Researchers have documented the presence of horseshoe crabs in Tawi-Tawi, a southern island province in the Philippines, for the first time. The discovery, based on interviews with coastal residents and fishers, provides new information about the distribution of these ancient marine creatures and could help guide future conservation efforts.
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According to Mongabay, the findings were published in a recent study after researchers from the Philippines investigated local reports of horseshoe crab sightings. Until now, scientific records of the animals in the country had been limited to the province of Palawan.
The research identified reports of two distinct types of horseshoe crabs, with characteristics resembling the tri-spine horseshoe crab (Tachypleus tridentatus) and the mangrove horseshoe crab (Carcinoscorpius rotundicauda). The tri-spine species is classified as endangered on the International Union for Conservation of Nature (IUCN) Red List, while the mangrove species is listed as data deficient, meaning there is insufficient information to assess its conservation status.
Local knowledge helps researchers locate ancient marine creatures
The investigation began in December 2023, when marine sciences associate professor Ivane Pedrosa-Gerasmio visited a market in Bongao, the capital of Tawi-Tawi. While there, she heard from local residents about sightings of horseshoe crabs in the area.
She shared the information with her student, Quesie Tolero Omnos, and the pair decided to investigate further. Their research involved interviewing 142 coastal residents across four municipalities to gather information about where the animals had been spotted, how frequently they appeared and whether communities had noticed changes in their numbers.
The researchers found that residents had encountered horseshoe crabs in a variety of coastal habitats, including sandy beaches, mangrove forests, rocky coral areas and seagrass beds. Some sightings were also reported in waters between 10 and 15 metres deep.
Locally, the animals are known as ‘bangkas’, a name inspired by their distinctive boat-like shape.
Why horseshoe crabs need protection
The interviews also revealed some of the challenges facing horseshoe crab populations in the region. Residents reported that the animals are sometimes collected for traditional medicinal purposes, including treatments for asthma and other illnesses. They are also used in certain cultural and spiritual rituals.
More than half of the people interviewed believed horseshoe crab numbers were declining. They identified possible contributing factors such as harvesting, climate change and industrial pollution.
Often described as living fossils, horseshoe crabs have existed for approximately 450 million years, making them older than the dinosaurs. Despite their ancient lineage, only four living species are known today, three of which occur in Asia.
Populations across the continent face a range of threats, including habitat destruction, accidental capture in fishing equipment, coastal development, pollution and overharvesting.
The researchers believe documenting the presence of these animals in Tawi-Tawi is an important first step towards protecting them. Beyond their ecological importance, horseshoe crabs also have cultural significance for coastal communities, while their biological properties have potential applications in pharmaceutical research.
Omnos emphasised that more scientific information is needed about their distribution, population numbers and the threats they face. This could help local authorities develop conservation plans informed by research and the experiences of the communities living alongside these remarkable marine animals.
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