Effect of Drought and Subsequent Recovery on Endangered Fountain Darter Habitat in Comal Springs, Texas
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The Edwards Aquifer of central Texas contains several aquatic endemic species dependent on the groundwater discharged from numerous springs, including those that comprise the Comal and San Marcos rivers. One of these endemics, the federally-endangered fountain darter Etheostoma fonticola is distributed in only these two rivers of the Guadalupe River drainage. Spring endemic fishes like the fountain darter can be more susceptible to extirpation and extinction events due to their stenothermal requirements and limited distribution. In 2007, central Texas endured drought conditions that spanned two years, culminating with the drought reaching D4-Exceptional status in the summer of 2009. This study evaluated the effect of drought, recovery, and a subsequent flood on fountain darter habitat, diet, invasive gill parasite levels, and associated fish and macroinvertebrate community structure and composition. Within all three periods, fountain darters were collected in greatest densities in Riccia fluitans habitat. Fountain darters were collected in highest densities during the drought with the fewest fountain darters collected during the post-flood period. Available stands of Riccia during the drought were diminishing, whereas they were sparse if present post-flood. During the recovery period, fountain darter captures decreased, corresponding with the reemergence of Riccia stands within the system. Fish community structure displayed highest species richness, abundance, and evenness during the drought period, though diversity was highest during the recovery period.
Macroinvertebrate community structure had the highest abundance and greatest diversity during the drought, while species richness was greatest during the recovery period. High scores on these indices during the drought period are likely a result of these organisms being concentrated to what available habitat was present in the system. Fish community composition varied between drought and post-flood, and recovery and post-flood periods, indicating the post-flood period had a larger role in characterizing the assemblage than the other two periods. Macroinvertebrate community composition varied among all three periods. This is likely due to the seasonal nature of macroinvertebrates, whom have varied life histories including timing of egg deposition and emergence times. Average prey items per digestive tract were highest during the drought, likely due to prey items being concentrated in habitats. The fewest prey items per digestive tract occurred during the post-flood period, possibly resulting from a lack of vegetation available to inhabit. Prey composition varied among all three periods, also likely influenced by seasonal trends and the generalist feeding behavior exhibited by the fountain darter. Gill parasite densities were greatest during the drought period, however, these densities did not exhibit any influence from the measured abiotic variables.