Nuanced influences of subtidal artificial shellfish structures on nekton communities in urbanised estuaries

Context Reef installation is increasingly considered for urbanised estuaries to enhance and restore ecological functions. Restoration structures are expected to provide nekton habitat benefits, but early outcomes are poorly understood. Aims This study assessed nekton assemblage variation associated with an oyster reef restoration site, situated within the anthropogenically modified Port River–Barker Inlet estuary. Methods Nekton communities and environmental variables were measured 6 weeks before, and 14 months following restoration, and at a control site. Modelling was used to assess spatio-temporal variation. Key results Video monitoring detected 34 species, with harvestable nekton comprising 60.3% of total abundances. Nekton assemblages were strongly influenced by interannual effects, with few outcomes being directly related to restoration activities. Restoration structures supported non-native gobies during the study. Conclusions These results suggest that small-scale restoration can have little detectable impact on urbanised fish communities in the early stages of estuarine restoration. Nekton were influenced by environmental variables with distinct seasonal variation. Implications In urban estuaries characterised by pre-existing artificial structures, small trial oyster reefs may be functionally redundant as nekton habitats until sufficient spatial-scale and functional changes are achieved.