HR: 11:00h
AN: NB22A-03    [Abstracts]
TI: Top-Down and Bottom-Up Forces in an Appalachian Stream: Can Consumers Differentially Mediate Effects of Nutrient Enrichment on Algae?
AU: * Dye, S E
EM: suedye@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30602 United States
AU: Pringle, C M
EM: cpringle@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30602 United States
AU: Meyer, J L
EM: jlmeyer@uga.edu
AF: Institute of Ecology, University of Georgia, Athens, GA 30602 United States
AB: The effect of nutrient loading on the biotic integrity of streams is of growing concern, given increased anthropogenic inputs from agriculture and urbanization. However, few studies have addressed the potential of top-down forces, both direct and indirect, to regulate increases in primary production that often result from nutrient enrichment. In this study, we examined the effect of nutrients on algal standing crop and community composition in response to both snails (Elimia proxima) and macroconsumers (fish and crayfish), in a 2³ factorial design. Insectivorous sculpin (Cottus bairdi), algivorous stonerollers (Campostoma anomalum) and omnivorous crayfish (Cambarus spp.) dominate the macroconsumer community in Betty's Creek, an Appalachian stream of northern Georgia. Snails had the strongest regulatory impact on nutrient-stimulated algae, both with and without macroconsumer predators. In contrast, stonerollers and crayfish were not able to directly suppress increased algal standing crop. However, reductions of invertebrate biomass by both sculpin and crayfish indirectly increased algae, regardless of nutrient addition. These results provide evidence for the existence of weak trophic cascades in lotic systems, even in complex food webs where consumers feed at multiple trophic levels. This work also documents the importance of grazer identity in the mediation of nutrient effects on algae.
DE: 1803 Anthropogenic effects
DE: 9901 NABS Student Award - Basic Research
SC: North American Benthological Society [NB]
MN: 2005 Joint Assembly