Fish distributions and nutrient cycling in streams: Can fish create biogeochemical hotspots?

Peter B. McIntyre, Alexander S. Flecker, Michael J. Vanni, James M. Hood, Brad W. Taylor, Steven A. Thomas

Research output: Contribution to journalArticlepeer-review

Abstract

Rates of biogeochemical processes often vary widely in space and time, and characterizing this variation is critical for understanding ecosystem functioning. In streams, spatial hotspots of nutrient transformations are generally attributed to physical and microbial processes. Here we examine the potential for heterogeneous distributions of fish to generate hotspots of nutrient recycling. We measured nitrogen (N) and phosphorus (P) excretion rates of 47 species of fish in an N-limited Neotropical stream, and we combined these data with population densities in each of 49 stream channel units to estimate unit- and reach-scale nutrient recycling. Species varied widely in rates of N and P excretion as well as excreted N:P ratios (6-176 molar). At the reach scale, fish excretion could meet >75% of ecosystem demand for dissolved inorganic N and turn over the ambient NH4 pool in <0.3 km. Areal N excretion estimates varied 47-fold among channel units, suggesting that fish distributions could influence local N availability. P excretion rates varied 14-fold among units but were low relative to ambient concentrations. Spatial variation in aggregate nutrient excretion by fish reflected the effects of habitat characteristics (depth, water velocity) on community structure (body size, density, species composition), and the preference of large-bodied species for deep runs was particularly important. We conclude that the spatial distribution of fish could indeed create hotspots of nutrient recycling during the dry season in this species-rich tropical stream. The prevalence of patchy distributions of stream fish and invertebrates suggests that hotspots of consumer nutrient recycling may often occur in stream ecosystems.

Original languageEnglish (US)
Pages (from-to)2335-2346
Number of pages12
JournalEcology
Volume89
Issue number8
DOIs
StatePublished - Aug 2008

Keywords

  • Biodiversity
  • Consumer nutrient recycling
  • Ecological stoichiometry
  • Ecosystem functioning
  • Ecosystem processes
  • Prochilodus mariae
  • Spatial heterogeneity
  • Tropical fish

ASJC Scopus subject areas

  • Ecology, Evolution, Behavior and Systematics

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