The world’s horseshoe crab populations are imperiled, because of overharvesting for use as food, bait and biomedical testing, and because of habitat loss from coastal reclamation and development. Shoreline alterations that are engineered to protect beaches from erosion and sea level rise due to climate change also affect their spawning habitats.
Regarded as a marine ‘living fossil’, the horseshoe crab is a marine chelicerate arthropod living in shallow coastal waters on soft sandy or muddy bottom and spawns mostly on intertidal beaches at summer spring high tides.
There are four extant horseshoe crab species: the American horseshoe crab (Limulus polyphemus) along the eastern coast of USA and in the Gulf of Mexico, and three Indo-Pacific species, the tri-spine horseshoe crab (Tachypleus tridentatus), the coastal horseshoe crab (Tachypleus gigas) and the mangrove horseshoe crab (Carcinoscorpius rotundicauda) in coastal waters of India, southeast Asia, China and Japan.
The horseshoe crab is a critical link to coastal biodiversity. One of their ecological functions is to lay millions of eggs on beaches to feed shorebirds, fish and other wildlife. Its large hard shell serves as microhabitat for many other species such as sponges, mud crabs, mussels and snails. Unfortunately, this ecological link can be broken in areas where population density is low.
As a result of overharvesting for use as food, bait and biomedical testing, and because of habitat loss, the American horseshoe crab is listed as Vulnerable to extinction and the tri-spine horseshoe crab is classified as Endangered on the IUCN Red List of Threatened SpeciesTM. The two additional Asian horseshoe crab species will soon be listed on the IUCN Red List.
In June 2019, during the IUCN SSC Horseshoe Crab Specialist Group international workshop in Guangxi, China, participants from 14 countries and regions endorsed the Beibu Gulf Declaration on Global Horseshoe Crab Conservation, to call for strengthening of policy making and better enforcement, more scientific investigations and research, sustainable management of horseshoe crabs, restoring natural populations and protecting their critical habitats, and promoting public and multi-party participation in horseshoe crab conservation.
In further extending their public outreach activities around the world, the IUCN SSC Horseshoe Crab Specialist Group have designated 20th June every year as the International Horseshoe Crab Day to showcase the collective conservation efforts for the four horseshoe crab species.
On the first International Horseshoe Crab Day, 20th June 2020 and throughout the week, there are symposia, webinars, public talks, film and video shows, exhibitions, workshops and eco-tours across the geographical range of horseshoe crabs. Owing to the coronavirus outbreak, most activities will be held online for global access except for some local events. Information on such activities will be posted on a webpage of the Beibu Gulf University, China.
The first International Horseshoe Crab Day is especially dedicated to Dr. Carl Shuster, Jr., honorary patron of this specialist group, who recently passed away at the age of 100. Carl’s life-long passion and interest in the science, conservation and public education of horseshoe crabs have inspired many people. He will be sorely missed.
Founded in 2012, the IUCN SSC Horseshoe Crab Specialist Group aims to protect horseshoe crabs in the world through collaborative effort in conservation of their populations and habitats, and in raising public awareness of their importance in evolutionary history, marine coastal ecology and sustainable biomedical uses.
Mark L. Botton, PhD., is a professor at the Department of Natural Sciences, Fordham University, New York, USA. He is the founding Co-Chair (North America) of the IUCN SSC Horseshoe Crab Specialist Group.
Paul K.S. Shin, PhD., is a retired associate professor at the Department of Biology and Chemistry, City University of Hong Kong, Hong Kong. He also serves as the founding Co-Chair (Asia) of the IUCN SSC Horseshoe Crab Specialist Group.