EPIPHYTIC DIATOM COMMUNITY AND CALCIUM CARBONATE CRYSTALS CHARACTERISTICS ON THE SURFACE OF FRESHWATER Ulva THALLI1

Summary. On the surface of the freshwater form of Ulva thalli the incrustations process takes place which resulted in the precipitate of calcium carbonate crystals (CaCO3). At the same time, this area is also inhabited by large numbers of periphytic communities, mainly by diatoms. Siliceous frustules and calcite crystals are responsible for the thalli roughness in all stages of its growth. Diatom communities colonizing young, thin thallus of Ulva were dominated by Cocconeis placentula and Melosira varians, and mature thalli by Cocconeis placentula and Navicula cryptocephala. The obtained data show that the surface roughness of thalli depends on the participation of calcium carbonate in the dry matter of Ulva and diatoms content does not change significantly with age of the macroalga thallus