Oral Presentation Freshwater Sciences 2023

Precipitation regime drives key differences in trophic structure, secondary production, and community assembly in stream fish communities across a steep rainfall gradient in coastal Texas, USA     (#402)

Christopher M Groff 1 , Christopher J Patrick 1 , Bradley A Strickland 1 , Sean K Kinard 1 , James D Hogan 2 , Matthew R Whiles 3 , Hannah B Vander Zanden 3 , Amber J Ulseth 4 , Desiree A Groff 1 , Christopher F Frazier 5 , Fernando Carvallo 6 , Victoria Jenkins 7 , Alexander T Solis 1 , Connor L Brown 5
  1. Virginia Institute of Marine Science, Gloucester Point, VA, United States
  2. Fisheries and Oceans Canada, Fredericton, New Brunswick, Canada
  3. University of Florida, Gainesville, FL, USA
  4. Sam Houston State University, Huntsville, TX, USA
  5. University of Kansas, Lawrence, Kansas, USA
  6. Colorado State University, Fort Collins, CO, USA
  7. James Cook University International, Townsville, Queensland, Australia

Global climate models predict increasing aridity for many regions in coming decades, along with increased magnitude and variability of precipitation events. In lotic systems, this can translate to substantial shifts in hydrologic regimes, resource bases, and network connectivity. The potential impacts of these shifts on the structure and function of biotic communities however, remains unclear. We used nine stream sites spanning the sharpest natural rainfall gradient in North America not associated with elevation change—the Texas coastal plain—to assess the impacts of aridity on trophic structure, secondary production, and community assembly in fish communities. Stable isotope data indicate compression of food chains with increasing aridity, as well as greater reliance on autochthonous carbon as a basal food resource and decreased connectivity with estuarine food webs. Species abundance, functional trait, and experimental data also point to decreased predation pressure and comparative release from potential top-down trophic control as systems become more arid and less hydrologically stable. Fish production increases with increasing aridity, however this is driven largely by changes in community composition across the gradient rather than species-specific shifts in biomass turnover. Regarding community assembly, analysis of functional trait distributions across sites suggests increased importance of environmental filtering and a diminished role of interspecific competition with higher aridity, as well as stronger selection for hypoxia tolerance. Lotic freshwater systems provide critical resources to human communities worldwide, with fisheries alone producing the staple dietary protein for 160 million people. Yet, the most productive flowing waters are found in regions with high aridification risk. Furthering our understanding of broad-scale aquatic community responses to drying climates will add to a growing body of research surrounding the effects of climate change on ecosystem structure and function, as well as inform our own responses to future environmental change as it relates to these key resources.