Permalink : http://hdl.handle.net/2115/75200

JaLCDOI : 10.14943/bull.fish.69.1.47

KEYWORDS : Plankton net;Mesh;Zooplankton;ZooScan;Imaging analysis

To evaluate the effect of net mesh size on filtering efficiency and zooplankton collection efficiency, we developed Quad-NORPAC net equipped four-different mesh sizes (63, 100, 150, and 335 µm). Based on zooplankton samples collected by Quad-NORPAC net at 13 stations off Fukushima during 2-12 June 2016, zooplankton settling volume and wet weight (335 µm) measured, and size and taxonomic data were captured by imaging analysis (ZooScan). As net mesh property, mesh porosity ranged between 22.8% (63 µm) and 45.5% (150 µm). Filtering volumes of four mesh nets were highly correlated (r2=0.97-0.99), while those of 63 µm was greatly lower than the others (i.e. that of 63 µm was factored as 0.598 of 335 µm). Zooplankton collection efficiency, which evaluated an abundance of 63 µm mesh as 100%, ranged for 66.8-120.1% for 100 and 150 µm, while was extremely low (6.5-32.3%) for 335 µm. Zooplankton collection efficiency varied with size and taxa. Thus, collection efficiencies of Gastropoda, Copepoda, Cladocera, and Appendicularia, the smaller-sized taxa (<500 µm in equivalent spherical diameter [ESD]), were substantially low (<10%), while those of Noctiluca scintillans, Cnidaria, and Euphausiacea, large-sized taxa (>500 µm ESD), were relatively high (40-80%). From the viewpoint of filtering efficiency and collection efficiency, within the four mesh sizes, 150 µm mesh net is considered to be sufficient for quantitative collection of zooplankton.