LB 2-19 - CANCELLED - Precipitation regime influences secondary production dynamics in stream food webs

The food web-level effects of temperature shifts associated with climate change have received considerable attention. Less appreciated is the idea that climate change alters precipitation rates and distribution, which affects food webs of flowing waters that are tightly coupled with hydrology. Using a model study system along the Texas Gulf Coast (annual rainfall shifts from 54 to 94 cm yr-1), we evaluated the role of precipitation regime in controlling energy flow dynamics and secondary production of macroinvertebrate and fish communities in nine freshwater streams. As expected, most (72–95%) production was driven by fast growing invertebrate taxa, including chironomids and oligochaetes. We found that both annual fish production and annual invertebrate standing stocks declined with increasing annual rainfall. For example, fish annual production averaged 1.8 ± 1.5 (SD) g AFDM m-2 yr-1 across sites, and our linear model predicted an average change in 2.4 g AFDM m-2 yr-1 across the 40 cm yr-1 rainfall gradient. Differences in community composition, rather than species-specific shifts in turnover rates across the gradient, drove the patterns we observed in production and biomass. Many stream ecosystems are vulnerable to fluctuations in hydrology that will be altered by future shifts in precipitation patterns associated with climate change. Our work suggests that these changes in rainfall patterns may modify energy flow patterns in aquatic food webs.