Parmales abundance and species composition in the waters surrounding Hokkaido, North Japan

Abstract

The abundance and species composition of Parmales (Bolidophyceae), a siliceous marine phytoplankton, were investigated in the waters surrounding Hokkaido, North Japan. In the Pacific Ocean, high Parmales abundances were observed in the Oyashio region (84.9–95.2 cells mL−1), in the surrounding area of the cold Oyashio Current, and in the Coastal Oyashio Water (35.1–41.4 cells mL−1) being low temperature and salinity in spring. In the Okhotsk Sea, Parmales abundance was moderate (>5 cells mL−1) in the Intermediate Cold Water, which is formed by convective mixing under the pack ice. On the other hand, their abundance was quite low in warm water masses, such as the Tsushima Warm Current in the Sea of Japan and the Soya Warm Current in the Okhotsk Sea. Parmales cells were also found in the sea ice in the Notoro-ko Lagoon connected to the Okhotsk Sea, suggesting that they have an ice algal life cycle. Triparma spp. were almost dominant in the study areas with the occasional contribution of Tetraparma spp. in the Okhotsk Sea. These results indicate that Parmales abundance and species composition are significantly influenced by water currents.