It takes approximately 25 minutes to reach Kariyachalli from the boat in the Thoothukudi mainland. At the end of the day, it is not an island but a line of sand and scrub land in the Gulf of Mannar where labourers are kneeling in the heat, tying a strand of the seagrass onto wooden frames. The government's figures indicate the island has decreased in size from 20.85 hectares in 1969 to 3.14 hectares last year. That's about 85 percent lost in a lifetime and officials predict it could disappear by 2036 if nothing is done. The island was estimated at several other places to be just under six hectares and the difference between these estimates indicates the speed of migration of the coast line.

Tamil Nadu has an answer in the form of a program of approximately $4.79 million (approximately ₹50 crore). It is housed in the World Bank-assisted TN-SHORE scheme and is part of the state's broader Coastal Restoration Mission (CRM) with a budget of ₹1,675 crore covering 14 districts. At the heart of the project is the installation of some 8,500 tonnes of artificial reef modules, which are dropped onto the seabeds based on information on currents, waves and sediment.

The deployment is expected to be completed by the end of September and the site will be monitored for four years or more. The cost comes to a startling $1.5 billion per hectare of the remaining land on the Islands. When it comes to the cost of a patch of sand, critics will say that's a lot to pay.

The defence is that it is not the sand that is being purchased. Kariyachalli is one of the 21 islands in the Gulf of Mannar and is along with the reefs and seagrass beds around them a breakwater for the Thoothukudi and Rameswaram coasts. The marine scientists refer to the 2004 Tsunami, that killed over 8,000 people in Tamilnadu. During their reading, these ecosystems absorbed the energy that would have fallen on the mainland and otherwise would have been much greater. Meanwhile, the reef cover around Kariyachalli has been reduced from approximately 500 hectares in 2005 to 197 hectares in 2021. That's a loss of approximately 61 per cent. An unringed island is just a target.

It is also important to know who the stripping company is. Coral was extensively harvested in the 1960s and 1970s, primarily for lime and building. Pollution, over-fishing and warming seas came afterwards. A previous study on the Gulf of Mannar said that a fisheries jetty was built without the consent of the forest department but caused new erosion. In other words, what was happening up to that point was already underway and is being accelerated by human decisions, and climate change is doing the rest. According to various studies that are mentioned in the same reporting, the Vembar and Keelakarai groups could disappear between 2064 and 2193, and Kariyachalli and surrounding Koswari may sink by 2036 at the present rate.

The state is not in a vacuum. The neighbouring Vaan Island, which was approximately 16 hectares in 1986, has reduced to just over 8 hectares in 2009, and its north end was lost in 2011. They then deployed approximately 10,600 reef modules in three transects by the researchers from IIT Madras and Suganthi Devadason Marine Research Institute. The structures are now colonised by corals, reef cover has increased continuously since 2018 and some of the lost land has been recovered. Those were the reasons which convinced the state to go for Kariyachalli, says wildlife warden Akhil Thampi. Transplanted corals also survived the 2024 bleaching event better than older ones did on Shingle Island.

The funky part of the story is that bleaching. It wiped out vast areas of coral in the area, and it begars the question – is anyone able to restore a reef faster than the sea gets hot? But the necessity of intervention, says researcher K. Diraviya Raj, is right there because the living coral is the raw material for adaptation and scientists are now looking for heat tolerant species. It's a good guess, but it is still a guess. Vaan is a very small island and one success on a very small island does not mean it will be successful on a chain of 21.

A second side to the economics exists that is not talked about. Over three hundred fishers from Tuticorin are being trained as conservation divers, thereby creating a small jobs scheme in a coastal defence project. Devkani, 47, a saltpan worker, told AFP that he used to borrow money at high interest rates during lean months but this time he didn't need to due to the seagrass work. These sorts of programmes typically only survive as long as the people on the fringes of them have a stake in the outcome.

Things aren't looking bright on the big picture. From the Maldives to the Pacific atolls, the costs are becoming heavy: for sea walls and reef-up, for small island national reclamation and there's no low-cost solution. There are many stories of failures in India. Home to tens of thousands of people, Ghoramara in the Sundarbans has been shrinking over the past few decades and the disputed New Moor island in the Bay of Bengal vanished in 2010. But the same physics applies and no one needs to debate the sovereignty of Kariyachalli.

So fair judgment is a guarded one. The fishing communities benefit with them, and they repair themselves and are cheaper than concrete walls. However, restoring is an option to gain time and it is no solution to reduce the emissions that are responsible for the warming of the water in the first place. The state has sought time and about ₹50 crore. It should be reciprocated with "public numbers": hectares of land, hectares of living reef and the condition of the coast behind them, which are published annually over the four years of monitoring.