In a mangrove clump in Balasore in coastal Odisha, a young man gingerly snips away at the tangles of a fishing net around an upturned crab-like struggling creature. The creature tries desperately to flip itself over with rapid movements of its menacing-looking tail.

As soon as it’s free of the net, the youth, a member of the Balasore-based Association of Biodiversity Conservation and Research, gently sets the crab down in the muddy estuarine waters. The crab glides away and disappears into the deep.

Related to spiders, this prehistoric creature is a horseshoe crab. A living fossil that is important to the food chain, horseshoe crabs were crawling on the planet a couple of hundred million years before dinosaurs. After outliving dinosaurs, 450 million years of survival later, their numbers spread across four species.

But they now, faced with a suite of threats, horseshoe crabs are rapidly disappearing.

According to the International Union for Conservation of Nature, all four extant species of horseshoe crabs are imperilled, because of overfishing for use as food and bait, production of biomedical products derived from their blood and because of habitat loss or alteration due to shoreline development and armouring against coastal erosion.

They are commercially harvested, particularly in the United States, by biomedical and cosmetic companies for their coveted blue blood. This is used to extract lysate, a chemical used to test for bacterial contaminants in injectable drugs or implants.

The International Union for Conservation of Nature Red List of Threatened Species describes the American horseshoe crab Limulus polyphemus as vulnerable. The otherthree Asian horseshoe crab species, Tachypleus tridentatus, T. gigas, and Carcinoscorpius rotundicauda, are currently listed as “data deficient”.

In India, habitat loss and the non-targeted catch of horseshoe crabs during traditional, semi-mechanised and mechanised fishing, are undoing the creature’s abiding presence, according to Zoological Survey of India scientist Basudev Tripathy.

Of the four species, Tripathy says so far, only two confirmed species of the crab are known to occur in India, restricted between the Ganga and Godavari estuary along Odisha, West Bengal and Andhra Pradesh coasts. They are the mangrove horseshoe crab, C. rotundicauda and the Indo-Pacific horseshoe crab, Tachypleus gigas. The mangrove horseshoe crab prefers to breed in muddy areas near mangroves while T. gigas loves beaches.

Both are listed under Schedule IV of India’s Wildlife Protection Act, 1972.

Tachypleus giga, one of the two species of horseshoe crabs found in India. Credit: Shubham Chatterjee/Wikimedia Commons
Tachypleus giga, one of the two species of horseshoe crabs found in India. Credit: Shubham Chatterjee/Wikimedia Commons

Death by net

Every full moon and new moon, horseshoe crabs emerge from the depths of the sea –jostling to spawn amid the lapping waves along selected stretches of Odisha and West Bengal coast. The crabs are also found sporadically along the coasts but the reason for their choice of these sites as breeding-spaces is not understood explained Tripathy.

The entanglement of individual crabs in nets along the shore due to fishing activities is a frequent hazard. In one survey, Tripathy and co-authors documented over 95% of previously recorded horseshoe crabs of both species at Ekakula as dead. At Balaramgadi, the authors found a huge dip in the crabs’ abundance along with a large number of dead T. gigas.

This year, the team at the Association for Biodiversity Conservation and Research found the crabs trapped in multiple discarded fishing nets in the Khandia estuary shore. In northern Odisha’s Balasore, the estuary boasts of the highest horseshoe crab population in the state.

“On a recent survey, we were shocked to discover that there were more than 500 horseshoe crabs trapped in nets after a single day,” said the association’s team leader and researcher Siddhartha Pati. “About 300 were still alive and we managed to free them and release them back into the sea.”

This is a common sight in Khandia estuary.

Said Pati: “After bringing their boats to the shore, fishers leave their nets hanging in the water where they spread out and the crabs that come to the estuary to spawn are trapped in them. When the tide lowers, the crabs are left to die, trapped in the nets. What is more pressing is the fact that the majority of them are females about to lay eggs.”

In the Sundarbans and on islands in West Bengal, salinity intrusion and changes in mangrove vegetation are added challenges.

“Unregulated tourism also poses a challenge to horseshoe crabs in the Sundarbans, especially in Sagar Island which had a sizeable population of the crabs,” Indian Institutes of Science Education and Research-Kolkata scientist Punyasloke Bhadury told Mongabay-India.

Horseshoe crabs are also common prey of wild animals.

Using local assistance

Pati, who steers community-driven art contests in Balasore to draw attention to the crabs, said local communities that revere the horseshoe crabs for its mythological importance can be tapped in for conservation.

“Many communities are not aware of the horseshoe crab’s ecological importance in signalling the health of oceans and sustaining the marine food chain which has resulted in indifference towards the crabs,” Pati said.

In addition, researchers said there are reports of crabs being traded and sold domestically in markets – for their medicinal, especially anti-rheumatic properties – in the hinterlands of Jharkhand and the coastal stretches of West Bengal.

“Recent reports suggest the crab is being trafficked during the night from the Odisha coast to countries linked by the Bay of Bengal,” said Pati. “But detailed information about smuggling routes and the people involved aren’t exactly known.”

Bycatch mortality of horseshoe crabs is one of the main reasons for its decline in India. Credit: Siddhartha Pati/MongaBayIndia
Bycatch mortality of horseshoe crabs is one of the main reasons for its decline in India. Credit: Siddhartha Pati/MongaBayIndia

Legal protection

The crabs are fussy about their nesting habitats, according to BP Dash of the horseshoe crab research unit at the department of bioscience and biotechnology ofFakir Mohan University in Balasore.

“They come when salinity is just right for them and the sand is porous enough,” Dash said. “Coastal developmental projects can bring about a change in these conditions and alter their breeding behaviour. We have observed that the breeding frequency decreases in the rainy season.”

Tripathy recommended the in-situ protection of habitats and encouraged declaring identified areas with high populations of horseshoe crabs as partially no-use zones – at least during their breeding season.

According to the Zoological Survey of India, there are 15 sites in Odisha and Bengal coast that are potential horseshoe crab habitats in need of protection. In West Bengal, there are seven sites where the population is at least more than 200 individual crabs with more than 10 mating pairs at a time. For Odisha, there are eight such spots.

“Besides, all along the coast including the above 15 sites, there are 35 sites identified as horseshoe crab habitats where the number ranges between 1-50 individuals during the breeding season,” said Tripathy.

Despite the odds stacked against them, advocates have pinned hope on a mix of tactics to help the primordial ocean dweller survive.

Artificial breeding

Dash, for example, promotes the laboratory-based artificial breeding and larval rearing of horseshoe crabs. In a sea-ranching project launched in 2017 by the Horseshoe Crab Research Group, around 50,000 newborn crabs raised in laboratories have been released onto beaches.

Injured mature pairs are collected and maintained in the laboratory at standard temperature and salinity. Crab sperm and eggs are collected via electrical stimulation. Then eggs are sprayed with sperm and seawater added for artificial fertilisation.

Said Sash, “We have the capacity to carry out artificial insemination and incubation of up to 1000 eggs at one time in our lab set up. These eggs hatch after 30 to 40 days.”

While the team is standardising procedures and protocols, Dash said there are challenges in rearing crabs in artificial setups.

“There are concerns as to the feed of the larvae and right conditions for its growth,” said Dash. “Most importantly, we need to ramp up efforts to track and monitor these juveniles once they are released. We need follow-up studies and long-term monitoring. So far the research in India is not very cohesive and we need to collaborate with communities and conservationists.”

A community-driven bycatch rescue programme initiated in Odisha in association with the Wildlife Trust of India. Credit: Siddhartha Pati/MongaBayIndia
A community-driven bycatch rescue programme initiated in Odisha in association with the Wildlife Trust of India. Credit: Siddhartha Pati/MongaBayIndia

Crowdsourcing knowledge

To shore up efforts, researchers and grassroots workers have now come together under a common platform, the Indian Horseshoe Crab Network. The network is an online platform for researchers working on the conservation of horseshoe crabs in the region.

“It brings together people working on several aspects such as habitats, fisheries, community level linkages and other conservation challenges pertaining to horseshoe crab such as linking the science of horseshoe crab with media,” said Bhadury.

Anwesha Ghosh of Indian Institutes of Science Education and Research-Kolkata, who also helped float the network, expressed faith in an increase of conservation efforts. “It will not happen in one fell swoop and not by one individual,” Ghosh told Mongabay-India. “Which is why it is essential to get everyone onboard.”

The platform intends to provide timely updates on work undertaken, the sharing of field and laboratory protocols related to the crab and its habitats and the publication of resources. The platform is also intended to serve as a medium to establish a collaborative research link among different groups working on conservation, Bhadury explained.

Rescue and rehabilitation efforts, sea ranching and release, bioprospecting and advancing research on the crabs are some of the subjects that have been raised by the network at its inception in April.

Horseshoe crabs sold in markets in Jharkhand for their anti-rheumatic properties. Credit: Siddhartha Pati/MongaBayIndia
Horseshoe crabs sold in markets in Jharkhand for their anti-rheumatic properties. Credit: Siddhartha Pati/MongaBayIndia

Former National Institute of Oceanography scientist Anil Chatterji, who collaborates with BP Dash on the sea ranching project believes augmenting research on the horseshoe crab can aid in developing alternatives that will circumvent the need to harvest the organism.

“We have been putting in efforts to cultivate amoebocytes, which are motile cells that can differentiate into any other cell in vitro, and then removing the lysate for rapid detection kit,” said Chatterji.

“Besides this, my group has also been successful in producing celluloid liquid crystal based device for rapid diagnosis of bacteria in any biological materials,” he added. “These two new modern technologies will help in conserving the horseshoe crab population, globally as in the future, blood from horseshoe crab will not be required.”

Chatterji is working with Dash on the characterisation of the embryonic or peri-vitelline fluid of the crabs’ fertilised eggs for biomedical application.

“We have also successfully isolated growth factors useful in stem cell research,” Chatterji said. “This is from the peri-vitelline fluid of developing eggs of the horseshoe crab. After characterisation, this factor will also be chemically synthesised and then commercialised. So for this research, we need not depend, in future, on horseshoe crab.”

Dash added: “Biomedical importance apart, it is important to save them as they are an indicator species and signal the health of the oceans. They have evolutionary significance and have gained some advantages over environmental changes in millions of years. We can learn a lot from them.”

This article first appeared on Mongabay.