Asia’s horseshoe crabs thrive on the shelf
May 27, 2025Biologists at the National University of Singapore (NUS) used horseshoe crabs’ genomes to shed light on their past and on their future.
Horseshoe crabs are often described as living fossils – they have existed in an almost unaltered state for nearly 400 million years, long before the emergence of dinosaurs. However, these horseshoe crabs are now under threat. There are only four species worldwide, three of which are found in Southeast Asia, and all are thought to be in decline because of coastal development and climate change.
A research team from the laboratory of Associate Professor Frank E. RHEINDT from the Department of Biological Sciences, NUS conducted a genomic study to better understand the long-term evolutionary resilience of these species. The team sampled genome-wide DNA data from approximately 250 horseshoe crabs across 11 countries, covering all three Asian species. Using comparative genomic methods and ancestral range reconstructions, the researchers aimed to uncover the factors that have historically enabled the long-term survival of these fascinating creatures, and those that may now threaten their continued existence.
Their findings were published in the journal Conservation Letters.
Their findings revealed that all three species exhibited their greatest level of genetic diversity on the Sunda Shelf, a vast area of shallow sea near Singapore connecting the western Indonesian Archipelago with mainland Asia.
Dr TANG Qian*, the key researcher on this study said, “Populations away from the Sunda Shelf emerged as relatively impoverished, indicating that the Shelf, with its enormous coastal and benthic landscapes has provided a refuge for horseshoe crabs to weather past climatic upheavals, including ice ages.”
However, this extraordinary evolutionary stability is about to be disrupted. Using a cutting-edge approach integrating genetic information with predictive climate models under various carbon dioxide emission scenarios, the team identified geographic areas in which each species will be particularly susceptible to changes in temperature, salinity, chlorophyll concentration and other environmental variables.
Prof Rheindt commented, “Overall, all three species of Asian horseshoe crabs will face substantial pressure to adapt to changing climatic conditions later this century unless the current level of emissions can be successfully reversed.”
Some species will be more vulnerable to climate change than others and some areas will serve as better refuges, while others are likely to be more directly impacted.
“Population genomics can be an invaluable tool to quantify and detect impacts on the environment that are otherwise invisible. Our study shows that we can integrate DNA information with palaeoclimatic data and future climate predictions to pinpoint populations and areas that require immediate mitigation efforts. With collective will and timely action, much can still be preserved,” added Dr Tang.
Photo of the moult of a young tri-spine horseshoe crab found on the beach at Beihai, China. Genomic data collected by NUS researchers on this species serves as a foundation for conservation efforts. [Credit: Dr Tang Qian]
Reference
Tang Q; John A; Wardiatno Y; Nishida S; Do VT; Xie XY; Pati S; Susanto HA; Hajisamae S; Nelson BR; Min WW; Hasan ME; Salles T; Chen YL; Qu YH; Lei FM; Venkatesh B; Rheindt FE*, “Evolution and Viability of Asian Horseshoe Crabs Appear Tightly Linked to Geo-Climatic Dynamics in the Sunda Shelf” Conservation Letters Volume: 18 Issue: 1 DOI: 10.1111/conl.13074 Published: 2025.
*Dr Tang Qian has recently moved to Harvard University, USA.