Seasonality, floods and droughts structure larval fish assemblages in prairie rivers

Prairie stream fish assemblages experience seasonal shifts in habitat conditions, often coupled with powerful disturbance regimes, where systems fluctuate widely between drought and deluge. These abiotic drivers, more often than biotic factors, structure fish assemblages. Scouring floods may reset stream communities to early successional seres, and droughts may progressively eliminate species from communities. Therefore, fish assemblage structure resilience depends on recolonisation and reproductive success following a disturbance. Many plains fishes have life history traits that facilitate the wide dispersal and immediate contribution of offspring following disturbance events. However, descriptions of temporal and spatial patterns in larval assemblage structure in prairie streams are scarce, and few studies evaluate the effect of disturbances on reproduction. The objectives of this research were to (i) study the timing and contribution of native prairie stream fishes to drifting larval fish assemblages in three eastern South Dakota basins (Vermillion, James and Big Sioux) and (ii) describe larval fish responses to floods in the James River. We sampled drifting larval fish diversity during the spawning season from 2010 to 2012 throughout each basin. We also examined the effect of flooding on larval fish assemblage structure using data collected near the confluence of the James and Missouri rivers during baseflow (2003, 2004 and 2012) and flood conditions (2010). Subtle variability in spawning traits of prairie fishes and an apparent seasonal progression of larval fish taxa that secondarily respond to disturbance regimes suggests reproductive efforts are adapted to maximise the potential for successful recruitment in these severe systems.