Seaweed kills coral reefs in Gulf of Mannar; govt steps in

CHENNAI: With the Kappaphycus alvarezii (red algae) — an invasive seaweed species — spreading to more islands in the Gulf of Mannar National Park, the State forest department has decided to resume works to remove the species from the sea and to survey the impacts of the invasive species including Kappaphycus.

Bakan Jagdish Sudhakar, wildlife warden of Ramanathapuram, where the national park is located, said the measures to remove Kappaphycus from the Gulf of Mannar were started in 2011 and removal works were conducted every year. “However, due to the lack of funds, the works were stalled for the last three years. Of the 21 islands in the gulf, only six are affected. Work to remove them will resume this year,” he said.

Apart from surveying the extent of the invasion, the department will study measures to be taken to restore degraded coral areas and maintenance of restored coral reefs.

Native to Southeast Asian countries such as the Philippines, Indonesia and others, the seaweed species was introduced in India during the mid-1990s for commercial cultivation. Carrageenan, an extract from seaweed, is used as a thickener in food products.

But the species outgrew coral reefs in the Gulf of Mannar. “Kappaphycus affects coral reefs only. As of now, there is no study to ascertain its impact on marine animals,” Bakan Jagdish Sudhakar, added.

Initially, the invasive species was found only around Shingle, Krusadai, Poomarichan (all Mandapam region) and Mulli (of Keelakarai region) islands. However, a study published in January 2023 pointed out the spread of Kappaphycus alvarezii to new reef sites in the Valai and Thalayari islands in the Keelakarai region. The study pointed out that live coral cover in invaded areas on Valai island decreased by 9.1 per cent and by 3.9 per cent on Thalayari island due to coral mortality.

The study pointed out that all seaweeds, whether native or invasive, affect coral reefs by overgrowth, abrasion, shading and by other means. But, invasive seaweeds like Kappaphycus alvarezii cause more damage to coral by their faster growth rate. Even a 0.5 cm fragment of the Kappaphycus can regrow into a full-grown colony, as per studies.

The state government had already prohibited the cultivation of Kappaphycus alvarezii between the north of Palk Bay and the south of the Thoothukudi district.

Another study conducted in 2008 warned that the invasive species would adversely affect native species like seagrass and coral reef fishes and disagreed with earlier arguments and assumptions that the alga was coral-friendly as well as suitable for commercial cultivation in the Gulf of Mannar.

Meanwhile in 2021, the central government, in its budget announcement, said a seaweed park would be set up in Tamil Nadu (outside the Gulf of Mannar) for commercial cultivation of seaweed including Kappaphycus alvarezii.