Ice-brine and planktonic microheterotrophs from Saroma-ko Lagoon, Hokkaido (Japan): quantitative importance and trophodynamics

International audienceCopyright (c) 1996 Elsevier Science B.V. All rights reserved. Biologists have rarely had the opportunity to investigate the community characteristics and dynamics of heterotrophic microorganisms in highly productive first-year sea ice. In this study, sterile seawater was used as a salinity buffer to extract the ice-brine microheterotroph communities (bacteria, flagellates and ciliates) from a coastal lagoon in Japan (Saroma-ko, Hokkaido; 44°N, 144°E) during the late winter (February−March) of 1992. This procedure reduced osmotic shock during the melting of ice cores and allowed the recovery of up to 323% more cells than the traditional melting method. Most of the organisms were concentrated in the bottom 3−4 cm of the ice, where abundances were up to 33 times higher than in the plankton. In ice and plankton samples, heterotrophic flagellates were dominated by small species (