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Marsh-nekton connectivity - A estuarine food web study in Yaquina Bay, Oregon using dual isotope analysis
Citation:
FOLGER, C. Marsh-nekton connectivity - A estuarine food web study in Yaquina Bay, Oregon using dual isotope analysis. Presented at Pacific Estuarine Research Society, Bellingham, WA, April 02 - 05, 2009.
Impact/Purpose:
Understanding temporal and spatial variability in community-level interactions of PNW estuaries has implications for ecosystem-based management principles.
Description:
Understanding temporal and spatial variability in community-level interactions of PNW estuaries has implications for ecosystem-based management principles. Here, we are analyzing the contribution of marsh derived food sources to non-commercial resident fish in Yaquina Bay, a temperate estuary on the central Oregon Coast. A dual stable isotope analysis (δ13C and δ15N) was used to distinguish relative resource use of isotopically distinct marsh and SAV mudflat habitats and to determine trophic linkages and energy flow between salt marsh and nekton communities. Elucidating the energy source and trophic status of these various components will provide a basis for quantifying marsh contribution to estuarine food webs via small estuarine fishes. The five most abundant fish species: Shiner perch (Cymatogaster aggregata), Staghorn Sculpin(Leptocottus armatus), Northern Anchovy (Engraulis mordax), English Sole (Pleuronectes vetulus), and Topsmelt (Atherinops affinis)were examined. The proportional contributions of the different food sources to the diets of the fish consumers were established using the IsoSource mixing model. We also obtained direct foraging numbers and determined prey species for two of the most abundant fishes caught in the tidal sloughs to link residency with prey utilization. Preliminary results showed a localized marsh isotope signal in the general population of the fishes examined. MANOVA and ANOVA revealed statistically significant spatial differences between the δ13C signal of most invertebrate prey and predator fishes. Fish caught closer to the mouth of the estuary had a δ13C of -14 ‰, reflective of trophic input from macroalgae/seagrass, while fish caught closer to marsh habitats had a δ13C of -19 ‰. These results suggest that marshes may influence adjacent habitats through the utilization of exported organic matter into the main channel. Although, marsh habitat and associated autochthonous marsh-derived production is considerably less abundant than in historical times, the persistence of a ‘marsh signal’ suggests that marshes play a large role in sustaining small resident fish populations in the estuary.