Un nuovo periodo di osservazioni sul fitoplancton del lago di Nemi

Summary

In 1940 I made some researches on the phytoplankton of Nemi lake and was particularly interested in the succession of the various populations which settled on the lake owing to the considerable lowering (23 meters) of its level between 1928–1932. The original level was reestablished only in 1943. The changing of the plankton depended on the modified ecological conditions of the water. Only in these last years the original phytoplanktonic facies was reestablished. Some typically pelagic species reappeared only many years afterwards, for instance Ceratium hirundinella 10 years later, Closterium aciculare 15 years later and Aphanizomenon flos-aquae only 18 years later. In Ceratium, after lowering of the lake level, some, by biometrical and statistical techniques, significantly different features were perceived.

The Nemi lake with all its hydrobiological vicissitudes offered us a wonderful example of gradual and slow colonization and by Ceratium an example of differentiation of a new local race in dependence on new surrounding conditions.