Variability of hydrological connectivity and fish dynamics in a wide subtropical–temperate floodplain

Abstract

Fish are subject to diverse stimulus in floodplain rivers resulting from interactions between environmental factors. In such complex and interconnected ecosystems, fish assemblages are thus highly dynamic across space and time. Here, we analysed fish assemblage structures in lotic/lentic habitats of a geomorphic unit of the Middle Paraná River during summer, autumn, and winter of seven consecutive years. We observed that three main factors trigger significant structural changes: seasonality, habitat characteristics, and floodplain connectivity. The last one appears to have a determinant role on fish structures. Processes of connection/isolation of floodplain environments produced significant variations in fish abundance and species richness.Main results showed that some ecological processes can be largely explained by connectivity variations, such as fish dispersal in the floodplain, fish concentration in remnant floodplain lakes, and migrations back to permanent floodplain water bodies.This study provided a quantitative measurement of connectivity to understand fish dynamics in a giant floodplain and highlights the importance of similar investigations to preserve the fish fauna in these rather unique ecosystems.

Discrimination of hydrologic variations for spatial distribution of fish assemblage in a large subtropical temperate river

“…lateral connectivity variations), which produced changes in ß‐diversity of fish assemblages. These results are in line with Tejerina‐Garro and de Mérona (), Mims and Olden (), Abrial et al (), Górski, Collier, Hamilton, and Hicks (), Rabuffetti et al (), Scarabotti, Demonte, and Pouilly (), Abrial et al (), highlighting the importance of the hydrology in the structuring of fish assemblages.…”

“…Ward, Tockner, and Schiemer () referred to this period as a ‘biological interaction phase’ because space decreases while density of individuals and species increases. Intense water recessions would conduce to significant isolation processes (Abrial et al, ), and thus, local internal factors (abiotic processes and interaction between species) would lead to a differentiation of fish assemblages between fluvial lakes of the Middle Paraná River (Scarabotti et al, ). However, during the studied period, no significant isolations of the floodplain habitats occurred (Figure ).…”

“…In the Middle Paraná River, the low‐water period usually occurs in August–September and levels may stay below 2.30 m at Santa Fe gauging station. During those conditions, most of the fluvial lakes in this area have no connection with the main channel (Abrial et al, ; Paira & Drago, ). The high‐water period usually occurs during December–March, and levels attain or surpass 4.50 m. The alluvial plain is completely flooded when the hydrological level reaches 5 m above the base‐flow level (Bonetto, Cordiviola de Yuan, Pignalberi, & Oliveros, ; García & Vargas, ).…”

“…A level of 4.50 m was used as the average reference level for bankfull, the level when water begins to flow into the adjacent alluvial plain within the study area given rise to the beginning of the flood pulse phase. A level of 2.30 m was used as the reference level for disconnection of most fluvial lakes from the river channel (Abrial et al, ; Drago, ). We followed Puckridge et al () and Tockner et al () in using the term ‘flow pulse’ to refer to a discrete rise and fall of the water level that remain confined within the channel banks.…”

Fish Structure in Channel Networks of a Large Anabranching Floodplain: Effect of Isolation/Connection Processes

“…We selected a sector of the large anabranching floodplain of the middle reach of the Paraná River. In this zone, many connections exist between lentic and lotic environments, conferring a high degree of connectivity to the system (Drago, 1980;Abrial et al, 2019). The permanent or temporary character of those connections depends on the frequency, magnitude, and duration of the flood and drought pulses (Drago et al, 2003).…”