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INTRODUCTION

The horseshoe crab, Limulus polyphemus is a marine resource that has become the center of controversy among its user groups. Over the past several years the demand for this unique and ancient animal has continually increased. However, population trends in recent years indicate a decline in the number of horseshoe crabs. They are an essential component to a healthy coastal ecosystem, an important part of the coastal economies of the eastern United States, and necessary for the protection of public health. Also, in each of these cases, there is no substitute for the horseshoe crab. Ensuring a stable population is crucial otherwise all of these areas will experience detrimental losses.

Horseshoe crabs play an important ecological role in the food web. Shorebirds primarily feed on horseshoe crab eggs exposed on the sand's surface. These migratory shorebirds arrive from their South American wintering grounds to use the Chesapeake Bay area as a refueling station. They feed on horseshoe crab eggs to build up their energy reserves for their continuing migration to Arctic breeding grounds. A decline in the number of horseshoe crabs will impact many species, particularly migratory shorebirds. Therefore, adequate spawning densities must be maintained to ensure availability of horseshoe crab eggs for shorebirds, some of which are federally-listed as threatened or endangered.

Bait fishing and trawling are also dependent on stable horseshoe crab population levels. Historically, horseshoe crabs were considered a "trash fish". At that point in time, they were ground up and used for fertilizer. When the commercial fishery arose, there were little or no harvest restrictions and no reporting regulations. This has resulted in poor population data for horseshoe crabs. The commercial fishery primarily harvests horseshoe crabs for bait in the American eel and whelk fisheries. The eel fishery prefers to use gravid females as bait because eels are more intensly attracted to females than males. With this type of harvest preference, the eel fishery may have an impact on horseshoe crab demographics. As long as the horseshoe crab fishery has few restrictions, and the eel and conch fisheries have a high demand, horseshoe crabs will be aggressively harvested. In 1996, fishing mortality accounted for at least 2 million individuals throughout the Atlantic Coast.

Biomedical companies are a concerned party in this horseshoe crab issue. These companies catch and bleed horseshoe crabs. The bleeding process is akin to blood donation, since the animals are returned to the ocean afterwards. It is estimated that up to 30% of the animal's blood is removed. Studies have shown that mortalities occuring from the bleeding process range between 3%-15%. This variance can be attributed to differing bleeding protocols. The biomedical company then extracts a compound from amebocytes (the only blood cell present) in the horseshoe crab's hemolymph. This preparation is called Limulus Amebocyte Lysate (LAL). LAL is used to detect endotoxins associated with gram-negative bacteria. These pathogenic bacteria can illicit a pyrogenic response, which involves fever, coma, or even death. Hence, the LAL assay is used by pharmaceutical and medical industries to ensure that their products (e.g., intravenous drugs, vaccines, and implantable medical and dental devices) have no bacterial contamination. The lysate has been shown to be more sensitive and faster to the detection of endotoxin than the USP rabbit test. The United States FDA estimates that 260,000 horseshoe crabs were caught and bled in 1997, as compared to 130,000 in 1989. Currently, there is no LAL substitute that offers comparable speed and sensitivity.

With demand for horseshoe crabs on the rise, it is important to continue conducting research that will offer a comprehensive understanding of this amazingly significant animal. More population and migration studies are needed for the formulation of appropriate management strategies. In the biomedical realm, more information is needed on post-bleeding mortality rates to perhaps alter bleeding protocols to yield lower mortality rates or even non-lethal levels. Also, the total blood volume of the animal is unknown, which leaves estimates of bleeding amounts with no baseline information. A further direction of study is to decrease or eliminate the need for harvesting horseshoe crabs by developing an optimal cell culture media for the maintenance of amebocyte cultures. At some point, there will also be the possibility of finding a way to culture amebocytes or even to clone specific components of LAL. Such alternatives can reduce the biomedical industry's impact on horseshoe crab populations.

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