Marine Biology

Horseshoe Crabs

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There’s a disappearing act going on in the Atlantic Ocean although it is not one of magic.   The American horseshoe crab (Limulus polyphemus) predates the dinosaurs and has thrived along the coastline from Maine to Mexico until recently. A lot of Mid-Atlantic beachgoers will easily recognize the horseshoe crab as that scary looking circular creature with lots of legs and a tail full of spikes, that occasionally washes up on the beach.  But the horseshoe crab population has dropped dramatically in recent years and they are becoming a bit of a rarity along eastern beaches. 

In an article entitled “Jurassic Beach”, by Jennifer Uscher, in the summer 2008 issue of Nature Conservancy magazine, it states that from the late 1960’s to 1996 the annual catch of horseshoe crabs has increased from 10 tons to 2,550 tons. The article identifies one reason for the increased demand to haul in horseshoe crabs, is an increased culinary demand in Asia for conch and American eel. Horseshoe crabs are used as bait to reel in the conch and eel.  Conchs themselves are decreasing in numbers and aren’t even legal to commercially catch in the United States.

As the horseshoe crab population declines it puts at risk other species who feed on the horseshoe crab such as the loggerhead sea turtle. Loggerhead sea turtles are already listed on the threatened species list.

 In a June 2005 article, entitled, “Horseshoe Crabs’ Decline Further Imperils Shorebirds” Juliet Eilperin, a Washington Post Staff Writer, writes that until recently hundreds of thousands of migrating shorebirds would stop over at Maryland, Delaware and New Jersey beaches for a feast that they couldn’t find elsewhere. 

Consuming up to 18,000 eggs a day, the birds such as the rust-colored red knot, doubled in size, within two weeks.  Because shorebirds depend on horseshoe crab eggs for food the declining horseshoe crab population has contributed to a declining shorebird population.

Both articles site yet another reason for a declining horseshoe crab population.A very unique reason; one that may seem odd to most people.  Eilperin explains that horseshoe crabs are being captured for their unique blood.  The Nature Conservancy expands on this further by saying that the compound lysate, found in the crab’s copper rich blood, has the ability to alert against infection  and according to one estimate has saved up to one million people since the compound was discovered by scientists in the 1950’s.

To supply the biomedical industry with this anti-infection compound, approximately 300,000 crabs are caught and bled each year, some returning to the ocean, with no lasting ill effects, but as much as 40 percent of these crabs die from trauma or are sold to the bait industry. 

According to the Nature Conservancy’s “Jurassic Beach” article, in 2006 Delaware and New Jersey announced a two-year moratorium on horseshoe harvesting.  Because of these efforts, the harvest declined by 70 percent between 1998 and 2006.  In 2008, fishermen won a law suit overturning that moratorium, arguing that by harvesting 100,000 male crabs in the state’s waters would not undermine conservation efforts.  

The article also notes that conservation efforts are continuing and the latest census and other studies show that the crab population is no longer dropping and has, in fact, stabilized but there are skeptics. It would seem that there needs to be more studies done but in the meantime these creatures need to continue to be protected until we can be assured that populations have stabilized. 

More about this author: Denise Calaman

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