Trophic cascade and biomanipulation: interface of research and management- a reply to the comment by DeMelo et al.

DeMelo et al. (1992) present a provoca­tive review of food-web experiments. Their open challenge to the conclusions of several studies is sure to evoke controversy. Food­web research in lakes has advanced to the point where a rigorous re-examination of accumulated results is beneficial, and we ap­plaud this effort. The purpose of our comment is to ques­tion some of the conceptual and philosoph­ical claims of DeMelo et al. We do not in­tend to argue about the case studies they reviewed. Rather, we wish to make three main points: the trophic cascade is not a single-factor theory; the results presented by DeMelo et al. do not contradict the trophic cascade hypothesis; and biomanipulation experiments can provide necessary and crit­ical tests of the trophic cascade hypothesis. DeMelo et al. regard biomanipulation, trophic cascade/' and top-down•• ideas as a single unified theory. However, the is­sues addressed in a trophic cascade hypoth­esis (Carpenter 1988a) are not directly equivalent to the goals of biomanipulation (Gulati et al. 1990) for the same reason that research is not management. We will elab­orate this point later. First, we reiterate our view of the trophic cascade. Our introductory paper described a tro­phic cascade hypothesis designed to explain the 50% or so ofobserved variability in pri­mary production that could not be attrib­uted to nutrient loading (Carpenter et al. 1985). That 􀆍aper, derived from a grant proposal written in 1982, came at a time when Eutropbication study in freshwater has turned into a phosphorus bandwagon. Oblivious to the large amount of variance about the phosphorus inputs-chlorophyll relationship, whatever its form, investigators are repeating studies of this same general model-it's the inthing to do .... My guess is that the existing model cannot be further refined without incorporation of other factors-for example, the effects of grazing or re­generation of nutrients from sediments by organ­isms. [Schindler 1981, p. 78]