Ecological Archives M085-006-A2

Jacob E. Allgeier, Craig A. Layman, Peter J. Mumby, and Amy D. Rosemond. 2015. Biogeochemical implications of biodiversity and community structure across multiple coastal ecosystems. Ecological Monographs 85:117132.

Appendix B. Details of field-based excretion methods.

Nutrient Excretion – empirical estimates

Fish were captured using hook and line or traps (n = 665 individual fish, 79 species, 46 genera, and 26 families). The aim was to incorporate a full suite of size classes for each species, as such the total size range of fish used in this study was very large (2–100 cm). Excretion rates were determined in situ following the methodologies of Schaus et al. (1997) as modified by Whiles et al. (2009) and Allgeier et al. (2014). Fish were incubated in bags containing a known volume (depending on fish size ranging 1–8 liters) of prefiltered (0.7 µm pore size Gelman GFF) seawater for ~30 minutes. This time interval was chosen based on the recommendations made by Whiles et al. (2009) and our own experimental time trials (n = 64 trials for 22 species for a suite of sizes classes) whereby water nutrients were analyzed from the bag (containing the fish) every 5 minutes for either 60 or 90 minutes to determine when excretion rate would asymptote relative to time. All bags were placed together in a holding tank of water at similar ambient temperature (20–23°C). Excretion rates (mg/h) were calculated based on the difference between the dissolved nutrient concentrations (soluble reactive phosphorus (SRP-P) and ammonium (NH4-N)) before and after the fish were incubated in the water. Values were control corrected through the use of multiple (typically n = 6) identical control incubation bags without fish. Water samples (filtered with 0.45 mm Whatman nylon membrane filters) were immediately placed on ice and, within 10 hours, analyzed for NH4 using the methodologies of Taylor et al. (2007), or frozen for transport to the Odum School of Ecology (UGA) for SRP analysis using the ascorbic acid method and colorimetric analyses (APHA 1995).

Each fish used for excretion experiments were weighed for wet mass and measured to standard length. Fish were dissected and stomach content was removed and recorded and then frozen for transport to Odum School of Ecology. Samples were lyophilized to a consistent dry weight then ground to a powder with a ball mill grinder. Larger individuals required blending to homogeneity before mill grinding. Ground samples were analyzed for %C and N content with a CHN Carlo-Erba elemental analyzer (NA1500) CN Analyzer, and for %P using dry oxidation-acid hydrolysis extraction followed by a colorometric analysis (Aplkem RF300). Elemental content was calculated on a dry weight basis.

Literature cited

Allgeier, J. E., C. A. Layman, P. J. Mumby, and A. D. Rosemond. 2014. Consistent nutrient storage and supply mediated by diverse fish communities in coral reef ecosystems. Global Change Biology.

Schaus, M., J. Vanni, T. E. Wissing, M. T. Bremigan, J. E. Garvey, and R. A Stein, M. H. 1997. Nitrogen and phosphorous excretion by detritivorous gizzard shad in a reservoir ecosystem. Limnology and Oceanography 42:1386–1397.

Taylor, B. W., C. F. Keep, R. O. Hall, B. J. Koch, L. M. Tronstad, A. S. Flecker, and A. J. Ulseth. 2007. Improving the fluorometric ammonium method: matrix effects, background fluorescence, and standard additions. Journal of the North American Benthological Society 26:167–177.

Whiles, M. R., A. D. Huryn, B. W. Taylor, and J. D. Reeve. 2009. Influence of handling stress and fasting on estimates of ammonium excretion by tadpoles and fish: recommendations for designing excretion experiments. Limnology and Oceanography-Methods 7:1–7.

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