Research Spotlights

The horseshoe crab, Limulus polyphemus, is a versatile model for scientific research. Scientists in a wide variety of fields including ecology, microbiology, biotechnology, pharmacology, immunology, and neurophysiology have focused their investigations on this extraordinary marine creature. As it is the most intensively studied marine invertebrate, you might think that we already know everything there is to know about the horseshoe crab. But every year, exciting new discoveries are being reported around the country. What questions are scientists asking this year? Where can you go to study horseshoe crabs? Click on the labeled states to learn more about current horseshoe crab research!

California

University of California, Santa Barbara
Dr. Robert Jacobs investigates the biochemical processes that cause inflammation or allergic responses in humans. He uses horseshoe crab amoebocytes (circulating blood cells) as a model to understand what intercellular events contribute to the immune response, and what biochemical reactions are required for healing wounds. California Sea Grant has provided funding for this research.
http://www.nsgo.seagrant.org
http://lifesci.ucsb.edu/EEMB/faculty/jacobs/index.html

University of California, Davis
Dr. Peter Armstrong studies proteins in the immune system of Limulus polyphemus. Recently, he discovered that mucous secreted from the carapace prevents fouling by organisms such as blue-green algae, tube worms, and barnacles. The mucous contains multiple proteins that help protect the horseshoe crab shell from biological invaders. Currently, Dr. Armstrong is investigating the role of a blood plasma protein, alpha2-macroglobulin, in the immune response. This protein may protect the horseshoe crab by preventing the harmful bacteria trapped inside the clot from escaping. Funding for this research has been provided by the National Science Foundation (NSF).
http://www.nsf.gov/
http://www.dbs.ucdavis.edu/faculty/fac_directory/?PArmstrong

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Delaware

University of Delaware, College of Marine Studies, Lewes,
and the Delaware Biotechnology Institute, Newark
Dr. Nancy Targett and Dr. Pamela Green are investigating an economical artificial bait that could be used as a substitute for adult female horseshoe crabs in the American eel and whelk fisheries. They are working to produce the protein from the horseshoe crab that attracts eels and whelks and then incorporate it into an artificial bait product. This research is supported by Delaware Sea Grant.
(http://www.ocean.udel.edu/seagrant). http://www.ocean.udel.edu/seagrant/research/marinebiotech.html#coastal4

Dr. Patrick Gaffney, at the University of Delaware is collaborating with Dr. James Pierce, at the University of the Sciences in Philadelphia, to investigate the population genetics of Limulus polyphemus. Recently they examined DNA from Chesapeake and Delaware Bay horseshoe crabs and determined the two populations to be genetically distinct.

The Delaware National Estuarine Research Reserve (DNERR)
DNERR has been conducting studies of horseshoe crab egg densities since 1997. The DNERR is a cooperative program between the Delaware Department of Natural Resources and Environmental Control and the National Oceanic and Atmospheric Administration. The goal of the program is to establish, protect, and manage natural estuarine habitats for research and education. The purpose of this multi-year study is to:

1. Develop a statistically sound methodology for sampling, extracting, and enumerating horseshoe crab eggs from beach sediments.
2. Develop an understanding of the role beach nourishment activities have on horseshoe crab egg densities.
3. Develop an understanding of between-beach differences in egg densities.
4. Evaluate the amount of horseshoe crab eggs available as food to migratory shorebirds.
5. Make recommendations regarding beach management for optimal horseshoe crab spawning habitat.

Horseshoe crab egg densities for each beach are estimated by taking core samples of sand and extracting the eggs through a multi-step process. The resulting egg numbers represent relative abundance of eggs within the sand. Parameters such as sand grain-size distribution, beach slope, and beach width are measured on each beach. These measurements, paired with estimated egg densities, may reveal important information about ideal beach conditions for horseshoe crab spawning and egg survival. In turn, natural resource managers can use this information to optimize beach conditions for spawning horseshoe crabs.

Funding for this project has been provided by the Delaware National Estuarine Research Reserve, the Delaware Coastal Programs, the Delaware Division of Fish and Wildlife, the National Oceanic and Atmospheric Administration, NOAA's National Ocean Service, and the U.S. Fish and Wildlife Service. For more information, contact Susan Love at slove@state.de.us or (302) 739-3451.

USGS Biological Resource Division,
Delaware Division of Fish and Wildlife, and the
Delaware National Estuarine Research Reserve
The USGS Biological Resources Division, in cooperation with the Delaware Division of Fish and Wildlife and the Delaware National Estuarine Research Reserve, is conducting a study to better understand the factors that determine the distribution of horseshoe crab eggs across the beach profile and availability of these eggs to shorebirds.

Horseshoe crabs lay eggs in the sand to a depth where the eggs are sufficiently protected from the elements, including hungry birds. However, some eggs migrate to the surface of the sand, becoming available as food for shorebirds. The eggs can be brought to the surface by a number of different factors including beach morphology, weather, and wave action. In addition, it is thought that spawning horseshoe crabs play a role in egg migration to the surface by disturbing previously laid eggs.

The purpose of this study is to:

1. Determine the effect of beach characteristics, weather, and level of spawning activity on egg availability to shorebirds.
2. Identify beach characteristics that affect egg availability.
3. Determine distribution of eggs in reference to high-tide line and determine beach characteristics that affect egg location.
4. Use information on variation in egg distribution to make recommendations on protocol to effectively sample egg densities.

For more information, e-mail Dave Smith at david_r_smith@usgs.gov.

Delaware Division of Fish and Wildlife, Fisheries Section
The Delaware Division of Fish and Wildlife, Fisheries Section, is charged with management of tidal and non-tidal water fisheries, and conducts a range of monitoring and research activities each year. Relative abundance of both juvenile and adult horseshoe crabs is monitored year-round by 30-foot and 16-foot trawl surveys. The Fisheries Section also collects data regarding commercial landings of horseshoe crabs and characterizes the commercial catch.

In addition, the Fisheries Section is:

1. Identifying juvenile horseshoe crab habitats in Delaware's Inland Bays.
2. Estimating horseshoe crab fecundity.
3. Funding the Delaware Bay spawning survey coordinator and participating in spawning surveys.
4. Participating in a joint study with the U.S. Fish and Wildlife Service and Old Dominion University to establish a method to reliably age horseshoe crabs using a lipofuscion technique.
5. Partially funding and cooperating in a large project to design a pilot coastwide benthic horseshoe crab sampling program, delineate the horseshoe crab stock using microsatellite DNA, identify techniques to identify pre-recruits, and investigate the feasibility of night time aerial videography.
6. Partially funding and cooperating in an initiative promoting the use of bait bags.
7. Participating in the ASMFC process through the Management Board, Technical Committees, Stock Assessment Committee, and the Plan Development and Review Teams.

For more information, contact Stewart Michels at smichels@state.de.us.

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Florida

University of Florida, Gainesville
Dr. Jane Brockmann studies the behavior, natural history, and population biology of horseshoe crabs in the Cedar Keys National Wildlife Refuge. She has also investigated mating behavior and nest-site selection in Delaware Bay. Her current research focuses on patterns in male mating behavior. Do males use chemical cues to detect their mates? Why do some females attract multiple males, when others only attract a few? Dr. Brockmann's research has been funded by the National Science Foundation (NSF), the University of Florida Foundation, and the Division of Sponsored Research.

University of Florida, Whitney Laboratory, St. Augustine
Dr. Barbara-Anne Battelle's research focuses on light sensitivity in the retina of the horseshoe crab. Currently, she is investigating the biochemical interactions between light-dark cycles and internal (circadian) clocks that alter the retina, enabling the horseshoe crab to see as clearly at night as it does during the day.

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Illinois

Northeastern Illinois University, Chicago
Dr. Mary Kimble studies embryonic development in horseshoe crabs. Specifically, she is interested in the evolution of homeotic genes that regulate embryonic development and the roles they play in the primitive horseshoe crab embryo.

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Indiana

Purdue University, West Lafayette
Dr. Gerald S. Wasserman studies sensory coding using horseshoe crabs as a model for understanding human vision.
http://www.psych.purdue.edu/~codelab/home.html

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Kansas

University of Kansas
Dr. Rachel Moore is currently working on all aspects of horseshoe crab evolution including a phylogeny of fossil and recent horseshoe crabs, describing new fossil taxa and documenting their distribution over the last 400 million years. Researching their habitat preference throughout their evolution and their relationship to other living and extinct chelicerate groups is also part of this project.
http://www.people.ku.edu/~ramoore/

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Maryland

USGS, University of Maryland Eastern Shore, and the
Maryland Cooperative Fish and Wildlife Research Unit, Princess Anne
Dixie Bounds of CFWRU, and Monica Williams, a graduate student at UMES, are studying the impact of horseshoe crab population dynamics on migratory shorebird abundance. They are investigating whether migratory shorebirds can locate suitable food resources and habitat adjacent to Delaware Bay if the horseshoe crab population were to collapse.
https://coopunits.org/Units/MD_FW

Joseph Margraf of CFWRU is evaluating current sampling methodologies to develop a population index for horseshoe crabs in Maryland and Delaware. He is also investigating techniques for estimating horseshoe crab egg densities, to assess the availability of eggs for migratory shorebirds.

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Massachusetts

Boston University Marine Program, Marine Biological Laboratory, Woods Hole
Dr. Ruth Carmichael is using stable-isotope analysis to determine habitat and food preferences of horseshoe crabs in Pleasant Bay, Massachusetts. The isotope analysis will help to evaluate the trophic position of horseshoe crabs in the bay and how far they travel to forage. Her research is supported by the Friends of Pleasant Bay.

Marine Biological Laboratory, Woods Hole, and Charles River Laboratories
Dr. Norman Wainwright, at the Marine Biological Laboratory, is working to understand the molecular defense mechanisms exhibited by the horseshoe crab in response to invasion by bacteria, fungi, and viruses. Several proteins found in Limulus hemocyte and hemolymph display microbial binding properties that contribute to antimicrobial defense. He also is collaborating with Charles River Laboratories on the Endosafe®-PTS (Portable Test System), a miniature machine no bigger than a large calculator, that can use the horseshoe crab Limulus Amebocyte Lysate (LAL) test to detect microbes on spacecraft and perhaps even on Mars and other planets.
http://www.mbl.edu/inside/what/news/press_releases/2003/2003_pr_6_24.html

Research in Dr. Daniel Gibson's lab examines the role of amino acid neurotransmitters in muscle twitches, the effects of molting hormones and pesticides on horseshoe crab growth and development, and learning behavior in horseshoe crabs.

Worcester Polytechnic Institute, Worcester
Research in Dr. Daniel Gibson's lab examines the role of amino acid neurotransmitters in muscle twitches, the effects of molting hormones and pesticides on horseshoe crab growth and development, and learning behavior in horseshoe crabs.

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New Hampshire

University of New Hampshire, Durham
Dr. Winsor Watson investigates the influence of tidal and circadian rhythms on mating behavior and locomotion in horseshoe crabs. He is also interested in the role of pheromones in mate selection.

Plymouth State University
Dr. Chris Chabot is involved in collaborative research with undergraduate students at PSU and Dr. Win Watson, UNH. Their goal is to investigate the role of environmental factors as well as endogenous factors on locomotor activity in Limulus.

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New Jersey

Rutgers University, New Brunswick
Dr. Robert Loveland investigates the life history and ecology of horseshoe crabs, focusing on conservation of this species. Recent research with undergraduate students examined the relationship between mating behavior and fouling patterns on the horseshoe crab carapace. New Jersey Sea Grant has provided funding for this research. In addition, Dr. Loveland collaborates with Dr. Botton (Fordham University) and the Cape May Bird Observatory to estimate horseshoe crab population trends based on egg density counts along New Jersey beaches.
http://www.njaudubon.org/research/crabs.html

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New York

Fordham University, New York City
Dr. Mark Botton studies conservation biology of shorebirds and horseshoe crabs in the Delaware Bay estuary. Recent research with undergraduate students investigated the effects of visual impairment on male mating success. Dr. Botton's research interests also focus on the effects of heavy metal pollution on horseshoe crab larvae and embryos. In addition, Dr. Botton collaborates with Dr. Loveland (Rutgers University) and the Cape May Bird Observatory to estimate horseshoe crab population trends based on egg density counts along New Jersey beaches. New Jersey Sea Grant has provided funding for this research.

S.U.N.Y Upstate Medical University, Syracuse
Dr. Robert Barlow is investigating the role of vision in potential mate selection. A "crabcam" mounted on the horseshoe crab carapace records what the horseshoe crab sees underwater. The recorded images are used to generate a computer model which helps Dr. Barlow analyze how the horseshoe crab brain processes signals transmitted from the eyes and optic nerve. Funding has been provided by the National Institutes of Health (NIH), the National Science Foundation (NSF), Research to Prevent Blindness, and the Lions of Central New York.

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North Carolina

University of North Carolina, Chapel Hill
Dr. Ken Lohmann and graduate student Bill Irwin are investigating the beach-finding mechanism in horseshoe crabs. Specifically, they are trying to establish if horseshoe crabs use the Earth's magnetic field as an orientation cue during seasonal migration to spawning beaches.

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Pennsylvania

University of the Sciences in Philadelphia, Philadelphia
Dr. James Pierce focuses on the use of biotechnology to understand genomic organization and evolution of homeobox genes and primitive immune systems in the horseshoe crab. Homeobox genes, and the proteins they encode, the homeodomain proteins, have turned out to play important roles in the developmental processes of many multicellular organisms. Recent research in his lab includes a genetic analysis of the Delaware Bay horseshoe crab population and the activity of an antimicrobial peptide from horseshoe crabs against an oyster pathogen.

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Rhode Island

University of Rhode Island, Graduate School of Oceanography, Narragansett
Dr. M. J. James-Pirri surveys spawning densities and population demographics (sex, size, age estimates) of horseshoe crabs in Cape Cod, Massachusetts. Her studies will establish a set of baseline data to evaluate long-term population trends in the Cape Cod region. She also has developed a tagging study to investigate whether horseshoe crabs return to their native spawning beaches. She collaborates closely with the Massachusetts Audubon Society, Wellfleet Bay Wildlife Sanctuary, and Monomoy National Wildlife Refuge. Her research is supported by the National Park Service.

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South Carolina

Marine Resources Research Institute, Charleston
The Marine Resources Research Institute (MRRI) is one of the largest sections within the Marine Resources Division of the South Carolina Department of Natural Resources. MRRI coordinates research on horseshoe crab population abundance and habitat requirements in South Carolina. MRRI has developed a tagging program to monitor horseshoe crab behavior, population characteristics, and mortality. The institute is also gathering information on critical feeding, spawning, and nursery grounds to assist in the management and conservation of horseshoe crabs.
http://www.dnr.state.sc.us/marine/mrri/horseshoe/intro.htm

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Virginia

Virginia Institute of Marine Science, Gloucester Point
Fisheries scientist Bob Fisher is examining alternatives to horseshoe crab bait for Virginia conch fisheries. Currently, he is investigating whether waste from local seafood industries will provide an effective binder matrix for alternative baits. He is also field-testing mesh bait bags as a means to reduce the amount of horseshoe crab bait used in conch pots. Funding has been provided by Virginia Sea Grant.
http://www.vims.edu/adv/staff.html
http://www.mbl.edu/animals/Limulus/issues/bait.html

Virginia Polytechnic Institute, Blacksburg
Dr. Jim Berkson and graduate student Beth Walls are studying the population dynamics of Chesapeake Bay horseshoe crabs. Berkson and Walls are also investigating techniques to reduce horseshoe crab mortality in the biomedical industry, a result of bleeding to obtain LAL. Both demographic studies and LAL-related mortality estimates will provide valuable information to develop effective management strategies for the horseshoe crab population. Funding for this research has been provided by Virginia Sea Grant and Bio Whittaker, which is now part of the Cambrex Corporation.

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Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech
Title: Biochemical Profiles Of The Hemolymph Of The Horseshoe Crab, Limulus polyphemus.
Dr. Stephen A. Smith believes that while the horseshoe crab's "blue blood" and the composition of the LAL have been studied in detail, basic biochemical parameters of the hemolymph of the horseshoe crab are lacking. Thus, hemolymph from fifty adult (29 male and 21 female) horseshoe crabs was collected for analysis. Hemolymph samples were analyzed using an automated chemistry system. Results of the biochemistry parameters for the hemolymph of the horseshoe crab were: total protein (8.15 g/dl), glucose (58.5 mg/dl), creatinine (0.7 mg/dl), cholesterol (0.8 mg/dl), sodium (389.5 mEq/l), potassium (12.5 mEq/l), chloride (445.1 mEq/l), calcium (39.0 mg/dl), magnesium (96.1 mg/dl), phosphorus (3.4 mg/dl), triglycerides (5.3 mg/dl), amylase (9.3 U/l)), lipase (32.7 U/l), alkaline phophatase (12.1 U/l), aspartate aminotransferase (5.4 U/l) and gamma glutamyl transferase (0.92 U/l).

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Virginia-Maryland Regional College of Veterinary Medicine, Virginia Tech
Title: Comparison Of Hemolymph Proteins From The Horseshoe Crab, Limulus polyphemus.
The horseshoe crab (Limulus polyphemus) has been described as one of the oldest living organisms on the planet, with it's closest relatives being in the Subphylum Chelicerata which contains the scorpions and spiders. To further examine this relationship, hemolymph from several adult horseshoe crabs was analyzed by SDS-PAGE and the protein bands separated. The bands were then compared to protein bands derived from the hemolymph of a scorpion, spider, lobster and blue crab. Results of the SDS-PAGE analysis of horseshoe crab hemolymph produced three major proteins that most likely represent the alpha-2 macroglobulin, hemocyanin and C-reactive protein, respectively. Western blot analysis was performed using a rabbit anti-horseshoe crab whole hemolymph antibody and the results demonstrated that the rabbit antibody clearly recognized all of the horseshoe crab protein bands in the gel. In addition, the rabbit anti-horseshoe crab antibody also recognized protein bands from the hemolymph of the scorpion and spider, but not those of the lobster and blue crab. This is further evidence that members of the Class Arachnida are more closely related to the horseshoe crab than are members of the Subphylum Crustacea. The title of this project is being conducted by Dr. Stephen A. Smith.

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West Virginia

USGS, Leetown Science Center, and
Aquatic Ecology Laboratory, Kearneysville
Dr. David Smith is developing a statistically robust census to analyze trends in horseshoe crab spawning activity in Delaware Bay. This project is coordinated among federal and state agencies, academic institutions, and private industry in Maryland, Delaware, and New Jersey.
http://biology.usgs.gov/pr/newsrelease/1999/6-8a.html

Inda

Project Swarajya
Cuttack, Orissa, India
Ashis Senapati is involved in a research project where Lysate of the Horseshoe crab will be collected from the sea of Orissa an eastern state of India and the lysate will be tested on some AIDS or HIV patients after taking blood samples.
http://www.projectswarajya.com/