Writing & Photography of Jim Murtagh

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The Writings & Photography of Jim Murtagh

Under a Spring Moon An Ancient Ritual

There's romance under the full moon. Below the water's surface, a few feet from the beach, horseshoe crabs are in the mood for love.

And that's just dandy for biology professor Dr. Sean Grace and his research student Miguel Reyes, who are prowling the dark waters at Clinton’s Town Beach in search of a pre-historic looking arthropod that has roamed coastal seas for 300 million years.

The scientists from Southern Connecticut State University shine their flashlights into the blackness of the Sound as they walk through the shallow water, searching for mating horseshoe crabs, all the while swatting at an unrelenting barrage of marsh mosquitoes. The artificial light illuminates the water column down to a depth of about three feet. Blue crabs, eels, and other night-time dwellers flee from the unwelcome intrusion.

The team of “living fossil” hunters is part of Project Limulus, a larger research project being conducted by Dr. Jennifer Mattei from Sacred Heart University, designed to study the ecology of the Long Island Sound horseshoe crab (Limulus polyphemus) population. Begun in 2003, Project Limulus is a community-based research project that encourages all people to become involved in scientific studies. The data collected by Mattei and her group of volunteers and students has the potential to directly impact Connecticut’s horseshoe crab management policy.

Over the course of her work, Mattei has acquired a fondness for this animal whose spiked shell and sharply pointed tail can be intimidating to many beachgoers who stumble across it, but Mattei says “They are the most benign creatures I have ever worked with.”

Reyes is studying the horseshoe crabs as part of his master’s thesis. His objective is to “figure out the population numbers, the stability of the population, and the ratio of males to females within the horseshoe crab population in Clinton .” A self-proclaimed “evolution fanatic” Reyes is fascinated by the animal that has managed to survive global mass extinctions caused by meteor impacts and the Ice Age.

Nature may have perfected the design of this animal, as its physical appearance has remained relatively unchanged since it began crawling on the sea floor 100 million years before dinosaurs even existed. It is called a “living fossil” because the earliest fossil records look remarkably like the specimens that are being collected today.

Grace reaches into the water and attempts to dislodge the prominent large brown dome of a female horseshoe crab that has buried itself in the soft sandy substrate. Four smaller satellite males encircle their mate, which is characteristic of their polyandrous mating behavior. As Grace lifts the mound from the water, all five animals rise as a single mass. The males refuse to release the grip of their boxing glove shaped front claws from the side of the female’s barnacle encrusted shell. Placed onto the beach upside down, the invertebrates try to right themselves with their long pointed tail, so they can return to the water and resume their rudely interrupted procreative activity.

Kneeling on the sand, Grace begins to record basic information about the horseshoe crabs. On a sheet of waterproof paper, he writes down the width of the animals’ shell and their sex. Then, one at a time, he turns the animals on their side and pierces the edge of its shell with an awl. Into the tiny hole, he inserts a thin plastic cinch-tie. The yellow tag has Mattei’s phone number and email address printed on it, along with a unique number that will identify the animal should it ever be recaptured. This data, along with tagging data obtained at several other Connecticut beaches including Milford Point and Sandy Beach, will be combined into Mattei’s database which already contains 10,000 specimens.

“Every time you go to the doctor’s office and get a vaccination, you need to thank a horseshoe crab.” states Grace as he releases the crabs. He is referring to the copper based, blue blood pulsing through horseshoe crabs that pharmaceutical companies extract and then refine into Limulus amoebocyte lysate, or simply LAL.

Horseshoe crab blood contains a unique clotting agent that immediately attaches to endotoxins produced by gram-negative bacteria. In layman’s terms, LAL instantly detects harmful bacteria, a test which used to require a live rabbit and 48 hours. LAL is so effective that Federal law requires injectable and intravenous drugs, as well as prosthetic devices, to be screened with an LAL test.On the opposite end of the beach, Reyes records the data from a lone male horseshoe crab that was actively cruising the shallows looking for a mate. During the next two hours, over a hundred horseshoe crabs will crawl to the water’s edge, appearing like a division of Sherman tanks invading the sandy dunes of an underwater dessert. Reyes hopes to tag 1,000 specimens over the next two weeks, and Mattei predicts more than 4,000 horseshoe crabs will be tagged between all the Project Limulus participants. “I think this is a good year. We have tagged more (this year) than we have in previous years.” notes Mattei.

The armor clad horseshoe crab is neither a crab nor a crustacean, but rather it is a close relative of scorpions and spiders. Crawling across the ocean floor, searching for meals of worms, clams and small oysters, the horseshoe crab relies on two prominent compound eyes protruding from the top of its spiny dome shaped shell, and another 12 photoreceptors scattered across its exoskeleton, to give the creature excellent vision, and help it find a mate.

For the first ten years of life, the horseshoe crab will molt one to two times per year. A final, “terminal molt,” will signal its transition into adulthood, after which it will begin to engage in the massive breeding frenzy that occurs during the spring tides. Females can lay up to 88,000 eggs which are fertilized externally by the males.

In addition to their medical value, horseshoe crabs are also harvested by fisherman as bait for eel and conch traps. Hand-harvesting is regulated by the CT DEP and requires a license. Harvesting is closed during the breeding season.

Mattei makes a point to teach all of her students that in the natural world “Everything is connected, and when you start pulling out links, you don’t know what will collapse next.” She hopes her research will lead to effective management practices for the horseshoe crab by determining if there is a single breeding population of crabs in the sound or distinct populations which inhabit specific beaches. “When you manage a species, you need to be careful about the genetics.” she says.

Horseshoe crabs also play an essential role in the survival of migrating shorebird species. As birds depart from their wintering grounds in Central and South America, they need to rely on an abundant food source to fuel them on their long journey northward. The bird’s migration is in concert with the horseshoe crab’s mating cycle and the vast quantity of newly laid eggs that will be available for nourishment.

If you are intrigued with the horseshoe crab and would like to participate in Project Limulus, Mattei says “What would help most is if people would walk the beaches and look for recaptures. When you see a tag, take an interest and call me.” Mattei’s phone number is on the tag and she asks that you report the tag number, the location where the horseshoe crab was found, and whether the animal was found dead or alive. Do not remove the tag.