Abstract
The relationship between the dominant diatom species and changes in nutrient concentrations, particularly soluble reactive silicon (SRSi), was studied from spring to summer of 1993 and 1994 in Lake Barato, central Hokkaido. The highest SRSi concentration in 1993 was lower than that in 1994. Although the SRSi concentration dropped markedly from May to July 1993, it did not decrease to the same extent in 1994. The dominant diatom species shifted from Melosira ambigua to Cyclotella meneghiniana with the 1993 drop in SRSi. In contrast, M. ambigua dominated throughout 1994. The relative abundance of M. ambigua in diatoms depended on the Si content per volume of diatoms, which was at a low level in June 1993. In the experiments on Si limitation in batch culture, the half-saturation constant (Km+Si0) for the growth rate of M. ambigua was higher than that of C. meneghiniana. In addition, the growth rate of M. ambigua was quite low at low Si concentrations. These facts suggest that M. ambigua is a species less resistant to Si limitation. The biomass of M. ambigua was considered to decrease by Si-deficiency in the early summer of 1993.
