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Horseshoe Crabs Need Compassion and Help to Survive

By Jordan Schaul An incidental encounter on a North American Atlantic coast beach with a horseshoe crab may have been your first introduction to this armored sea creature with a spiked tail. Hopefully, it won’t be your last. Some horseshoe crab populations are in trouble and that could mean trouble not only for vertebrate marine...

By Jordan Schaul

An incidental encounter on a North American Atlantic coast beach with a horseshoe crab may have been your first introduction to this armored sea creature with a spiked tail. Hopefully, it won’t be your last.

Some horseshoe crab populations are in trouble and that could mean trouble not only for vertebrate marine life, but for basic and applied research in human and veterinary medicine, and the sustainable commercial fishery of horseshoe crabs.

Horseshoe crab photo 1.jpg

Horseshoe crabs have gone basically unchanged for 360 million years. But can they survive human predation?

NGS stock photo by Robert Sisson

These harmless, invertebrate, indicator species of marine ecosystem health have played an important role in human health research and are the most studied invertebrate animals in the world.

Horseshoe crab biomedical research has contributed to ophthalmology and vision science, wound healing (for example, development of surgical sutures and wound dressings), and the detection of bacterial contamination in pharmaceuticals (such as intravenous drugs and vaccine injections). In the future, horseshoe crab blood may also be used to develop probes for studying life on other planets.

These bizarre marine organisms are also critical to shorebirds who depend upon horseshoe crab eggs for food.

Horseshoe crab photo 2.jpg

Many males fertilize the eggs of one female horseshoe crab.

NGS stock photo by Robert Sisson

There is a correlation between shorebird migration and horseshoe crab spawning, and recently researchers have suspected that there might be a correlation between shorebird declines and horseshoe crab over-harvesting.

The Mid-Atlantic Sea Grant Programs and the NOAA sponsored University of Delaware website dedicated to the horseshoe crab indicates that “new management practices for the horseshoe crab fishery will benefit migratory shorebirds.”

Scientists who monitor horseshoe crab populations have witnessed a decline in American horseshoe crabs (Limulus polyphemus) along the east coast of North America.

The declining numbers of these semi-aquatic, militant-looking arthropods may not elicit as much attention as the potential fate of polar bear populations in the Arctic, but it should. Horseshoe crab populations influence numbers of marine turtles and seabirds among other predators which prey upon them, including a host of other charismatic vertebrate fauna. As horseshoe crab populations plummet, so may the population of predators.

Horseshoe crab photo 3.jpg

Many males fertilize the eggs of one female horseshoe crab.

NGS stock photo by Robert Sisson

The loss of these invertebrates themselves would be tragic. Horseshoe crabs, although not true crabs, have been around longer than most other creatures on Earth. They are of great interest to invertebrate paleoecologists given their prehistoric existence dating back 450 million years.

Related to Spiders and Scorpions

Horseshoe crabs are actually related to scorpions and spiders, although often mistaken for crustaceans. The elegant, but simplistic design includes a basic, hard, curved exoskeleton (carapace) protecting an underbelly of soft tissue–characteristics that have permitted them to evade predation by a variety of species that have long gone extinct.

Physiological ecologists conducting studies on these popular laboratory invertebrates praise the horseshoe crab’s great tenacity. They are able to survive a year without food, and endure extreme temperatures, and dramatic changes in salinity levels.

But researchers are not the only people fond of these jointed-leg members of the subphylum Chelicercata. Amateur naturalists and recreational beachgoers are recording their sightings around the world, from Taiwan to the Yucatan through the Just Flip Em’ program which assists in census studies dedicated to the conservation of horse shoe crab species.

Horseshoe crab photo 4.jpg

A horseshoe crab is covered with parasitic animals.

NGS stock photo by Robert Sisson

Compassionate beach visitors are asked to turn over any animals found in distress. As horseshoe crabs emerge from the sea to spawn on beaches they are sometimes inadvertently flipped on their backs and expire. Hundreds of thousands die when left stuck in this position every year.

As concern for their decline increases, studies of their reproductive ecology become more important and in particular their preferred spawning sites. Scientists are now examining spawning beach site selection among horseshoe crabs to aid in conservation efforts. Parameters of interest include beach slope, sand grain size, presence of peat in the substrate, and ocean currents and migration patterns.

Last spring, biologists with the Florida Wildlife and Fish Conservation Commission were seeking volunteers to assist with data collection, seeking “the date, time, location, [and other] environmental conditions, such as tides and moon phase. If possible, [they were soliciting people to] specify roughly how many [were] coupled and how many [were] juveniles (4 inches wide or smaller).” Census work will resume next spring.





Jordan Schaul is a conservation biologist and a collection curator with the Alaska Wildlife Conservation Center. He received his PhD in conservation/veterinary preventive medicine from Ohio State University and a master’s degree in zoology. He is a council member (ex officio) of the International Association for Bear Research and Management (IBA), a member and coordinator for education and outreach for the Bear Specialist Group of the International Union for the Conservation of Nature, an advisor to the Bear Taxon Advisory Group of the Association of Zoos and Aquariums, correspondent editor and captive bear news correspondent for International Bear News, and member of the advisory council of the National Wildlife Humane Society, which promotes high standards for wild carnivore care and welfare among private sanctuaries in North America. He is the creator of the Zoo Peeps brand which hosts a blog for the global zoo and aquarium community and two wildlife conservation oriented radio programs. He enrolled in clinical degree programs in veterinary medicine and has been on leave to pursue interests in animal management/husbandry science and conservation education.

The views expressed in this article are those of Jordan Schaul and not necessarily those of the National Geographic Society. Read more blog posts by Jordan Schaul.

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