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Stable isotopes of C and S as indicators of habitat use by fish in small oregon Coast range streams
Citation:
CHURCH, M., J. L. EBERSOLE, C. Kendall, B. Miller, K. RENSMEYER, AND P. J. WIGINGTON JR. Stable isotopes of C and S as indicators of habitat use by fish in small oregon Coast range streams. Presented at 6th International Conference on Applications of Stable Isotope Techniques to Ecological Studies, Honolulu, HI, August 25 - 29, 2008.
Impact/Purpose:
We are using stable isotopes of C, N, O and S (H planned) to study the ecology of coho salmon in streams of the Oregon Coast Range. We have found isotopes of C and, surprisingly, S to be very useful in discriminating rearing habitats in our small streams.
Description:
We are using stable isotopes of C, N, O and S (H planned) to study the ecology of coho salmon in streams of the Oregon Coast Range. We have found isotopes of C and, surprisingly, S to be very useful in discriminating rearing habitats in our small streams. We found 13C values of coho salmon juveniles at dietary equilibrium in late summer in tributaries of a highly shaded, low-order stream system in the Oregon Coast Range to vary spatially as much as 6‰. Values of 13C in sculpin and trout closely parallel those for coho. Values show a linear relationship to available light (i.e., possible autochthony vs. allochthony) only for sites with shading less than 90%. In contrast, 13C values were linearly related to temperature at all sites – and especially strong for sites with shading between 90% and 100%. We hypothesize that these patterns are dominated by out-gassing of 13C-depleted CO2 as a function of increasing heterotrophic stream metabolism driven by temperature and cumulative downstream effects. In a parallel study, we found low 34S values of muscle tissue of coho salmon smolts from a low-gradient stream system with wetland areas. We also found sculpin (which remain more locally resident than coho) of that system to show clustering of 34S values by locations sampled, with fish more proximate to wetland areas being lower (relative to fish from free-flowing habitats) in δ34S by up to 12‰. These results indicate significant incorporation of reduced sulfur into aquatic food webs, most likely via incorporation of bacteria with reduced and 34S-depleted sulfur by chironomids at the food web base. The δ34S values reflect lengthy occupation by fish of habitats with reducing environments (e.g., beaver ponds) during stream rearing. We propose that 34S might serve as a useful indicator of habitat use patterns in mixed-environment systems, especially ones with a range of red/ox conditions. These findings have interesting implications for food web dynamics in such systems, contrasting a relatively closed nutrient cycling (sulfur example) with a more open system (carbon example) in these specific cases.