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Home , Horseshoe crab

NT OF E TH TM E R I A N P T E E R D

I . O U.S. Fish & Wildlife Service

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M A 49 R CH 3, 18 The Horseshoe polyphemus A Living

Since horseshoe have a hard shell, they must molt to grow. Horseshoe crabs will molt at least six times in their first year of life and about 18 times before they reach sexual maturity. Females are generally larger than males and may molt more than males to reach the larger size. Once crabs are sexually mature, which takes at least nine years, they won’t shed their shells again. When the male crab completes his final molt, his first set of claws becomes modified into a A Primitive Ancient Creature her. The male clasps onto the female’s boxer-glove shape that he uses to clasp Horseshoe crabs are evolutionary shell with a modified pair of claws. The onto a female for spawning. Adult crabs survivors that have remained relatively female drags him around during the may live another eight to 10 years, unchanged in appearance for 350 million spawning process. In addition to the making the total lifespan of a horseshoe years. The horseshoe crab is not actually attached male, several other males may crab as long 20 years. a true crab, but a member of an ancient also attempt to fertilize the female’s eggs group of , closely related to by arranging themselves on and around Physical Characteristics spiders and . There are four the spawning couple during the egg- The horseshoe crab has a unique and of horseshoe crabs around the laying process. A female may have five or primitive body structure. The body is world and only one in North America. more males attempting to mate with her composed of three parts: the prosoma The species in North America is the in a single egg-laying episode. (head), (central area) and most abundant in the world and ranges telson (tail). The horseshoe crab’s name on the Atlantic coast from Maine to the During spawning, the female crab is derived from the prosoma, resembling Yucatan Peninsula. partially buries herself in the sand while the shape of a horse’s shoe. The telson she deposits a cluster of about 4,000 tiny helps the crab to flip itself over if waves Amazing Spectacle green eggs. In an evening of egg laying, on the beach turn it over. As dangerous In the late spring and early summer, a female crab can lay several egg as the telson may look, it is not horseshoe crabs arrive on the beaches en clusters, and she may repeatedly venomous or used as a weapon by masse to lay their eggs. The peak of over several nights to lay 100,000 or the crab. spawning on the Atlantic coast occurs in more eggs. Bay where thousands of crabs Horseshoe crabs have several pairs of will arrive on the sandy beaches in May New Life Beginning eyes. Two large compound eyes on the and June. Delaware Bay provides an The eggs will hatch within two to four prosoma are sensitive to polarized light excellent spawning area for crabs weeks. The larvae will emerge from the and can magnify sunlight 10 times. A because the sandy beaches are protected sandy beaches and enter the water pair of simple eyes on the forward side of from harsh wave action. The beaches’ during a high nearly a month later. the prosoma can sense light sand and pebble mixture is perfect for The larvae look like miniature adult from the moon. In addition, multiple eye incubating horseshoe crab eggs. horseshoe crabs without tails. spots are located under the prosoma, with more on the underside of the tail. Crabs arrive on the spawning beaches After hatching, horseshoe crabs spend Horseshoe crabs occasionally swim during the high of full and new their first few years of life on the tidal upside down and may once have used moons when the water rises highest on flats and move out farther from shore as these eyes more than they do today. the beach. they get older. Adults spend the winter in deep bay waters and off-shore areas. Horseshoe crabs use book to get When the female is ready to lay her As spring approaches, the crabs move oxygen from the water. The parts of the eggs, she crawls up to the high water en masse toward the beaches to are in small flaps resembling the line on the beach with a male attached to prepare for spawning. pages of a book. If these primitive gills stay moist, horseshoe crabs can remain Horseshoe crab plays a vital role compared to using a whole crab in each out of water up to four days. Crabs in human medicine. The straw-colored, trap. The bait bags have reduced the stranded on the beach during spawning -based blood turns blue when demand for bait by 50 to 75 percent in bury themselves in the sand or fold exposed to high concentrations of recent years. Research is also being done themselves in half to conserve water oxygen. Horseshoe crab blood contains to identify alternative baits for the conch until the tide rises again. primitive large blood cells called and fisheries to further reduce the amoebocytes. A clotting agent called need for horseshoe crabs as bait. Horseshoe crabs have no jaws or teeth. Limulus Amoebocyte Lysate is derived Instead, they have an impressive array from the amoebocytes of the horseshoe Despite restrictive measures taken in of spiny mouth bristles at the base of five crab. When the LAL comes in contact recent years, populations are not pairs of legs to maneuver food items with bacterial toxins, a clotting reaction showing immediate increases. Because such as razor clams, soft-shelled clams occurs. Pharmaceutical companies test horseshoe crabs do not breed until they and marine worms into their centrally the sterility of vaccines, drugs, reach nine or more years of age, it may located mouth. To chew its food, the crab prosthetics and other medical devices take some time before the population must simulate walking movements. using LAL. There is no synthetic measurably increases. substitute for the LAL test. The Shorebird Connection What the Future Holds The largest population of horseshoe Threats to Survival Unfortunately, we often learn the value crabs in the world is found in Delaware Human development threatens of a species after its population is Bay. During the spawning season, many horseshoe crab survival in the United decimated. However, in the case of eggs are exposed to the beach surface by States and in other parts of the world. horseshoe crabs, we know their wave action and the digging action of Human disturbance can adversely affect ecological role, importance to the mating crabs. Once an egg is exposed to spawning activities. Beach development biomedical industry and importance in air, it can dry out quickly, preventing it and shoreline modifications prevent the commercial fishery. We have the from hatching; however, it still plays a crabs from reaching sandy areas or opportunity to manage and protect vital role in the ecosystem. These strand them once they reach spawning horseshoe crab populations at a exposed eggs are the primary food areas. Recreational vehicle traffic on sustainable level and also provide crabs source for migrating shorebirds making beaches can crush the crabs and destroy for ecological and commercial uses now the journey from South America to the their nesting habitat. Oil spills from and in the future. Arctic along the Atlantic Flyway. barges or tankers also pose threats to breeding and young crabs. These human For additional information contact: Delaware Bay hosts the second largest activities not only harm crabs, but also U.S. Fish & Wildlife Service population of migrating shorebirds in interfere with feeding and resting Delaware Bay Estuary Project North America. The shorebirds in the activities of millions of migrating 302/653 9152 Atlantic Flyway use only a few areas for shorebirds at a critical time in their lives. feeding and rest on their trip from South U.S. Fish & Wildlife Service America to the Arctic. More than a Horseshoe Crab Harvest and Management Maryland Fishery Resources Office million shorebirds fly nonstop from In the late 1800s and early 1900s, up to 4 410/263 2604 places as far away as Peru, Suriname million horseshoe crabs were harvested www.fws.gov/northeast/marylandfisheries and Argentina’s Tierra del Fuego – as annually and used as fertilizer or much as 5,000 miles. More than half of food. Currently, crabs are harvested for Federal Relay Service the total flyway population of red knots, bait in conch and American eel fisheries for the deaf and hard-of-hearing ruddy turnstones and semipalmated on the Atlantic Coast. Horseshoe crabs 1 800/877 8339 sandpipers depend on Delaware Bay’s suffered a substantial increase in harvest horseshoe crab eggs as a rich food in the 1990s that spurred the need for U.S. Fish & Wildlife Service supply. Hundreds of thousands of other management on a coast-wide scale. 1 800/344 WILD migratory birds representing several http://www.fws.gov species also converge on Delaware Bay In 1998, the Atlantic States Marine during mid to late May. Fisheries Commission, representing 15 August 2006 states from Maine to Florida, developed Every year nature provides an incredible a horseshoe crab management plan. The spectacle in late May as these ravenously ASMFC plan and its subsequent hungry birds start arriving. Each bird addenda established mandatory state-by- can double its weight in less than two state harvest quotas and created the weeks by eating thousands of horseshoe 1,500-square-mile Carl N. Shuster Jr. crab eggs. Then they fly on to their Horseshoe Crab Sanctuary off the mouth summer breeding grounds in the Arctic. of Delaware Bay.

The Medical Connection Active management, as well as Of all marine species, horseshoe crabs innovative bait conservation techniques have contributed the most to medical and have successfully reduced commercial physiological research. Most of what we horseshoe crab landings in recent years. know about human vision was drawn from Conch and eel fishermen have been using a Nobel Prize-winning scientist’s work mesh bait bags in their traps, so they use with cells found in horseshoe crab eyes. only a portion of one crab per trap,