Reef islands in want of restoration

Afloat the turquoise waters within the Gulf of Mannar, alongside the Tamil Nadu coast from Rameswaram to Tuticorin, are islands that home the nation’s richest marine biodiversity. Greater than 4,223 species of wildlife are discovered right here. The area was named a Marine Nationwide Park in 1986 and the nation’s first Marine Biodiversity Reserve three years later.

However there’s now hassle on this marine paradise. Two out of twenty-two islands have already vanished, with erosion threatening those that stay. A recent study of the islands within the Gulf of Mannar by the CSIR-Nationwide Institute of Oceanography discovered that roughly 5.40% of the general floor areas of those islands has lowered since 1973.

Moreover, many of those islands are additionally slowly shifting in direction of the mainland, pushed by rising sea ranges and ocean swells.

How islands erode

The islands within the Gulf of Mannar are unfold throughout 10,500 sq. kilometres and divided into 5 predominant archipelagos: Rameswaram (one island), Mandapam (seven islands), Keelakarai (seven islands), Vembar (three islands), and Tuticorin (4 islands). Poovarasanapatti, an island within the Keelakarai group, disappeared earlier than 1973, and Villanguchalli within the Tuticorin group disappeared fully by 2000.

Accretion (development) and erosion throughout these islands are mediated by quite a lot of elements, together with wave dynamics, wind speeds, the frequency and depth of storms. More and more, ocean swells play a job too. “Ocean swells are lengthy length waves with increased vitality in comparison with common waves. We now have seen an increase within the variety of swells reaching the Gulf of Mannar in current many years,” stated Mani Murali R., analysis scientist on the NIO and co-author of the paper.

The examine discovered that the southern Tuticorin island teams had probably the most discount of their floor areas from 1973 to 2020, lowering by 63.97 hectares or 83.04%. This was adopted by the Keelakarai islands (74.93 ha, 33.35%), Mandapam islands (153.92 ha, 29.60%), Vembar islands (56.48 ha, 28.14%), and Rameswaram islands (325.87 ha, 3.43%). General, the imply erosion price throughout the examined shorelines was calculated to be 1.7 metres per yr.

Rising sea ranges and frequent ocean swells are additionally slowly pushing the southern teams of islands in direction of the mainland. The impact of swells “manifests as erosion of the seaward shoreline and accretion of the adjoining continent-facing shore,” says the examine, including, “Consequently, the islands exhibit a internet inward migration towards the adjoining continental shore. It’s important to spotlight that this migratory response is related to a considerable lower in island dimension.”

Years of coral reef mining within the Eighties have helped speed up island erosion, stated Gladwin Asir, assistant professor on the Suganthi Devadason Marine Analysis Institute (SDMRI) in Tuticorin, which research the islands and works on reef restoration. “Coral reefs act as a barrier and cut back the speed of a wave,” he defined, including, “When a wave comes from the ocean, it strikes up a sloped space because it approaches the land. With out the coral reefs, the peak of the wave is elevated, and its impression is harsher.”

Islands that skilled accretion, or an total development of their planform areas, is probably going as a consequence of sediment redistribution from the altering wave dynamics, stated Mani. The sediment is generated from lifeless coral reefs in these islands.

The function of reef restoration

In keeping with the Intergovernmental Panel on Local weather Change’s newest evaluation stories, the Gulf of Mannar is already experiencing an annual sea stage rise of three.38 mm per yr, pushed by world warming. “Collectively, underneath the eventualities of 1 metre and two metre-sea stage rise, submergence could happen in an space measuring 627.30 hectare and 1284.21 hectare,” says the examine. The overall space of the islands collectively is 12,497.25 hectares. “The findings additional spotlight that sandy areas, mangroves and tidal flats will expertise probably the most vital impacts, adopted by land vegetation, barren land, and built-up areas,” the examine provides.

Coral reef restoration presents a chance for mitigation, the examine says. An experiment by SDMRI, deploying trapezoidal synthetic reefs within the Vaan Island of the Gulf of Mannar noticed excessive charges of survival amongst transplanted corals. Researchers transplanted 50 fragments of dwell corals utilizing synthetic reef modules at a depth between 1.5 and a couple of.5 m with the assistance of scuba divers. The transplanted corals had an average survival rate of 62%, 22 months after being transplanted. “Curiously, the surviving fragments have withstood two delicate bleaching occasions in 2019 and 2020,” says a paper documenting the experiment.

“It’s crucial that nature-based options be deployed, and never engineered concrete constructions to forestall erosion,” stated Murali, including, “These are fragile ecosystems that are dealing with erosion regardless of being uninhabited, with none anthropogenic stress. Deploying nature-based options akin to synthetic reefs can assist obtain Sustainable Improvement Targets as effectively.”

In keeping with the examine, restoring coral reefs can assist obtain sustainable targets associated to wash water and sanitation, local weather motion, life under water and life on land.

Learn extra: Coral transplantation helps, however not the one answer

Banner picture: An aerial view of Rameshwaram island on the southeastern tip of Tamil Nadu, which straddles the Gulf of Mannar Biosphere. Picture by Tracy Hunter through Wikimedia Commons (CC BY 2.0).