The lump of dead coral was an indication of ecological stress, says Dr Edward Patterson, director of the Suganthi Devadason Marine Research Institute in Tuticorin, Tamil Nadu. Ecologically, Pamban Island is in one of India’s most fragile zones and this chunk of coral, casually handed out and called a stone, was just one sign of it.

In 1914, after three years of intense labour by 600 workers, India completed its first sea bridge from Mandapam, a town on the southeastern tip of Tamil Nadu, to Pamdan island. More than 100 years later, the Pamban rail bridge is still operational. In 1988, a road bridge was built parallel to the railway bridge. The twin bridges extend for two kilometres over the deep blue waters of Palk Bay, where the Indian Ocean meets the Bay of Bengal.

The Gulf of Mannar Marine National Park is on the seaward side of Pamban island. With a chain of 21 uninhabited islets spread out in the waters between the coastal towns of Rameshwaram and Tuticorin, it is an ecological paradise, with more than 4,000 species of flora and fauna. It is also home to 117 species of coral, making it one of the most diverse coastal regions in the world.

The coral cover in the region has also been credited with affording some protection from the 2004 tsunami that hit southern India, he adds.

Coral reefs in India are protected under Schedule 1 of India’s Wildlife (Protection) Act. The act was passed in 2001, but coral mining was a huge problem until 2005, Patterson says.

“People used crowbars, pickaxes, even dynamite to blast through massive areas of reefs. Coral had commercial value in the construction industry. And destructive fishing practices were a big threat,” he adds. “The total reef area was 110 sq km, but over time, 32 sq km of the reef ended up degraded.”

Today, though regulation in this area is more vigilant, much of the damage has already been done. India’s growing climate catastrophes pose a further threat. Over the past three years, the nation has been battling intense heatwaves in the summer, each worse than the last, with some cities recording temperatures above 50 degrees Celsius (122 degrees Fahrenheit).

In the 2016 heatwave, amid viral videos of people frying eggs on hot streets, there was a grave indication of climate change that went largely unnoticed. An estimated third of the world’s coral reefs were affected by bleaching, and the Gulf of Mannar lost 16 per cent of its coral cover.

Gilbert Mathews, a scientist and assistant professor at the Suganthi Devadason Marine Research Institute, is a certified diver and part of an eight-member team that has been trying to re-establish lost coral cover on the reef. He and his team have been monitoring the area since 2016, assessing the health of the reefs. Their goal is to transplant coral from healthy colonies to the stressed areas of the reef, choosing as donors the species of corals that have proven to be more resilient to bleaching.

“We cut 8cm to 10cm fragments from the different species of live corals,” he says. The fragments are placed in bins on their boats. Each bin is filled with seawater and equipped with aerators to minimise stress on the corals. No more than five per cent of the live corals are harvested for transplantation. Sometimes, fragments of the branching corals are found on the seabed or floating on the surface of the water and these stray pieces are gathered for transplant too.

Although coral transplantation has been carried out successfully in other coastal reef areas of the world, the Gulf of Mannar posed challenges, including heavy sedimentation, leading to poor visibility.

Transplanting the harvested coral onto the existing natural substrate wasn’t possible because the existing coral colonies were already so fragile. “We needed an artificial substrate – a life-supporting biodegradable material that we could transplant these live coral fragments to,” says Mathews. “So we developed 15cm by 6cm concrete slabs.”

Around 4,000 of these square grey slabs have been used in the Gulf of Mannar to construct the man-made reefs. They are set in frames and placed in clusters of 10 to 15 for each acre of reef that has been experiencing stress.

“On the boat, the live corals collected in bins are attached to these slabs using sturdy jute ropes,” Mathews says. “Divers then move the coral and slab to the degraded reef areas.”

In the weeks after transplantation, the corals are constantly monitored. If seaweed grows too abundantly on any of these colonies, it must be carefully removed to avoid putting the man-made reefs under further stress.

Coral rehabilitation is considered a success when the transplanted corals spawn during the March spawning season. At that time, free-swimming coral larvae from the spawning corals attach themselves to submerged rocks or other hard surfaces.

Dead coral has proved to be the ideal artificial substrate for the transplants, says Mathews. Whenever dead coral is available, it is used to create artificial substrates for the transplantation process. When people remove dead corals from coastal areas, they seldom realise they are taking away a precious part of the ocean and a chance to revive coral life.

In the most recent survey in 2018, it was found that coral cover in the region increased from 22 per cent in 2016 to 24 per cent. While a two percentage point increase may appear small, it can have significant impact on the environment, researchers say. “Two of the 21 islands in this area have already submerged due to extensive coral mining,” says Patterson. Restoring coral cover near the other islands could help prevent them from sinking into the sea.

“While we have no control over future bleaching episodes, it’s heartening to know that we can control how we react to it,” says Mathews.

“There used to be a lot more of these beauties in these waters,” he says. “And to me, sighting one again was a sign of hope.”