In a channel, which will be cut off soon, an investigation has been started in rihich the influence of the changing ecological factors will be studied. A ar’s cycle of Diatoms, investigated in the period March 1959 to March 1960 elded some interesting results. In early June Eucampia zoodiacus E. showed a aximum, whereas Guinardia flaccida (Castr.) Perag. showed its maximum in July, mhen Eucampia zoodiacus E. was in its turn rare. Porosira glacialis (Grun.) Jorgensen, which comes from more Northern areas showed a maximum in early April. Coscinodiscus gigas praetexta (Janisch) Hustedt appeared regularly from late August, (temp. 20,4° C), until February 1960 (temp. 3,3° C). Hustedt mentions this species as occurring in the Mediterranean Sea. Some additions are made to the existing descriptions of the two last mentioned pecies.