Pecos River food webs: investigating impacts of salinization, non-native species, and other environmental changes

Authors: Allison A. Pease, Jessica L. East, Jared H. Breaux, Cassie M. Vaughan

Year: 2016 (xlviii)

Abstract

The Pecos River is impacted by threats common in semi-arid regions including diminished discharge, increased salinity, and non- native invasive species. We assessed variation in local food webs along the longitudinal gradient of the main-stem Pecos River by estimating carbon sources, trophic positions, and assemblage-wide trophic structure for aquatic consumers at twelve sites using stable isotope analysis. We collected additional specimens of Gulf Killifish, Fundulus grandis, in order to investigate the feeding ecology of this non-native species in the Lower Pecos. In Pecos River food webs, consumer richness, food-chain length, and assemblage-wide niche breadth were inversely related to specific conductivity. Mixing models revealed differences in sources of dietary carbon supporting fish production along the longitudinal fluvial gradient, with a shift toward reliance on algal production in the salinized reaches of the river. Trophic niche breadth was greatest for assemblages in less degraded sites with higher fish species richness. Local food webs in salinized sites were dominated by euryhaline species and had shorter food chains and narrower assemblage-wide niche breadths. Stomach contents analysis revealed that F. grandis were piscivorous, consuming more fish prey than has been reported from native coastal ecosystems. Our results suggest that salinization and altered flow regimes in portions of the Pecos River constrain the diversity of consumers and trophic resources in local food webs. The non-native, piscivorous F. grandis also potentially threatens native species in these reaches.