A naval air station on India's southernmost island in the Andaman and Nicobar archipelago has been keeping a watchful eye on any external threats but over the years, an unlikely enemy has slipped in undetected and gathered strength.
Plastic litter from South-east Asia has been accumulating along the shores of Great Nicobar, one of the archipelago's biggest islands, posing a threat to its rich and unique ecosystem.
The waste comprises mostly beverage and cosmetic bottles.
The issue has come under scrutiny after a report in the Oct 10 edition of India's leading science journal, Current Science. A 2014 study of the waste picked up from five spots on the island and featured in the report found that 97.8 per cent of the plastic litter was of non-Indian origin. A major portion had originated in Malaysia (40.5 per cent), followed by Indonesia (23.9 per cent), Thailand (16.3 per cent) and Singapore (7.4 per cent).
A survey last year found that the problem of foreign litter had increased significantly.
The Bay of Bengal island is about 180km from Sumatra in Indonesia. Given this proximity, the study's authors inferred that the litter has been swept in from South-east Asian countries by currents via the Malacca Strait.
Dr Biraja Kumar Sahu, one of the two authors of the report, told The Straits Times the waste poses a significant threat to the Great Nicobar island's fragile environment. "These plastic items may carry with them foreign organisms that, if introduced to the island, can establish themselves here and dominate local species. This can be dangerous to other organisms."
The island is home to the Great Nicobar Biosphere Reserve, listed in 2013 under Unesco's Man and the Biosphere Programme.
Its core and buffer zones account for over 85 per cent of the island's 103,870ha. It hosts a wide variety of flora and fauna, including 11 species of mammals, 32 kinds of birds, seven species of reptiles and four types of endemic amphibians.
Percentage of plastic waste that came from Malaysia. The plastic was picked up from five spots along the shores of Great Nicobar.
Percentage of plastic waste that came from Singapore.
The animals include the Nicobar megapode, a bird that builds nests on the ground, and the Nicobar treeshrew, a small mole-like mammal. The reserve is also home to the indigenous Shompens, a hunter-gatherer tribe that numbers about 200. They are not found on any other island.
Dr Sahu said certain compounds used in manufacturing plastics, such as bisphenol-A and poly-brominated diphenyl ethers, can also leach into the local environment. "They are known to be endocrine disrupters and can alter the endocrine system of local organisms that may be especially vulnerable because of their geographically isolated status."
The endocrine system is the collection of glands that produce hormones that regulate a range of functions, including metabolism, reproduction and sleep.
The problem of foreign plastic litter on the island has been present for several years and was first reported in 2003 in Current Science.
The researchers now want to carry out further studies to explore any seasonal variations in waste accumulation, and quantify the waste. Indian plastic waste has also increased farther north elsewhere in the Andaman group of islands.
Local government agencies in Great Nicobar have been trying to deal with the situation by cleaning the beaches regularly.
The Nicobar district's deputy commissioner Monica Priyadarshini told The Straits Times that the plastic collected is taken to the district headquarters, where it is shredded and used to build roads.
But Dr Sahu, a scholar at the Institute of Minerals and Materials Technology in Bhubaneswar, said manual cleaning of beaches is an "immediate remedy", something which he said is limited to the island's popular beaches.
"We need international collaboration... in the long run, including ensuring that the plastic waste is collected and recycled at the source in these South-east Asian countries," he added.