Trophic relationships in northeastern stream ecosystems: Importance of the quality of food sources for macroinvertebrates

Monica Torres Ruiz, Fordham University


This dissertation aimed to produce a better understanding of temperate stream food webs, with emphasis on the quality of autochthonous versus allochthonous food sources for macroinvertebrates. Fatty acids (FA) were used as quality and trophic markers in studies of seven New York streams, although nutritional stoichiometry of carbon, nitrogen and phosphorus, and stable isotopes (SI) were also assessed in the last study. In addition controlled laboratory feeding experiments were performed with the net-spinning caddisfly, Hydropsyche sp. to test for essential FA synthesis and elongation capabilities. In-stream primary producers had significantly greater FA (total and essential FAs 18:3ω3, 18:2ω6, 20:5ω3, 20:4ω6) compared to leaf litter entering seven New York streams. Decomposition and microbial colonization of litter entering the Muscoot River in spring and fall decreased in FA quality. Macroinvertebrates in both the Muscoot and Cross River had high content of omega-3 and omega-6 FAs; among these, 20:5ω3 was particularly important. The essentiality of FAs was supported by limited synthesis and elongation capabilities of Hydropsyche sp, with omega-3 FAs being preferentially assimilated over omega-6. It was also demonstrated that Hydropsyche accumulated FAs that were present in the food provided. Several important temporal and spatial differences were observed in the FA and C/N and C/P of macroinvertebrates and food sources. These studies suggest in-stream primary producers are the main sources of essential FAs and nutrients for macroinvertebrates and marker FAs confirm this. However SI and FA analysis of trophic interactions suggest some animals (in times of year, or areas of streams that are more shaded) also rely on the leaf litter community of fungi and bacteria. In the study of trophic interactions, SIs and FAs complemented each other. Use of both enhanced the understanding of stream food webs although they had the drawback of relying on theoretical values for fractionation and metabolic transformation. Overall these data suggest that there are strong imbalances in the elemental and complex nutrient content of macroinvertebrates and their food sources. These studies strongly suggest that food selectivity for high quality autochthonous sources and/or omnivory may be common mechanisms by which stream invertebrates adapt to these conditions.

Subject Area

Ecology|Freshwater ecology

Recommended Citation

Torres Ruiz, Monica, "Trophic relationships in northeastern stream ecosystems: Importance of the quality of food sources for macroinvertebrates" (2007). ETD Collection for Fordham University. AAI3271277.