Lazzaro, X. IRD-France & UFRPE/Pesca-Brazil, lazzaro@cyb.com.br
Starling, F. CAESB/DRCH, flrms1@mymail.com.br

 
THE ROLE OF FISH-ZOOPLANKTON INTERACTIONS IN TEMPERATE VS. TROPICAL LAKE AND RESERVOIR TROPHIC FOOD WEBS: CONSEQUENCES FOR BIOMANIPULATION
 
The relative role of nutrients and food web is still debated, but large herbivorous cladocerans (mainly Daphnia spp.), as both selective prey of planktivorous fish and selective grazers of nanophytoplankton, are key organisms controlling plankton community structure and productivity, thus regulating temperate lake trophic states. This contrasts with most frequent situations of intermediate regulation (weak cascades) induced by dominance of opportunistic filter-feeding omnivorous fish and inefficient small-sized zooplankton grazers (rotifers, few cladocerans) in tropical lakes. Higher omnivorous fish biomasses, 0+ fish presence (continuous reproduction), and small-bodied zooplankton (allometric laws) enhance internal nutrient cycling. High N:P ratios of small cladocerans plus low N:P ratios in fish excretion favor N-limitation and cyanobacteria dominance. Thus, in tropical systems, eutrophication may be promoted by internal loading via fish and zooplankton nutrient recycling and stoichiometric conditions. However, intense trophic cascades dominate oligo-mesotrophic temperate lakes and occur in some tropical reservoirs, whereas intermediate regulations occur in most topical lakes but are encountered in some eutrophic temperate reservoirs. Functioning of temperate and tropical lakes may not differ, but a continuum of intermediate food web situations may exist between two extreme models. Consequences for biomanipulation approaches are discussed using data from mesocosm and whole-lake experiments, and bioenergetics modeling.
 
Day: Thursday, Feb. 4
Time: 11:30 - 11:45am
Location: Hilton of Santa Fe
 
Code: SS22TH1130H