EFFECT OF SILICATE ENRICHMENT ON ICE ALGAE AT LOW-SALINITY IN SAROMA-KO LAGOON, HOKKAIDO, JAPAN

The response of ice algae to low salinity was determined at three leve ls of silicate enrichment during the winter of 1992 in Saroma-ko Lagoo n, Hokkaido, Japan. Regardless of the silicate concentration, the chlo rophyll a content decreased by 50% of its initial value within the fir st day of exposure to low salinity water (22 psu) and continued to dec rease gradually thereafter. The degree of decrease after the first day was a function of silicate concentration. The size distribution of th e ice algae at the beginning of the incubation was 52% in the size cla ss > 10 mu m, 39% in 10-2 mu m and 9% in 2-0.2 mu m. Within two weeks of silicate enrichment, the 2-0.2 mu m fraction decreased to less than 1% while the > 10 mu m fraction increased to more than 90%. Low salin ity and low silicate concentrations reduced the chlorophyll a biomass and photosynthetic activity. Silicate enrichments, even at the low sal inity, enhanced photosynthetic activity and the relative abundance of the > 10 mu m cells. Our results suggest that ice algae may not surviv e if trapped in the low salinity lens that is present immediately belo w the ice during melting because of possible osmotic damage associated with silicate deficiency. However, ice algal cells may recover from t he damage when they sink into the high salinity and silicate-rich unde rlying water in Saroma-ko Lagoon. The ecological role of low salinity water is discussed in relation to vertical flux of ice algae.