The importance of flooded terrestrial habitats for larval fish in a semi-natural large floodplain (Volga, Russian Federation)

We assessed the importance of flooded terrestrial habitats for fish larvae in a semi-natural large floodplain (Volga, Russian Federation) by comparing abundances at the shoreline of permanent waterbodies with flooded terrestrial habitats. We found that overall larval abundance at the shoreline of permanent waterbodies was 6 to 10 times higher than in flooded terrestrial habitats and was highly consistent over the sampled waterbodies during the 2 year study. The potential mechanisms underlying these results are that shoreline habitats receive an influx of food with retreating warmer water from flooded terrestrial habitats, whereas the risk of hypoxia and stranding is lower at the shoreline than in flooded terrestrial habitats. Furthermore, the risk of predation is also lower at the shoreline compared to the open water habitats. Thus, we hypothesize that, rather than directly providing nursery habitat, the most important function of flooded terrestrial areas for the recruitment of fish in river floodplains is the production of food organisms that become available for larvae and juveniles with the retreating water.