Urbanisation alters fatty acids in stream food webs

Abstract

Fatty acids are essential to macroinvertebrate growth and reproduction and can indicate food web structure and nutritional quality of basal resources. However, broad‐scale examinations of how catchment land cover and associated stressors affect the proportions of fatty acids (FAs) in stream food webs are few. Here, we: (1) examine relationships among proportions of FAs among benthic periphyton and macroinvertebrate collector/gatherers, shredders, and predators; and (2) test if relationships between periphytic and macroinvertebrate FAs were altered due to the intensity of urban development in catchments. Proportions of the ≥20‐C eicosapentaenoic acid (EPA 20:5ω3), arachidonic acid (ARA 20:4ω6), and docosahexaenoic acid (22:6ω3) indicated collector/gatherers had a diet richer in periphyton than in shredders, which had significantly lower proportions of these FAs. Collector/gatherers were in turn likely to be high‐quality sources of ω3 and ≥ 20‐C FAs for predators, which also had significantly greater EPA and ARA proportions than those in shredders. Linoleic (18:2ω6) and α‐linolenic acid (18:3ω3) comprised the greatest proportions of FAs in shredders, which suggested a diet dominated by leaf litter and associated hyphomycetes. As catchment urbanisation increased, proportions of total ω3 FAs and EPA in periphyton were significantly greater. This pattern also was seen through macroinvertebrate consumers and predators, given that proportions of these FAs in macroinvertebrates also were significantly correlated with factors associated with catchment urbanisation. The significant increase in total ω3 FAs and EPA proportions within shredders indicated that periphyton growth, and their FAs, increased on leaf litter, probably due to greater nutrient concentrations associated with catchment urbanisation. Proportions of total ω6 FAs in biota were not significantly correlated with factors associated with urban development, which could indicate that they were of sufficient abundance for consumers regardless of urban intensity or possible changes in their sources. Our study provides an informative first step that identified notable differences in proportions of FAs among macroinvertebrates in urban streams and an increase in proportions of total ω3 FAs and EPA in periphyton, consumers, and predators as catchment urbanisation increases. Identifying how FA relationships within food webs change in response to catchment alterations and stressors could inform land use and management decisions by linking environmental changes to measures important to ecosystem outcomes.

The dark side of rocks: An underestimated high‐quality food resource in river ecosystems

“…The other ω3 PUFA, DHA, was low or absent in biofilms and invertebrates, and its functional role for invertebrate neural development may be fulfilled by EPA (Ahlgren et al, 2009;Stanley-Samuelson, 1994 (Guo et al, 2016a;Kühmayer et al, 2020;Torres-Ruiz et al, 2007), no matter whether EPA was from light or dark biofilms. Moreover, increased human disturbances in aquatic ecosystems, such as warming, eutrophication, riparian degradation and sedimentation (Burdon et al, 2013), are likely to decrease the availability of algal EPA for aquatic consumers (Guo et al, 2015;Hixson & Arts, 2016;Müller-Navarra et al, 2004;Whorley et al, 2019). In streams with high-nutrient inputs and high levels of removed riparian vegetation, algal communities in light biofilms can become dominated by filamentous green algae (deficient in EPA; Mosisch et al, 2001), whereas in dark biofilms, which are shaded and perhaps cooler from subsurface flows, a higher proportion of diatoms (rich in EPA) is expected (Mosisch et al, 2001).…”

Lipid Composition Differences of Periphyton, Crustaceans, and Small Fishes in Response to Eutrophication and Management in the Florida Everglades,USA

“…For the other fauna, we found that fish and crustaceans had significantly higher contents of PUFA relative to periphyton. In the absence of de novo production, consumers may be more general in their feeding in order to ensure adequate consumption of necessary lipids or are retaining certain PUFA relative to the resource base (Guo et al, 2016; Sanchez and Trexler, 2018; Whorley et al, 2019).…”

“…Consumers are dependent on a suite of PUFA for growth and health that are largely produced only by primary producers (Taipale et al, 2009). Therefore, changes in algal species composition will alter the relative abundances of important PUFA which could have negative bottom‐up effects on consumers (Galloway and Winder, 2015; Whorley et al, 2019). For example, loss of eukaryotic algae for bacteria, cyanobacteria, or detritus will be reflected in declines of important PUFA, notably n‐3 and n‐6 FA families, for organic matter rich in branched, methylated, or monounsaturated FA (MUFA) (Bossio et al, 2006; Vestal and White, 1989; Willers et al, 2015).…”

Conservation Across Aquatic-Terrestrial Boundaries: Linking Continental-Scale Water Quality to Emergent Aquatic Insects and Declining Aerial Insectivorous Birds

“…Novel benthic invertebrate monitoring metrics could build on these ideas to emphasize the proportion or abundance of individuals with flying adult stages in future monitoring efforts. Measures that directly quantify the timing and amount of insect-mediated energetic subsidies from streams and lakes across a spectrum of watershed-scale stressors-while giving appropriate weight to the importance of insects that provision higher levels of nutritional macromolecules (such as fatty acids; Whorley et al, 2019) to riparian consumers-could also be useful in predicting potential consequences of poor water quality for terrestrial insectivores.…”