Resting stage cells of diatoms in deep waters in Kumano-Nada, central part of Japan

Abstract

The abundance and species composition of viable resting stage cells of diatoms were investigated in deep waters (200, 500 and 1,000 m depths) collected at neighboring stations in Kumano-Nada, central part of Japan, in April, August and October 2006. Viable resting stage cells were enumerated by the modified extinction dilution method [most probable number (MPN) method] based on incubation. Resting stage cells were detected from all samples, except at 500 m depth in August, in a range of abundances between 200–4,415 cells L⁻¹. The resting stage cells of diatoms observed belonged to four genera of the Centrales, Chaetoceros spp. (C. curvisetus, C. socialis and Chaetoceros sp.), Leptocylindrus danicus, Skeletonema spp. and Thalassiosira spp., and two of the Pennales, Cylidrotheca closterium and Navicula sp., along with one centric and three pennate unidentified diatoms, in total. It is indicated, in this study, that the abundances enumerated by the MPN method could represent those of disassembled resting stage cells originally aggregated in marine snow, of which the sinking rate is reportedly great (e.g. 68 m day⁻¹). This, eventually, suggests that the abundance and species composition of resting stage cells in the deep waters reflected the states of blooms occurring just before our samplings in the surface water of the Kumano-Nada region. In this region, coastal upwelling occasionally occurs, implying that such resting stage cells sinking from the euphotic layer to deeper depths might have some chance to return to the surface and be able to act as a “seeding population” for further blooms.