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Landscape-scale food webs of fish nursery habitat along a river-coast mixing zone
Citation:
Hoffman, J., J. Kelly, Greg Peterson, AND A. Cotter. Landscape-scale food webs of fish nursery habitat along a river-coast mixing zone. Estuaries and Coasts. Estuarine Research Federation, Port Republic, MD, 38(4):1335-1349, (2015).
Impact/Purpose:
A key ecosystem service of coastal wetlands is to serve as fish nursery habitat, providing the basis for regional recreational and commercial fisheries. Coastal wetlands are complex ecosystems, embedded in a a mosaic of habitats situated between the land and open water. They are therefore subject to varying exchanges between the watershed and open water that may influence fish production. In this study, we characterized the trophic connections of fish larvae in their nursery habitat to identify the major fluxes of material that may impact fish production. We found that every fish studied relied on energy produced from more than one habitat, and that there was widespread reliance of watershed derived energy. The study advances our understanding of how different energy flows support fish growth and thus can influence ecosystem services.
Description:
We used carbon and nitrogen stable isotope analysis to study connections between allochthonous energy use and ecological connectivity of fish larvae in a complex coastal mosaic. We quantified fish larvae support by autochthonous and allochthonous material in three coastal river-wetland complexes in Lake Superior, sampling across the watershed-coast interface in river, river mouth, and coastal regions. Fish stable isotope ratios, after adjusting for trophic fractionation, generally were intermediate between the OM sources measured, indicating widespread reliance on multiple OM sources. Based on a two stable isotope mass balance model, fish growth was largely supported by autochthonous sources (generally 60% to 90%), including phytoplankton, benthic periphyton, and aquatic vegetation. Terrestrial derived OM supported between 10-25% and as much as 43% of fish larvae somatic growth in river and river mouth regions, but did not support fish larvae growth in coastal regions. Patterns in isotopic composition of OM sources and fish larvae did indicate connectivity between river mouth and coast regions through bi-directional movement of fish larvae across the wetland-coast interface. Food web complexity, as measured by the number of OM sources supporting fish larvae growth, was higher in the river and river mouth regions than in coastal waters. Principal component analysis revealed that terrestrial OM utilization was greatest in those fish larvae occupying shallow water habitat in river mouth regions and positively correlated with the number of OM sources supporting fish larvae. This positive relationship between allochthonous OM support and food web complexity was unexpected and suggests that consumer-prey interactions across connected habitats functioned in conjunction with landscape-scale features (e.g., distance to lake, riverine influence) to determine utilization of allochthonous OM sources.
