Testing IsoSource: stable isotope analysis of a tropical fishery with diverse organic matter sources.
Abstract: We sampled consumers and organic matter sources (mangrove litter,
freshwater swamp-forest litter, seagrasses, seagrass epiphytes, and
marine particulate organic matter [MPOM]) from four estuaries on
Kosrae, Federated States of Micronesia for stable isotope (δ13C and δ34S)
analysis. Unique mixing solutions cannot be calculated in a
dual-isotope, five-endmember scenario, so we tested IsoSource, a
recently developed statistical procedure that calculates ranges in
source contributions (i.e., minimum and maximum possible). Relatively
high minimum contributions indicate significant sources, while low
maxima indicate otherwise. Litter from the two forest types was
isotopically distinguishable but had low average minimum contributions
(0–8% for mangrove litter and 0% for swamp-forest litter among
estuaries). Minimum contribution of MPOM was also low, averaging 0–13%
among estuaries. Instead, local marine sources dominated contributions
to consumers. Minimum contributions of seagrasses averaged 8–47% among
estuaries (range 0–88% among species). Minimum contributions of
seagrass epiphytes averaged 5–27% among estuaries (range 0–69% among
species). IsoSource enabled inclusion of five organic matter sources in
our dual-isotope analysis, ranking trophic importance as follows:
seagrasses > seagrass epiphytes > MPOM > mangrove forest >
freshwater swamp-forest. IsoSource is thus a useful step toward
understanding which of multiple organic matter sources support food
webs; more detailed work is necessary to identify unique solutions.
Benstead, J. P., J. March, B. Fry, K. Ewel, and C. M. Pringle. 2006. Testing IsoSource: stable isotope analysis of a tropical fishery with diverse organic matter sources. Ecology 87:326-333.
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