CORRELATION BETWEEN CELL DENSITY AND DOMINANT GROWTH FORM OF EPILITHIC DIATOM ASSEMBLAGES

Abstract

The correlation between the algal cell density and the growth form of freshwater epilithic diatoms was investigated in field observations. Three sampling stations were set in the Asa-Kawa River, Japan to examine the possible effects of water pollution on the correlation. The developmental process of epilithic algal communities reported by some preceding workers was reflected by the relationship in the intermediately polluted station: relative abundance of adnate diatoms decreased and that of rosette forming diatoms increased with increase in the algal cell density. Relative abundance of stalked diatoms increased with increase in the algal cell density at low density, but it began to decrease at densities above 10⁵ cells.mm-″². However, in the less polluted and in the considerably polluted stations, no significant correlation was found. Slow growth and grazing pressure in the less polluted station, and water pollution in the considerably polluted station were the possible driving forces for the establishment of the algal community in those waters.