Planktonic food web structure along the Sau Reservoir (Spain) in summer 1997

We studied the planktonic food web in eutrophic San Reservoir (Catalonia, N E Spain). Along the longitudinal axis from the Ter River downstream to the dam, we characterized a microbial succession of food web dominance of bacte ria-HNF-ciliates. The Ter River transports a large load of organic material into the reservoir, with a bacterial density of similar to9.10(6) large ce lls per ml. While at the first lacustrine station of the Reservoir HNF were the dominant bacterial consumers, at the others, an oligotrich ciliate, Ha lteria grandinella, was the main protozoan bacterivore. Most of the bacteri al production in the reservoir epilimnion was consumed by grazing. The spat ial succession of the resevoir microbial food webs was followed downstream by maximum densities of their potential predators among zoo-plankters - rot ifers, and early developmental stages of copepods.