The importance of omega-3 polyunsaturated fatty acids as high-quality food in freshwater ecosystems with implications of global change

Traditionally, trophic ecology research on aquatic ecosystems has focused more on the quantity of dietary energy flow within food webs rather than food quality and its effects on organisms at various trophic levels. Recent studies emphasize that food quality is central to consumer growth and reproduction, and the importance of food quality for aquatic ecosystems has become increasingly well recognized. It is timely to synthesise these findings and identify potential future research directions. We conducted a systematic review of omega-3 polyunsaturated fatty acids (& omega;3-PUFAs) as a crucial component of high-quality food sources in freshwater ecosystems to evaluate their impact on a variety of consumers, and explore the effects of global change on these high-quality food sources and their transfer to higher trophic consumers within and across ecosystems. In freshwater ecosystems, algae rich in & omega;3 long-chain PUFAs, such as diatoms, dinoflagellates and cryptophytes, represent important high-quality food sources for consumers, whereas cyanobacteria, green algae, terrestrial vascular plants and macrophytes low in & omega;3 long-chain PUFAs are low-quality food sources. High-quality & omega;3-PUFA-containing food sources usually lead to increased growth and reproduction of aquatic consumers, e.g. benthic invertebrates, zooplankton and fish, and also provide & omega;3 long-chain PUFAs to riparian terrestrial consumers via emergent aquatic insects. Consumers feeding on high-quality & omega;3-PUFA-containing foods in turn represent high-quality food for their own predators. However, the & omega;3-PUFA content of food sources is sensitive to global environmental changes. Warming, eutrophication, increased light intensity (e.g. from loss of riparian shading), and pollutants potentially inhibit the synthesis of algal & omega;3-PUFAs while at the same time promoting the growth of lower-quality foods, such as cyanobacteria and green algae. These factors combined could lead to a significant reduction in the availability of & omega;3-PUFAs for consumers and constrain their overall fitness. Although the effect of individual environmental factors on high-quality & omega;3-PUFA-containing food sources has been investigated, multiple environmental factors (e.g. climate change, human activities, pollution) will act in combination and any synergistic effects on aquatic food webs remain unclear. Identifying the sources and fate of & omega;3-PUFAs within and across ecosystems could represent an important approach to understand the impact of multiple environmental factors on trophic relationships and the implications for populations of freshwater and riparian consumers. Maintaining the availability of high-quality & omega;3-PUFA-containing food sources may also be key to mitigating freshwater biodiversity loss due to global change.

Automated summary

Traditionally, research on aquatic ecosystems focused on the quantity of dietary energy flow within food webs rather than food quality. Recent studies emphasize the importance of food quality for consumer growth and reproduction. This review evaluates the impact of omega-3 polyunsaturated fatty acids as high-quality food sources in freshwater ecosystems and explores the effects of global change on these food sources and their transfer to higher trophic consumers.