Kariyachalli, a small island in the Gulf of Mannar off Thoothukudi in Tamil Nadu, has lost more than 80% of its landmass over the past 50 years and could disappear entirely by 2036, according to Tamil Nadu forest department data. The state has launched a roughly Rs 50 crore ($5.2m) project to slow the loss by rebuilding the coral reefs that once protected the island’s shoreline.
The island shrank from 20.85 hectares in 1969 to just 3.14 hectares in 2025, as rising seas and weakening coral cover removed the natural barrier that once absorbed wave energy before it reached the shore. Reef cover around Kariyachalli fell from about 500 hectares in 2005 to 197 hectares by 2021, a decline officials link to warming sea temperatures, coral bleaching events and past physical damage to the reef structure.
To reverse the trend, the Tamil Nadu government has deployed roughly 8,500 artificial reef modules around the island, concrete and steel structures designed to give coral larvae a stable surface to colonise while also breaking up wave energy before it erodes the remaining shoreline. The approach follows an earlier, similarly designed restoration at nearby Vaan island, which officials cited as a working precedent before committing to the larger Kariyachalli project.
A precedent from a neighbouring island
Akhil Thampi, a wildlife warden involved in the project, said the results from Vaan island’s restoration were promising enough to justify replicating the method at Kariyachalli. The Gulf of Mannar hosts four of India’s major coral reef systems, and Kariyachalli is one of them, giving the restoration work significance beyond the single island’s fate.
K. Diraviya Raj, an associate professor at the Suganthi Devadason Marine Research Institute, said corals placed on the new modules are expected to adapt to changing climatic conditions over time and form the basis of a future reef, rather than simply replacing what was lost. Supriya Sahu, a senior Tamil Nadu state official overseeing coastal resilience work, framed the stakes in blunter terms, warning that without resilience measures, the coast faces direct exposure to storm surges and sea-level rise.
Lessons from 2004 still shape coastal policy
The urgency behind Tamil Nadu’s reef investment traces back to the 2004 Indian Ocean tsunami, which killed more than 8,000 people in the state and exposed how exposed low-lying coastal communities and islands were without intact natural barriers. Reefs, mangroves and sand dunes all blunt wave energy before it reaches inhabited coastline, and their loss over the past two decades has pushed several Indian states to treat reef and mangrove restoration as core infrastructure spending rather than a conservation side project.
Kariyachalli itself is uninhabited, but its disappearance would remove a natural buffer for fishing grounds and shipping lanes that nearby coastal communities depend on, and would mark the loss of one of only four major reef systems recorded along India’s coastline. The Rs 50 crore committed so far covers reef-module deployment and monitoring, though officials have not said how long sustained funding will be needed to judge whether the restoration has genuinely reversed the island’s decline, or merely slowed it.
The Gulf of Mannar Marine National Park, which includes Kariyachalli among its 21 islands, draws its ecological value from exactly this kind of reef-island-seagrass combination, where each habitat reinforces the others against erosion and storm damage. Losing one island in the chain does not immediately threaten the wider park, researchers say, but it does set a precedent for how the remaining islands might fare as sea temperatures and storm intensity both continue to rise across the Indian Ocean.
