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Introducing
the Amazing Horseshoe Crab
Where on earth can you find
a creature with ten legs and ten eyes, that chews with its feet
and has blue blood? The answer
of course is Delaware Bay, and the creature is the horseshoe crab
--- an animal frequently seen in recent news, but
still poorly
understood by many people.
 In
terms of longevity, horseshoe crabs are one of life on Earth’s
most amazing success stories. They've been here for about 360
million years, 100 million years before early dinosaurs
arrived on the scene. In all that time, they've changed so
little that you could take a horseshoe crab from today
and
fit
it into a fossil imprint from 150 million years ago, and
it would be an almost exact match.
Not
true crabs at all, horseshoe crabs are an extraordinary member
of the phylum Arthropoda,
with today's scorpion as their closest relative. The past
decade has seen a notable decrease their numbers, which
is unfortunate
because
they have a tremendous, but little understood impact on our daily
lives.
What
good are horseshoe crabs anyway? For starters, they are
a significant resource for our commercial fishing economy, which
uses them as bait for eels and conchs. They are appealing
for anyone going to the beaches in May and early June
to observe their spawning.
Horseshoe
crabs are perhaps most important to us through their usefulness
to the medical community. Anyone who has had a vaccine
or an artificial body part is benefiting from the horseshoe
crab.
The
crab has blue blood that is specially adapted to clot when it
comes in contact with gram negative bacteria. Any medicine,
vaccine,
or prosthetic device must first be tested by Limulus Amoebocyte
Lysate (LAL), made from the blood of the crab, to ensure
that it is free from contamination by gram negative bacteria,
which can cause fever, sickness and even death in humans. The
crab's shell is made of very pure chitin, a
source material for wraps for burn
patients
and surgical sutures that speed healing while lessening
pain.
The
horseshoe crab's most crucial role of all relates to its place
in the Delaware Bay's food chain. Every spring, when the
crabs are
laying
their eggs, thousands of migratory
shorebirds, such as the Red Knot, fly to the region to fatten
up on horseshoe crab eggs. If these eggs were not available
these shorebirds would not be as able to "bulk up" for the northern
legs of their migration flight to
their Arctic breeding grounds
 .
Many
factors affect the lives of horseshoe crabs. Natural mortality
is high during spawning, with crabs becoming stranded on the
beach combined with predation by gulls and other birds that
eat overturned
crabs. Using horseshoe
crabs as bait to catch eels and conchs removes more from the population.
This year alone a reported 369,000 horseshoe
crabs
were taken by 38 licensed fishers. About a
quarter million are harvested annually coast-wide
for use in
the
biomedical
industry.
Although the majority of these crabs are bled and returned
safely to the water, 20,000-37,000 crabs generally die
annually in the process.
Habitat
loss is one area where a difference can still be made. Recent
scientific studies by DNREC’s
Coastal Zone Management Program are investigating
approaches to Delaware Bay beach replenishment projects
to help prevent beachfront lands and properties
from eroding away, optimize conditions for horseshoe crab
spawning and egg development and use by shorebirds.
Although
we don't yet have all of the answers concerning horseshoe crab
and shorebird population interactions, more rigorous conservation
and habitat management measures are being taken while more research
is conducted and better horseshoe crab population support measures
are developed for implementation.
For
more information on this topic, check out
the following web sites:
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