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Super Typhoon Ragasa struck Hong Kong last month, washing large amounts of marine debris — especially plastic items such as bags, bottles, food packaging and fishing nets — onto the sandflats and mangroves of Shui Hau Wan on Lantau Island. This has severely impacted the habitat of horseshoe crabs, which are listed as “Endangered” on the IUCN Red List of Threatened Species. Today, horseshoe crab experts from Ocean Park and Ocean Park Conservation Foundation, Hong Kong (OPCFHK) led a team of 10 volunteers and three Lantau residents recently appointed as “Lantau Mudflat Wardens” to inspect the situation and conduct a coastal cleanup to reduce ecological threats to horseshoe crabs at the site.
Horseshoe crab nursery grounds threatened by marine debris
Howard Chuk, Executive Director of Zoological Operations and Conservation at Ocean Park Corporation and Foundation Director of OPCFHK, said, “The sandflats at Shui Hau Wan are severely polluted by marine debris, many times more than normal. Plastics and abandoned fishing gear (commonly known as “ghost nets”) are scattered across the sandflat. Ghost net entanglement and microplastic ingestion both cause a drastic increase in mortality risk for horseshoe crabs, especially juveniles. It is essential to clean the sandflat and provide a safe living environment for the horseshoe crabs there through human intervention.”
Chuk continued, “Mudflats and sandflats are typically located in calmer intertidal zones with abundant sediment. They are nutrient-rich and expansive. Leaf litter from mangroves along riverbanks provides nutrients as well as shelter for mudflat organisms, including various resident and migratory shorebirds, crustaceans and mudskippers, fostering unique biodiversity. The sandflats of Shui Hau Wan on Lantau Island are a critical habitat for the endangered horseshoe crab, offering ideal breeding and nursery conditions. The surrounding ecosystem is rich in food supply, such as small invertebrates and algae, essential for the growth and reproduction of horseshoe crabs. They spawn and rear their young ones here. Juvenile horseshoe crabs must live on the mudflats for up to ten years before maturing and moving to nearshore seabeds. Any damage to these mudflats therefore greatly reduces their chances of reaching adulthood.”
Conservation efforts are key to reversing horseshoe crab endangerment
OPCFHK is a pioneer in horseshoe crab conservation in Hong Kong. Key initiatives include:
• Partnering with City University of Hong Kong (CityU) on the “Juvenile Horseshoe Crab School Rearing Programme” since 2009, encouraging secondary school students and corporations to care for juvenile horseshoe crabs. To date, over 370 schools and corporates have joined the programme, engaging more than 7,000 participants and releasing 2,000 horseshoe crabs back into the wild for population restoration.
• Conducting horseshoe crab population surveys in Hong Kong since 2014, covering various breeding and nursery mudflats. Last year, in collaboration with the Department of Mechanical and Automation Engineering at The Chinese University of Hong Kong (CUHK) and the Department of Chemistry at City University of Hong Kong (CityU), a two-year pilot programme using autonomous unmanned aerial systems (UASs) and artificial intelligence (AI) technology for horseshoe crab population surveys at the Ha Pak Nai mudflat was introduced, significantly improving the effectiveness of these population surveys.
• Data collection at monitoring stations in Ha Pak Nai, Sha Tau Kok, Luk Keng and Tung Chung Bay for the “Asian Horseshoe Crab Observation Network Programme” that covered 25 monitoring stations handled by conservation organisations and research teams from the Chinese Mainland and Hong Kong.
• With funding from the Lantau Conservation Fund, OPCFHK has partnered with Lantau residents and community groups since July 2024 on the “Safeguarding the Lantau Intertidal Mudflat Biodiversity” programme. Through education and community engagement, the project raises awareness — particularly among Lantau residents, fishers and tourism operators — of the ecological importance of intertidal mudflat ecosystems. Local residents are recruited and trained as “Lantau Mudflat Wardens” to conduct regular patrols, take record of issues such as ghost net entanglement and marine debris, and work with OPCFHK on removal actions to protect Lantau’s natural resources.
Join us at the next cleanup
OPCFHK organises coastal cleanups on a regular basis to clear marine debris that may entangle horseshoe crabs or other organisms, reduce habitat pollution and mobilise public support for conservation. 16 cleanups were conducted between July 2024 and June 2025, resulting in the removal of over 300 kilograms of trash thanks to the participation of more than 300 volunteers.
Members of the public who are interested in joining OPCFHK’s cleanup activities can complete and return the OPCFHK volunteer registration form to us at opcf@oceanpark.com.hk or fax (852) 2553-5840. This is also a great opportunity to observe and learn about mudflat ecology! Stay tuned for OPCFHK’s announcements on volunteer recruitment for individual cleanup events. The next cleanup will take place on 18 October at Shui Hau Wan. Interested participants can email gr@oceanpark.com.hk or register via the online form (OPCFHK volunteer registration is not required for this event). For details, please visit Ocean Park and OPCFHK’s official social media pages.
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