Spatiotemporal Variability of Fish Assemblage Structure in The Roaring River, Tennessee

Abstract

Stream fish assemblages vary across spatial and temporal scales within riverine landscapes. From a spatial perspective, small tributaries nested within larger mainstream habitats have fish assemblages that are nested subsets of those distributed throughout a drainage. From a temporal perspective, fish assemblages exhibit dynamic swings in species occurrences over short-term and long-term periods. We used fish community samples from 10 sites in the Blackburn Fork Watershed in Northcentral Tennessee to assess temporal change in assemblage structure across three samplings years, 1976, 2015, and 2016. We hypothesized that (1) a spatial pattern of increasing species richness across increasing stream sizes would persist through time, and (2) temporal change in fish assemblage structure would be greater between 1976 vs 2015 compared to 2015 vs 2016 given the larger amount of elapsed time between samples. We found support for our initial hypotheses in that species richness and diversity were consistently higher in larger streams compared to smaller streams, regardless of the sampling occasion. Temporal turnover in assemblage composition was highest for 1976 vs 2015 (7 species replacements), intermediate for 1976 vs 2016 (5 species replacements), and lowest for 2015 vs 2016 (2 species replacements). These findings largely support our second hypotheses but also illustrate assemblage turnover even over relatively short time periods. Our findings suggest spatial structuring of fish assemblages is evident across a range of temporal scales (from 1 to 40 years) despite temporal variability in the identities of the species captured.