\u201cThese small crabs are very important for the coastal ecosystem and in most marine litter studies, they are neglected,\u201d said Fulmali.<\/p>\n
![\"A](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/03\/1_hermit_inside_bottle-768x512.jpg\")
A plastic bottle with a hermit crab trapped inside, spotted on Trinket Island. The bottle orientation makes it possible for the hermit crabs to enter easily but exit becomes impossible due to the slippery inner surface and incline. Image by Mayur Fulmali.<\/p>\n
Approximately 4-12 million metric tonnes of plastic waste enters oceans annually, causing widespread harm. The study notes that Nicobar Islands are particularly vulnerable to marine debris because they are located near the Malacca Strait, one of the world\u2019s busiest shipping routes. Various ocean currents transport enormous quantities of plastic waste from neighbouring countries and deposit it on these shores.<\/p>\n
Hermit crabs are small, scavenger invertebrates that maintain beach health and are food for many species in water and on land. They clean the beach, cycle nutrients, and disperse seeds. Coastal communities also rely on these animals for nutrition and livelihood. They are a delicacy in some parts of Nicobar Islands and used as fishing bait, explained Prabakaran.<\/p>\n
Investigating the litter<\/p>\n
While working in Nicobar Islands, Fulmali noticed hermit crabs trapped in plastic bottles. \u201cI saw a pattern that there are some crabs which are exclusively found in specific bottle sizes,\u201d he said. He decided to investigate this through a study.<\/p>\n
In the coming months, Fulmali conducted field work on hermit crab entrapment alongside his daily job of assessing sea turtle nesting sites. He collaborated with Prabakaran, who specialises in coastal and marine ecosystems and has been working in the Nicobar Islands since 2009. \u201cAll these beaches have an invariably heavy amount of plastic deposition. And this has little to do with India, as the majority of this plastic comes from international waters,\u201d Prabakaran told Mongabay-India.<\/p>\n
When the researchers looked at the data they collected from these beaches, the scale of the problem became clear. The study found that over eight out of 10 crabs were entrapped in plastic and glass bottles and the rest were trapped in other containers such as styrofoam boxes, helmets, and fishing floats. Among all the trapped animals, less than a percent were found alive, indicating a very low chance of survival.<\/p>\n
![\"Researchers](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/03\/5_hermit_in_a_single_500ml_bottle-768x512.jpg\")
Researchers counted 106 hermit crab shells inside one 500 ml bottle, showcasing the lethality of a single small plastic bottle. Image by Vishnu T.
\nWhen a bottle\u2019s mouth becomes a deadly filter<\/p>\n
The primary finding of the study is how the opening of the bottle acts as a size-selective filter. Hermit crabs whose shells are smaller than the opening can enter, since they travel with their shells. Crabs with larger shells are protected from getting trapped in smaller bottles. \u201cSmall-sized crabs are most vulnerable to bottles that are between one and two litres,\u201d said Fulmali. The team found the highest number of crabs trapped in one and half, two, and five-litre bottles, a finding that surprised Fulmali, who initially expected larger bottles to be the biggest traps.<\/p>\n
However, the vulnerability varies by species. Four hermit crab species of the genus Coenobita were found in the containers: C. perlatus, C. rugosus, C. cavipes, and C. violascens. Among these, C. rugosus was particularly abundant and more vulnerable because it resides close to beach vegetation where plastic accumulates.<\/p>\n
The study also found that plastic bottles are not the only culprit. Different types of containers pose a threat to hermit crabs including containers modified by people for storage and fishing as well as plastic-coated paper plates which have a slippery surface that prevents escape.<\/p>\n
More research needed on interaction between plastic and animals<\/p>\n
During field work, every morning Fulmali and his local assistants would get up at 5 a.m., walk a couple of hours along the coast and sometimes even climb a hill to get to a beach. Upon arrival, they would set up camp and begin the work. First, they laid small rectangular plots using sticks and ropes within plants on the beach, where a high amount of marine debris get stuck, washed ashore by the waves. Next, they thoroughly searched the debris for containers. \u201cYou first look for bottles with missing caps and then take the bottle and just shake it. And if you hear some noise, look inside and you might come across some small hermit crabs,\u201d Fulmali told Mongabay-India.<\/p>\n
Although, the visits to the remote beaches were not easy. Fulmali collected bottles in gunny bags to measure them later at camp. There were hundreds of very small hermit crab shells inside these, making measurement and identification difficult.<\/p>\n
During the night, sometimes other crabs scuttled into the camp, attracted to bags containing samples and attempted to drag them away. In their search for new housing, they would tear up plastic bags to find the shells stored in them.<\/p>\n
![\"Marine](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/03\/2_littered_beach-768x512.jpg\")
Marine litter collected at the hightide line along Vikas Nagar beach on Kamorta Island. At night, hermit crabs march towards the sea to replenish their water requirements and while crossing the hightide line they must cross the marine debris, elevating chances of entrapment. Image by Mayur Fulmali.<\/p>\n
Hermit crabs are known as scavengers for good reason \u2013 they even wiped clean the pots with stubborn food residue that were left outside the tents at night.<\/p>\n
Once the team collected all the samples and measured the shells and bottles, they returned to the lab where they categorised the containers by volume, ranging from small to extra large. Then they analysed the data to figure out which container volume traps the most amount of crabs and investigate the link between shell size and bottle opening diameter.<\/p>\n
Vasantkumar Rabari, a zoologist teaching at the Maharaja Sayajirao University of Baroda, who specialises in plastic pollution impacts on coastal fauna, appreciated the study\u2019s systematic methodology. The researchers focused on bottle opening diametre but acknowledge that other factors such as material, colour, and shoulder steepness require further investigation. \u201cThis is an observation-based study. There needs to be controlled experimental research to understand whether hermit crabs actively enter different-sized bottles and why they are unable to escape\u201d, noted Rabari.<\/p>\n
Most research in India focuses on microplastics inside animals\u2019 bodies and there is a lack of studies examining interactions between macro\/mega plastics and animals and its ecological consequences, he explained.<\/p>\n
The study\u2019s findings are a cause of concern. If pollution remains unchecked, smaller hermit crabs will decline, impacting the shore ecosystem and the coastal food web.<\/p>\n
Design solutions and policy changes<\/p>\n
To prevent hermit crab deaths, researchers propose modifying bottle design \u2013 making the mouth bigger, changing the shoulder angle and neck to reduce steepness \u2013 to make escape easier. \u201cIf you just modify a little bit of the slope, giving more grooves for them to get some grip to climb up, then that could solve a lot of issues,\u201d said Prabakaran. But the larger fix is preventing plastic debris from getting into the sea, he emphasised.<\/p>\n
Beyond design solutions, the researchers propose broader policy changes: holding manufacturers accountable for plastic waste, implementing deposit-return systems, restricting single-use plastics in coastal areas, and establishing community-led waste collection points.<\/p>\n
![\"Researcher](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/03\/6_hermit_field_work-768x512.jpg\")
Researcher Mayur Fulmali sorts and measures hermit crab shells found inside plastic debris at Vikas Nagar beach on Kamorta Island. Plastic containers of various shapes and sizes can act as traps for hermit crab. Image by Vishnu T.<\/p>\n
Keeping these small crabs safe requires more work. The team recommends future research on whether bottle shapes play a role in trapping animals, a population assessment of affected crab species, and establishing a global citizen science network to map entrapment hotspots. Rabari emphasised the need for expanding research to other coastal regions: \u201cStudies on the interaction of macro, micro and mega plastic with fauna should be conducted throughout the coastline of India.\u201d<\/p>\n
This study documents the toll of plastic pollution on hermit crabs in the Nicobar islands, at a time when the National Green Tribunal has approved the \u20b9810 billion-Great Nicobar Island project<\/a>, amid ecological concerns of large developmental projects in ecologically-sensitive islands.<\/p>\n
![\"\"](\"https:\/\/www.newsbeep.com\/nz\/wp-content\/uploads\/2026\/03\/8269ab565186842002250e59ca89d4951ea558bf1e301c5b839b5fd8e2469af6.jpeg\")
<\/p>\n