Urbanisation of coastlines through seawall construction has led to widespread habitat homogenisation, loss of intertidal biodiversity, and increased vulnerability to biological invasions. Nature-based solutions (NBS) through eco-engineering offer a promising pathway to restore ecological function on artificial structures, yet the mechanistic understanding of how different habitat complexity levels affect biodiversity, trophic functioning, predation dynamics, thermal stress, and invasion success remains limited. This study addresses this gap through an integrated approach combining a manipulative field experiment on a Hong Kong seawall with controlled laboratory trials.

To inform experimental tile design, we first established quantitative baselines of intertidal substrate complexity using 3D scanning and fractal dimension analysis on natural rocky shores. These baselines guided the fabrication of concrete tiles with five graded complexity levels—from flat to highly complex—deployed across three tidal heights on a Hong Kong seawall. Over 12 months, we will monitor species richness, abundance, functional traits, and invasion success across 75 tiles, while also assessing surface temperature regulation and predation refuge effects through exclusion experiments. In parallel, laboratory experiments will examine the interactive effects of complexity and surface temperature on the survival and growth of native and invasive invertebrate recruits under simulated intertidal conditions. Additional trials will test how complexity mediates predation vulnerability using common intertidal predators.

We predict that high-complexity tiles will support greater species richness and more diverse trophic structures, while also buffering thermal extremes and providing refuge from predation. However, invasive species may show context-dependent responses, suggesting that complexity may not uniformly benefit native over non-native taxa, with important implications for invasion success and management.

This research will provide the first experimental framework linking measurable complexity metrics to biodiversity, thermal buffering, trophic outcomes, and invasion dynamics on tropical artificial shorelines. By identifying optimal complexity combinations and their underlying ecological mechanisms, we aim to offer evidence-based guidelines for NBS eco-engineering that can enhance native biodiversity while managing invasive species impacts, contributing directly to UN Ocean Decade goals of sustainable coastal development.