Testing of trophic cascade within a headwater spring community: implications for water quantity management
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A management strategy for protecting the federally-listed Fountain Darter Etheostoma fonticola during unnatural low flow conditions is the removal of piscine carnivore Largemouth Bass Micropterus salmoides. However, headwater spring communities include Red Swamp Crayfish Procambarus clarkii, which is prey for Largemouth Bass and a potential predator of the Fountain Darter. Removal of Largemouth Bass could produce an unintentional cascading effect by increasing crayfish consumption of the Fountain Darter. The purpose of this study was to test for cascading effects of benthic fish predation by quantifying the number of Fountain Darters consumed by crayfish only, bass only, and crayfish and bass combined within vegetated and non-vegetated experimental units. Three water temperature trials were conducted to mimic low-flow winter temperatures (18°C), average spring-flow temperatures (22°C) and low-flow summer temperatures (27°C). Among temperature trials, bass only and crayfish and bass combined consumed about equal numbers (P > 0.05) of Fountain Darters, whereas crayfish only consumed the fewest number (P < 0.05) of Fountain Darters, except at 22°C. Largemouth Bass did not consume more crayfish than darters; therefore, removing Largemouth Bass appears to be a viable option in reducing Fountain Darter predation. However, removal efforts should be monitored to further assess efficacy of the management strategy.