Document: JIM-3-73-13

Role of nutrient regeneration by fish in a neotropical stream.

HOOD, J.M.* ¹, M.J.VANNI ¹ and A.S.FLECKER ²

Miami University, Oxford, Oh, USA 45056 ¹
Cornell University, Ithaca, NY, USA 14853 ²

Abstract:
Although fish are often abundant and sometimes have strong top-down effects in streams, little is known about their role in stream nutrient cycles. We examined the importance of nitrogen and phosphorus excretion by two epibenthic grazing armored catfish Ancistrus triradiatus and Cheatostoma milesi in a nitrogen-limited neotropical stream, Rio Las Marias. The roles of these catfish species as nutrient regenerators were evaluated by comparing nutrients supplied by fish with algal nutrient demand. We developed a bioenergetics model to quantify nitrogen and phosphorus excretion rates of A. triradiatus and C. milesi. Daily nitrogen and phosphorus excretion rates were combined with estimates of A. triradiatus and C. milesi population densities in order to estimate nutrient supply by fish on an areal basis. We estimated algal nutrient demand by measuring carbon fixation and C:N:P stoichiometry of algae. Our preliminary results suggest that A. triradiatus and C. milesi each supply 8% of algal nitrogen demand and 13% of phosphorus demand. Rio Las Marias contains several other abundant species of fish that may significantly contribute to the stream's nutrient dynamics. Consequently, in a nitrogen-limited stream, such as Rio Las Marias, fish may help maintain high algal standing stocks. These results suggest the density and distribution of these armored catfish species may have important ecosystem-wide effects potentially including: Increased nutrient availability in areas with high fish densities, changes in algal species composition, or enhanced ecosystem stability.

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This abstract is being presented at: 9:45 AM in session:
Oral Session #70: Aquatic Ecology.