CS08 Biogeochemical Cycles
Date: Tuesday, June 11, 2002
Location: Poster Session - VCC
 
RoyerTV, University of Illinois, Urbana, USA, royer@uiuc.edu
Tank, J, L, University of Notre Dame, Notre Dame, USA, tank.1@nd.edu
Chaloner, D, T, University of Notre Dame, Notre Dame, USA, chaloner.1@nd.edu
 
USE OF STABLE ISOTOPES TO DETERMINE THE BIOMASS OF DECOMPOSERS ON DECAYING SALMON TISSUE
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Decay of anadromous salmon carcasses represents a pulse of nutrients and organic carbon to streams in southeast Alaska. We examined the colonization of dead fish tissue by Saprolegnia, the dominant fungal-like, mycelial decomposer on decaying carcasses. A large difference in del 15N values between salmon tissue and Saprolegnia (8-10 per mil) allowed us to use a stable isotope mixing model to determine Saprolegnia biomass on fish tissue through time. After 40 days of colonization, Saprolegnia represented 12% of the decaying tissue mass, increasing to 27% on day 60 and 30% on day 80. Decomposer biomass represented a substantial portion of the sample mass. The mean decay coefficient for colonized fish tissue was 0.0175 per day, but increased to 0.0215 per day when decomposer mass was subtracted. Decay of salmon tissue was faster than generally reported for leaf litter, but similar to non-woody plants. Stable isotopes indicated that Saprolegnia obtained carbon from the fish tissue, but nitrogen from the water column. Despite the high substrate quality of tissue, microbial decomposers appear to rely on the water column as a nitrogen source.