Bottom-up effects of streambed drying on consumer performance through changes in resource quality

Abstract

Stream flow intermittency and subsequent streambed drying, which already occurs in most biomes worldwide, is expected to increase in many regions due to both climate change and increased water demand. We studied the effects of streambed drying on leaves and epilithic biofilm and their effects on potential consumers. In the field, resources were conditioned according to the following treatments: (i) continuously submerged (PERM), (ii) submerged, exposed to the dry streambed and then submerged again (INT), or (iii) conditioned in the dry streambed and only allowed instream conditioning for 1 week (DRY, only for leaves). The results showed that drying affects resource quality, and the effects on biofilm were more severe than those on leaves. Both DRY leaves and INT biofilm showed lower microbial colonization and nitrogen accrual, whereas INT leaves had similar characteristics to PERM leaves. Drying resulted in decreased shredder and herbivore consumption rates and detritivore growth. Our results suggest that bottom-up effects of drying through changes in resource quality can constrain detritivore growth in temporary streams, potentially affecting stream secondary production and invertebrate-mediated organic matter cycling under a drier climate scenario.