How does drought disrupt the transfer of essential omega-3 Polyunsaturated Fatty Acids (PUFA) from freshwater to terrestrial ecosystems?

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

Freshwater and terrestrial 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 fresh waters, and we examined how drought-related stress may influence their production, accumulation, and trophic transfer. Existing studies indicate that warming and drying-induced shifts in basal resource composition, altered consumer production and emergence phenology, and reduced capacity for ω3 LC-PUFA bioconversion are poised to disrupt ω3 LC-PUFA fluxes from the aquatic to the terrestrial environment. Accumulation of ω3 LC-PUFA in organisms is strongly influenced by life-history traits, including drought adaptations (e.g., resistance versus resilience strategies), temporal integration of diet, and feeding ecology. We confirmed and illustrated these patterns via a case study assessing intermittent stream invertebrates at Pinnacles National Park, California. Finally, we identified key challenges and recommendations for advancing ω3 LC-PUFA research. These include (i) explicitly considering organismal life histories; (ii) improving experimental 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 composition. 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 urgent attention.