Could vanish by 2036: India races to save shrinking island with artificial reefs

Kariyachalli is a rapidly eroding island in Tamil Nadu’s Gulf of Mannar. It has lost more than 80 percent of its landmass in about half a century. The island matters because its reefs, seagrass and surrounding waters help protect the mainland from waves, storms and rising seas.

The decline is dramatic. Kariyachalli covered 20.85 hectares in 1969 but only 3.14 hectares last year. Damaged coral reefs and disappearing coastal habitats provide less protection against incoming waves. Without those natural defences, erosion can remove soil and land faster.

Government estimates warn that Kariyachalli could disappear entirely by 2036 if erosion continues unchecked. Restoration teams are therefore installing artificial reefs, transplanting corals and rebuilding seagrass meadows. These projects aim to slow erosion, strengthen the island’s defences and preserve livelihoods connected to the marine ecosystem.

Artificial reefs are large structures deliberately placed underwater. Around Kariyachalli, they are designed to support coastal protection while giving marine life new habitat. They cannot replace every role of a natural reef, but they can help rebuild a damaged reef system.

About 8,500 modules, each weighing several tonnes, are being lowered around the island. Engineers selected their positions using information about seabed conditions, ocean currents and wave patterns. The structures interrupt and spread incoming wave energy before it reaches the fragile shoreline. Their surfaces also give coral larvae places to settle and grow.

The deployment phase is expected to finish by the end of September. Scientists will monitor the site for at least four years. The project is part of a US$4.79 million state conservation programme, alongside coral transplantation and seagrass restoration.

The island’s land loss is severe. Kariyachalli measured 20.85 hectares in 1969, but government estimates recorded only 3.14 hectares last year. That means roughly 17.71 hectares disappeared, leaving the island with about 15 percent of its former area. The article describes this as more than 80 percent loss.

The nearby coral reef decline is also striking. Around Kariyachalli, reef cover fell from approximately 500 hectares in 2005 to 197 hectares in 2021. About 303 hectares of reef cover disappeared during that period, or roughly three-fifths of the earlier area.

These losses are connected. Healthy reefs help absorb wave energy, while seagrass and islands help stabilise coastal sediments. As reefs weaken, waves can reach the shoreline with greater force. That increases erosion and leaves Kariyachalli more exposed to storms and rising seas.

Human activity damaged the Gulf of Mannar’s reefs long before today’s restoration work began. Coral mining during the 1960s and 1970s severely harmed reefs around the islands. Pollution and over-fishing then placed additional stress on corals and the wider marine food web.

Climate change has intensified the damage. Warming seas cause coral bleaching, a stress response that can kill corals when heat is severe or prolonged. The region suffered a severe bleaching event in 2024. Losing living coral reduces reef structure and the natural ability to soften waves. Weakened reefs also provide less habitat for fish and other species.

Together, these pressures have made the islands more vulnerable to erosion. Around Kariyachalli, reef cover fell from roughly 500 hectares in 2005 to 197 hectares in 2021. Less reef protection allows stronger wave energy to reach the island, especially during storms and rising seas.

Coral reefs, seagrass meadows and small islands form natural coastal defences. Reefs disrupt incoming waves before they reach shore. Seagrass roots and leaves help hold sediments in place, while small islands absorb part of the water’s force. Together, these ecosystems reduce erosion and protect coastal communities.

The article links this protection to the 2004 Indian Ocean tsunami. More than 8,000 people were killed in Tamil Nadu, but marine scientists say the islands, seagrass and coral beds absorbed some of the tsunami’s impact. Their physical structure acted as a barrier, preventing an even larger disaster.

These habitats also support marine life. Seagrass meadows provide nursery grounds, and reefs support fish and endangered dugongs. When pollution, mining, bleaching or erosion damages them, both coastal protection and livelihoods decline. Restoring them therefore addresses safety, biodiversity and local income together.

Restoration around Kariyachalli uses several methods at once. Workers are installing artificial reef modules, transplanting coral colonies and rebuilding seagrass meadows. The aim is to recreate natural barriers, slow erosion and restore habitat for fish and other marine life.

The artificial modules break incoming wave energy and offer hard surfaces for corals to colonise. Seagrass frames help establish plants that stabilise sediments. Nearby results provide reasons for optimism. On Vaan Island, about 10,000 artificial reef modules helped recover part of the lost landmass. On Shingle Island, transplanted corals survived the 2024 bleaching event better than older colonies.

The approach is not guaranteed. Kariyachalli’s deployment phase should finish by the end of September, followed by at least four years of monitoring. Scientists are also seeking heat-resistant corals. Success will depend on whether restored habitats can withstand future heatwaves and storms.

Corals live with microscopic algae inside their tissues. In general, when seawater becomes unusually warm, this partnership breaks down and corals expel the algae. The coral then loses much of its colour and an important energy source, creating the condition called bleaching. Bleached corals can recover if temperatures fall, but prolonged heat can kill them.

This makes reef restoration difficult. Transplanted corals and young colonies must survive the same warming seas that damaged established reefs. The Gulf of Mannar experienced a severe bleaching incident in 2024, killing large numbers of corals. Heat stress can therefore erase restoration gains before new reefs become strong enough to protect shorelines.

Scientists still argue restoration is necessary to preserve coral biomass and future reefs. They are also searching for naturally heat-resistant coral species. Nearby Shingle Island offers some encouragement, because transplanted corals endured the 2024 event better than older colonies.