Provision of refugia and seeding with native bivalves can enhance biodiversity on vertical seawalls

Recent studies have suggested that increasing habitat complexity of artificial seawalls by modifying surface heterogeneity could enhance exploitable habitat and therefore species richness and abundance. We tested the effects of adding complex tiles (with crevices/ledges) of different heterogeneity (i.e., flat tiles resembling the seawall vs. tiles with crevices of 2.5 cm or 5.0 cm depth) and seeding with native rock oysters, Saccostrea cuccullata (unseeded vs. seeded) on species richness and abundances of intertidal marine organisms on two vertical seawalls in Hong Kong. Tiles were affixed to the mid-intertidal zone of the seawalls for 12 months. The results showed that the tiles with crevices had greater species richness and cover of sessile epifauna than flat tiles. Seeding tiles with S. cuccullata also facilitated natural recruitment of the same species. Our results support the hypothesis that using eco-engineering to increase habitat complexity can enhance the biodiversity of intertidal marine organisms on seawalls. •We tested if eco-engineered tiles could enhance biodiversity on artificial seawalls.•The tiles with crevices harboured more mobile and sessile epifauna species.•Seeding of oysters on the tiles promoted their recruitment on the tiles.•Adding crevices onto the tiles effectively reduced overall temperature of the tiles.•Eco-engineered tiles can enhance habitat heterogeneity and biodiversity on seawalls.