Biomanipulation as an application of food-chain theory: Constraints, synthesis, and recommendations for temperate lakes

The aim of this review is to identify problems, find general patterns, and extract recommendations for successful biomanipulation. An important conclu sion is that the pelagic food chain from fish to algae may not be the only process affected by a biomanipulation. Instead, this process should be view ed as the "trigger" for secondary processes, such as establishment of subme rged macrophytes, reduced internal loading of nutrients, and reduced resusp ension of particles from the sediment. However, fish reduction also leads t o a high recruitment of young-of-the-year (YOY) fish, which feed extensivel y on zooplankton. This expansion of YOY the first years after fish reductio n is probably a major reason for less successful biomanipulations. Recent, large-scale biomanipulations have made it possible to update earlier recomm endations regarding when, where, and how biomanipulation should be performe d. More applicable recommendations include (1) the reduction in the biomass of planktivorous fish should be 75% or more; (2) the fish reduction should be performed efficiently and rapidly (within 1-3 years); (3) efforts shoul d be made to reduce the number of benthic feeding fish; (4) the recruitment of YOY fish should be reduced; (5) the conditions for establishment of sub merged macrophytes should be improved; and (6) the external input of nutrie nts (phosphorus and nitrogen) should be reduced as much as possible before the biomanipulation. Recent biomanipulations have shown that, correctly per formed, the method also achieves results in large, relatively deep and eutr ophic lakes, at least in a 5-year perspective. Although repeated measures m ay be necessary, the general conclusion is that biomanipulation is not only possible, but also a relatively inexpensive and attractive method for mana gement of eutrophic lakes, and in particular as a follow-up measure to redu ced nutrient load.