Landscape and Hydro‐Climatic Drivers of Fish Communities in Floodplain Wetlands

Floodplain wetlands are characterised by dynamic hydrological regimes and seasonal patterns of wetting and drying. They support distinct communities of fish, many of which are adapted to dynamic and variable conditions. Seasonal hydrological variation and the degree of water permanence influence physicochemical conditions and local habitat, which together with the surrounding landscape strongly influence the distribution and persistence of fish within individual wetlands.

This study aimed to evaluate how broad‐scale landscape and temporal environmental factors of wetland ecosystems and biological traits of wetland fishes can determine occurrence patterns in floodplain wetland fish assemblages.

We analysed inundation and environmental data spanning 37 years (1986–2022) across floodplain wetlands in the southern Murray–Darling Basin (MDB), Australia. Fish occurrence records for 14 species (10 native and 4 introduced) were sourced from public databases and combined with remotely sensed estimates of inundation frequency and land‐cover data to assess species‐environment‐relationships. To better understand the potential influence of biological determinants of habitat use (i.e., biological traits and species interactions), we also incorporated species‐specific traits related to life history, trophic levels and potential population growth, as well as phylogenetic relatedness. We applied Joint Species Distribution Models (JSDMs) to evaluate how environmental and biological factors jointly shape wetland fish community structure.

Fish assemblages were primarily structured by environmental conditions, with water temperature, wetland area, and inundation regime identified as influential factors. Species‐specific responses to these environmental filters were heterogeneous. Biological traits, including life history, trophic level and resilience, collectively explained 26% of the variance in species occurrences, highlighting their role in determining habitat use. Spatial effects, accounting for variation among wetland locations and catchments, also contributed significantly to community structure. Phylogenetic relatedness did not influence species co‐occurrence. After accounting for environmental, trait‐based, and spatial factors, residual species associations suggested the potential for biotic interactions such as competition or facilitation acting at different scales.

Fish communities in floodplains wetlands of the southern Murray–Darling Basin (MDB) are predominantly shaped by environmental filtering, with hydrology (inundation) the dominant factor, moderated by species traits and spatial context. This underscores that effective conservation and restoration of floodplain fish communities will require management strategies that buffer thermal extremes and enhance wetland permanence, along with maintaining a mosaic of wetland areas and considering landscape connectivity to accommodate both environmental influences and species‐specific habitat requirements.