Drought may alter the flux of essential omega-3 fatty acids from streams to terrestrial ecosystems

Madeline Pratt Hannappel , Robert Joseph Fournier, Adrianne P Smits, Lauren Esposito, Albert Ruhi

Stream and riparian food webs are connected via cross-ecosystem subsidies, including essential nutrients like omega-3 fatty acids that originate in the aquatic environment (microalgae) but support terrestrial consumers. Although global change stressors could be disrupting these linkages, most research to date has focused on subsidy quantity rather than quality. Here, we reviewed the literature on omega-3 long-chain polyunsaturated fatty acids (ω3 LC-PUFA) in streams and other freshwaters, and we examined how drought-related stress may influence their production, accumulation, and trophic transfer. Although direct evidence linking drought conditions to changes in stream ω3 LC-PUFA dynamics is limited, existing studies point to several disruptive mechanisms: warming- and drying-induced shifts in basal resource composition and primary production, altered consumer community composition and emergence phenology, and reduced capacity for ω3 LC-PUFA bioconversion. ω3 LC-PUFA accumulation in organisms is driven primarily by species identity and further shaped by life-history traits such as drought adaptations (e.g., resistance and resilience strategies), temporal integration of diet, and feeding ecology. We explored these mechanisms via a case study on intermittent stream invertebrates at Pinnacles National Park, California, and found largely taxon-specific patterns rather than consistent responses to hydrology. Finally, we identified key challenges and recommendations for advancing ω3 LC-PUFA research. These include (i) explicitly considering organismal life histories; (ii) improving sampling design to strengthen inference; (iii) considering underground ecological processes; (iv) advancing research on consumer fitness responses to ω3 LC-PUFA limitation and on ‘upgrading’; (v) measuring rates and fluxes; and (vi) scaling up and forecasting fatty acid flux under increasingly dry futures by integrating models of hydrology, organismal biology, and community dynamics. We contend that the disruption of cross-ecosystem linkages, not just in resource magnitude but also in quality, is a “blind spot” of global change ecology that demands immediate attention.