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Former Natural History Museum (London) paleontologist Fortey gives us the stories of those plants, animals, and other creatures that have survived from Earth's early days--the planet's \"true marathon runners.\"

Horseshoe crabs have persisted for more than 200 million years, and fossil forms date to 450 million years ago. The American horseshoe crab ( Limulus polyphemus ), one of four extant horseshoe crab species, is found along the Atlantic coastline of North America ranging from Alabama to Maine, USA with another distinct population on the coasts of Campeche, Yucatán and Quintana Roo in the Yucatán Peninsula, México. Although the American horseshoe crab tolerates broad environmental conditions, exploitation and habitat loss threaten the species. We assessed the conservation status of the American horseshoe crab by comprehensively reviewing available scientific information on its range, life history, genetic structure, population trends and analyses, major threats, and conservation. We structured the status assessment by six genetically-informed regions and accounted for sub-regional differences in environmental conditions, threats, and management. The transnational regions are Gulf of Maine (USA), Mid-Atlantic (USA), Southeast (USA), Florida Atlantic (USA), Northeast Gulf of México (USA), and Yucatán Peninsula (México). Our conclusion is that the American horseshoe crab species is vulnerable to local extirpation and that the degree and extent of risk vary among and within the regions. The risk is elevated in the Gulf of Maine region due to limited and fragmented habitat. The populations of horseshoe crabs in the Mid-Atlantic region are stable in the Delaware Bay area, and regulatory controls are in place, but the risk is elevated in the New England area as evidenced by continuing declines understood to be caused by over-harvest. The populations of horseshoe crabs in the Southeast region are stable or increasing. The populations of horseshoe crabs in the Florida Atlantic region show mixed trends among areas, and continuing population reductions at the embayment level have poorly understood causes. Within the Northeast Gulf of Mexico, causes of population trends are poorly understood and currently there is no active management of horseshoe crabs. Horseshoe crabs within México have conservation protection based on limited and fragmented habitat and geographic isolation from other regions, but elevated risk applies to the horseshoe crabs in the Yucatán Peninsula region until sufficient data can confirm population stability. Future species status throughout its range will depend on the effectiveness of conservation to mitigate habitat loss and manage for sustainable harvest among and within regions.

Horseshoe crabs are the only extant xiphosurans and are believed to be morphologically unchanged for more than 200 million years. Of the four extant species namely, Limulus polyphemus, Tachypleus tridentatus, Tapinauchenius gigas and Carcinoscorpius rotundicauda, the latter three are found in Asian waters. Recent evidences showed that Asian horseshoe crabs are facing serious threats such as degradation of their spawning grounds and habitat, environmental pollution, overexploitation as a culinary delicacy and biomedical bleeding practices. Baseline data on the distribution and existing population of the wild horseshoe crabs remain poorly known in several Asian regions. Several studies have clearly revealed that pressure due to over-fishing of wild stock has increased tremendously in the last decade. Due to an increase in demand for Tachypleus Amebocyte Lysate (TAL) analogous to Limulus Amebocyte Lysate (LAL) in the United States, there is an urgent need to comprehensively address their fishing and conservation measures in the Asian region. This review addresses the overall studies on three species of Asian horseshoe crabs in relation to their fishing practices, local exploitation of their wild stock either for human consumption (or) by biomedical industries. The authors have structured the discussion on an international scale to address the existing problems in fishing and conservation of horseshoe crabs. Since no specific regulatory force or legislative protection act or a policy to preserve their natural stock are available to this date, this paper strongly recommends representative countries to include horseshoe crabs under their wildlife protection act to avoid further unsustainable exploitation of their wild populations.

Horseshoe crabs are an ancient species facing modern threats. While their importance to the conservation of endangered birds has garnered them increasing protections in recent years, disparate and insufficient management strategies across regions have precluded population recovery. Six datasets spanning 22–46 years for Atlantic horseshoe crabs ( Limulus polyphemus ) in the Long Island Sound, USA region were analyzed from regional monitoring programs conducted for general biodiversity assessments that had not been previously aggregated for the evaluation of this species. In these datasets, a decline of 2–9% per year in L. polyphemus count per sample was observed, with significant individual declines in 5 of the 6 datasets (all datasets from bays and harbors). The central Long Island Sound dataset exhibited a significantly slower rate of decline, driven by higher counts per sample in recent years, which should be monitored to determine if an improving trend will be sustained or if the recent higher counts were anomalies. An increasing proportion of females, mean prosomal width, and mean weight of L. polyphemus were also observed. With management activities at the local, regional, and national level impacting the potential for population recovery in this species, it is critical for policymakers at all levels to be aware of the severe decline in observations of this species across data sources, pointing to a need for urgent action to prevent local extinction.

The American Horseshoe crab, Limulus polyphemus, a species considered a phylogenetic relict, has been widely studied in its distribution in the United States due to its relevance in the fishing and biomedical industry. However, there is little information on the genetic status of the Mexican population which is relevant for the conservation of this endangered species. Here, using nuclear microsatellites markers, we evaluate the genetic diversity and structure of L. polyphemus in different localities of its Mexican distribution in the Yucatán Peninsula. A total of 103 individuals from four Mexican localities from the Gulf of Mexico (Champotón and Ría Celestún), northern coast of Yucatán (Yum Balam), to Caribbean coast (Sian Ka’an), were analyzed. Our results show low to moderately low values of different genetic diversity parameters and possible inbreeding processes for the two localities situated at the disttibution extremities (Champotón and Sian Ka’an). Also, we detected a strong genetic structure with two clusters, one pooling the Ría Celestún, Yum Balam and Sian Ka’an samples, and the other corresponding to Champotón, the most isolated population in the southern Gulf of Mexico. These patterns of genetic diversity could be related to anthropogenic activities (contamination, illegal fishing) that have impacted these populations for decades, resulting in a decrease in their populations.The observed genetic structure seems to be related to the dispersal behavior of the species and the circulation pattern on the Yucatán Shelf and the Campeche Bank. Our results highlighted the existence of two management units that should be considered in proposing management and conservation strategies for this species, especially focused on localities at critical risk.

The horseshoe crab, Limulus polyphemus, has recently been found to spawn regularly in salt marshes, despite the long‐held assumption that salt marsh sediments are not conducive for embryonic development. Here, we tested the prediction that eggs laid in the salt marsh would develop more slowly and be less viable than eggs laid on beaches. We flagged the nests of spawning horseshoe crabs in the marshes and beaches of three states—South Carolina, Connecticut, and New Hampshire—and then excavated those nests one or three weeks later. We staged the excavated embryos to compare developmental progress between marshes and beaches. We found that, in general, habitat type did not affect embryonic development rate or the viability of embryos; instead, temperatures experienced by embryos drove most developmental patterns. Horseshoe crabs also buried their eggs in the marsh at shallower depths than at the beach, possibly to avoid deleterious conditions found deeper in marsh sediments. These results indicate that salt marshes are viable habitats for horseshoe crab recruitment and should be considered for the proper management and conservation of this species. Recent research has found that horseshoe crabs spawn regularly in salt marshes. However, it remained unclear if eggs laid in salt marsh sediments are viable. In this study, we show that eggs laid in salt marsh habitats develop similarly to those laid in beach habitats, suggesting that salt marshes are viable spawning habitats for horseshoe crabs.

Every year the Atlantic horseshoe crab (Limulus polyphemus) arrives on shore to spawn, a sight once taken for granted. However, in addition to the gradual climate changes impacting all ecosystems, commercial demand from the widespread application of Atlantic horseshoe crab blood in industrial endotoxin testing and steady use as eel and whelk bait has brought the future of this enduring species into question. In response, regulations have been adopted to enhance the traceability and record keeping of horseshoe crab harvest, which has historically been difficult to track. However, these regulations do not restrict or limit LAL harvest in any significant manner. Still, sometimes-lethal biomedical bleeding process and associated behavioral changes pose a risk to horseshoe crab viability after bleeding and once returned to the waters. As a result, regulators and environmentalists are concerned that current trends and overfishing of this marine arthropod will significantly impact the surrounding ecosystem. This review examines their role and recent trends in the biomedical industry that are impacting these ancient creatures and the derivative effect on shorebirds, while considering emerging alternatives where feasible, as well as ways to ensure sustainable and pragmatic harvesting strategies. Ultimately, healthy populations of horseshoe crabs are vital to restoring and maintaining ecosystems while balancing the need for medical and research applications entirely dependent on these unique creatures.

Xiphosurids (Merostomata, Xiphosura) are a group of chelicerates with a rich and complex evolutionary history that is constantly being updated through new discoveries. In this study, we re-estimated the divergence time of the extant horseshoe crab species with new fossil calibration points and addressed the inter- and intraspecific relationships of the American horseshoe crab through a phylogeographic perspective. In order to achieve our objectives, three datasets were compiled from fragments of different lengths of the COI gene that include sequences from 154 individuals, representing the Mexican populations. In addition to these, the datasets also included previously published sequences corresponding to individuals from different US populations and Asian horseshoe crab species. Firstly, we estimated the divergence times of extant horseshoe crab species by Bayesian methods using multiple fossil calibration points. Subsequently, we investigated the phylogeographic relationships and demographic history of Limulus polyphemus in the Americas utilizing various datasets. The time of divergence of the two Asian species clades was estimated to be approximately 127 million years ago (Ma). Phylogeographic relationships between the Asian and American species are linked through a minimum of 86 mutational steps. In America, phylogeographic relationships reflect differentiation between US and Mexican populations of L. polyphemus. We detect signs of demographic expansion for the Mexican population during the last 75,000 years, as well as an absence of phylogeographic structuring. The evolutionary history of horseshoe crabs is older than previously believed; however, the current distribution and demographic changes have probably been influenced by environmental events of the recent past, such as the glacial–interglacial periods that occurred during the Pleistocene.

Most populations of migrant shorebirds around the world are in serious decline, suggesting that vital condition-dependent rates such as fecundity and annual survival are being affected globally. A striking example is the red knot (Calidris canutus rufa) population wintering in Tierra del Fuego, which undertakes marathon 30 000 km hemispheric migrations annually. In spring, migrant birds forage voraciously on horseshoe crab eggs in Delaware Bay in the eastern USA before departing to breed in Arctic polar deserts. From 1997 to 2002 an increasing proportion of knots failed to reach threshold departure masses of 180-200 g, possibly because of later arrival in the Bay and food shortage from concurrent over-harvesting of crabs. Reduced nutrient storage, especially in late-arriving birds, possibly combined with reduced sizes of intestine and liver during refuelling, had severe fitness consequences for adult survival and recruitment of young in 2000-2002. From 1997 to 2002 known survivors in Delaware Bay were heavier at initial capture than birds never seen again, annual survival of adults decreased by 37% between May 2000 and May 2001, and the number of second-year birds in wintering flocks declined by 47%. Population size in Tierra del Fuego declined alarmingly from 51 000 to 27 000 in 2000-2002, seriously threatening the viability of this subspecies. Demographic modelling predicts imminent endangerment and an increased risk of extinction of the subspecies without urgent risk-averse management.

Beach nourishment is commonly conducted to protect human infrastructure but rarely for the primary purpose of improving wildlife habitat. To improve horseshoe crab spawning and shorebird feeding habitat in the Delaware Bay, New Jersey (USA), we removed 2000 t of shoreline rubble and placed sand on 16 ha of degraded shoreline spanning 8 beaches. Horseshoe crab egg cluster abundance varied annually, seasonally and spatially. Beaches restored using sand with grain size fractions similar to native sand had horseshoe crab egg cluster abundances matching or exceeding those of high-quality reference beaches. Deeper sand with a higher coarse-grain fraction resulted in the highest egg cluster abundance across all sites and beaches, while finer-grained sand used on a subset of restored beaches was associated with lower egg cluster abundances. These patterns were also reflected in shallow egg availability for shorebirds, with egg cluster abundance correlating positively with shallow egg abundance. Over time, sand placed on beaches moved cross-shore and longshore, and overwashed into marshes. Longshore sand movement nourished adjacent beaches and ebb shoals at creek mouths. Such shoals attract spawning horseshoe crabs and have high densities of surface eggs available for shorebird feeding, but experience high attrition of egg clusters. This study demonstrates that investments in beach restoration provide important benefits for horseshoe crabs and shorebirds. Outcomes can be further improved by expanding project scope and integrating other coastal restoration strategies. Restoration will be critical for the conservation of coastal species as sea levels rise and current and past coastal management practices continue to degrade habitats.