Enhancing biodiversity on Singapore’s seawalls: Large-scale testing of eco-engineering solutionsOcean Sprawl

Annie Ann Nee Chew¹, Rania Hartanto¹, Rosa Celia Poquita-Du¹, Kingsley Griffin¹, Yeow Chong Tan², Cheng Soon Teo², Gladys Xue Ting Ong², Terence Hui Yang Peh², Jia Wen Brenda Teo², Meng Yang Charmaine Koh², Xiang Yun Zee Tan², Peter Todd¹

¹National University of Singapore, Singapore - ²Housing and Development Board, Singapore

Coastal development, sea level rise, and increasing frequency and severity of storms are driving the expansion of artificial coastal defences such as seawalls. These generally replace natural shorelines, leading to biodiversity loss and reduced ecosystem services. Ecologically engineering artificial coastal structures can improve their capacity to support bio-diverse communities while still retaining their engineering function. Retrofitting with blocks or tiles to encourage the natural colonisation of marine organisms is the most viable option for increasing biodiversity on pre-existing species-poor permanent sea defences. Concrete tiles designed by the Experimental Marine Ecology Lab, National University of Singapore, are moulded with complex structural components (at 4 mm to 56 mm scale) and have been demonstrated to increase native biodiversity on local shores. BioBoss2, the latest iteration, is a hexagonal tile that incorporates complex topographical components that have been shown previously to increase species richness. Determining the optimal density to deploy enhancement tiles remains an ongoing challenge. Here, we test four densities (15%, 20%, 25%, and 30% cover) using species richness as an indicator of efficacy. We also compare the effects of two surface textures (rough and smooth). Tiles were installed along a 1.125 km section of seawall revetment in Singapore. Each configuration was replicated five times, resulting in 40 sections randomly allocated along the seawall, with a 15-meter gap between adjacent sections. A total of 1,500 tiles were deployed, making this the largest-scale installation of its kind in the world. The outcomes of this ambitious ecological engineering project will inform marine conservation and planning strategies in areas where coastal development is both intensive and inevitable.