Comparison of fatty acids and elemental nutrients in periphyton, invertebrates, and cutthroat trout (Oncorhynchus clarki) in conifer and alder streams of western Washington state

Abstract

Organism growth and reproduction are often limited by nutrient availability in freshwater ecosystems where, in some cases, food webs are primarily supported by allochthonous organic matter. Therefore, we hypothesized that the composition of riparian vegetation would influence the variability of N, P, and fatty acid content of in-stream consumers. Specifically, we predicted that organisms living in alder streams would have higher levels of N, P, and polyunsaturated fatty acids than organisms in coniferous streams. To determine this, we sampled fresh and aged leaf litter, periphyton, invertebrates, and cutthroat trout (Oncorhynchus clarki) from 6 streams in western Washington state: 3 streams had high densities of nitrogen-fixing red alder (Alnus rubra) in the riparian zone, whereas 3 had high densities of conifers. We found fresh alder litter had twice the total polyunsaturated fatty acid concentrations of hemlock vegetation while there were few statistical differences among aged alder and aged hemlock vegetation. Multidimensional plots showed fatty acid profiles were unique to vegetation and fish while periphyton and invertebrates shared the same multidimensional space. We used a mixed model to determine the relative importance of vegetation type (fixed factor: conifer or alder), trophic levels (fixed factor: periphyton, primary consumer, or fish), and streams (random factor) on individual fatty acid concentrations. Total polyunsaturated fatty acids, 16:0, 20:1, 20:3n6 and total n3 were the only fatty acids influenced by stream vegetation (vegetation ? stream model or full model). 67% of the fatty acids were best supported by the trophic ? stream model. Nitrogen, P, Ca, Fe, C:N, N:P, and C:N:P were all best supported by the trophic level ? stream model, and Zn was the only nutrient supported best by the full model. Correlations of n3 and n6 fatty acid concentrations between periphyton and primary consumers, and primary consumers with trout indicated several fatty acid metrics, such as n3:n6, showed food resources may affect relative fatty acid abundances of consumers. Although vegetation type did not influence relative fatty acids of stream organisms, the importance of trophic level likely indicates organisms have different physical requirements for fatty acids. The significance of a random Handling Editor: Piet Spaak.

Reconciling the role of organic matter pathways in aquatic food webs by measuring multiple tracers in individuals

“…Terrestrial vegetation, particularly grasses and herbaceous plants, had high ALA, in line with results for trees from diverse biomes (mangroves [Carreon-Palau et al 2013], alder and hemlock [Volk and Kiffney 2012]). Terrestrial vegetation, particularly grasses and herbaceous plants, had high ALA, in line with results for trees from diverse biomes (mangroves [Carreon-Palau et al 2013], alder and hemlock [Volk and Kiffney 2012]).…”

“…Though terrestrial sources did not contain C20 and C22 PUFA, they had high contents of C18 PUFA (ALA and LIN), the precursors for C20 and C22 PUFA synthesis. Terrestrial vegetation, particularly grasses and herbaceous plants, had high ALA, in line with results for trees from diverse biomes (mangroves [Carreon-Palau et al 2013], alder and hemlock [Volk and Kiffney 2012]). Highly processed terrestrial material tends to be lower in ALA (Torres-Ruiz et al 2007), much like we observed for leaf litter.…”

Effects of spawning Atlantic salmon (Salmo salar) on total lipid content and fatty acid composition of river food webs

“…Fatty acid profiles readily distinguished between biofilm, invertebrates, and Atlantic salmon parr at all sampling periods, a result also found in other studies involving salmonids (e.g., Heintz et al. , Volk and Kiffney ). The variability in FA profiles was accredited to inherent differences between trophic groups combined with assimilation of marine‐derived FAs in the MDN treatments.…”

Spatial variation in periphyton fatty acid composition in subtropical streams

“…Our study was conducted in early summer in subtropical areas with the stream temperature range 17–25 °C, thus SAFA% appeared to be higher and PUFA% lower. A field investigation in six headwater streams in western Washington State (Volk & Kiffney, ) with a 7‐day average temperature of 11.5–12 °C, showed a similar proportion of periphyton SAFA (48%) to our results, but PUFA (28%) were lower than the artificial stream study (Hill et al ., ). These differences confirm that periphyton FA compositions are influenced by the interplay of several different environmental factors.…”