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Red swamp crayfish (Procambarus clarkii) were first recorded in Topanga Creek in 2001. With the onset of drought in Southern California resulting in low flows in 2011-2014, the population rapidly increased. Within the Santa Monica Mountains, P. clarkii has been linked to diminishing numbers of California newt (Taricha torosa), a species of special concern (Kats et al. 2013). To address these concerns, a student-based citizen science program was conducted from November 2013 through February 2014 to remove crayfish from a 200 meter reach of Topanga Creek. The following data was collected and compared between the removal reach and an upstream, adjacent 200 meter non-removal reach (control): water quality (temperature, salinity, pH, conductivity, dissolved oxygen, turbidity), nutrient levels (nitrate, nitrite, ammonia, orthophosphate), benthic macroinvertebrate community metrics, crayfish demographics and catch-per unit effort (removal reach only). The results indicate that red swamp crayfish presence or removal does not affect water quality or nutrient levels in Topanga Creek. However, benthic macroinvertebrate communities were significantly different between reaches; the presence of crayfish correlated with lower BMI abundance, a higher proportion of tolerant taxa, and lower feeding group complexity.

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