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Using Stable Isotope Mixing in a Great Lakes Coastal Tributary to Determine Food Web Linkages in Young Fishes
Citation:
HOFFMAN, J., G. S. PETERSON, A. M. COTTER, AND J. R. KELLY. Using Stable Isotope Mixing in a Great Lakes Coastal Tributary to Determine Food Web Linkages in Young Fishes. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 33(6):1391-1405, (2010).
Impact/Purpose:
Our objectives were to determine whether we can detect a stable isotope gradient along the river-Great Lake hydrologic continuum in a coastal river and use it to identify changes across this gradient in the food web supporting young-of-year (YOY) and juvenile fish production.
Description:
Our objectives were to determine whether we can detect a stable isotope gradient along the river-Great Lake hydrologic continuum in a coastal river and use it to identify changes across this gradient in the food web supporting young-of-year (YOY) and juvenile fish production. We studied the drowned river mouth ecosystem of the St. Louis River, an important nursery habitat on Lake Superior’s western shore. We sampled five stations along the river-Great Lake continuum to obtain carbon (C) and nitrogen (N) stable isotope ratios of organic matter (OM) sources, zooplankton, zoobenthos, littoral macroinvertebrates, and common fishes. There was an isotopic gradient; the C stable isotope ratios of the zooplankton and fishes were significantly different among stations and increasingly enriched towards the river mouth owing to Lake Superior’s hydrologic influence. The patterns among fishes, however, varied. Black crappie and rock bass were robust indicators of local food webs their isotopic ratios were significantly different among stations; consistent with consumption of local prey; and at either end of a large C stable isotope range (ca. 6‰ d13C) found at every station. Isotopically light black crappies were indicators of a bentho-pelagic trophic pathway and isotopically enriched rock bass of a littoral trophic pathway. In contrast, white perch and round goby had similar C and N isotopic ratios among stations, implying that they frequently move across the system and do not represent local conditions. Further, the isotopic data indicated that the diversity of OM sources contributing to fish production increased towards Lake Superior, implying important Great Lake-tributary relationships that merit further study.