Diel Fish Community Turnover within Riffle Habitats in Little Creek, Tennessee

Abstract

Habitat homogenization can decrease biodiversity by reducing niche spaces used by native species and facilitating the invasion of non-native species. However, less is known about the manner in which organisms utilize heterogeneous habitats across temporal scales. Multiple organisms exhibit cyclic patterns of habitat use across a range of temporal scales (from daily to annual), including habitat shifts over short-term diel cycles. We used triple-pass electrofishing surveys of stream fish communities in shallow riffle habitats of Little Creek, Putnam County, TN, during four sampling occasions to test for diel changes in community composition, diversity, and biomass. We hypothesized that: (1) a subset of species present in riffles during diurnal hours would be absent during nocturnal hours, (2) diversity would be higher during diurnal hours compared to nocturnal hours, and (3) total fish biomass would be higher during daylight hours. We found that the species richness and diversity increased in a downstream direction regardless of diurnal versus nocturnal sampling for three of four sampling occasions. Species richness and diversity were significantly greater during nocturnal compared to diurnal sampling for three of four sampling occasions. There was no apparent spatial or temporal pattern for total fish biomass. Our study showed that fish community diversity and richness increased in riffle habitats during nocturnal hours despite consistency in total fish biomass. Furthermore, although this pattern occurs consistently across a natural gradient in stream size and habitat heterogeneity, nocturnal increases in richness and diversity did not occur during every sampling occasion.