Lagoonal Back Bay Beaches as Spawning Habitat for Horseshoe Crabs

-The distribution of migratory shorebirds within Delaware Bay, New Jersey, was examined relative to prey abundance and the physical characteristics of the intertidal beaches. Red Knots (Calidris canutus), Sanderlings (C. alba), Ruddy Turnstones (Arenaria interpres), and peeps comprised nearly 100% of the shorebirds on seven study beaches from mid-May to early June in both 1990 and 1991. The most abundant food item on these beaches was horseshoe crab (Limulus polyphemus) eggs, and there were few other available macroinvertebrates. Beaches preferred by shorebirds had higher numbers of crab eggs; the density of eggs in some surface (0-5 cm) sediments exceeded 1 05 / M2. In general, both horseshoe crab eggs and shorebirds increased along the bay shore from Higbee's Beach (near Cape May Point) to Moore's Beach, 32 km up-bay. However, shorebirds were widely distributed within the bay, possibly because eggs were sufficiently abundant on most beaches to support foraging by at least four birds per meter of shoreline. Shorebirds aggregated near shoreline discontinuities, such as salt-marsh creeks and jetties, that acted as concentrating mechanisms for passively drifting eggs. Sediment grain size and heterogeneity were probably not a primary determinant of shorebird distribution within Delaware Bay. Intertidal sand flats were not extensively used by foraging shorebirds, but the potential importance of nearby salt marshes as foraging sites requires further investigation. Received 20 January 1993, accepted 27 March

A decline in red knots (Calidris canutus rufa) has been attributed to horseshoe crab (Limulus polyphemus) egg shortages on the Delaware Bay, an important foraging area for migrating knots. We studied the movements and distribution of 65 radiotagged red knots on Delaware Bay from May to June 2004 and related movements to the distribution and abundance of horseshoe crab eggs and other prey and to other habitat characteristics. The number of horseshoe crab eggs was the most important factor determining the use of Delaware Bay beaches by red knots (logistic regression cumulative Akaike's Information Criterion adjusted for small sample size [AICc] w = 0.99). The knots shifted from emergent marsh and peat-beaches to sandy Delaware Bay beach when crab eggs became abundant, which also suggested the importance of crab eggs. While red knots used sandy beach zones more than expected, given their availability, 44% of red knot low tide locations were in bay and coastal emergent marsh. The abundance of Donax variabilis (AICc w = 0.95) and Mytilus edulis (AICc w = 0.94) spat, both food for red knots, had a relationship with red knot use of sandy beaches. Levels of disturbance and the abundance of laughing gulls (Larus atricilla) also were important factors in red knot sandy beach use, although secondary to prey resources (AICc w < 0.4). These results are consistent with the hypothesis that the abundance of horseshoe crab eggs on sandy beaches is driving movement and distribution of red knots and that there is little alternative food during the migratory stopover in Delaware Bay. Our findings that red knots disproportionately use Delaware Bay sites with abundant eggs and that there is a lack of surplus eggs at areas used and unused by red knots support the continuation of management for sustained yield of horseshoe crabs and other food resources at this stopover.

Biology.- Limits on the Global Distribution of Horseshoe Crabs (Limulacea): Lessons Learned from Two Lifetimes of Observations: Asia and America.- Horseshoe Crabs - An Ancient Ancestry Revealed.- The Ecological Importance of Horseshoe Crabs in Estuarine and Coastal Communities: A Review and Speculative Summary.- Relationships Between Sandpipers and Horseshoe Crab in Delaware Bay: A Synthesis.- Horseshoe Crabs, Their Eco-biological Status Along the Northeast Coast of India and the Necessity for Ecological Conservation.- American Horseshoe Crabs, Limulus polyphemus, in Mexico: Open Possibilities.- Basic Habitat Requirements of the Extant Species of Horseshoe Crabs (Limulacea).- The Relationship Between Small- and Large-Scale Movements of Horseshoe Crabs in the Great Bay Estuary and Limulus Behavior in the Laboratory.- Ecology of Horseshoe Crabs in Microtidal Lagoons.- Phylogeography, Demographic History, and Reserves Network of Horseshoe Crab, Tachypleus tridentatus, in the South and East China Seaboards.- Genetic Structure of Japanese Populations of Tachypleus tridentatus by mtDNA AT-Rich Region Sequence Analysis.- Reproductive Competition and Sexual Selection in Horseshoe Crabs.- Vision in Horseshoe Crabs.- Sperm Attachment on the Egg of Malaysian King Crab, Carcinoscorpius rotundicauda.- Distribution and Development of Limulus Egg Clusters on Intertidal Beaches in Delaware Bay.- Comparisons in Prosomal Width and Body Weight Among Early Instar Stages of Malaysian Horseshoe Crabs, Carcinoscorpius rotundicauda and Tachypleus gigas in the Laboratory.- Emergence Behavior of Juvenile Tachypleus tridentatus Under Simulated Tidal Conditions in the Laboratory and at Two Different Sediment Temperatures.- Distribution of Juvenile Horseshoe Crabs in Subtidal Habitats of Delaware Bay Using a Suction-Dredge Sampling Device.- Conservation.- History of Horseshoe Crab Harvest on Delaware Bay.- Biomedical Applications of Limulus Amebocyte Lysate.- The Effect of Hemolymph Extraction Volume and Handling Stress on Horseshoe Crab Mortality.- Horseshoe Crabs in Hong Kong: Current Population Status and Human Exploitation.- Comparative Status and Assessment of Limulus polyphemus with Emphasis on the New England and Delaware Bay Populations.- An Integrative Approach to Horseshoe Crab Multiple Use and Sustainability.- Strategies to Conserve and Enhance Sandy Barrier Habitat for Horseshoe Crabs (Limulus polyphemus) on Developed Shorelines in Delaware Bay, United States.- Conservation Program for the Asian Horseshoe Crab Tachypleus tridentatus in Taiwan: Characterizing the Microhabitat of Nursery Grounds and Restoring Spawning Grounds.- The Effects of Water Quality on Horseshoe Crab Embryos and Larvae.- Heavy Metal Concentration in Horseshoe Crab (Carcinoscorpius rotundicauda and Tachypleus gigas) Eggs from Malaysian Coastline.- A Discussion of Horseshoe Crab Management in Five Countries: Taiwan, India, China, United States, and Mexico.- Clinical Evaluation, Common Diseases, and Veterinary Care of the Horseshoe Crab, Limulus polyphemus.- Aquaculture Methods and Early Growth of Juvenile Horseshoe Crabs (Limulus polyphemus).- Larval Culture of Tachypleus gigas and Its Molting Behavior Under Laboratory Conditions.- Diet Composition of Juvenile Horseshoe Crabs: Implications for Growth and Survival of Natural and Cultured Stocks.- Effect of Sediment Type on Growth and Survival of Juvenile Horseshoe Crabs (Tachypleus tridentatus).- The Conservation Network of Horseshoe Crab Tachypleus tridentatus in Taiwan.- The History of Horseshoe Crab Research and Conservation in Japan.- Public Awareness and Community-Based Conservation for the Horseshoe Crab at Saikai National Park in Nagasaki Prefecture, Japan.- Public Participation in Studies on Horseshoe Crab Populations.- Green Eggs and Sand: A Collaborative Effort of Scientists, Teachers, Resource Managers, and Stakeholders in Educating About Limulus polyphemus.- Community Building: An Integrated Approach to Horseshoe Crab Conservation.

Recent and dramatic declines have been documented in several shorebird populations that stage in Delaware Bay during spring migration. As a result, considerable attention has been given to issues such as the reliance of sandpipers on Delaware Bay American horseshoe crab (Limulus polyphemus) eggs for refueling and how to best manage the horseshoe crab fishery to insure adequate resources for migratory shorebirds. In this chapter, we synthesize over 25 years of shorebird research and monitoring data in Delaware Bay to support the premise that horseshoe crab eggs are an essential element for migrating sandpipers during northbound passage through the bay. We then discuss long- and short-term trends in American horseshoe crab populations resulting from changes in demand and harvest regulations, and how this has affected shorebird population viability. Regulatory actions have led to recent increases in some demographic elements of the Delaware Bay crab population, but such changes have not yet translated into increased crab egg availability or population recovery indices in shorebirds. Because reduced availability of horseshoe crab eggs has severe consequences for migratory sandpipers at the individual and population levels, current conservation strategies that include harvest reductions on American horseshoe crabs in the Delaware Bay region must persist into the foreseeable future to insure the recovery of horseshoe crab populations and the long-term health of migratory sandpipers in Delaware Bay.

Understanding how events during one period of the annual cycle carry over to affect survival and other fitness components in other periods is essential to understanding migratory bird demography and conservation needs. Previous research has suggested that western Atlantic red knot (Calidris canutus rufa) populations are greatly affected by horseshoe crab (Limulus polyphemus) egg availability at Delaware Bay stopover sites during their spring northward migration. We present a mass-based multistate, capture-recapture/resighting model linking (1) red knot stopover mass gain to horseshoe crab spawning abundance and (2) subsequent apparent annual survival to mass state at the time of departure from the Delaware Bay stopover area. The model and analysis use capture-recapture/resighting data with over 16,000 individual captures and 13,000 resightings collected in Delaware Bay over a 12 year period from 1997–2008, and the results are used to evaluate the central management hypothesis that red knot populations can be influenced by horseshoe crab harvest regulations as part of a larger adaptive management effort. Model selection statistics showed support for a positive relationship between horseshoe crab spawning abundance during the stopover and the probability of red knots gaining mass (parameter coefficient from the top model b̂ = 1.71, = 0.46). Our analyses also supported the link between red knot mass and apparent annual survival, although average estimates for the two mass classes differed only slightly. The addition of arctic snow depth as a covariate influencing apparent survival improved the fit of the data to the models (parameter coefficient from the top model b̂ = 0.50, = 0.08). Our results indicate that managing horseshoe crab resources in the Delaware Bay has the potential to improve red knot population status.

Horseshoe crab (Limulus polyphemus) eggs are a dietary staple of the red knot (Calidris canutus) during its spring stopover on the Delaware Bay. Numbers of knots stopping in Delaware Bay declined in the 1990s concurrent with a decline in horseshoe crabs, leading to the hypothesis that reduced horseshoe crab egg abundance limited the red knot population. Management efforts, including a seasonal harvest moratorium in the Delaware Bay, have been instituted to restore crab populations to levels of sustainable use by multiple users, including migratory birds. Our objective was to evaluate the sufficiency of horseshoe crab eggs in Delaware Bay in May–June 2004 and 2005 for knots to refuel for their migratory flight to the Arctic breeding grounds. We examined egg counts to determine if there were fewer high egg‐density sites later than earlier in the day and season, as migrating birds might deplete this resource. We studied foraging rates at red knot locations to determine if foraging probes increased with time of day and season as birds depleted surface eggs by pecking, then began probing for subsurface eggs. Finally, we experimentally tested whether red knots and their competitors depleted horseshoe crab eggs. Crab egg numbers at knot foraging sites did not decline throughout the day or season in 2004. In both years, we found no evidence that knots switched from pecking to probing with increases in time since sunrise or start of the stopover. Egg numbers were similar in exclosed and accessible plots on crab nesting depressions and in areas of open intertidal zone, but were significantly lower in accessible than in exclosed plots in the wrack line. Our results indicate that horseshoe crab eggs in Delaware Bay were sufficient to support the refueling of the present‐day stopover population of red knots. If an increase in the availability of crab eggs to foraging birds does not result in an increase in knot numbers, managers must prioritize mitigation of limiting factors at other historically important spring stopovers and on the poorly understood breeding and wintering grounds in addition to the Delaware Bay. © 2011 The Wildlife Society.

North American horseshoe crabs (Limulus polyphemus) have been continuously harvested in Massachusetts for the production of Limulus amebocyte lysate (LAL); since the mid 1970s as bait for American eel (Anguilla rostrata); and since the mid 1990s as bait for whelk (Busycon ssp.). Harvest regulations were promulgated by the Atlantic States Marine Fisheries Commission (ASMFC) in 1998 over concern for the observed decline of the Red Knot (Calidris canutus), a correlation between its feeding behavior (horseshoe crab eggs during the spring migration), and a decline in spawning horseshoe crabs likely due to harvesting for bait. Generally, horseshoe crab harvest for the production of LAL (biomedical use) is exempted from harvest regulations, since the animals bled for LAL production are returned alive to the ocean, and mortality is considered low. However, evidence is accumulating that mortality of bled horseshoe crabs is higher than originally thought (29 % vs 15 %); that females may have an impaired ability to spawn following bleeding and release; and that bled crabs become disoriented and debilitated for various lengths of time following capture, handling, bleeding, and release. This paper reviews the latest evidence for mortality and impairment of horseshoe crabs bled for biomedical use, especially in Massachusetts where horseshoe crab populations in small bays and inlets are particularly vulnerable, and since State regulations allow for using bled crabs as bait rather than returning to the site of capture. A novel management plan is proposed that can satisfy all affected parties as well as insure a continued supply of horseshoe crabs for the vitally important production of LAL. This plan may also serve as a model for other areas of the Atlantic coast where biomedical harvest occurs.

Considerable concern regarding the abundance of the American horseshoe crab (HSC) Limulus polyphemus, along the east coasts of New Jersey and Delaware prompted past moratoriums on collecting HSC for bait in New Jersey. The parallel population decline in migratory shorebirds such as Red knots Calidris canatus, Ruddy turnstones Arenaria interpres and others that seasonally feed on the copious quantities of HSC eggs laid along this shoreline resulted in reduced HSC collection permits to numbers considered sustainable. In New York State’s Marine District, which is mostly comprised of the Long Island coastline, there is no reliable or routine habitat inventory network existing for determining HSC populations or habitat. Shorebird data, which have been collected by Audubon Chapters, the National Park Service and the US Fish and Wildlife Service, as well as academia, have hinted at declining HSC populations. However, due to the lack of a formal and extensive or reliable inventory network, assessing changing trends in HSC population levels is unattainable or mostly inaccurate. Molloy College’s Long Island HSC Network provides survey forms and a website to (1) collect data on Long Island sites which support HSC; (2) count HSC for as reliable an estimate of the HSC population as practical; (3) sex and age individual HSC at each site; and most importantly (4) establish a network that can be repeated annually to detect precipitous changes in HSC population numbers, distributions, and habitat. Data collection for HSC will aid in protecting the HSC population as well as bird species number which require HSC eggs as food during significant migratory periods.

Each May, red knots (Calidris canutus rufa) congregate in Delaware Bay during their northward migration to feed on horseshoe crab eggs (Limulus polyphemus) and refuel for breeding in the Arctic. During the 1990s, the Delaware Bay harvest of horseshoe crabs for bait increased 10-fold, leading to a more than 90% decline in the availability of their eggs for knots. The proportion of knots achieving weights of more than 180 grams by 26–28 May, their main departure period, dropped from 0.6–0.8 to 0.14–0.4 over 1997–2007. During the same period, the red knot population stopping in Delaware Bay declined by more than 75%, in part because the annual survival rate of adult knots wintering in Tierra del Fuego declined. Despite restrictions, the 2007 horseshoe crab harvest was still greater than the 1990 harvest, and no recovery of knots was detectable. We propose an adaptive management strategy with recovery goals and annual monitoring that, if adopted, will both allow red knot and horseshoe crab populations to reco...

Understanding variations in metal levels in biota geographically and under different environmental conditions is essential to determining risk to organisms themselves and to their predators. It is often difficult to determine food chain relationships because predators may eat several different prey types. Horseshoe crab (Limulus polyphemus) eggs form the basis for a complex food web in Delaware Bay, New Jersey, USA. Female horseshoe crabs lay thumb-sized clutches of eggs, several cm below the surface, and often dislodge previously laid eggs that are brought to the surface by wave action, where they are accessible and critical food for migrant shorebirds. This paper compares metal and metalloid (chromium [Cr], cadmium [Cd], lead [Pb], mercury [Hg], arsenic [As] and selenium [Se]) concentrations in horseshoe crab eggs collected on the surface with concentrations in eggs from clutches excavated from below the sand surface, as well as examining metals in eggs from different parts of the Bay. The eggs were all collected in May 2019, corresponding to the presence of the four main species of shorebirds migrating through Delaware Bay. These migrating birds eat almost entirely horseshoe crab eggs during their stopover in Delaware Bay, and there are differences in the levels of metals in blood of different shorebirds. These differences could be due to whether they have access to egg clutches below sand (ruddy turnstones, Arenaria interpres) or only to eggs on the surface (the threatened red knot [Calidris canutus rufa] and other species of shorebirds). Correlations between metals in clutches were also examined. Except for As and Cd, there were no significant differences between the metals in crab egg clutches and eggs on the surface that shorebirds, gulls, and other predators eat. There were significant locational differences in metal levels in horseshoe crab eggs (except for Pb), with most metals being highest in the sites on the lower portion of Delaware Bay. Most metals in crab eggs have declined since studies were conducted in the mid-1990s but were similar to levels in horseshoe crab eggs in 2012. The data continue to provide important monitoring and assessment information for a keystone species in an ecosystem that supports many species, including threatened and declining shorebird species during spring migration.

Shorebird use of horseshoe crab (Limulus polyphemus) eggs as food items has been well documented along the Atlantic coast of the United States at northeastern stopover sites such as the Delaware Bay. However, the relationship between migratory shorebirds and horseshoe crab eggs has not been well studied in the South Atlantic Bight. The objective of our study was to assess the spatial and temporal overlap between the density of horseshoe crab eggs and the relative abundance of foraging shorebirds during spring migration in the Cape Romain-Santee Delta Region (CRSD), South Carolina, USA. The CRSD is a site of international importance for shorebirds that supports ∼100,000 shorebirds annually. We also sought to determine if horseshoe crab eggs were present in the diets of shorebirds at these sites. We monitored study plots between March and June 2015–2016 at predicted horseshoe crab spawning sites on beaches throughout Cape Romain National Wildlife Refuge. We conducted weekly shorebird surveys and collected core samples of beach substrate twice per month to measure densities of horseshoe crab eggs. We found a positive correlation between number of foraging shorebirds and horseshoe crab eggs for both years. In a molecular analysis of shorebird fecal samples, 95% of the samples tested contained DNA from horseshoe crab eggs. The spatial and temporal overlap between shorebirds and horseshoe crab eggs, and the dietary analysis of fecal samples, suggest that there are areas of localized horseshoe crab spawning that shorebirds can utilize as a food source during spring in Cape Romain National Wildlife Refuge.

The horseshoe crab fishery on the US Atlantic coast represents a compelling fishery management story for many reasons, including ecological complexity, health and human safety ramifications, and socio-economic conflicts. Knowledge of stock status and assessment and monitoring capabilities for the species have increased greatly in the last 15 years and permitted managers to make more informed harvest recommendations. Incorporating the bioenergetics needs of migratory shorebirds, which feed on horseshoe crab eggs, into the management framework for horseshoe crabs was identified as a goal, particularly in the Delaware Bay region where the birds and horseshoe crabs exhibit an important ecological interaction. In response, significant effort was invested in studying the population dynamics, migration ecology, and the ecologic relationship of a key migratory shorebird, the Red Knot, to horseshoe crabs. A suite of models was developed that linked Red Knot populations to horseshoe crab populations through a mass gain function where female spawning crab abundance determined what proportion of the migrating Red Knot population reached a critical body mass threshold. These models were incorporated in an adaptive management framework wherein optimal harvest decisions for horseshoe crab are recommended based on several resource-based and value-based variables and thresholds. The current adaptive framework represents a true multispecies management effort where additional data over time are employed to improve the predictive models and reduce parametric uncertainty. The possibility of increasing phenologic asynchrony between the two taxa in response to climate change presents a potential challenge to their ecologic interaction in Delaware Bay.

Adaptive management requires that predictive models be explicit and transparent to improve decisions by comparing management actions, directing further research and monitoring, and facilitating learning. The rufa subspecies of red knots (Calidris canutus rufa), which has recently exhibited steep population declines, relies on horseshoe crab (Limulus polyphemus) eggs as their primary food source during stopover in Delaware Bay during spring migration. We present a model with two different parameterizations for use in the adaptive management of horseshoe crab harvests in the Delaware Bay that links red knot mass gain, annual survival, and fecundity to horseshoe crab dynamics. The models reflect prevailing hypotheses regarding ecological links between these two species. When reported crab harvest from 1998 to 2008 was applied, projections corresponded to the observed red knot population abundances depending on strengths of the demographic relationship between these species. We compared different simulated horseshoe crab harvest strategies to evaluate whether, given this model, horseshoe crab harvest management can affect red knot conservation and found that restricting harvest can benefit red knot populations. Our model is the first to explicitly and quantitatively link these two species and will be used within an adaptive management framework to manage the Delaware Bay system and learn more about the specific nature of the linkage between the two species.

Horseshoe crab eggs: A rare resource for predators in Long Island Sound

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.