Crabs: Ancient Wonders of the Seashore: Part I
Each spring, between mid–May and mid–June, thousands of fierce–looking
sea creatures crawl from the sea to mate and lay eggs along the
sandy shorelines and mudflats of New York City. These harmless
animals called horseshoe crabs are not really crabs at all, but
more closely related to arachnids (spiders and scorpions). A living
fossil, the horseshoe crab evolved long before the dinosaurs with
an ancestral heritage dating back to the Triassic Period two hundred
million years ago. Currently, four species exist worldwide. One
species populates the Atlantic coast from Maine to Mexico with
the largest concentrations found in Delaware Bay. Named Limulus
polyphemus after the one–eyed giant of Greek mythology, this horseshoe
crab actually has nine eyes: one large compound eye on each side
of its shell, two small ones in the front center and five light–receptive
organs underneath. The other three species of horseshoe crabs
are found in the Indian and Pacific Oceans.
During high tides, especially at new and full moons, these “crabs”
emerge from the water to spawn. The larger females are usually
accompanied by one or more smaller males that attach themselves
to her back by specially adapted clasper claws. At the high tide
line, the female will dig a nest in the wet sand and lay up to
4,000 tiny greenish eggs. The attached male fertilizes the eggs
as they are laid and then both move back to deeper waters to feed
on benthic animals such as marine worms, crustaceans and mollusks.
About a month later the eggs hatch out, each one containing a
tiny, though tail–less replica of the adult crab. The little crabs
will molt their shells several times yearly during the first few
years of life and then once yearly thereafter. They reach adult
size in about 10–13 years and may live another 7–10 years. Before
molting takes place, a new skin forms under the existing shell.
The old shell splits open along the front and the crab walks out.
The crab then takes in water and digs into the sand. This new
skin is stretched larger and hardens around the crab to form a
new shell. The molted shells can be found along beaches at any
time of year and make nice coffee table or shelf decorations.
The eggs provide a bonanza for migrating shorebirds arriving in
New York City from their winter homes in Central and South American.
Some birds such as black–bellied plovers and red knots may have
traveled several thousand miles across the ocean, making their
first landfall in the estuaries of New York and New Jersey. Peak
shorebird migration coincides with the peak horseshoe crab egg–laying
period. The horseshoe crab eggs provide critical nourishment for
many shorebird species as they head to their Arctic breeding grounds.
At the Jamaica Bay Wildlife Refuge in Broad Channel, Queens, I
have observed these mating rituals and feeding frenzies for many
years and still am amazed by the abundance and diversity of participants.
Besides red knots, sanderlings, ruddy turnstones and about 20
other species of shorebirds, the egg feast attracts many laughing
gulls, glossy ibis and even Canada geese, whose goslings feed
on animal matter as well as vegetation.
Snowy egrets join in, not to feed on eggs, but the mummichogs,
silversides and other small fish that are taking part in the bountiful
melee. Larger predators, such as herring and black–backed gulls
will frequently take advantage of overturned horseshoe crabs and
peck out their gills, leaving a beach-front strewn with dead and
dying crabs. Despite this heavy onslaught, the crabs keep coming
ashore, determined to carry out the reproductive urge as they
have done for millions of years, long before the advent of Homo
sapiens. Horseshoe crab programs are becoming more popular and
each spring both Urban and National Park Rangers as well as school
groups visit NYC shorelines to tell the fascinating story of this
prehistoric wonder, the ageless horseshoe crab. For information
about horseshoe crabs, beach cleanup days, and other nature programs
in the greater New York City area contact: The American Littoral
Society, 28 West 9th Road, Broad Channel, N.Y. 11693. Telephone:
Don Riepe is a long–time resident of the Jamaica Bay area, Don
is currently a supervisory park ranger for the National Park Service
and Director of the Northeast Chapter of the American Littoral
Society, a coastal conservation organization.
Education Update, Inc., P.O. Box 20005, New York, NY 10001. Tel:
(212) 481-5519. Fax: (212) 481-3919. Email: email@example.com.
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the publisher. © 2001.