Eco-engineered vertical seawall panels with augmented habitat complexity can create a novel and biodiverse ecosystem in a coastal megacity.

Vertical seawalls are extensive and rapidly expanding in coastal cities and ports but provide inadequate habitat for intertidal fauna and flora as they lack necessary refugia from heat and desiccation stresses, lowering intertidal biodiversity. Ecological engineering through retrofitting suitable habitats aims to promote marine biodiversity through habitat provision. Two eco-engineered panel designs with augmented habitat complexity were tested on a seawall in a highly developed subtropical marina. One panel was commercially available, with a repetitive pattern of short extrusions - the Imported Commercially Available Design (ICAD). The other was a locally designed, double-sided panel with deep intrusions and shade behind the panel - the Hong Kong Design (HKD). Taxonomic richness of the intertidal fauna and flora on the panels were compared to flat, concrete panels (flat panel, representing a worst-case scenario) and scraped seawall plots (seawall control) for 18 months. Marine biodiversity on both eco-engineered panels was significantly higher than the flat concrete panels, and the HKD was colonised by the highest taxonomic richness (64 total taxa). The HKD had greater abundance of suspension feeders, higher richness within key functional groups, and enabled colonisation at higher tidal levels compared to the flat panel and seawall control. When compared to nearby vertical seawalls, the HKD and ICAD contributed to an increased within-site β diversity and functional diversity. These results imply that implementing similar eco-engineering of grey infrastructure while reducing other anthropogenic stressors can contribute to the aim of creating biodiverse intertidal ecosystems within coastal cities and ports.