Each spring, the Delaware Bay hosts the second largest concentration of shorebirds in North America. Between 500,000 and 1 million shorebirds stop on the shores of the Delaware Bay for 10 to 14 days where they gorge themselves on fat-rich crabs eggs. This world-renowned spectacle is being jeopardized by the harvest of adult horseshoe crabs.
The drastic decline in numbers of shorebirds, their weight gain rates and adult horseshoe crabs and crab eggs provide irrefutable evidence of an impending ecological catastrophe. In addition, dollars from the Delaware Bay ecotourism industry dwarfs the horseshoe crab bait industry. This is truly a case where the science and economics argue for conservation. This disaster will only be averted through an immediate halt to the harvest of adult crabs.
For over a decade, NJ Audubon has been the leading voice for conservation of
this incredible natural history phenomenon. In 2002, we launched a conservation
campaign with partners calling for an immediate moratorium on the horseshoe
crab harvest of the Delaware Bay population. Our actions included holding press
conferences, letter writing drives, testifying in Trenton and Washington D.C.
and conducting massive public education. In 2003, we expect to achieve a moratorium
on the harvest of horseshoe crabs on the Delaware Bay.
Horseshoe Crab Trawl Survey Pilot Study
The horseshoe crab, Limulus Polyphemus, is an ecologically and economically important species. Horseshoe crabs occur from Maine to Florida along the Atlantic coast and in the eastern Gulf of Mexico. They occur from coastal bays out to the continental slope, mostly at depths less than 20 meters. On the Atlantic coast, horseshoe crabs spawn on intertidal sandy beaches in spring and summer. In Delaware Bay, their eggs provide a large part of the energy needs of migrating shorebirds in the spring. They can be an important dietary component for endangered loggerhead turtles, and may be important predators of economically important soft-shell and surf clams. They are commercially harvested as bait for the American eel and whelk fisheries. They are harvested by the biomedical industry for their blood, from which limulus amoebocyte lysate (LAL) is derived. LAL is the most sensitive means available for detecting certain bacterial endotoxins in injectible drugs and implantable devices. Despite their importance, fisheries managers have largely ignored horseshoe crabs until recently.
As early as the mid-1800s, millions of horseshoe crabs had been harvested annually for use as fertilizer. Harvest for this purpose ceased in the 1960s concurrent with the apparent lowest abundance of the spawning population. Populations rebounded through the early 1990s, but as harvesting efforts by the biomedical industry and bait fishery increased, total landings again decreased through the late 1990s. Because they reportedly do not mature until 9-10 years of age, and live for up to 19 years, horseshoe crabs are susceptible to over fishing. In recognition of their importance and unique life history characteristics, efforts were begun to assess the status of horseshoe crab populations.
In order to properly manage the species, accurate information on abundance
levels and trends is necessary. Although state and federal agencies conduct
regular surveys to monitor finfish resources, there is no reliable information
for horseshoe crabs. Because of the lack of adequate stock assessment information,
the Atlantic States Marine Fisheries Commission (ASMFC), which manages horseshoe
crabs, is seeking to develop a trawl survey which specifically targets horseshoe
crabs. This pilot study is intended to determine factors, which affect horseshoe
crab distribution and catchability, in order to develop the protocol for such
The pilot study was conducted in the Atlantic Ocean in the vicinity of Delaware Bay, which is the primary spawning site for horseshoe crabs. The study area extended from above Cape May, New Jersey to below Ocean City, Maryland, and from shore out to 12 nautical miles. Distribution of horseshoe crabs is believed to be affected by distance from shore and bottom topography. In particular, fishermen target trough areas - depressions that run generally parallel to shore and are composed mostly of mud. The area was sub-divided into an Inshore zone from 0 to 3 miles and an offshore zone from 3 to 12 miles. The study area was divided into grids of one-minute latitude by one-minute longitude. Grids that contained troughs were treated separately from non-trough grids. Randomly selected grids were sampled in each of the four treatment combinations: Inshore/Trough, Inshore/Non- trough, Offshore/Trough, and Offshore/Non-trough. Horseshoe crabs are thought to be more active at night, and therefore more susceptible to the trawl. Therefore, each grid was sampled both in Daylight and at Night. Sampling occurred over 16 days between 10 September and 12 October 2001.
Sampling was done from a chartered 55 foot-long commercial fishing vessel, using a flounder trawl. This gear is commonly used by the fishermen, and is more effective in digging crabs out of the bottom than the typical gear of most research trawls. Trawls were towed for 15 minutes at 2.5 - 3 kts.
Crabs were measured for prosomal width (mm PW), and identified to sex and maturity.
Horseshoe crabs were classified as Immature; Newly Mature, those that are mature
but have not spawned yet; and Mature, crabs which have spawned at least once.
A total of 7383 horseshoe crabs were collected in 96 tows. Twelve tows were completed in each of the treatment combinations. Preliminary examination of the data indicates that horseshoe crabs were most abundant in inshore trough tows. (Figure 1) Catches were generally greater within troughs than in non-trough areas. Likewise, catches were higher inshore than offshore. For all treatment combinations, average catches were greater at night than during the day. Immature horseshoe crabs < 175 mm were absent or sparse in offshore collections during the day, but about equally abundant in trough and non-trough areas inshore. Catches of small crabs were greater at night for all treatment combinations. (Figure 2)
Immature females ranged from 110 to 308 mm. Mature and Newly Mature females were 214 to 317 mm. Immature males were 110 to 223 mm, and Mature and Newly Mature males were 174 to 260 mm. (Figure 3) Females comprised 71% of the Immature, and 69% of the Newly Mature crabs. However females represented only 43% of the mature crabs.
Although the study was not designed to examine latitudinal differences, length frequency distributions suggest that small crabs were more abundant in the southern half of the study area than in the north. (Figure 4)
Even these preliminary results illustrate the importance of the criteria used in any trawl survey for horseshoe crabs. Topography and distance from shore are strong determinants of horseshoe crab distribution, and time of day affects their catchability. A broad geographic coverage is necessary to adequately describe the demographics of the population as a whole.
This study was funded by the states of New Jersey, Delaware and Maryland through ASMFC and by the National Fish and Wildlife Foundation
Field Season 1: Summer 1999.
2,500 horseshoe crabs tagged and released following blood extraction process.
Demographic information collected and maintained in data base.
Estimated mortality for young-adult, male horseshoe crabs following blood extraction to be 15%.
Submitted manuscript of results of mortality experiment to The Virginia Journal of Science. Manuscript accepted, published in Fall, 2000 issue.(Walls, E. A. and J. M. Berkson. 2000. Effects of Blood Extraction on the Mortality of the Horseshoe Crab, Limulus polyphemus. Virginia Journal of Science. 51(3): 195- 198.)
Field Season 2: Summer 2000.
2,500 horseshoe crabs tagged and released following blood extraction process.
Demographic information collected and maintained in data base.
Estimated mortality for young-adult, male horseshoe crabs following blood extraction to be 6.7%.
Presented results of initial mortality study at 2000 meeting of the Society for Conservation Biology, Missoula, Montana. (June 2000)
Field Season 3: Summer 2001.
2,500 horseshoe crabs tagged and released following blood extraction process..
Demographic information collected and maintained in data base.
Estimated mortality for young-adult, male horseshoe crabs following blood extraction to be 7.5%.
Presented initial results of tagging study (including tag recovery rates and movement patterns)at 2001 meeting of the Society for Conservation Biology, Hilo, Hawaii. (July 2001)
Submitted manuscript concerning various aspects of the horseshoe crab and its
fishery to Reviews in Fisheries Science. Manuscript accepted, published in Spring,
2002 issue.(Walls, E. A., J. M. Berkson, and S. Smith. 2002. The Horseshoe Crab,
Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study. Reviews
in Fisheries Science. 10(1): 39-73.)
This master's project has been divided into three components, each with its own main goal.
Component 1 involves the tagging of horseshoe crabs bled by BioWhittaker, the largest producer of LAL. As originally mandated by the Atlantic States Marine Fisheries Commission (ASMFC), 2,500 horseshoe crabs will be tagged each summer following the blood extraction process as performed by BioWhittaker. Information for each tagged crab including gender, age, and size is recorded and maintained in a database by the United States Fish and Wildlife Service (USFWS). Re-sighted crabs are reported to USFWS, and from these reports, information concerning movement patterns and long-term survival of horseshoe crabs will be obtained.
Component 2 involves the collection of demographic data for horseshoe crabs. Throughout the course of three field seasons (Summer 1999, Summer 2000, and Summer 2001), demographic samples of horseshoe crabs obtained by BioWhittaker in trawls of the Atlantic Ocean will be examined. These samples will be analyzed to compare the age, size and sex distributions of horseshoe crabs caught in BioWhittaker's trawling processes both spatially and temporally. Fluctuations in these distributions across the various locations BioWhittaker obtains horseshoe crabs as well as over the course of three field seasons will be examined.
Component 3involves the estimation of the effect of BioWhittaker's blood extraction process on survival of horseshoe crabs. In this part of the project, groups of bled and not-bled crabs are maintained in tanks at Virginia Tech's Seafood and Agricultural Research Center in Hampton, Virginia. Differences in mortality rates between the two groups are examined. Initial results show a 15% increased mortality in bled horseshoe crabs as compared to not-bled horseshoe crabs. This third component will quantify the impact of biomedical use of horseshoe crabs on horseshoe crab populations.
Reducing Post- bleeding Mortality of Horseshoe Crabs Used in the Biomedical
The horseshoe crab, Limulus Polyphemus is a marine resource that has become the center of controversy among its user groups. Over the past several years the demand for this unique and ancient animal has continually increased. However, population trends in recent years indicate a decline in the number of horseshoe crabs. They are an essential component to a healthy coastal ecosystem, an important part of the coastal economies of the eastern United States, and necessary for the protection of public health. Also, in each of these cases, there is no substitute for the horseshoe crab. Ensuring a stable population is crucial otherwise all of these areas will experience detrimental losses.
Horseshoe crabs play an important ecological role in the food web. Shorebirds primarily feed on horseshoe crab eggs exposed on the sand's surface. These migratory shorebirds arrive from their South American wintering grounds to use the Chesapeake Bay area as a refueling station. They feed on horseshoe crab eggs to build up their energy reserves for their continuing migration to Arctic breeding grounds. A decline in the number of horseshoe crabs will impact many species, particularly migratory shorebirds. Therefore, adequate spawning densities must be maintained to ensure availability of horseshoe crab eggs for shorebirds, some of which are federally listed as threatened or endangered.
Bait fishing and trawling are also dependent on stable horseshoe crab population levels. Historically, horseshoe crabs were considered a "trash fish". At that point in time, they were ground up and used for fertilizer. When the commercial fishery arose, there were little or no harvest restrictions and no reporting regulations. This has resulted in poor population data for horseshoe crabs. The commercial fishery primarily harvests horseshoe crabs for bait in the American eel and whelk fisheries. The eel fishery prefers to use gravid females as bait because eels are more intensely attracted to females than males. With this type of harvest preference, the eel fishery may have an impact on horseshoe crab demographics. As long as the horseshoe crab fishery has few restrictions, and the eel and conch fisheries have a high demand, horseshoe crabs will be aggressively harvested. In 1996, fishing mortality accounted for at least 2 million individuals throughout the Atlantic Coast.
Biomedical companies are a concerned party in this horseshoe crab issue. These companies catch and bleed horseshoe crabs. The bleeding process is akin to blood donation, since the animals are returned to the ocean afterwards. It is estimated that up to 30% of the animal's blood is removed. Studies have shown that mortalities occurring from the bleeding process range between 3%- 15%. This variance can be attributed to differing bleeding protocols. The biomedical company then extracts a compound from amoebocyte (the only blood cell present) in the horseshoe crab's haemolymph. This preparation is called Limulus Amoebocyte Lysate (LAL). LAL is used to detect endotoxin associated with gram-negative bacteria. These pathogenic bacteria can elicit a pyrogenic response, which involves fever, coma, or even death. Hence, the LAL assay is used by pharmaceutical and medical industries to ensure that their products (e.g., intravenous drugs, vaccines, and implantable medical and dental devices) have no bacterial contamination. The lysate has been shown to be more sensitive and faster to the detection of endotoxin than the USP rabbit test. The United States FDA estimates that 260,000 horseshoe crabs were caught and bled in 1997, as compared to 130,000 in 1989. Currently, there is no LAL substitute that offers comparable speed and sensitivity.
With demand for horseshoe crabs on the rise, it is important to continue conducting research that will offer a comprehensive understanding of this amazingly significant animal. More population and migration studies are needed for the formulation of appropriate management strategies. In the biomedical realm, more information is needed on post-bleeding mortality rates to perhaps alter bleeding protocols to yield lower mortality rates or even non-lethal levels. Also, the total blood volume of the animal is unknown, which leaves estimates of bleeding amounts with no baseline information. A further direction of study is to decrease or eliminate the need for harvesting horseshoe crabs by developing an optimal cell culture media for the maintenance of amoebocyte cultures. At some point, there will also be the possibility of finding a way to culture amoebocyte or even to clone specific components of LAL. Such alternatives can reduce the biomedical industry's impact on horseshoe crab populations.
The horseshoe crab is an ecologically, economically, and medically important species. In all of these cases, there is no known substitute for this animal. Presently, there are not enough horseshoe crabs to meet the needs of the commercial fishery, migratory shorebirds, and biomedical industry. There is growing concern over this predicament resulting in biomedical companies searching for ways to reduce the mortalities in their process,or better yet, to reduce the need for horseshoe crabs altogether.
In an effort to reduce the biomedical industry's impact on the declining horseshoe crab population, I'll be investigating ways to reduce the post-bleeding mortality of horseshoe crabs used for LAL production. Additionally, I will also conduct amebocytes culture to explore one possible alternative to harvesting horseshoe crabs. My project is partitioned into three components.
I will first determine the total blood volume in different size classes of horseshoe crabs. The inulin dye dilution method is a non-lethal technique in which this objective can be achieved. The data obtained will be crucial in determining the percent of blood that is extracted from individuals.
Studies have shown bleeding mortality to be between 3%-15%. This is, in part, due to differing bleeding methods employed. The major factor, though, is that inserting a large guage needle into the cardiac sinus and allowing the crab to bleed until blood clots up the needle conduct currently bleeding? This process results in variance of extracted amounts of blood. Some horseshoe crabs may yield a higher or lower volume of blood for their size. This would of course affect the animals' mortality rates. In order to decrease horseshoe crab mortality in the biomedical industry, I will identify the relationship between mortality and bleeding amount for different size classes. Thie basis of this study is that the percentage of blood volume extracted is directly correlated to mortality rate. Bleeding according to specified percentages of their total blood volume will identify bleeding threshold levels. Mortalities will be observed and bleeding thresholds will be identified. This information would allow biomedical companies to modify their bleeding protocols to bleed at a non-lethal level. Bleeding at these facilities would then be conducted according to a specific percentage of a horseshoe crab's total blood volume.
My final goal is to culture the LAL containing amoebocyte. This is a relatively unexplored territory. A few attempts have been made to culture amoebocyte, however they were unsuccessful. In my efforts, I will utilize new information regarding the horseshoe crab's blood chemistry and phylogenetic relatedness to scorpions to modify artificial culture media so as to provide optimal conditions for maintaining and potentially culturing amoebocyte. In attempting to establish the most favorable culture conditions, I would also like to look at two different cell culture methods (monolayer versus suspension). Once appropriate culture conditions are established, I will attempt to culture amoebocyte. Like human hemopoeitic cells, amoebocyte is believed to be an end-stage cell and do not reproduce. Consequently, the tissue that gives rise to amoebocyte cells must be identified, or embryonic tissue must be cultured under appropriate conditions and factors to produce amoebocyte.
Clean Ocean Action
Horseshoe Crab- Limulus Polyphemus - Related Species - Tachypleus gigas &
New Jersey is famous for the horseshoe crab. During the month of May and June, this unique animal comes a shore on Back Bay beaches to spawn. Millions of shorebirds time their arrival to coincide with the spawning of the horseshoe crab. People come from around the world to see this phenomenon of the crabs and birds.
Introduction, Populations and Anatomy
On the eastern coast of North America from mid May to the end of June one of the marvels and mysteries of nature accrue. Millions of creatures that time has past by invade the beaches of the Delaware and Chesapeake Bay. For millions of years the American horseshoe crab, Limulus Polyphemus, has been coming ashore to lay their eggs on the beaches of these Bays, in a spectacular annual mating migration.
Horseshoe crabs date back over 350 million years to a time before the dinosaurs walked the earth. They have survived numerous mass extinctions. The modern horseshoe crab has evolved little since his fossilized ancestor roamed the ocean floor. Thus the horseshoe crab is often referred to as a "Living Fossil".
There are four living species of horseshoe crabs. Three species are found in the Indo-pacific Ocean, the other species is found along the eastern cost of North America. Populations of the three Indo-pacific species ranges throughout Southeastern Asia from the southern coast of Japan to the northern tip of Australia and westward to the coast of Sumatra, just north east of India. The population of two Asian horseshoe crabs species are consider to be threaten and the third species is on the endanger list. On the other hand the population of the American species is estimated to be 2 to 4 million crabs. The American horseshoe crab ranges from the Gulf of Maine to the Gulf of Mexico. About 98% of the population is found between Cape May, New Jersey to Cape Hatteras, North Carolina. The highest concentration of crabs is found in the Delaware Bay. In 1990 and 1991, Delaware Bay population was estimated to be around 1.2 million crabs with 81% found along the New Jersey coast.
Along the harbor beach front across from the Nature Center of Cape May, horseshoe crabs can be seen spawning during high tide. In 1991 over 2,000 crabs were found along this area of the harbor. For the fourth year, the horseshoe crab census has tracked the spawning activity of the horseshoe crabs in the Delaware Bay. On Saturday, June 5th scientist and volunteers will hit the Delaware Bay beaches in both New Jersey and Delaware to try to estimate the 1993 population of horseshoe crabs.
Horseshoe crabs can be considered as impostor crabs, or false crabs. For they are more closely related to spiders and scorpions than crabs. True crabs have two sets of antennae, a pair of jaws, one set of claws, and ten legs. Horseshoe crabs have no jaws or antenna, Six pairs of claws and ten legs each with a claw and two extra claws from mouth parts The body of the American horseshoe crab can be divided into three regions; prosoma, opisthosoma, and telson.
The prosoma is the frontal region of the crab and is shaped like the footprint of a horse. It's this structure that gives the crab its name. Some of the surface features of the prosoma include the eyes, mouth, and other sensory organs, walking legs and feeding appendages. The horseshoe crab has two sets of eyes and other light sensing organs on the prosoma. The largest pair of eyes is the compound eyes, which are located on the sides of ridges on the prosoma. They are similar to the eyes of insects and other crabs. The other set of eyes are located at the base of first forward spine and are known as median eyes. These eyes are simple eyes. To the casual observer, the median eyes may resemble a nose on the crab.
The underside of prosoma has the five sets of legs. Two pairs of these legs are specialized for feeding. The first pair of walking legs can be used to distinguish between male and female crabs. The tips of the first pair of legs in male have been modified into a specialized structure known as "claspers". These claspers are used for holding on to the back of the opisthosoma of female crabs during pairing. The second to fourth set legs are used for walking and gathering food. The tips of these legs form slender long pinchers, which grab food and move it to the mouth. The last set of legs have specialized ends for pushing in soft sediment.
The opisthosoma is the triangular shaped region of the crab. The surface structures in this region include the book gills and reproductive organs. Book gills are the respiratory organ of the crab and are also used in locomotion. There are six sets of gill flaps associated with the book gills. The first flap called the operculum contains no gills. It covers and protects the gills and reproductive organs. Each remaining flap has around 80 gill membrane sheets used in respiration. The opisthosoma has two flanges at its base on ether side of the telson. On female horseshoe crabs, this area is known as the "clasping site" and is the part of the opisthosoma that the male grabs during pairing.
The telson, also known as the tail spine, is a long pointed triangular shaped tail. Average length of the telson is less than the combined length of the prosoma and opisthosoma. Muscles enable the telson to move in a 360-degree range. The telson is used in turning the crab over when it is upside down and in passive defense. The telson can be used to protect the gills while the crab is on it's back. In a way, the telson of the horseshoe crab resembles the tail of another marine animal, the stingray. Unlike a stingray, the horseshoe crab posses no stinger or poison in its tail.
"Sexual Dimorphism" is a term used to describe the physical difference between males and females of a species. In adult horseshoe crabs the difference of the sexes is easy to distinguish. Males are usually smaller than female crabs. The tip of the male first walking leg modified to form the monodactyl, one fingered, clasper. The tip of the female first walking leg remains the same didactylus, two fingered, pinchers.
The horseshoe crab is a docile animal and can easily be handled for a closer examination. While handling the horseshoe crab always take care not to injure the animal. Horseshoe crabs are important biomedically and a great natural resource. The best way to pick up and hold the horseshoe crab is by the front of the prosoma. It is not recommended to pick up the crab by the tail. The tail does not contain any poison and will not sting, but carrying the crab by the tail may cause injury to the horseshoe crab. The only way of getting injured is by mishandling the crab. While holding the crab, always be aware of where the tail is and where other people are standing. One place the crab should not be held is between the prosoma and opisthosoma. The back edge of the prosoma is sharp and can cause an injury. Claws of the horseshoe crab are not very sharp and the crab does not pinch very hard.
Migration & Spawning, Development, Predator & Pray
Every year in the spring the American horseshoe crab migrates from the mid-Atlantic portion of the continental shelf, from depth up to 750 feet, to their nesting beach in the Delaware and Chesapeake bays. Vertically blanking the beach for miles, number of 2 crabs per square feet has been recorded during the spring mass spawning. There are approximately 83% more male than females during the spawning. Males surround thus female crabs when they come a shore to lay their eggs. The male crab paired, or clasped directly behind the female is known as the suitor male crab. All other male crabs around the female are called satellite males. Satellite and suitor males both fertilize the female's eggs externally. The reproduction of horseshoe crabs is unique. They are the only arthropod that has external fertilization and it occurs at the ocean's edge.
Eggs are laid in "nests" which are buried below the sand. Nests maybe up to one meter deep and range on the beach from three meters above the low water line to the spring high tide mark. Each female crab is capable of lay up to 3650 eggs per nest. Development of the egg is mainly temperature related and varies according to the location of the nest in the beach. Under control laboratory condition eggs begin to hatch 14 days after being fertilized. In the development of the young crab, it will undergo four molts in the egg before it hatches.
The young horseshoe crab hatches in a form call a "trilobite larvae". This larva is a very hardy animal that can tolerate a wide range of salinity and temperatures. The trilobite larva carries a yolk sac that supplies the young crab with food. For this reason the larvae doesn't need to feed before it undergoes its first molting process after hatching. After this first molt the young crab resembles a miniature of the adult crab. In its first year the horseshoe crab will undergo the molting process six times. Juvenile crabs are four times more active at night than during the day.
Horseshoe crabs have a hard shell, or exoskeleton made of chitin. To grow, the crab must shed it exoskeleton by molting. The molting process involves the opening of a seam at the forward base of the prosoma. Then the crab then slowly crawls out of its old outer shell. As the new crab emerges from the shell it begins to take on water and swell to its new size. Molting can be difficult and dangerous procedure. If a crab takes on water to fast and swells up to large before emerging from the old molt, it may become entrapped in the old exoskeleton and die. New exoskeletons are soft for a short period of time. During this time the horseshoe crab is more vulnerable to predation.
Growth of horseshoe crabs is a stair step process. In each step of its growth, the crab will remain a certain size for a long period of time. Then the crab will shed its exoskeleton, and suddenly the crab has become much larger in a very short time. Young crabs shed their shells in a few minutes a here as adults may require several hours to complete the process. Since horseshoe crabs do not retain any hard structure throughout its lifetime, it is very difficult to determine the age of an individual. The estimate life span for the American horseshoe crabs is any where between 16 and 40 years.
Horseshoe crab feed on nematodes, polychaete worms, soft shell clams and mussels. Because horse shoe crabs feed on juvenile mussels and clams, fishermen have long regarded these crabs as pest that should be destroyed whenever possible to protect their fisheries from predation.
There are a large number of marine and terrestrial animals feed on the eggs and young of the horse shoe crab. Sand shrimp, fiddler and blue crabs, American eel, killifish, weakfish, and summer and winter flounders are a few of these marine predators.
Horseshoe crab eggs provide a high-energy resource that is a crucial food source for millions of migratory shorebirds. Many of these birds are on the endangered species list. These shorebirds gorge themselves on the eggs of the crab before continuing their migratory trip north to there nesting grounds. Pectral sandpiper, ipalmated sandpiper, red-black sandpiper, least sandpiper, black-bellied plover, semipalmated plover, red knot, ruddy turnstone and sanderling are a few of the birds that feed on the horseshoe crab's eggs. Some of these birds can eat up to 9,000 eggs per day.
Adult crabs do not as many predators. The sharp and strong jaw of the loggerhead
turtle has no problem cutting through the hard shell of adult horseshoe crab.
Pufferfish have been seen feeding on the softer gills and legs of the crab,
and adult horseshoe crabs have been found in the stomach con tents of leopard
sharks. Sea gulls will attack and feed on the soft undersides of overturned
adult horseshoe crab.
Humans & The Horseshoe Crab
Despite surviving for 350 million years and successfully passing through several mass extinctions, the horseshoe crab is not exempt from disappearing from this earth. Already in Japan, one species of horseshoe crab has been depleted through habitat loss and over collection to the point that it has been declared a national monument to protect it from total extinction.
The American horseshoe crab population currently is very healthy but mans impact on the crab can quickly change that status. In the later half of the 1800's, millions of horseshoe crab were harvested annually from the Delaware Bay to be ground up for fertilizer and food for livestock. By the 1950's a population that was in the millions had been reduced to a population that was only in the tens of thousands.
Today horseshoe crab is used in the fishing industry and is a very important animal in biomedical research. Within the last fifteen years horseshoe crabs have been harvested and used as bait, for the newly developed eel and whelk fisheries. It is estimated that over a million crabs are used annually for this industry. Because of unique properties of its blood, the horseshoe crab is an important animal for research in the field of biomedicine. Approximately 150,000 crabs are collected every year for research and education. Many of these crabs are returned to the environment.
The unique phenomena of horseshoe crabs and shorebirds along the Delaware Bay in late May and early June has developed into an ecotourism industry. Thousands of people come from around the world to see this wonder of nature. Since the early 1990's, a festival to celebrate the horseshoe crab is held in Cape May County. The festival provides a great opportunity to learn about the latest development in research on the horseshoe crab.
The unique properties of the horseshoe crab's blood maybe why this species has been around for such a long time. In the 1950's, the blue, copper-based blood of the horseshoe crab was found to contain a clotting agent that would react with toxins produced by bacteria. These toxins called "endotoxins" are found in the outer membrane of gram-negative bacteria. The white blood cells, or amebocytes, of the horseshoe crab were found to be the specific component of the coagulation system.
There are five companies along the eastern coast of the United States that produce Limulus Amebocytes Lysate (LAL). This lysate is used in detecting bacterial contamination of drugs and medical devices. It is also used in determining the difference between bacterial and viral spinal meningitis.
The LAL assay is very simple and can test very small samples of solution for bacterial contamination. The assay requires equal amounts of LAL reagent and test solution to be mixed together. The mixture is then incubated at 37 degrees Celsius. After an hour, the solution is checked to see if it has turned into a gel. If the solution has jelled, then bacterial endotoxins are present. The previous endotoxin test involved injecting the ears of rabbits with a sample of solution to be tested. If the rabbit developed a fever with in 24 hours, the solution was considered to be contaminated with bacterial endotoxins. The LAL assay is faster, more economical, and has a greater sensitivity than the rabbit test. Since rabbits are not used, the LAL assay is also more humane. The dairy industry is now experimenting with LAL assay. They are using it to determine the shelf life of their dairy products. Currently, scientists have not found a way to synthetically make Limulus Amebocytes Lysate.
Resent biomedical research on horseshoe crabs revels that it has many other organic chemicals that may be useful in combating diseases and infections. The most recent one involves certain very potent inhibiting compounds found in the blue blood of the crab. These compounds under certain laboratory conditions stop the growth of some cancer cells. Other researchers are studying the effect sutures material and wound dressings made with horseshoe crab chitin. Chitin cover sutures are found to enhance the healing time of some wounds by as much as 50%. Chitin dressing for burns patient dramatically increased healing while reducing pain in comparison to the standard burn treatment.
Concerns for the horseshoe crab has brought about regulations to protect the animal. The New Jersey Department of Environmental Protection and Energy, Division of Fish, Game and Wildlife enacted laws to regulate the harvest of horseshoe crabs. Violators of the laws are punishable by a fine up to $3,000. The law requires a permit to harvest horseshoe crab and sets limitations on when and where horseshoe crabs can be harvested. Anyone found in possession of a horseshoe crab within the prohibited area during the prohibited time shall be in violation of the law.
Finally, the American horseshoe crab has been around for millions of years. With man's new awareness of the environment, may be the American horseshoe crab will be around for another million years. Let us not let the American horseshoe crab go the way of Japanese species. Protection of nesting beaches, smart fisheries' management and the prevention of ecological disasters like the Prince William Sound oil spill will let future generations of birds, turtles, fishes, and humans reap the benefits of this most unique marine creature, American horseshoe crab.
Horseshoe Crab to Test for Toxins (National University of Singapore)
A breakthrough in genetic engineering has created a rare win-win situation that benefits both man and horseshoe crab. Clotting enzyme in the horseshoe crab has many benefits.
A NUS breakthrough in genetic engineering has created a rare win-win situation that benefits both man and horseshoe crab. The fortuitous development earned Associate Professors Ho Bow (Department of Microbiology) and Professor Ding Jeak Ling (Department of Biological Sciences) a prize at the Asian Innovation Awards, handed out by the Far Eastern Economic Review.
The husband-and-wife team has achieved a bioengineering feat in successfully cloning the enzyme that clots the blood of the horseshoe crab, making it one of nature's most sensitive sensors for toxic contaminants. The ugly, hard-shelled living fossil survives in its natural habitat of some of the dirtiest waters in the world because of the anti-toxins in its blood.
Artificially-produced enzyme can help protect the endangered species
Since the 1950s, the ability of the horseshoe crab's blood to clot when it comes into contact with bacteria has been tapped by pharmaceutical companies to test the purity of sterilised medical equipment and products. The revenue earned from this source of naturally harvested blood has been estimated at US$50 million.
In developing the technology to produce the enzyme in a controlled environment, the two researchers have found an alternative source of sensor that is more stable and chemically consistent than nature's endowment. The good news for the horseshoe crab, which has already become an endangered species in the world, is the conservation protection offered by the artificially produced clone.
A patent for the discovery of the compound, called Factor C has been issued in the United States. The technology for its production was licensed to the American biotech company BioWhittaker, which is keen to use it to develop sterility test and antibiotics. Prof Ding and Ho earlier won Singapore's National Technology Award for their contribution to genetic engineering research.
Horseshoe Crab Studies Providing New Insight Into Valuable Ancient Creatures
NOTE TO NEWS EDITORS: PLEASE SEE PRESS ADVISORY ON HORSESHOE CRAB MEDIA EVENT
http:// biology.usgs.gov/pr/newsrelease/1999/6-8b.html (U.S. Department of the Interior-U.S. Geological Survey)
Reproducible photos for this release may be found at:
http://biology.usgs.gov/pr/newsrelease/1999/6-8a.tif (Horseshoe crab eggs are an invaluable food source for shorebirds on their migratory journey north. Photo courtesy of Bill Hall, University of Delaware.)
http://biology.usgs.gov/pr/newsrelease/1999/6-8b.tif (Hundreds of thousands of horseshoe crabs annually lay and fertilize their eggs on the Delaware Bay area beaches. Photo courtesy of Bill Hall, University of Delaware.)
http://biology.usgs.gov/pr/newsrelease/1999/6-8c.tif .Horseshoe crabs laying and fertilizing eggs. Photo courtesy of Bill Hall.
They look like props from the movie Jurassic Park - but these ancient organisms were around long before the dinosaurs. Some of their closest evolutionary relatives have been extinct for hundreds of millions of years. But while countless other species have come and gone, the horseshoe crab has survived and is of great importance.
At the end of May and during June, hundreds of thousands of these prehistoric creatures emerge from the waters of Delaware Bay to lay and fertilize their eggs in the wet sand. On some beaches scientists and volunteers who will carefully count their numbers across a series of sampling plots will meet them.
The census was designed by USGS scientists in cooperation with researchers from the U.S. Fish and Wildlife Service, several state management agencies, a biomedical company, and several universities to determine the size and status of the Delaware Bay horseshoe crab population. This information is crucial because today these ancient organisms lie at the center of a far- reaching network of ecological, medical and economic relationships. The census is a project of the Atlantic States Marine Fisheries Commission, a multistate and federal partnership.
The horseshoe crabs of Delaware Bay provide a critical food source for about a million migratory shorebirds that pass through the region every spring. After spending the winter in South America, species such as the red knot, ruddy turnstone, semipalmated sandpiper and sanderling feast on protein-rich horseshoe crab eggs before moving on to their Arctic breeding grounds. For most of these birds, Delaware Bay is the most important stopover on a migratory journey of up to 10,000 miles.
Though horseshoe crabs are found along the Atlantic coast from Yucatan to Maine, the Delaware Bay population is the world's largest. USGS biologist and statistician Dr. David Smith, of the Leetown Science Center, says the bay's long stretches of protected, sandy beaches provide ideal habitat for spawning. "What has evolved is a dependence of migratory shorebirds on the superabundance of horseshoe crab eggs in Delaware Bay," Dr. Smith says.
But in recent years declines in horseshoe crab numbers have been reported from a number of locations. The evidence is spotty, and until recently no systematic horseshoe crab surveys have been conducted. But biologists say there are numerous reasons for concern: commercial harvesting of horseshoe crabs is increasing, and much of the sandy beach habitat needed for spawning has been lost.
Evidence also suggests that red knots and other migratory shorebirds are in serious decline, though the causes remain unknown. Biologists want to know if these trends are related to reductions in horseshoe crab eggs available to the migrating birds. "It's clear that we need to know more about horseshoe crab status and trends," says Dr. Smith.
A Vital Link:
Despite their name, horseshoe crabs are more closely related to spiders and scorpions than to true crabs. In the early spring, as shorebirds wintering in South America begin preparing themselves for northward migration and breeding, horseshoe crabs along the Atlantic coast of North America emerge from their muddy beds on the continental shelf and begin their own journey towards shallow waters.
Birds and horseshoe crabs by the millions converge on the bay beaches of Delaware, Maryland and New Jersey. Horseshoe crabs gather in massive numbers just offshore, often waiting for the highest tides -- associated with the full or new moon -- to crawl up on the beach and lay their eggs. During these mass-spawning events crab densities may exceed 100,000 per mile of beach, with each female laying thousands of eggs.
Egg laying continues to a lesser extent at other evening high tides throughout May and early June. "Some crabs are spawning any time the tide is up," says Gregory Breese, a biologist with the FWS Delaware Bay Estuary Project. Shorebirds, said Breese, mainly eat the eggs when horseshoe activity is highest. Horseshoe crabs bury clusters of pale green eggs in the sand, but during mass spawning vast numbers of eggs get churned up to the surface where they are eaten by the birds.
Breese says some shorebirds may journey non-stop from as far away as southern Argentina before arriving at Delaware Bay. With their energy stores exhausted, the birds gorge themselves on the rich, abundant food source. In less than two weeks they may more than double their body weight, allowing them to continue their journey to the far north.
Shorebirds aren't the only organisms for which horseshoe crabs and their eggs are a vital food resource. Many small fish feed on the countless eggs that are washed out into the bay, and later on the hatched larvae. Juveniles of larger ocean fish, which use the protected waters of Delaware Bay as a giant nursery, also consume eggs and larvae. Juvenile and adult horseshoe crabs are a dietary staple for the threatened loggerhead turtle.
Human Pressures: Horseshoe crabs have long been important to humans as well. Their relatively simple biology has made them a popular organism for basic biomedical research. Important early advances in understanding human vision and neurobiology were made through studies of the horseshoe crab's primitive eyes and long optic nerve.
Today a multi-million dollar industry exists around the collection of horseshoe crab blood. A clotting agent called Limulus Amoebocyte Lysate (LAL) is extracted from the blood, and used to test for the presence of gram-negative bacteria. Human blood and all commercially produced intravenous drugs are tested for bacterial contamination using LAL.
Blood extraction from horseshoe crabs is usually non-lethal, and thus the pharmaceutical industry is not thought to be a major factor affecting crab populations. Of much greater concern to researchers and managers is the increased harvesting of horseshoe crabs for use as bait in American eel and whelk fisheries.
University of Delaware biologist Dr. Bill Hall says the high density of horseshoe crabs in the Delaware Bay region makes harvesting them for bait cost-effective. "This is one of the few places where it's economical to fish for them," he says. Concern over the possible effects of this harvest prompted Dr. Hall to join with Benjie Swan of Limuli Laboratories and Dr. Carl Schuster of the College of William and Mary to organize a volunteer-based survey of horseshoe crabs spawning on Delaware Bay beaches in 1990.
"There is much concern about the harvest," says Dr. Smith. "There's enough data to suggest that the number of crabs spawning in the bay has dropped recently, enough that shorebirds may be threatened." But though the volunteer surveys provided some indication of a decline, the project was not initially designed to provide a valid statistical sample of the entire Delaware Bay population.
Commercial harvesting isn't the only factor that may be putting the squeeze on horseshoe crabs. Delaware Bay's miles of sandy beaches are steadily shrinking. "There's some pretty high rates of shoreline retreat and beach loss due to erosion and apparent sea level rise," Breese says. Development and shoreline hardening can also eliminate horseshoe crab habitat.
USGS and other biologists note that if the horseshoe crab population were to become seriously depleted, recovery might require decades. Though prolific in terms of egg production, horseshoe crabs are long-lived animals which do not breed until they reach nine or 10 years of age.
A Cooperative Response: With concerns over horseshoe crabs mounting, ecologist Dr. Joe Margraf and colleagues at the USGS Maryland Cooperative Fish and Wildlife Research Unit began a study in 1996 to determine how horseshoe crab use of spawning beaches varies through time and space. Their goal was to develop a rigorous sampling method for use in population monitoring. The researchers found that, to be most representative and consistent, surveys should be concentrated in the shallowest waters and should be carried out on the higher of the two daily high tides, immediately following a new or full moon.
In 1998, the Atlantic States Marine Fisheries Commission implemented a management plan for the species along the Atlantic Coast. Adopted last October, the plan calls for the collection of information necessary to manage the horseshoe crab fishery and to insure protection for the diverse animals that rely on horseshoe crabs and their eggs for food. The plan also specifically mandates that the bay states of New Jersey, Delaware and Maryland develop and implement a statistically sound methods for monitoring the status of horseshoe crab populations.
This interstate management plan led to the current cooperative research program involving USGS scientists, resource managers from the three states, and outside researchers. Under Dr. Smith's guidance a new, statistically sound sampling protocol is being implemented, which will help researchers determine the true size of the population and keep track of any downward trends. "Starting this year, we'll be getting a much better handle on variability in horseshoe crab numbers," says Breese.
"Our current project builds on the volunteer-based survey and incorporates the recommendations of Dr. Margraf and his coworkers," Dr. Smith says. "We're focusing now on larger spatial and temporal scales -- how best to select beaches, and how often beaches should be sampled to monitor the bay-wide population."
Another component of the cooperative effort -- funded in part through the USGS State Partnership program -- is to assess genetic variability in horseshoe crabs across their geographic range. Investigators are confident that unique DNA "markers" can be identified that will allow them to determine the distribution and movement patterns of different horseshoe crab populations. Fishery managers can use this information to monitor fishing pressures on specific populations.
Currently, says Dr. Smith, researchers do not know whether horseshoe crabs taken by trawlers farther out on the continental shelf belong to the Delaware Bay breeding population. "It's not clear 'whose' crabs they're taking out there," he says. "Are they from Delaware Bay or somewhere else?" The answer -- which the genetic studies should provide -- will affect how horseshoe crabs are managed in the Delaware Bay region.
Peter Himchak, of the New Jersey Division of Fish, Game and Wildlife, says the new horseshoe crab census is an ambitious undertaking, which will require extensive volunteer support. Eight beaches on both sides of the bay have been chosen for sampling. Teams of volunteers and staff of natural resource agencies will count adult horseshoe crabs along established transects during evening high tides. Biologists will also conduct sample counts of horseshoe crab eggs. Dr. Bob Loveland of Rutgers University and Dr. Mark Botton of Fordham University will lead the effort to measure spawning success by counting live eggs deposited in the sand by female horseshoe crabs at the same beaches where the crab surveys take place.
Researchers say the expanded census program is building on the success of previous volunteer surveys. Dr. Hall continues to coordinate the survey effort. "The census attracts a lot of dedicated volunteers, people who are not biologists," says Dr. Smith. "It's great to see this kind of interest."
Additional volunteers are needed to assist biologists in counting horseshoe crabs during nighttime high tides. Interested persons should contact Ms. Benjie Swan at (609) 465-6552 or Dr. Bill Hall at (302) 645-4253, email@example.com. More information about the project can be found online at http://ael.er.usgs.gov/groups/stats/Limulus/
The horseshoe crab research is one of several projects supported this year under the USGS State Partnership Program. Cooperators include the New Jersey Division of Fish, Game and Wildlife; the Delaware Division of Fish and Wildlife; and the Maryland Department of Natural Resources. The State Partnership Program is a competitive funding initiative that seeks to foster collaboration among scientists and resource managers from States, Tribes, the USGS, and other Department of Interior agencies.
As the nation's largest water, earth and biological science and civilian mapping agency, the USGS works in cooperation with more than 2000 organizations across the country to provide reliable, impartial, scientific information to resource managers, planners, and other customers. This information is gathered in every state by USGS scientists to minimize the loss of life and property from natural disasters, to contribute to the conservation and the sound economic and physical development of the nation's natural resources, and to enhance the quality of life by monitoring water, biological, energy, and mineral resources.
This press release and in-depth information about USGS programs may be found on the USGS home page: http:// www.usgs.gov. To receive the latest USGS news releases automatically by email, send a request to firstname.lastname@example.org. Specify the listerver(s) of interest from the following names: water-pr: geologic-hazards-pr; biological-pr; mapping-pr; products-pr; lecture-pr. In the body of the message write: subscribe (name of listserver) (your name). Example: subscribe water-pr Joe smith.
Student Exploration: Studying Horseshoe Crab Population Decline
By Neil Hogan
About 170 students in grades four through six, from area public schools, got up close and personal with "living fossils", thanks to the Connecticut Audubon Coastal Center. In the process, they contributed to research study on the alarming decrease in the horseshoe crab population in Long Island Sound. The students - from Roosevelt Elementary School in Bridgeport, Lordship Elementary School in Stratford and Troup Middle School in New Haven - participated in a two-phase research project on horseshoe crabs, called Project Limulus, after the species scientific name Limulus polyphemus.
In a preparatory visit to each school, Richard Julian, education director at the Connecticut Audubon Coastal Center, introduced students to the fascinating history and lifestyle of the crabs. Julian explained how horseshoe crabs are not true crabs. Rather they are chelicerates, more closely related to arachnids such as spiders and scorpions, than crabs. He also demonstrated the life cycle and habits of the horseshoe crabs that are as common as sunbathers along Connecticut's seashore during the May and June. Limulus migrates to the shore from the deeper waters of Long Island Sound. Females drag males behind them into the inter-tidal zone and dig into the sand where they lay their eggs for fertilization by the males.
In the second phase of Project Limulus, the students visited area beaches to
collect specimens as part of a research study. Richard Julian and Milan Bull,
director of the Connecticut Audubon Coastal Center, led the Bridgeport and Stratford
students on a field trip to Long Beach in Stratford, and the New Haven students
on an excursion to Silver Sands State Park in Milford. The students searched
out the horseshoe crabs, measured them, determined their gender and noted their
condition relative to injuries and the presence of harmful organisms on them.
One of the major benefits, says Julian, is that the project engaged the students in real scientific research rather than mere simulation or viewing through pictures and illustrations the work of scientists. "This project involves the students in a larger and very significant scientific effort directed by two researchers at Sacred Heart University in Fairfield," explained Julian.
At the university, marine biologists Gregory Watkins-Colwell and Jennifer Matei have undertaken a long-range research project. Their efforts parallel a similar federally sponsored research in the Delaware Bay to assess a rapid decline in the horseshoe crab population (reference Connecticut Audubon News, Summer 2001 issue, page 1 article, Horseshoe Crabs and Shorebirds by Watkins-Colwell)Back to top
In the 2000 season, crab egg production was at its lowest level in a decade in Delaware Bay, a drop-off that threatens not only the crabs themselves but the birds that depend on the eggs for food. According to the Watkins- Colwell article in Connecticut Audubon News, the decline has been triggered by increasing use of the horseshoe crabs for fertilizer for agriculture and for bait to catch eels and whelks.
Before releasing the horseshoe crabs back to the beach, Julian and Bull tagged them using the protocol followed by the Sacred Heart researchers to assess changes in population on Connecticut's shoreline. The end result, according to Julian, was a win-win situation for everyone. The students supplemented their classroom studies with a hands-on and important research project. Their efforts and those of the Coastal Center educators furthered the important study of the changes in horseshoe crab population in Long Island Sound. The researchers at Sacred Heart got some needed assistance with their ambitious project. And through the students and the publicity generated by their efforts, the general public was alerted to the serious danger to the horseshoe crab population.
The Greater Bridgeport Area Foundation funded the Coastal Center's participation in the research. Because of the many benefits from the effort, Julian is hopeful the funding will be extended so that another group of students can participate in this real science project this spring. Attention Teachers: If you would like to schedule a Project Limulus Research Project for your students, please contact Richard Julian at 203-878-7440 for more information.
Archived from CT Audubon Society News Spring 2002
Archive of Spotlight Feature Articles
The Horseshoe Crab -- Putting Science to Work to Help "Man's Best Friend"
-- University of Delaware
Sea Grant College Program
The largest population of horseshoe crabs in the world lives in Delaware Bay. This ancient animal plays a critical role in the bay's ecology and in human medicine. The crab's eggs fuel shorebirds migrating north to Arctic nesting grounds each spring. A compound in the crab's blood is used by the pharmaceutical industry to test intravenous drugs, as well as prosthetics, for bacteria. There is concern, however, that the Delaware Bay's horseshoe crab population is declining, and Delaware Sea Grant scientists are working to stem the tide.
Horseshoe crabs provide important benefits. Each spring, the crab's eggs feed hungry shorebirds that stop along Delaware Bay to fuel up for the migration north to Arctic nesting grounds. In human medicine, one of the crab's most important contributions is a compound in its blood, which is used by the pharmaceutical industry to test intravenous drugs for bacteria. Blood for this test is removed without harming the animal. (Photo by Bill Hall)
Dog and cat lovers continually debate about which animal is man's best friend. But ask Bill Hall, marine education specialist for the University of Delaware Sea Grant College Program, his opinion, and he will tell you that the hands-down winner is the horseshoe crab. While few may know it, this prehistoric creature with the helmet-shaped body and spear-like tail has saved countless human lives.
"Horseshoe crabs are critical to the welfare of migrating shorebirds that stop along the Delaware Bay each spring to fuel up for the flight north to Arctic nesting grounds. Some of these birds double and even triple their weight by feasting on horseshoe crab eggs," Hall says.
"Yet the horseshoe crab is just as important to humans as it is to wildlife,"
he notes. "This animal's blood contains a unique clotting agent that the
pharmaceutical industry uses to test intravenous drugs for bacteria. No IV drug
reaches your hospital pharmacy without its horseshoe crab test. So if you or
someone you love has ever been hospitalized, you owe a lot to the horseshoe
Bill Hall, marine education specialist for the University of Delaware Sea Grant College Program, helps organize a regional census of the Delaware Bay's spawning horseshoe crab population. (Photo by Robert Cohen)
Hall helps organize a regional census of the Delaware Bay's spawning horseshoe crab population. Now in its tenth year, volunteers from Delaware and New Jersey conduct the census on selected bay beaches each May and June. This year, the census will be expanded to additional beaches along both sides of the bay with support from the Atlantic States Marine Fisheries Commission.
"Delaware Bay is the world's population center for horseshoe crabs, but during the past few years, we've noted a significant downturn in the animal's population, from 1.2 million spawning females down to about 400,000," Hall says.
"Scientists believe the decline is due to over fishing of the crab for eel and conch bait and to the loss of the sandy beaches it needs for spawning," he notes. "The census is designed to help resource managers and scientists gain a better understanding of the horseshoe crab's status and what we can do to guard our 'golden goose.' "
Developing an Artificial Bait to Reduce Fishing Pressure On the Horseshoe Crab
In Sea Grant research, University of Delaware marine biologist Nancy Targett
is developing artificial bait that chemically mimics the horseshoe crab to reduce
the crab's use as eel and whelk bait. (Photo by Robert Cohen)
In Sea Grant research at the University of Delaware, marine biologist Nancy Targett has been working to minimize fishing pressure on the horseshoe crab through biochemistry. She has made significant progress toward identifying the stimulant in female horseshoe crabs that makes them such irresistible bait for eels and whelks. With this information, she wants to develop artificial bait that will attract eels and whelks just as well as female horseshoe crabs do.
Targett and her graduate students are in the home stretch in chemically characterizing the attractant. The next step will be to incorporate the compound into a variety of artificial bait types and test their effectiveness. Several commercial fishermen in Delaware have contacted Targett, offering to test the baits when they are ready.
"The fishing industry is very supportive of this effort," Targett says. "With their help, our goal is to develop an artificial horseshoe crab bait that will work as well as the traditional one. The result should be a win-win situation for the fishermen as well as the horseshoe crab, resulting in more horseshoe crabs for spawning and sustainable uses in medicine."
Horseshoe Crab Facts: Although called a "crab," the horseshoe crab is actually closely related to spiders and scorpions. It is also one of the Earth's oldest creatures, having appeared here 100 million years before the dinosaurs.
Scientists have learned a lot about the human eye by studying the horseshoe crab's large compound eyes. The horseshoe crab also has numerous smaller eyes called photoreceptors on its top shell and along its tail. Sensitive to light, they help synchronize the crab's internal clock with daily cycles of light and darkness.
The horseshoe crab's sword-like tail, called the telson, isn't poisonous, as some people believe. When the crab has been overturned, it simply uses its tail as a lever to flip itself to an upright position.
Horseshoe Crab Model Connects with Kids: Outreach specialists at the University of Delaware Sea Grant College Program have spearheaded a number of efforts to educate the public about the horseshoe crab, from a public forum to set research and management priorities, to public service announcements in the program's long-running Sea Talk radio series. Listen to 60-second audio clip on horseshoe crab census.
The Horseshoe Crab Model, a life-sized paper model that can be cut out and taped together, also has been developed to help teach the public, especially youngsters, about the crab. Developed with funding from the Delaware Department of Education, more than 25,000 copies of the model have been distributed to Delaware teachers and their students and a variety of other audiences in the U.S. and abroad.
Mrs. Anderson's fifth-grade science students at St. John the Beloved School in Wilmington, Delaware, show off their horseshoe crab models. (Photo by Jack Buxbaum). After her fifth-grade science class tackled the model, Mrs. Sheila Anderson, a teacher at St. John the Beloved School in Wilmington, Delaware, wrote:
"Thought you might like to see the fruits of your labors (see photo). The horseshoe crabs were a great hit! We're studying classification of invertebrates and they fit right into science as well as 'across the curriculum' into our study of Indians in Delaware. We learned they used the shells to scoop water out of canoes and the tails to spear fish. Thanks for a great project!"
In addition to the model parts, the eight-page publication provides information about the horseshoe crab's ecological and economic importance along with a crossword puzzle to test readers' knowledge. The Horseshoe Crab Model has been so popular that Delaware Sea Grant is now preparing a second printing of 30,000 copies. As a teacher aid, the second edition will include information on how the classroom activity meets national and state science education standards. A four-page educational bulletin about the horseshoe crab also is available from Delaware Sea Grant. For more information, contact the University of Delaware Marine Communications Office at MarineCom@udel.edu.
The University of Delaware Sea Grant College Program conducts research, graduate education, and public outreach efforts relating to the wise use, conservation, and management of marine and coastal resources. The program's current research priorities focus on the coastal ocean, environmental technology, coastal engineering, marine biotechnology, and fisheries. The National Sea Grant College Program in the National Oceanic and Atmospheric Administration (NOAA), U.S. Department of Commerce; the State of Delaware; and the University of Delaware fund the program. For more information, visit the program's Web site at http:// www.ocean.udel.edu/seagrant. Virginia Tech
Date: http://www.sciencedaily.com/releases/2002/05/020508072036.htm 2002-05-09
Horseshoe Crabs Survival Rate After Biomedical Bleeding Is High
BLACKSBURG, Va - Faculty from the Department of Fisheries and Wildlife Sciences in the College of Natural Resources and the Department of Biomedical Sciences and Pathobiology in the College of Veterinary Medicine at Virginia Tech had the first ever major review article on horseshoe crabs published in the journal, Review in Fisheries Science journal. Elizabeth A. Walls, while a graduate student in fisheries and wildlife sciences; Jim Berkson, assistant professor in fisheries and wildlife sciences; and Stephen A. Smith, professor in biomedical sciences; reviewed the general biology, ecology, and life history of the horseshoe crab in the article "The Horseshoe Crab, Limulus polyphemus: 200 Million Years of Existence, 100 Years of Study."
The review article discusses the various economic stakeholders involved with the horseshoe crab, including eco-tourism groups associated with bird- watching, the commercial fishermen who use the horseshoe crab as bait, and the biomedical industry with its increasing demand for horseshoe crab blood for endotoxin testing. The article reviews the reported economic impacts of horseshoe crabs, the status and management of the horseshoe crabs now and projected in the future, and alternatives to using horseshoe crabs as a blood source.
"We do have results from a number of our studies at this point," Berkson says. "We have found that the mortality of horseshoe crabs that undergo the biomedical bleeding process is only 7.5 percent. That is astounding considering how much blood is taken out of the crabs. We would expect it to be much higher. This may be an indication of how the crabs have survived for 350 million years."
Berkson adds, "We also have new information on where horseshoe crabs are found in the ocean, how far they migrate, and the presence of possible nursery grounds, where juveniles are at particular risk from the commercial fishery."
Virginia Tech's Horseshoe Crab Research Center opened this year in response to the multiple uses for the horseshoe. "LAL is a chemical found in horseshoe crab blood used to detect the presence of endotoxins in injectible drugs and implantable devices. The chemical is more important than ever due to the anti-terrorism efforts," explains Berkson. "All vaccines, including smallpox and anthrax, must be tested for the presence of endotoxins using LAL." The research at the Horseshoe Crab Research Center is designed to provide the information needed to sustainably maintain this essential natural resource.
Editor's Note: The original news release can be found here.
Note: This story has been adapted from a news release issued for journalists and other members of the public. If you wish to quote any part of this story, please credit Virginia Tech as the original source. You may also wish to include the following link in any citation:
How long horseshoe crabs live, whether they return to the beach of their birth for spawning, why their life cycles seem directed by the moon, where they disappear to for the other 10 months of the year-all these questions remain mysteries. Somehow, the horseshoe crab has thrived for 500 million years, and Sue Schaller wants to know why.
"You've got an animal that predates dinosaurs by 200 million years, and it hasn't changed much at all. It hasn't had to evolve," said Schaller, a biologist who has studied Maine's horseshoe crabs for the past three years.
One rainy afternoon recently, Schaller and four local volunteers, dressed in
slickers and hip waders, are hiking along the shore of Taunton Bay near Shipyard
Point in Franklin.
It's the height of the spawning season, and Schaller's crew is peering into the cloudy water, looking for the green- brown, helmetlike shells of visiting horseshoe crabs.
"They vacation on the bay," Schaller jokes.
The biologist finds a mating pair, a small male grasping a larger female in hopes of being nearby when she begins to release her eggs. As Schaller turns the crabs over, they gesture threateningly with long spike-like tails, known as telsons. They flap their hinged shells, and wave the pincher-tipped walking legs and daisy like swimmerets that surround their mouths.
The horseshoe crab is the sort of fanciful, frightening creature that appears
more frequently in science fiction stories than in zoology texts.
"I love 'em," Schaller said. "Once you scratch the surface and get over the fear thing, they really are intriguing."
Horseshoe crabs were misnamed centuries ago, when mariners thought the odd creatures' sloped shells resembled horse's feet.
Related to Long-Extinct Trilobites
But horseshoe crabs aren't actually crabs. They're chelicerates, the zoological classification that includes spiders, scorpions and mites. In fact, the 500 million-year-old animal is more closely related to long-extinct trilobites than to any living creature.
Horseshoe crabs can walk along the sea bottom on six pairs of legs, or swim upside down or right side up depending on where they're trying to go.
Schaller is here because Shipyard Point boasts the world's most northerly breeding population of the creatures. The Taunton Bay group is tiny compared to the hundreds of thousands of horseshoe crabs massing on the beaches of Cape Cod and Delaware Bay this month, but that's what makes it an ideal research site. The small population creates the possibility that every individual animal can be tagged and studied.
Horseshoe crabs are rare in Maine because the Atlantic is so cold and the rocky coastline provides few of the shallow, sandy estuaries in which they prefer to spawn, Schaller said.
Last summer, she visited 15 such pockets of horseshoe crab habitat scattered throughout the central and south coast of Maine. With the help of more than 70 volunteers, she began to count individuals and was surprised at the size and health of Maine's population. At the Damariscotta Mills site, 275 crabs were spotted on a single day.
"As you walk along, you don't necessarily see lots of animals, but there are more than we thought," she said.
Crabs Tagged With Plastic Markers
Taunton Bay is the only site where survey animals are being tagged, by drilling a small hole in the shell's outer edge and attaching a plastic marker. More than 1,300 crabs were so identified last summer. Schaller believes the population could be much larger. Only a quarter of the animals counted this summer sported the bright yellow research tags.
"We're not getting a lot of returns, and we don't know where they're going," she said.
This year's survey was reduced from 15 to seven key sites, because funding from the Maine Outdoor Heritage Program was not renewed. Funded or not, Schaller hopes to continue the survey indefinitely, and answer some of the big questions about horseshoe crabs that have confounded researchers for decades.
Schaller, a former U.S. Fish and Wildlife biologist, has already proved that horseshoe crabs possess the rare ability to regenerate lost body parts in a manner similar to starfish.
In Massachusetts, Delaware and even southern Maine, horseshoe crabs are in high demand as bait in eel pot fisheries-a U.S. $70 million business according to the Atlantic Marine Fisheries Commission.
The crabs are also harvested for their blood, a valuable commodity for medical researchers. A substance extracted from horseshoe crab blood is used in hospitals to detect the presence of bacteria in biomedical equipment.
Commercial harvesters have generally overlooked eastern Maine's small, scattered populations.
Fishing regulations are virtually unheard of, and federal research suggests that larger horseshoe crab populations may be in decline. However, the knowledge of a horseshoe crab's life history, which would be essential for drafting good regulations, just doesn't exist.
With her living laboratory in Taunton Bay, and the ongoing efforts of local volunteers, Schaller hopes to provide that key information.
"It's a backwater kind of place that people don't value, but for wildlife and for fisheries, it's one of the treasures of the coast of Maine," said Steve Perrin, a Bar Harbor naturalist and president of the Friends of Taunton Bay conservation group. "It's kind of an honor to have such an ancient being come here and choose this bay."
(Bangor Daily News)