Spot a horseshoe crab in Singapore? Researchers want to know

Their blue-tinged blood contains a clotting enzyme crucial for bacterial testing and vaccine development, including for Covid-19. In 2020, nearly 700,000 horseshoe crabs were harvested for their blood, according to the National Geographic magazine.

Despite their importance, there remains many gaps in the knowledge of horseshoe crabs native to South-east Asia, said research fellow Lee Bee Yan from the National University of Singapore’s Tropical Marine Science Institute, who heads the project.

Lee, a crab expert, hopes to compile the “much-needed” information on the distribution, abundance and habitat use of horseshoe crabs in Singapore.

There are four living species of horseshoe crab globally. Singapore is home to two of them – the coastal horseshoe crab (Tachypleus gigas) and the mangrove horseshoe crab (Carcinoscorpius rotundicauda).

The coastal horseshoe crab is more commonly associated with sandy shore habitats, while the mangrove horseshoe crab is typically found in mangroves and mudflats, said Lee.

Both species are listed as “vulnerable” in the Singapore Red Data Book, which compiles the descriptions and conservation statuses of threatened plants and animals in the Republic.

Under the International Union for Conservation of Nature (IUCN) Red List of Threatened Species, which details the extinction risk of fauna, flora and fungi globally, the two species are globally listed as “data-deficient”.

This was based on the last assessment conducted in 1996, and means there is a lack of information to make an informed assessment of the species’ risk of extinction.

Lee is hoping data collected on the horseshoe crab can help with future IUCN Red List assessment for the species, as well as conservation work.

Research has shown that there are now fewer suitable habitats for horseshoe crabs because of coastal development and habitat changes, Lee said.

Nature Society Singapore surveys conducted since 2007 at a mudflat at the end of Kranji Road – where mangrove horseshoe crabs have been sighted – estimated that the number of horseshoe crabs there has fallen to the lower two-digit range over the past decade.

This is compared with about 400 to 500 individuals about 16 years ago, said Lester Tan, chairman of the society’s marine conservation group. Tan is not involved in Lee’s project.

Since April 2026, Lee has been conducting studies at coastal sites – Coney Island, Changi Beach, East Coast Park and Sentosa – where she collects information on the distribution, abundance and habitat use of horseshoe crabs.

“Understanding where these species occur and how their populations are changing is an important step towards their long-term conservation,” she said.

To help in this effort, she is also recruiting volunteers who are interested in marine conservation and citizen science. They do not need a background in science or prior experience working with horseshoe crabs to volunteer.

Sign-ups are now open, and are expected to close in the second half of 2027, said Lee.

“Engaging the public in biodiversity monitoring can increase awareness of Singapore’s coastal ecosystems and the conservation challenges faced by marine species,” she added.