- The beach surface is exposed to direct sunlight to provide sufficient incubation. However, horseshoe crabs in Florida nest much higher up on the beach (than in the Delaware Bay) to avoid the anaerobic conditions at the mean high tide line (Penn and Brockmann, 1994). , Horseshoe crabs have three main parts to the body: the head region, known as the "prosoma", the abdominal region or "opisthosoma", and the spine-like tail or "telson". , A large-scale project to tag and count horseshoe crabs along the North American coast was started in 2008, termed Project Limulus. The study found that light and dark cycles influence locomotion, but not as much as tidal activity.. The smaller male grabs on to the back of a female with a "boxing glove" like structure on his front claws, often holding on for months at a time. ), sand ribbon worm (Cerebratulus spp. Therefore, the presence of large numbers of horseshoe crabs on a beach is not necessarily an indicator of habitat suitability (Shuster, 1994). Also, a pair of ventral eyes is located near the mouth, as well as a cluster of photoreceptors on the telson. The brain and the heart are located in the prosoma. By the 1960s, only 42,000 horseshoe crabs were reported to be harvested annually (Finn et al., 1991). Not surprisingly, Shuster (1996) identified that food for the horseshoe crab is abundant on the continental shelf in areas where horseshoe crabs abound. Eggs are laid in clusters or nest sites along the beach, usually between the tide marks. Males versus Females , The blood of horseshoe crabs contains one type of blood cell, the amebocytes. A large compound eye with monochromatic vision is found on each side of the prosoma;[note 1] it has five simple eyes on the carapace, and two simple eyes on the underside, just in front of the mouth, making a total of nine eyes. Erosion of the substrate in which eggs are deposited would increase egg and larval mortality. Horseshoe crabs show rapid seaward orientation on beaches with slopes of approximately six degrees (Botton and Loveland, 1987). ), gem clam, macoma clam, razor clam, and soft-shell clam by horseshoe crabs in Cape Cod Bay, Massachusetts. The telson (i.e., tail or caudal spine) is used to steer in the water and also to flip itself over if stuck upside down. The New Jersey Division of Fish, Game and Wildlife (1997) identified a female dominated sex ratio of 1:1.4 based on 1996 trawl surveys. However, Brockmann (1990) only identified up to 15 egg clusters each season in Florida. The horseshoe crab must molt (shed its chitinous exoskeleton) to grow. The blood in the circulation of these creatures, which generally live in cold environments with low oxygen tensions, is grey-white to pale yellow, and it turns dark blue when exposed to the oxygen in the air, as seen when they bleed. Until recently it was thought that the genus Limulus "ranges back only some 20 million years, not 200 million", but the discovery of Limulus darwini pushes that date back to at least the late Jurassic, 148 million years ago. , A protein from horseshoe crab blood is also under investigation as a novel antibiotic. Thompson (1998) identified that preferentially selected spawning sites were located adjacent to large intertidal sand flat areas.  In June 2007, Delaware Superior Court Judge Richard Stokes has allowed limited harvesting of 100,000 males.  However, this north-south pattern does not exist in the Yucatán Peninsula, the southernmost population of the species, where some subpopulations are intermediate between the Delaware Bay and Florida horseshoe crabs, and others are smaller, averaging about 3⁄4 the size of Florida horseshoe crabs. The horseshoe crab must molt (shed its chitinous exoskeleton) to grow.
 The main area of annual migration is Delaware Bay along the South Jersey Delaware Bayshore. Offshore trawl collections indicate a reversed sex ratio, with females outnumbering males from 3:2 to 2:1 (Rudloe, 1980) or a nearly even sex ratio 1.17 males per female (Swan et al., 1993). A variety of other marine organisms including mussels, gnathobases, barnacles, and other sessile organisms may attach to horseshoe crabs. continuing through August (Rudloe, 1980). Eggs and larvae are preyed upon by large invertebrates including sand shrimp (Crangon septemspinosa), blue crab (Callinectes sapidus), green crab (Carcinus maenas), and spider crab (Libinia spp.) Between 1880 and 1930, the harvest was 1.5 to 1.8 million animals (Finn et al., 1991). Advertisement. North from Cape Cod they gradually become smaller and south from Georgia they gradually become smaller. The optimum temperature for egg development has been estimated to be between 30C and 35C (Jegla and Costlow, 1982). The second pair of appendages, the pedipalps, are used as walking legs; in males they are tipped with 'claspers', which are used during mating to hold onto the female's carapace. The sexes are similar in appearance, but females are typically 25 to 30% larger than the male in length and width, and can reach more than twice the weight. Furthermore, the nerves are large and relatively accessible.
Penn and Brockmann (1994) conclude that the dissimilarity is due to differences in grain size (aerobic sediments occur at higher elevations in Florida than in Massachusetts, New Jersey, and Delaware). However, spawning has been observed on mud, sod, and peat banks. comm., 1995).
Earth Matters Foundation Horseshoe Crab Campaign. Researchers from the University of New Hampshire and Plymouth State University found that 18 percent of a group of bled female horseshoe crabs died after being released. Animals that survive the process may be more lethargic when released and less likely to mate.  The temperature preference varies depending on the population, with the northernmost being the most cold-resistant: in the Great Bay in New Hampshire they show increased activity above 10.5 °C (51 °F) and in Delaware Bay they are active above 15 °C (59 °F).
The mean nest depth in Delaware was found to be 9.3 ± 3.9 centimeters (Penn and Brockmann, 1994). What kind of animals make nests on the beach? , Horseshoe crabs are often referred to as living fossils, as they have changed little in the last 445 million years. This molt into the first juvenile instar occurs approximately 20 days after emergence (Jegla and Costlow, 1982). In Florida, females average about 21.5 cm (8.5 in) and males 16 cm (6.3 in). The smooth shell or carapace is shaped like a horseshoe, and is greenish grey to dark brown in colour. It is the tail that earns this order its name Xiphosura, which derives from the Greek for "sword tail". A wide range of marine species become attached to the carapace, including algae, flat worms, mollusks, barnacles, and bryozoans, and horseshoe crabs have been described as 'walking museums' due to the number of organisms they can support. Molting occurs several times during the first two to three years. Delaware Bay beaches are characterized as coarse-grained and well-drained, whereas Florida beaches are fine-grained and poorly drained (Penn and Brockmann, 1994). , Enzymes from horseshoe crab blood are used by astronauts in the International Space Station to test surfaces for unwanted bacteria and fungi. In South Carolina, the 1997 male-to-female ratio in each estuary sampled was higher than in the preceding years (i.e., 1996 and 1995) (Thompson, 1998), indicating a population changing due to environmental conditions or overharvesting. Depth of eggs in the sediment range from five to 20 centimeters below the surface (mean 11.5 ± 2.8 centimeters) (Rudloe, 1979; Brockmann, 1990). Shuster (1996) suggested that a shift in the normal 1:1 sex ratio toward less than one female per male becomes an important indicator, pointing specifically to overharvesting of females. External parasites and ectocommensals do not usually attach to sub-adult horseshoe crabs due to the frequency of molting (Shuster, 1982).
Larvae feed on a variety of small polychaetes, nematodes, and nereis (Shuster, 1982). 1994), with a median grain size of 0.7 mm. Horseshoe crabs select locations for their nests that will maximize egg development; Penn and Brockmann (1994) found the mean nesting location for horseshoe crabs on Delaware Bay beaches to be about equal to the mean high tide line. ), silver perch (Bairdiella chrysoura), weakfish (Cynoscion regalis), kingfish (Menticirrhus saxatilis), silversides (Menidia menidia), summer flounder (Paralichthys dentatus), and winter flounder (Pleuronectes americanus) (Shuster, 1982). Lacking jaws, it grinds up the food with bristles on its legs and a gizzard that contains sand and gravel. The sex ratio in 1996 and 1997 was 4:1 (Maryland Department of Natural Resources, 1998). However, the sex ratio cannot be ascertained readily from spawning counts because the mating behavior of the males is to concentrate along the shoreline, whereas females generally move into deeper water after spawning (Shuster, 1996).  Atlantic horseshoe crabs can be seen in waters that range from brackish (almost fresh water) to hypersaline (almost twice the salinity of sea water), but their optimum growth is at salinities around or slightly below sea water (20–40‰). A horseshoe crab is said to be stranded when, through the action of the waves or other causes, the animal is on its back and is unable to right itself. [full citation needed] The larvae form and then swim for about five to seven days. of their inshore movement from deep bay and coastal waters appears to  New Jersey beaches campaign "ReTURN the Favor," trains volunteers to rescue impinged and overturned horseshoe crabs while collecting data on natural and man-made hazards.  This species is found in the Gulf of Mexico and along the Atlantic coast of North America. On the underside of the prosoma, six pairs of appendages occur, the first of which (the small pincers or chelicerae) are used to pass food into the mouth, which is located in the middle of the underside of the cephalothorax, between the chelicerae.