Variability of calcification of Phacotus lenticularis (Chlorophyta, Chlamydomonadales) in nature and culture

In north-eastern German hardwater lakes, the unicellular flagellate Phacotu s lenticularis (Chlorophyta, Chlorophyceae, Chlamydomonadales) occurs regul arly in mass developments during the summer months. The most striking chara cteristic of this chlamydophycean alga is the presence of a calcified two-s helled lens-like lorica. The morphology of P. lenticularis loricae in 10 la kes was studied by scanning electron microscopy. Four lorica morphotypes co uld be discriminated; several were observed together even within a single w ater sample. We developed an artificial culture medium that imitated the ch emical conditions of hardwater lakes to such an extent that calcified loric ae were formed that were highly similar to those found under natural condit ions. Phacotus strains from three of the lakes were studied with respect to their calcification patterns under defined culture conditions. Each strain produced a lorica morphology that corresponded to one of those occurring i n the lake from which it had been isolated. The new culture medium is poten tially useful for investigations focusing on the mechanisms of calcificatio n in other freshwater organisms or autochthonous calcite precipitation.