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.