Horseshoe crab  (Limulus polyphemus)

The population of horseshoe crabs has declined dramatically (4). In the past they were killed in very large numbers by clam diggers, as the species preys on clams. They were also used for animal food (3). In the 1920s and 30s between four and five million individuals were harvested each year (3). At present they are harvested in very large numbers for use as eel and conch bait; in 1996 alone, at least two million horseshoe crabs were killed for this reason (2). Horseshoe crabs have also been used extensively in the biomedical industry for the manufacture of surgical sutures, making dressings for burn victims, and in eye research (2). Furthermore, the copper-based blue blood of this species clots when it comes into contact with toxins released from bacteria. This clotting property, called Limulus Amebocyte Lysate (LAL) is harnessed by pharmaceutical companies needing to test the safety of drugs and other fluids that are to be used on humans (4). In order to make LAL, the companies harvest live horseshoe crabs from breeding beaches and remove a third of their blood before releasing them back into the sea. Studies have shown that 10 to 15 percent of the individuals bled in this way die as a result, accounting for the loss of 20,000 to 37,500 horseshoe crabs each year (2). The world market for LAL is a $50 million per year industry, and this species is essential in its production (2). Other threats facing this ancient species include habitat loss and shoreline development, as well as pollution (2). This unique species is exceptionally vulnerable as it matures very slowly, gathers in large numbers making them ‘easy pickings’ and by the fact that changes in abundance are not easy to detect. Furthermore, once the population has been reduced it can take as long as ten years for it to recover after harvesting, which roughly corresponds to the length of time it takes for individuals to reach maturity (2). Natural strandings are also a source of considerable mortality (2).

It is a sad fact that this ancient living fossil, which has been carrying out its unique life cycle for literally millions of years, is now threatened by human activities. It is clear that the massive level of harvesting of this species must be carefully controlled if the horseshoe crab is to survive, and finding a sustainable level of exploitation is essential (2). It must be carefully managed both as a valuable biological resource, and in its own right, as an amazing remnant of an ancient lineage that pre-dates the dinosaurs. Current actions to conserve this species include tagging and radio-tacking schemes that aim to shed light on the migratory patterns and spawning behaviour of this species. Hopes are that the more we learn about this species, the more likely it is that increasingly effective conservation actions can be devised (2). The Delaware-based Ecological Research and Development Group (ERDG) have been working towards the conservation of the horseshoe crab for a number of years. It places a strong emphasis on educating people about this species and encouraging locals to get involved in conservation action. In 2000 the residents of Broadkill Beach, Delaware designated the three-mile stretch of coast as a horseshoe crab sanctuary, which bans harvesting on the beach. Local people also venture out to return stranded crabs to the water (2). In 2002 the ERDG helped a second Delaware shorefront community, Kitts Hummock, to set up a sanctuary. These are encouraging signs and indicate that decisive conservation action can take place without government intervention (2).