Exploration of Seasonal Dynamics of Food Resources and Diets of Fish in Upper Cibolo Creek and the Impacts of Turbidity on Growth and Survival of Devils River Minnow (Dionda diaboli)

Food resources such as algae and macroinvertebrates are important for the survival and distribution of fish. These resources vary spatio-temporally along natural gradients such as upstream to downstream and due to natural processes, such as seasonal leaf loss. Urbanization is a major factor that can affect food resources in creeks by altering natural processes such as hydrology and erosion, leading to changes in conditions such as water quality and habitat. Thus, an important aspect of managing fish populations in stream undergoing urbanization is to understand feeding preferences of fish, patterns of spatio-temporal variability in food resources, and how urbanization may change such patterns. Cibolo Creek in Boerne, TX is undergoing increasing urbanization, including the discharge of wastewater effluent, yet sections of the creek are protected, allowing for study of relatively unimpacted food resource dynamics. To better understand natural spatio-temporal patterns of food resources and their environmental controls in Cibolo Creek, I conducted a three-year study measuring biofilm biomass, algal biomass, particulate organic matter, macroinvertebrates, and diatom communities seasonally at several sites with different habitat and water quality conditions. I also analyzed the gut contents of several fish species to determine their seasonal food preferences. Additionally, I looked at how turbidity, which can increase in urban environments, affects the feeding behavior, growth, and survival of the threatened Devils River Minnow. My findings revealed that season and habitat type were the main driving factors for changes in algal biomass and coarse and fine particulate organic matter. Diatom communities showed strong seasonal changes, while macroinvertebrate communities showed stronger responses to habitat types than seasonality. Fish species also exhibited seasonal variations in their diet preferences, with many showing a preference for certain macroinvertebrate taxa. In the Devils River minnow study, short-term increases in turbidity increased time to initiate foraging, but not to a degree that translated to individual physiological effects. These results provide insight into the natural seasonal dynamics of food resources and fish diets and the potential impacts of urbanization on fish foraging and food webs, informing local management efforts to minimize the effects of urbanization on aquatic ecosystems.