A cost-effective approach to enhance scleractinian diversity on artificial shorelines

Abstract

Seawalls, which have replaced many natural shorelines in coastal cities, are increasingly built to alleviate the impacts of rising sea levels. To mitigate the consequential loss of biodiversity, novel approaches such as ecological engineering have been adopted to enhance the biodiversity on these artificial structures. However, the majority of research to date has focused on physical modifications of intertidal seawalls, and such habitat enhancement efforts are labour- and cost-intensive. We examined the feasibility of transplanting nursery-reared scleractinian corals on subtidal seawalls in Singapore with the help of volunteers. Fragments of six hard coral species (Pocillopora damicornis, Hydnophora rigida, Merulina ampliata, Podabacia crustacea, Echinopora lamellosa, Platygyra sinensis) were tested. Fragments of all species fared well in the nurseries with a mean survival rate of 98.5% and 1.1 to 4-fold increase in live tissue area. Six months after transplantation to a seawall, only 50% of P. damicornis transplants survived, while those of M. ampliata decreased in size. Transplants of the other four species exhibited sustained growth and high survival rates (>90%), suggesting that they were more suitable than the former two species as candidates for transplantation onto subtidal seawalls. Scleractinian cover at the transplant site increased from 3% to 20% and generic richness increased from two to eight. The estimated project costs were almost US$ 23,000 if only researchers were involved in the effort, but the inclusion of volunteers in fieldwork and data analyses could help to bring the expenditure down by up to 23%. The study demonstrated the feasibility of transplanting corals onto subtidal seawalls to mitigate the impacts of coastal development, and highlighted its potential for application on other artificial structures. The findings also show that synergy between the community and scientists helps to reduce overall costs and is beneficial for biodiversity enhancement initiatives.