Fossil of Mesolimulus, a horseshoe crab species that existed during the Late Jurassic period, about 150 million years ago.
Despite its ancient origins, the horseshoe crab has managed to persist through the ages. Because the horseshoe crabs we see today are mostly the same in shape and structure to those seen in the fossil record, horseshoe crabs are referred to as "living fossils."
The reason that the horseshoe crab and other living fossils remain similar for such a long period of time is that there simply hasn't been enough environmental pressure on them to change in any significant way.
To put it simply: If it ain't broke don't fix it.Horseshoe crabs are living fossils.
The History
The horseshoe crab is one of the oldest living species on Earth, with fossils dating back as far as 400 million years ago, before the arrival of dinosaurs or flowering plants. It has survived through five of Earth’s extinction events, where in each case 75-90% of species on Earth disappeared.
Horseshoe crabs are a keystone species.
Horseshoe crab eggs and larvae are a vital supply of nutrients for birds, fish, and reptiles. The horseshoe crab is a "keystone species" in that it plays a crucial role in supporting other species. If it were to be removed, there would likely be ecological collapse on the Atlantic Coast.
Each spring, horseshoe crabs travel from deep Atlantic waters to the shore for their breeding season. Beaches are swarmed with mating horseshoe crabs, with females laying tens of thousands of eggs at a time in clusters buried under the sand.
An ecosystem has evolved around the horseshoe crab's breeding season. The eggs are a calorie-dense food source for foraging fish and turtles. Migratory birds on their northbound journeys have adapted to time their stopover in Delaware Bay to coincide with the mass spawn of eggs. They serve as a critical source of fuel for their several thousand mile journey.
The fatty, nutrient-rich horseshoe crab eggs supply vital energy for the birds to replenish their fuel reserves before they continue their migration to the Canadian Arctic.
Footage of horseshoe crab spawn circa 1986, prior to the overharvesting of the 1990s. Note the mats of eggs forming "drift lines" across the beach, a phenomenon rarely observed today.
By 1970, one hundred years later, synthetic fertilizers became the industry standard and the horseshoe crab harvest declined.
In the 1990s commercial fisheries began the bait harvest for crabs at an unprecedented rate. Little to no regulations were in place to control the harvest, and horseshoe crab populations along the Atlantic Coast were decimated as a result.
Bowers Beach, DE in 1922 at the height of the fertilizer harvest.
Horseshoe crabs have a history with humans.
People have been using horseshoe crabs for a long time. There is evidence that Native Americans shaped their hard shells into tools for farming and spears for fishing. They passed on their use of crabs to European colonists, who used the crabs as fertilizer for their crops. By the 1870s over a million horseshoe crabs were being harvested annually from Delaware Bay, to be steamed and ground into fertilizer and hog feed.
Horseshoe crab blood is used in the biomedical industry.
The effects of bleeding on crabs have been cause for concern. The biomedical industry self-reports mortality rates of 15%, but industry experts put estimates significantly higher. Additionally, bled crabs that are released into the natural environment have been observed to engage in less reproductive behavior and display disoriented patterns of movement, putting further strain on an already depressed population.
(Image from PBS documentary
"Crash: A Tale of Two Species")
Horseshoe crab blood is uniquely sensitive to bacteria. It developed this property as a method of protection against the hordes of bacteria in the ocean. When their blood comes into contact with a pathogen, it solidifies and forms a clot, preventing it from spreading through the crab's bloodstream.
Because their blood reacts this way, the biomedical industry developed a method of extracting blood, separating the clotting agent, and using it to detect toxins in medical equipment. That clotting agent is limulus amebocyte lysate (LAL), and is valued at $15,000 a quart.
The use of LAL began to take hold around the same time as the bait harvest in the 1990's. Today around 500,000 crabs are harvested annually for biomedical bleeding.
There has been a push to protect horseshoe crabs.
Habitat loss has put a further strain on horseshoe crab populations. Beaches along the Atlantic Coast have been scarred from development, beach stabilization and erosion, limiting the amount of available grounds for breeding horseshoe crabs.
Habitat restoration has proven to be an important component of protecting horseshoe crab populations. The article to the left, from a 2001 article of NJ's The Daily Journal, describes the success of restoration efforts at Thompsons Beach.
Following the explosion in bait harvests and bleeding of the 1990s, horseshoe crab populations were in serious trouble.
As a result of pressure from scientists and conservationists concerned about the future of the horseshoe crab, the ASMFC devised the Interstate Fishery Management Plan in 1998. Several attempts were made to regulate the harvest, including harvest quotas, yearly stock assessments, and a 2008 moratorium on harvest in New Jersey.
In 2012, the ASMFC began using the Adaptive Resource Management (ARM) Model to establish a limited male-only harvest with the intention of restoring crab populations.
As of today crab numbers unfortunately show no sign of recovery, and remains at 1/3 of the population before the overharvest of the 1990s.
