The microbial loop – 25 years later

The background for and the subsequent impact on biological oceanography of the article Azam et al. [Azam, F., Fenchel, T., Field, J.G., Gray, J.S., Meyer-Reil, L.A., Thingstad, F. 1983. The ecological role of water-column microbes in the sea. Mar. Ecol. Prog. Ser. 10, 257-263.] is discussed. It is concluded that its influence in terms of stimulating further research and in changing the earlier paradigm of marine plankton food chains was to a large extent due to the fact that the term “microbial loop” occurred there for the first time. The progress in understanding microbial biota and microbial interaction during the last 25 years will also be reviewed.