A Test of the Dependence of Secondary Production on Unicellular Algae in Running Water Ecosystems

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9318205 Lewis Studies of salt marshes, seagrass communities, and flood plains have shown that the consumer food webs of aquatic ecosystems may be strongly dependent on production of unicellular algae, even when organic matter from vascular plants is abundant. These findings suggest that the relative importance of unicellular algae in supporting consumer biomass in running waters, which are often dominated by organic matter from vascular plants, may have been underestimated. The proposal outlines a plan for testing this concept over a broad gradient of physical conditions in two rivers of the Colorado Rockies. The study plan is based on the application of stable isotope mentodology, which has been shown by means of pilot studies on the proposed field sites to provide good discrimination between vascular plant carbon and algal-derived carbon. The working hypotheses is that the overall contribution of algal carbon to secondary production is high whenever physical conditions permit sufficient irradiance at the substrate to support algal growth. The drainage basins, and includes corollary measurements of secondary production so that relative contributions of algal carbon to consumer production can be quantified. The study will clarify the relative importance of algal carbon over a wide range of physical conditions in the presence of organic carbon derived from vascular plants.