Species found in Hong Kong:
Tachypleus tridentatus (Chinese horseshoe crab) Carcinoscorpius rotundicauda (Mangrove horseshoe crab)
Species found in other places: Limulus polyphemus (American horseshoe crab) Tachypleus gigas (Southern (Malaysian) horseshoe crab)
|IUCN Conservation Status
American horseshoe crab –
Near Threatened (1996)
Chinese horseshoe crab, mangrove horseshoe crab, Southern (Malaysian) horseshoe crab – Data Deficient (1996) [Needs Updating]
|Estimated Wild Population:
About 20 years
Sand and mudflat for juveniles; sea bottom of 20-30 meters in depth for adults
Horseshoe Crabs are an ancient group of marine chelicerates. Although its name has the word "crab", it is not genetically related to crabs. Rather, they have closer lineages with trilobites and arachnids (e.g. spiders and scorpions).
The body of the horseshoe crab is distinctly divided into three parts: an anterior large prosoma (head and thorax); a posterior, small and hexagonal opisthosoma (abdomen); as well as a long tail (telson). The prosoma and opisothosoma together look like a helmet, the dorsal front part of which two compound eyes are located. Under the "helmet" are six jointed legs, mouth and gills in the form of five overlaid flaps. The long, straight and rigid tail allows it to balance its body and flip itself over when it is turned upside down.
During breeding season, horseshoe crabs move to shallow coastal waters. Males select females and cling onto her back. The female digs a hole in the sand and lays her eggs while the male fertilizes them at the same time. The female can lay between 60,000 and 120,000 eggs in batches of a few thousand. However, the survival rate of a horseshoe crab in its first year is only one in ten thousand (~0.001%).
The horseshoe crab has a significant evolutionary and biological value. The horseshoe crab has existed since the Late Ordovician Period (4.75 million years ago), about 230 million years prior the early appearance of dinosaurs on Earth. Body forms of the horseshoe crab have changed very little over the years and thus the species is considered "living fossil". The extract of horseshoe crab blood can be made into Tachypleus Amebocyte Lysate (TAL) which is an efficient detector for bacterial endotoxins. It is widely used in testing drugs, products and devices that come in contact with human blood in medical uses and has a tremendous contribution to our medical development.
|Estimated Wild Population:
Wild Population in Hong Kong:
The wild population of horseshoe crab had dropped by over 90% between 2000 and 2009. A study in 2012 indicated that the number of local juvenile horseshoe crabs only amounts to less than 10,000. (4,500 juvenile Chinese horseshoe crabs and 3,000 mangrove horseshoe crabs)
IUCN Red List of Threatened Species:
American horseshoe crab – near threatened
Chinese horseshoe crab, mangrove horseshoe crab, Southern (Malaysian) horseshoe crab – data deficient
|Human exploitation for food, conch fishery baits and medical uses||Loss of spawning and nursery beaches owing to urban development and pollution||Being entangled and killed by fishing nets or gears abandoned in the sea|
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