Differences between main-channel and off-channel food webs in the upper Mississippi River revealed by fatty acid profiles of consumers

James H. Larson; Michelle Bartsch; Steve Gutreuter; Brent C. Knights; Lynn Bartsch; William B. Richardson; Jonathan M. Vallazza; Michael T. Arts

doi:10.5268/iw-5.2.781

USGS · 70141293

Differences between main-channel and off-channel food webs in the upper Mississippi River revealed by fatty acid profiles of consumers

James H. Larson·Michelle Bartsch·Steve Gutreuter·Brent C. Knights·Lynn Bartsch·William B. Richardson·Jonathan M. Vallazza·Michael T. Arts

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Abstract

Large river systems are often thought to contain a mosaic of patches with different habitat characteristics driven by differences in flow and mixing environments. Off-channel habitats (e.g., backwater areas, secondary channels) can become semi-isolated from main-channel water inputs, leading to the development of distinct biogeochemical environments. Observations of adult bluegill ( Lepomis macrochirus ) in the main channel of the Mississippi River led to speculation that the main channel offered superior food resources relative to off-channel areas. One important aspect of food quality is the quantity and composition of polyunsaturated fatty acids (PUFA). We sampled consumers from main-channel and backwater habitats to determine whether they differed in PUFA content. Main-channel individuals for relatively immobile species (young-of-year bluegill, zebra mussels [ Dreissena polymorpha ], and plain pocketbook mussels [ Lampsilis cardium ]) had significantly greater PUFA content than off-channel individuals. No difference in PUFA was observed for the more mobile gizzard shad ( Dorsoma cepedianum ), which may move between main-channel and off-channel habitats even at early life-history stages. As off-channel habitats become isolated from main-channel waters, flow and water column nitrogen decrease, potentially improving conditions for nitrogen-fixing cyanobacteria and vascular plants that, in turn, have low PUFA content. We conclude that main-channel food webs of the upper Mississippi River provide higher quality food resources for some riverine consumers as compared to food webs in off-channel habitats.

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Source-reported bounding extent: 43.61917644272345° to 43.95921358836687° latitude; -91.4117431640625° to -91.17965698242188° longitude. This indicates report coverage, not an exact sampling location. View area on OpenStreetMap.

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James H. Larson, Michelle Bartsch, Steve Gutreuter, Brent C. Knights, Lynn Bartsch, William B. Richardson, Jonathan M. Vallazza, Michael T. Arts. 2015. Differences between main-channel and off-channel food webs in the upper Mississippi River revealed by fatty acid profiles of consumers. https://doi.org/10.5268/iw-5.2.781

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