Coastal cities are expanding seaward, and ports, marinas and engineered shorelines now dominate large sections of the world’s estuaries. These urban‑industrial seascapes are often assumed to be degraded, low‑value environments for biodiversity. Yet despite their prevalence, we still lack a clear understanding of how fish and other mobile fauna use these modified habitats, how ecological processes operate within them, and whether they can contribute positively to coastal ecosystem function. This knowledge gap is increasingly important as coastal development accelerates and natural habitats continue to decline.
A central challenge is that urban marine environments are structurally complex, spatially heterogeneous and heavily influenced by human activity. Traditional ecological surveys often struggle to capture the full extent of fish use across these environments, particularly in deeper waters, under pontoons, or around large industrial structures where access and visibility are limited. As a result, management decisions are frequently made with limited empirical evidence about the biodiversity values of these built systems.
Recent advances in sonar imaging, remote video and other non‑invasive technologies are beginning to transform this picture. Emerging evidence shows that ports, marinas and associated infrastructure can support abundant, diverse and behaviourally dynamic fish communities. Large engineered structures such as pylons, pontoons and deep harbour basins can create novel habitat opportunities—providing refuge, foraging surfaces, vertical complexity and sheltered microhabitats that some species use extensively. Fish also exhibit surprising behavioural plasticity in these environments, including strong substrate association and orientation behaviours that mirror those seen in natural overhangs and reef structures.
Together, these insights challenge the assumption that urbanised seascapes are uniformly poor habitat. Instead, they highlight the need to recognise and better understand the ecological roles of built coastal infrastructure. As coastal development continues, evidence‑based approaches will be essential for designing, managing and enhancing urban marine environments that support biodiversity alongside economic and social uses.