The Horseshoe Crab
COMMON NAME IN FRENCH: limule or le xiphosure
ENGLISH NAME: horseshoe crab
LATINE NAME: Limulus sp.
FamilY: Limulidae
They belong to the Arthropoda branch, which includes spiders, scorpions, ticks and marine crustaceans. Its ancestors belonged to the trilobite family which became extinct 350 million years ago.
In the exhibition: the horseshoe crab can be viewed in the Biodiversity Zone, after the Tropical Lagoon.
Geographic distribution: they are unevenly distributed along two corridors where they reproduce, more precisely in the Atlantic, from the south of Canada to the Gulf of Mexico, with the largest concentration in the world in Delaware Bay, and in the Pacific, in the mangroves and estuaries which stretch from Indonesia to Japan.The horseshoe crab on view at Nausicaa (Limulus polyphemus) lives along the east coast of the USA.
Habitat: tThe horseshoe crab changes its habitat as it progresses through its lifecycle. However, little is known about their lifestyle outside of their mating season and until their juvenile growth stage.
Its biology: with its articulated carapace or shell, the horseshoe crab, a relative of spiders, ticks and mites, has 5 pairs of articulated legs. It has a pair of additional appendages enabling it to eat. Near its tail, its has 5 pairs of gills allowing it to breathe. The horseshoe crab can fill itself with water to expand its new carapace and molt. The animal is particularly vulnerable during this period. Its long rigid tail, called a telson, helps it to steer and to right itself should it be overturned.
Size and weight: it can measure up to 60-70 cm in length, including its telson (tail) and can weigh up to 5kg.
Diet: marine worms of the class Polychaeta
Reproduction: “Their reproductive cycle is linked to the spring and autumn spring tides and to the lunar cycle. At full moon, adult crabs converge in large numbers on sandy beaches. The females lay up to 20,000 eggs in a nest close to the tidal limit, providing an important source of food for birds and other marine animals. After hatching, the small horseshoe crabs stay hidden in the sand for safety. They emerge from the sand after a few weeks, at high tide, and return to the sea until their first molt, after which they live on the sea bed”. They grow quickly (their size increases by 25 to 30% at each molting) but reach maturity late: 9 years old for males, or after 16 molts, and around 10 years old for females, or after 17 molts. Adults crabs then molt once a year.
Threats and protective measures:
The IUCN has listed the species Limulus polyphemus as “Near threatened (NT)”:
http://www.iucnredlist.org/apps/redlist/details/11987/0
The horseshoe crab has few natural predators. Neverthless, it has qualities which make it commercially attractive for humans. And it can be harvested by hand on the beach. Care is therefore needed to avoid any unauthorized harvesting. Since the beginning of the 1990s, there have been preservation efforts undertaken to stem a significant reduction in their numbers.In Japan, for example, artificial beaches have been built to create additional nesting areas. In the USA, the only endemic species (Limulus poylphemus) is under close surveillance and strict fishing quotas are in force.
Both of these countries also carry out an annual census of these animals.
Anecdotes:
- The horsehsoe crab’s blood is blue. This coloration is due to the presence of a copper-rich protein, rather than the iron-rich protein which gives human blood its red colour.
- The swiss artist Hans Rudi GIGER, who created the famous Alien, drew inspiration from the horseshoe crab for at least 2 of the 4 development stages of his alien creatures.
Species characteristics and ability to occupy an ecosystem niche in the context of biodiversity: horseshoe crabs are true living fossils. They are more ancient than the dinosaurs. So what’s so special about them? “They are almost permanently buried, they have survived major extinctions and demonstate the tenacity to occupy an ecological niche, and share it with others at the same time» (Georges BROSSARD, Founder of the Montreal Insectarium ). “On many individuals authentic cases of biocenosis can be found”, says Dr. DAIGNEAULT, an oceanographer." Among the colonisers which can be found both on and under its carapace (shell), there can be a multitude of invertebrates. These often include colonies of bryozoa, different species of gastropods, bivalves, crustaceans and algae, and so much so that certain xiphosures could be described as ‘walking reefs’”. The relationship between the crab and its guests is almost always commensalist (guest organisms which benefit in some way from its host without harming it), but sometimes may be slightly mutualist. For example, the camouflage provided by such a heterogeneous fauna when it is evenly distributed over the crab also benefits the crab.
Resilience: horseshoe crabs are true living fossils (more than 500 million years old) so they are more ancient than the dinosaurs and have survived every mass extinction event. Their population size appears to vary with environmental conditions.When the horseshoe crab is injured, blood cells form a blood clot which destroys bacteria.
Simplified extract from Marin Malin n° 9, Nov-Dec 2004:
« The horseshoe crab is very primitive and this is perhaps why it is so long-lived: it can live on sandy, rocky or muddy beds, it can survive well out of water, it can withstand the strong sun and heat and can survive in oxygen-poor waters. Its vital organs are protected by hairs and by two carapaces. In short, it is extremely versatile!»
Services provided to humanity: medical research, pharmaceutical and cosmetic products. When the horseshoe crab is injured, blood cells form a blood clot which destroys bacteria. The bacteria it is effective against are also dangerous for humans. Researchers have found that a protein can be extracted from the crab’s blood cells and used to detect bacterial contamination in intravenous medicines, vaccines and other drugs. This is known as the LAL test.The LAL test is the most sensitive and specific available for detecting the presence of endotoxins in medicines, biological products, medical and surgical devices and in other substances.
The reagent LAL was discovered during research carried out by Dr. Frederik BANG et Dr. Jack LEVIN in the 1960s. The test was marketed in the 1970s by Dr. Stanley WATSON. The LAL test (Limulus amebocyte lysate) has been in use ever since to detect bacterial contamination in medicines, vaccines, biological products, medical and surgical devices and certain cancers and forms of meningitis.
In addition, whenever an organisation like CEMBREU (European Medical and Bioclimatic Centre for Research and University Teaching) carries out an environmental survey for an allergy sufferer inside the building where they live, this test is one of those used to detect the presence of endotoxins.
A simplified extract from Marin Malin n° 9, Nov-Dec 2004:
“This blood clots when bacteria are present. So it’s like an alarm bell for scientists who want to ensure that their medical devices are microbe free”.
To make use of this inherent property, horseshoe crabs are collected during the summer from the shallow waters off the atlantic coast of North America. Scientists take about 20% of each crab’s blood (this rate allows the horseshoe crabs returned to the sea to recover).
H.KEFFER was awarded the Nobel Prize for Medicine in 1967 for his research on the optic nerve, and this research originated in large part in experiments on horseshoe crabs.
The horseshoe crab also contains chitin. Chitin is used in pharmaceutical and cosmetic products such as contact lenses, suntan lotions and hair fixatives. This substance is also known for its antibacterial and antacid properties and is used in the manufacture of surgical thread and self-healing dressings for severe burns.
In France, it is even used in the process used to clarify wines.
SOURCES
Books:
Martin DAIGNEAULT. Limules. Une histoire naturelle. Ed. Institut Océanographique, Paris, 2004.
Collectif. Océan. Encyclopédie universelle. Ed. Geo/Gallimard, 2006
Articles:
In French:
La Limule : un drôle de casque au sang bleu. Marin Marlin, n°9, novembre-décembre 2004, p 35
In English:
UICN. Biodiversity loss – it will make you sick. News - Press Release, 23 April 2008
Article de l'UICN consacré aux nombreuses possibilités d’application dans le domaine de la médecine entre autres, de propritété
http://www.iucn.org/knowledge/news/?841/Biodiversity-loss-it-will-make-you-sick
Websites:
In French:
Océarium du Croisic
http://www.ocearium-croisic.fr/pages/3-oceans/nautilus/le-limule.php
Catalogue SITI (ITIS) : Système d'Information Taxonomique Intégré
http://www.cbif.gc.ca/pls/itisca/next?taxa=&p_format=&p_ifx=&p_lang=fr&v_tsn=82701
Site d’un producteur de chitine : France Chitine
http://www.france-chitine.com/chitosan.html
Other sources:
CEMBREU (Centre Européen Médical Bioclimatique de Recherche et d'Enseignement Universitaire)
http://cembreu.fr/
Commercialisation du test LAL :
http://www.eprofeel.com/recherche_produit.php?q_search=test+lal&q_type=_produit&q_s=
In English:
UICN : statut sur la liste rouge des espèces menacées de l’espèce Limulus polyphemus
http://www.iucnredlist.org/apps/redlist/details/11987/0
Site spécialisé sur les xiphosures et en particulier sur l’espèce Limulus polyphemus
http://horseshoecrab.org/
et plus particulièrement pour le volet médical :
http://www.horseshoecrab.org/med/med.html
Laboratoire de Biologie Marine de Woods Hole, Massachussetts :
http://www.mbl.edu/
1ère société à commercialiser le LAL : Associates of Cape Cod, Inc
http://www.acciusa.com/
