Kuroshio flowed in offshore path. The copepod biomass was high around the Honshu coast (<50 km). Stations with high copepod biomass were observed in the 100-200 km north-east (downstream) of the Izu Ridge, but they were located near the Honshu, around the Boso peninsula. Island-mass effect of the Izu-ridge on zooplankton biomass thus cannot be distinguished from the coastal effect and the effect should be examined by rate process (spawning rate and/or growth rate) in species level.