CHENNAI: A decade-long artificial reef restoration of Vaan Island in the Gulf of Mannar has generated socio-ecological benefits worth Rs 61.67 crore, more than double the project’s inflation-adjusted cost, according to a technical assessment by the Tamil Nadu Coastal Restoration Mission and its partners, Suganthi Devadason Marine Research Foundation and IIT Madras.
The study found that the intervention delivered an adjusted benefit-cost ratio (BCR) of 2.34, confirming that nature-based coastal restoration can produce significant economic returns alongside ecological gains.
Vaan Island, one of 21 uninhabited coral islands, had suffered severe erosion, shrinking by 92% between 1969 and 2015. Its area reduced from about 20 hectares to 1.53 hectares largely due to coral mining, sea-level rise and reef degradation. To arrest the decline, scientists deployed 10,600 specially designed artificial reef modules around the island beginning in 2015. The report termed the outcome “conclusive proof that severe coastal loss is reversible”.
Geomorphic monitoring indicates the island area has expanded to over 2.3 hectares since then. The reef modules also facilitated rapid biological colonisation, supporting an average of 81 coral colonies per module. Fish population recorded a sharp recovery, with reef-associated fish density rising from 106 to 875 individuals per hectare, an eight-fold increase. The intervention also preserved 26 native plant species. Economic valuation shows mainland coastal protection is the single largest benefit, contributing Rs 28.57 crore, about 46% of the total value.
Regulating and supporting ecosystem services such as sediment trapping and nutrient cycling accounted for another Rs 13 crore. Direct fisheries and epibenthic gains together contributed about Rs 13.43 crore. Against an inflation-adjusted project cost of Rs 26.37 crore (from the original Rs 17 crore spent in 2015), the project generated a positive net present value of Rs 35.3 crore.
Additional chief secretary Supriya Sahu said the valuation “translates ecological gains into economic evidence”, strengthening the case for scaling up nature-based coastal restoration along vulnerable shorelines. Researchers said the Vaan Model offers a blueprint to protect 20 eroding islands in the Gulf of Mannar, two of which have submerged.
The state has commenced a Rs 50 crore restoration project for Kariyachalli Island. Sahu said deployment of artificial reefs there will be completed within a month.