Biomanipulation in a theoretical and historical perspective

In limnology, nutrients have historically been regarded as main regulators of the ecosystem; that is, organisms in lakes were seen as regulated from the bottom of the food chain. Long after the seminal works of Hairston et al. (1960), Hrbacek et al. (1961) and Brooks & Dodson (1965) this `bottom-up' view prevailed. It was not until the late 1970s and 1980s that these new theories gained recognition, considering the `top-down' effect; that is, the impact of predation on lower trophic levels. The decision to subject Lake Ringsjon to a biomanipulation was based on the fact that the phosphorus reductions accomplished during the 1970s did not have the positive effects expected. In addition, several theories had been proposed which predicted the effects of manipulations at the top of the food chain on lower trophic levels. In this paper, we describe how these different theories influenced us at the time the studies of Lake Ringsjon were initiated, and how difficult it may be to convert scientific theories into large-scale manipulations.