The first biomanipulation conference: a synthesis

At the First Biomanipulation Conference held in Amsterdam (8-11 August 1989), studies presented considered mainly trophic interactions in lakes, enclosures and laboratory systems. Studies on the interactions between phytoplankton and zooplankton emphasized the edibility of the phytoplankton i relation to the zooplankton size structure and the trophic state. Most lake experiments involved 50-100 reduction in fish standing stock or alternatively heavy stocking with piscivorous fish. The most dramatic effects of biomanipulation were found in shallow, eutrophic lakes which exhibited radical changes in ecosystem structure because of changes in light climate and consequently, luxuriant development of macrophytes. There was till much controversy about the top-down effects in relation to trophic state, especially those concerning the role of fish and zooplankton in the development and succession of phytoplankton. Many experiments showed indirect effects within the food web, emphasizing the importance of feedbacks and the complexity of the food web rather than the simplicity of the food chain. The stabilizing effects of refugia for zooplankton and fish on the ecosystem were stressed. Shallow lakes responded generally more rapidly to biomanipulation a d this was most successfully accomplished when TP concentration was < 50/~g 1- ', even though in a few cases at 10-20 fold higher TP concentration