Gulf of Mannar coral reefs
The Gulf of Mannar coral reefs, located between Sri Lanka and India, are part of a rich marine ecosystem that includes 21 islands and spans approximately 87 miles (140 kilometers). This region is recognized for its diverse marine life and is classified as one of India’s four major coral reef systems. The reefs feature a variety of forms, including fringing, patch, and platform reefs, and are home to around 3,600 species of flora and fauna. Notable coral genera found here include Acropora and Montipora, while the region supports a vibrant fish population, including 450 species, making it a vital area for biodiversity.
The Gulf of Mannar is also significant for its economic activities, mainly fishing and the harvesting of marine resources. However, these activities, along with climate change, pollution, and natural disasters, pose serious threats to the coral reefs. In response, conservation efforts have been initiated, including the establishment of the Gulf of Mannar Biosphere Reserve, the first of its kind in South Asia. Despite these efforts, challenges such as coral bleaching and habitat degradation continue to threaten this unique ecosystem.
Gulf of Mannar coral reefs
- Category: Marine and Oceanic Biomes
- Geographic Location: Asia
- Summary: The Gulf of Mannar’s coral reefs are among the richest marine zones of global significance—but with ever-increasing anthropogenic stress, its biodiversity is under threat.
Coral reefs in the Gulf of Mannar falling under the Indo-Malayan realm are formed around a chain of twenty-one islands that lie along an 87-mile (140-kilometer) coastline between the west coast of Sri Lanka and the southeastern tip of India. Their average distance from the mainland is five miles (eight kilometers). There are four island groups in the Gulf of Mannar, known as the Tuticorin, Vembar, Keezhakkarai, and Mandapam groups. These islands actually form the Pamban-to-Tuticorin barrier reef, which is about 87 miles (140 kilometers) long and 16 miles (25 kilometers) wide.
Other reef forms—shore, platform, patch, and fringing reefs—are also seen in the Gulf of Mannar. Narrow fringing reefs surround the islands, extending 33 feet (100 meters) from the shore. Patch reefs are also found and typically are 0.6 to 1.2 miles (1 to 2 kilometers) long, 17 feet (50 meters) wide, and 6.5 to 30 feet (2 to 9 meters) deep. Reef flats are extensive on all islands.
Biological Riches
The Gulf of Mannar coral reefs are one of the four major coral reefs in India. The Gulf of Mannar biome is comprised of three main ecosystems, namely coral reefs, mangroves, and seagrass beds. Approximately 3,600 flora and fauna species make it one of the richest coastal regions of India. The most commonly occurring genera of corals are Acropora, Montipora, and Porites. The coral fauna includes 117 species divided among thirty-two genera. Of these, seven species belonging to seven genera are ahermatypic (non-reef builders) and as such are considered of no economic value. Major reef-building corals (hermatypic) that are found in this area are Pocillopora (two species), Acropora (twenty-five species), Montipora (twenty species), the key reef-builders Pavona and Gonipora, Porites, and Favia (five species), Favites (six species), and Goniastrea (three species).
Ornamental coral fishes and associated marine fauna are found in the reefs. Some important ones belong to the family Chaetodontidae (butterfly fish), Amphiprion spp. (clown fish), Holocentrus spp. (squirrel fish), Scarus spp. (parrot fish), Lutjanus spp. (snapper fish), Abudefduf saxatilis (Sergeant major), green turtles, Olive Ridley turtles, and the globally endangered marine mammal dugong (Dugong dugong). Of the 2,200 fish species in Indian waters, 450 species (20 percent) are found in the Gulf of Mannar, making it the single richest coastal area in the Indian sub-continent in terms of fish diversity. Other faunal composition is also very rich in the Gulf, including 168 migratory bird species, 79 species of crustaceans, 108 species of sponges, 260 species of mollusks, and 100 species of echinoderms. Fishery in the gulf is dominated by lesser sardine, silver belly, sciaenid, mackerel, anchovy, threadfin, bream, holothurian, lobster, mollusks, and prawns.
Around twenty different mangrove species occur and act as important nursery habitats for many faunal species. One mangrove species, Pemphis acidula, is endemic to the area; five others occur here and nowhere else in India. The main seaweeds are Gracilaria, Gelidiella, Hypnea, Sarconema, Hydrodathrus, Caulerpa, Sargassum, and Turbinaria. All six genera and eleven species of seagrass recorded in India occur in the Gulf of Mannar. Six of the world’s twelve seagrass genera and eleven of the world’s fifty species occur here. The biome also harbors 147 species of marine algae (seaweed). These seagrass and algal beds, in turn, support complex ecological communities and provide feeding grounds for many animals.
Conservation and Threats
To conserve the rich coastal biodiversity, the Gulf of Mannar Biosphere Reserve was established by the government of India with assistance from the United Nations; the World Wildlife Fund; and the International Union for Conservation of Nature, through its Commission on National Parks and Protected Areas. It was the first marine biosphere reserve not only in India, but in all of South and Southeast Asia. Krusadai Island within the Reserve is considered a “biologist’s paradise” and harbors, for example, three species of seagrass that are found nowhere else in India. Representative members of every animal phylum known (except amphibians) are found on this island. Krusadai Island is also home to an endemic Hemichordate called balanoglossus (Ptychodera flava), a taxonomically unique living fossil that links vertebrates and invertebrates.
The major economic activities in the coral reefs of the Gulf of Mannar are fishing; coral mining for the lime industry, brick manufacturing and road construction; harvesting of sacred chanks (Turbinella pyrum), sea cucumber, pipe fishes, sea horses, and seaweeds. Indiscriminate exploitation of reef-dwelling and reef-building corals, natural calamities and major bleaching events, excessive siltation, agricultural run-off, and sewage discharge are among the leading causes of the destruction and degradation of coral reefs in the Gulf of Mannar. Research shows that corals have been quarried here since the early 1960s.
Corals of the Gulf of Mannar have faced several major natural calamities, including the tsunami of 2004. Some research indicated that after the tsunami, the proportion of live coral—48.5 percent—was reduced to only 36 percent. The Gulf of Mannar appears to have had a barrier reef ecosystem originally; that has been lost over time largely due to anthropogenic causes. Legitimate and sustainable exploitation of the coral and associated organisms can conserve the rich biodiversity found here.
Climate change has also threatened the reefs. Scientists have observed bleaching and coral death in the area because of global warming since 1998. The most significant bleaching occurred in 2010 and 2016, when 50 percent of the corals near some islands were bleached and 16 percent died. However, efforts were made to save the corals. In 2018, Chennai's National Centre for Coastal Research (NCCR) implemented the transplantation of corals near six islands. The project was relatively successful and continued into the 2020s. Despite this success, the coral cover in the Gulf of Mannar decreased significantly between 2005 and 2021, from 37 percent to 27.3 percent according to the Suganthi Devadason Marine Research Institute. This decline significantly impacted the local fishing communities. In 2023, the Global Environment Facility and the Energy and Resource Institute worked together to construct 300 regional artificial reefs to attract marine life back to the gulf. Also of concern is the increase in marine debris, such as nets, ropes, lines, and fish traps on the coral. This makes the coral more susceptible to fragmentation and disease.
Bibliography
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Linden, Olof, et al. Coral Reef Degradation in the Indian Ocean: Status Report 2002. Cordio and University of Kalmar, 2002.
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Perinchery, Aathira. "Mannar's Corals Stand Strong in the Face of Growing Threats--With a Little Help." Science, 19 Jan. 2021, science.thewire.in/environment/coral-reef-bleaching-gulf-of-mannar-nccr-mandapam-artificial-reefs-climate-change. Accessed 15 Dec. 2024.
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