Subsidies of long-chain polyunsaturated fatty acids from aquatic to terrestrial environments via amphibian emergence

Resource subsidies across aquatic-terrestrial boundaries can alter predator distribution and biomass and elicit trophic cascades. Most studies have focused on the size of cross-boundary fluxes, but the impact of a subsidy is also mediated by quality and relative abundance of similar resources in the recipient habitat. Long-chain polyunsaturated fatty acids (LC-PUFAs) are necessary for proper physiological function, are unevenly distributed across the landscape, and animals differ greatly in their ability to synthesize them from biochemical precursors, which creates the potential for limitation and increases their possible importance as a subsidy. We examined whole-body LC-PUFA content and export in eight species of emerging amphibian metamorphs across eight temporary ponds in a wetland complex. We found that whole-body content and export of LC-PUFAs varied across species, but were generally within the ranges of other amphibian studies and several freshwater fish and aquatic insects. Anurans exported higher amounts of LC-PUFAs than salamanders, largely due to the higher emergence biomass of anurans. As such, the export of LC-PUFAs closely mirrored the biomass export for each species. Larger ponds exported higher amounts of eicosapentaenoic acid and docosahexaenoic acid, but some smaller ponds exported more per unit wetted area, indicating the potential importance of small ponds at a landscape scale. Given their vital physiological roles, the uneven distribution of aquatic-origin LC-PUFAs could have far reaching effects on terrestrial predators.