Nutritional Quality of Basal Food Resources in Aquatic Ecosystems

Catharina Rose Grubaugh, Fordham University


Trophic interactions are key to ecosystem function, and the nutritional quality of food resources can shape these feeding interactions. Theoretically, elemental and biochemical compositions of food resources will correlate with one another because the relative amounts of biomolecules present in a food resource will determine its elemental composition. However, the relationship between elemental and biochemical paradigms of nutritional quality in nature are not clear. Protein content of periphyton measured using a modified Lowry method was positively correlated with N content, but the mean directly measured protein content was <1/2 of the mean protein content estimated with the traditional 6.25 mg protein/mg N conversion factor. The mean N ? protein of the periphyton in my study was 2.47 ± 1.10 (SD), less than all applicable published conversion factors suggested for use in aquatic and marine ecosystems, which ranged from 4.44 to 6.48. The N content of seston enriched with inorganic N and P increased in response to P enrichment, but protein, carbohydrate, and lipid contents decreased, and seston N correlated negatively with protein, carbohydrate, and lipid contents. In stream periphyton, protein and lipid contents varied with differences in the assemblage composition of the periphyton and correlated with several environmental variables, most notably with light availability. However, these variations in biochemical composition did not translate into variations in elemental composition, and, of the nutritional quality measurements used in this study, only N and carbohydrate contents correlated significantly. In all three studies, biochemical composition provided a more detailed picture of the nutritional quality of these basal food resources, as would be expected. However, analyzing data from elemental and biochemical compositions together allowed me to better understand the ecosystem dynamics that affected the nutritional quality of these basal food resources. These results highlight the importance of both elemental and biochemical measures of nutritional quality but also emphasize the differences between these paradigms and caution against using one set of measurements to predict the other.

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Recommended Citation

Grubaugh, Catharina Rose, "Nutritional Quality of Basal Food Resources in Aquatic Ecosystems" (2017). ETD Collection for Fordham University. AAI10621600.