Influence of stream intermittency on PUFA transfer to alpine riparian spiders

An increasing number of streams are becoming intermittent due to global warming and water abstraction. The transfer of omega-3 polyunsaturated fatty acids (PUFAs)—particularly eicosapentaenoic acid (EPA)—from aquatic to terrestrial systems is a key ecosystem service likely to be affected by increasing intermittency. Here, we investigated how flow intermittency affected EPA transfer to riparian spiders along 9 headwater streams of an alpine catchment (Val Roseg, Switzerland) with different degrees of intermittency. We used fatty acid analysis to test if there were differences in fatty acid content in spiders sampled along streams varying in degree of intermittency. In addition, we used compound-specific isotope analysis ( 2 H-CSIA) to determine the origin of different fatty acids present in spiders. We found altered fatty acid profiles, characterized by lower content of the omega-3 fatty acids EPA and docosahexaenoic acid (DHA) in spiders collected along streams that dried periodically during multiple times of the year. In contrast, spiders from streams experiencing seasonal drying during winter did not show altered fatty acid profiles compared to spiders from perennial streams. δ 2 H values indicated that fatty acid sources also differed between streams varying in intermittency. Our results suggest that stream intermittency affects subsidy transfers from aquatic to riparian ecosystems, indicating far-reaching consequences for riparian communities in resource poor alpine environments, but potentially also lower elevation fluvial systems.