Geoscience Reference
In-Depth Information
jor electric utilities, which has overseen the largest salt marsh reclamation project in the world, returning some
800 hectares (2,000 acres) of once-dyked salt marsh hay farms to the sea.
This morning, the results of this habitat transformation were on full display. A heavy morning mist hung
over the marsh, forming a gray backdrop against which the silhouettes of drowned birch trees seemed projec-
ted as if onto a movie screen. The scene before me was perhaps the most primeval and, at the same time, the
most exhilarating that I have ever witnessed in the natural world. Thousands of horseshoe crabs—so named for
their shape and size—were plowing heedlessly, blindly it seemed, onto the muddy banks of a tidal creek. Some
were overturned, others were stranded among the dead stalks of salt marsh cordgrass, still others were pushing
through the marsh muds in their instinctive drive to find an egg-laying site. There to greet them were thou-
sands of shorebirds and laughing gulls and a small cadre of glossy ibises.
Horseshoe crabs come ashore to lay their eggs, as they have done for 400 million years.
I had seen shorebirds feeding across the vast mudflats of the Bay of Fundy and seabirds diving relentlessly
into schools of shrimplike krill, but never had I witnessed a feeding frenzy of such intensity. Red knots and
dunlins were climbing over each other to get at the bounty of crab eggs. In their density and heedless behavior
they seemed more like swarms of insects than birds. But it was perhaps the sound of this feeding frenzy—the
unrestrained electric chattering of the shorebirds and the eerie chorus of laughing gulls—that stamped the
spectacle as something primeval. Its pedigree reaches back through the ages, to a time before there was anyone
to wonder at its mystery. This coming together of species in pursuit of food and the opportunity to mate has
been aptly described by shorebird biologist J. Peter Myers as “sex and gluttony on Delaware Bay.”
Horseshoe crabs are so-called living fossils, among the most primitive creatures still thriving on the planet.
They arose in the Ordovician period, 400 million years ago, and have seen little reason to change their success-
ful breeding behavior ever since. They have been repeating their spawning ritual since long before there was a
Delaware Bay—or even a North American continent and an Atlantic Ocean as we know them today.
It is inaccurate to call them crabs at all, because they are arthropods more closely related to terrestrial
spiders than to marine crustaceans. Their common name derives from the shape of the front portion of their
body, or prosoma, which resembles a horseshoe. Underneath this impressive dome-shaped covering are five
pairs of legs, four of which are tipped with pincers, which act as a food mill for grinding molluscs and worms
and delivering them to the mouth at the base of the legs. The middle portion of the body, the opis-thosoma, has
