Thermal Tolerance, Survival, and Recruitment of Cyprinids Exposed to Competition and Chronic Heat Stress in Experimental Streams

Abstract

AbstractWe examined survival, competition, and recruitment among cyprinids that were subjected to interspecific and intraspecific competition and chronic heat stress in large, outdoor experimental streams. The study was conducted in 2011 during the hottest summer (also one of the driest summers) recorded in Texas. We measured survival of Red Shiners Cyprinella lutrensis, Blacktail Shiners Cyprinella venusta, and Central Stonerollers Campostoma anomalum stocked at varying densities to examine competitive interactions. Trophic interactions among Blacktail Shiner density treatments were assessed with stable isotope analysis (SIA), and mitochondrial markers were used to examine the lineage of young‐of‐the‐year shiners spawned during the study. Stocking survival was significantly greater for Red Shiners, and both shiner species demonstrated higher overall survival rates than Central Stonerollers. Although SIA results were variable among replicate streams, more generalist foraging patterns were observed for Blacktail Shiners in the high‐density treatment (intraspecific competition; no Red Shiners present) relative to the low‐density Blacktail Shiner treatment. Less trophic redundancy was observed in the interspecific competition treatment (Blacktail Shiners and Red Shiners co‐occurring) compared with the same density of Blacktail Shiners only (high‐density treatment). Despite the potentially lethal water temperatures, including 4 d on which water temperatures exceeded 37°C, mitochondrial sequences showed that both Red Shiners and Blacktail Shiners were able to spawn during the study. These results collectively highlight potential mechanisms for explaining fish assemblage responses at local and landscape scales, such as the Red Shiner's recent range expansion and increased abundance in some areas of Texas. Our findings are relevant for forecasting regional changes in fish species distributions in response to more frequent droughts and warmer summers due to climate change.Received March 1, 2013; accepted March 11, 2014