Hydrological connectivity and habitat condition shape fish assemblages on a tropical agricultural floodplain

Abstract Coastal floodplains are ecologically rich transitional zones that support diverse fish assemblages and deliver essential services to estuarine and marine ecosystems. Despite these services, these systems are increasingly fragmented by agricultural, urban and industrial expansion, and hydrological modification, which can each impair connectivity and habitat quality. Using a 15-year dataset from the Burdekin floodplain in tropical Australia, we assessed fish community structure and water quality in relation to wetland condition and connectivity. Despite some restoration efforts, fish assemblages remained depauperate in sites with restricted estuarine access, particularly for diadromous and commercially important species such as Lates calcarifer. Dissolved oxygen levels were frequently hypoxic, driven by nutrient enrichment and dense aquatic vegetation, limiting fish survival even during connected flow events. Multivariate analyses identified estuarine connectivity as a key predictor of assemblage structure, though local habitat quality moderated ecological responses. These findings highlight the limitations of narrowly focused aquatic plant restoration and emphasizes the need for integrated, whole-of-system approaches. As global targets aim to restore 30% of degraded ecosystems by 2030, including those critical to coastal fisheries, evidence-based and locally tailored strategies are essential. This study underscores the role of floodplains as important components of coastal seascapes and provides insights to guide more effective restoration, contributing to biodiversity goals and sustainable fisheries management.