Contrasting impacts of jetties on fish assemblages and seagrass in a temperate estuary

Context Artificial structures are increasing in coastal environments owing to population expansion, necessitating an understanding of their impacts. Jetties are common in estuaries and can affect aquatic vegetation, yet effects on fish, and whether they are density dependent, remain unclear. Aims Examine the effect of private jetties and their density on fish assemblages and seagrass meadows in Lake Macquarie, New South Wales (NSW), Australia. Methods Fish assemblages were quantified using remote underwater video systems and remotely operated vehicles, with fish and seagrass metrics compared among control, low-density (≤6 jetties per 150 m) and high-density (≥10 jetties per 150 m) treatments. Key results Compared with controls, jetty sites had altered fish assemblage composition and greater species diversity, abundance and fisheries important species including Acanthopagrus australis. Seagrass cover and canopy height were reduced adjacent to jetties at two of three locations. Jetty density effects were complex, with both low- and high-density treatments showing inconsistent responses across locations. Conclusions Jetties modified fish assemblages by adding structure into the seascape, although this occurs at the expense of adjacent seagrass habitat. Implications These findings improve understanding of jetty impacts to guide future development, emphasising the need to assess environmental impacts and protect seagrasses while providing socio-economic benefits from infrastructure.