Summary: 1
Ecology, 78(1), 1997, pp. 1­20
1997 by the Ecological Society of America
``TOP­DOWN'' TROPHIC INTERACTIONS IN LAKES: EFFECTS OF FISH
ON NUTRIENT DYNAMICS
MICHAEL J. VANNI, CRAIG D. LAYNE,1
AND SHELLEY E. ARNOTT2
Department of Zoology, Miami University, Oxford, Ohio 45056 USA
Abstract. We conducted enclosure experiments over two summers in Tuesday Lake,
Michigan, to assess how a gradient of zooplanktivorous fish biomass affected the dynamics
of nutrients (nitrogen, N, and phosphorus, P), and their partitioning among ecosystem
compartments. In both years, fish (the cyprinid Phoxinus eos) reduced the abundance of
large zooplankton species and increased the biomass of phytoplankton as predicted by the
top­down control hypothesis.
Fish had strong effects on the dynamics and fluxes of N and P. Total P concentrations
in the water column declined over time in all enclosures, but fish slowed the rate of decline.
Thus total water column P increased with increasing fish biomass. Total N increased less
strongly with increasing fish biomass, and thus the total N:P ratio decreased with increasing
fish biomass. The concentrations of particulate carbon, nitrogen, and phosphorus in the
water column also increased with increased fish biomass. Particulate N:P ratio decreased

Source: Arnott, Shelley - Department of Biology, Queen's University (Kingston)

Collections: Environmental Sciences and Ecology; Biology and Medicine