Does construction material, installation depth, and topographical complexity influence the biodiversity and species assemblage of marine enhancement units?Ocean Sprawl

Yan Le Su¹, Peter Todd¹, José Emiliano¹, Dmytro Kosiachevskyi¹

¹National University of Singapore, Singapore

Coastal urbanization has led to the proliferation of seawalls to safeguard shores from erosion and flooding. However, seawalls tend not to support high species richness prompting the use of ecological engineering techniques, such as deploying enhancement units to restore lost topographical complexity. These units introduce various microhabitats and water-retaining features, which are important for the recruitment and survival of marine flora and fauna but are often absent on seawalls. While previous studies have examined enhancement tiles with differing levels of complexity or material, studies contrasting the effectiveness of these units between intertidal and subtidal depths remain limited. Additionally, concerns persist regarding the carbon footprint of ordinary Portland cement (OPC)-based concrete commonly used for fabricating these units. In our study, we manipulated the topographical complexity, material, and installation depth of a new enhancement unit, the ’RockUrchin,’ to assess their effects on biodiversity in Singapore. ’Pitted’ and ’Smooth’ RockUrchins made from OPC and a green concrete ’UrbaX’ were deployed at intertidal and subtidal depths. Preliminary surveys conducted three months after deployment revealed significant differences in biotic cover, composition, and faunal species richness between depths and complexities. However, material had no significant effect on biotic cover, composition, and faunal species richness. We will also present results of a re-survey to be conducted approximately 20 mo after initial deployment.