The bird, the crab, the eggs, the blood, and the ends of the earth

kw: book reviews, nonfiction, natural history, horseshoe crabs, red knots, migration, ecology, environment

For anyone who lives along Delaware Bay or the Delaware River, there are two main choices for a day at the beach or shore. The local terms are "Delaware beach" and "Jersey shore". Having sampled both, I found I love the northern beaches of Delaware the best. Beach towns and parks from Rehoboth Beach down to Fenwick Island, and on to Ocean City, MD, are great fun, but we enjoy Cape Henlopen, Delaware's northernmost Atlantic beach, the most.

Those who visit the Cape in late Spring, near the full moon in May or earliest June, can witness an amazing spectacle right out of the geologic past: the spawning of the horseshoe crabs. These trilobite-like critters, bigger than dinner plates, and little changed in bodily form for 400 million years, crawl ashore by the thousands to mate and lay eggs in the sand. Right along with them, running among them, little sandpipers called Red Knots pick and probe in the sand for the nourishing eggs. Knots are not the only egg-eating shorebirds, but at times they are the most numerous, as this photo shows.

At both Cape Henlopen and Cape May, NJ, and at many sandy beaches that line Delaware Bay, crabs lay eggs and shorebirds feed frantically. The Knots are particularly frantic. They've just crossed the western Atlantic from northeastern South America, and they have several thousand more miles to go to their Arctic breeding grounds. They have an amazing weight-gain and muscle-building metabolism that allows them to eat half their weight daily, and to double their weight, mainly by adding flight muscle and a layer of fat, in just a couple of weeks. They will lose most of that added weight flying 3,000 or more miles north by mid-June.

The Western Atlantic Flyway for Red Knots begins at Tierra del Fuego, Chile, the "uttermost part of the Earth" at the southern tip of South America. It ends at the other "uttermost part of the Earth" in northern Canada. That is, in the March-to-July time frame. Six months later, it is the same route in reverse.

Think of it: little birds that weigh only a couple of ounces, fueled by a few ounces of shellfish (on South American coasts) and horseshoe crab eggs (on North American coasts), make a journey that we bulky humans find harrowing and quite expensive (at current Coach rates, flying from Punta Arenas, Chile to Iqaluit, Canada costs $2,625 one way, with four stops to change planes). The birds do this twice yearly.

Deborah Cramer, as she writes in The Narrow Edge: A Tiny Bird, an Ancient Crab, and an Epic Journey, made that trip just once, to see the Red Knot in all its habitats. The airline fares were the least of the expenses. There are no hotels near Bahia Lomas, and it takes almost as long to go that last 80 miles (130 km) from Punta Arenas by truck and boat, as it took to get to Punta Arenas from Massachusetts. She had to depend on an invitation from scientists who take advantage of an oil company's camp. Similar "camp-out" style dwellings awaited her on Southampton Island, in northern Hudson Bay, Canada. I presume she had hotels to stay in along the Delaware Bay and other mid-journey stopovers.

The book's entertaining travelogue provides one level of reading pleasure. But most importantly, it shows the interlocking lives of creatures of air and sea that actually affect human health throughout the world. Horseshoe crabs, it turns out, are a bountiful source of several benefits, and the most important is safeguarding our medicines.

Several generations ago, horseshoe crabs were harvested by the millions for bait and fertilizer. Better sources of fertilizer since the mid-1900's reduced the carnage somewhat, but by then their population was probably no more than 5% of what it had been. Their spawning runs were once legendary, with their little green eggs feeding tens to hundreds of millions of shorebirds, and still lying in heaps along the beaches. The shore birds now, seemingly abundant to our impoverished eyes, number less than a percent what they once did. Not only are there fewer crabs, they lay fewer eggs, ultimately because of a curious property of their blue blood.

Horseshoe crabs, and large arthropods in general, do not have as sophisticated an immune system as we and all mammals have. But horseshoe crabs in particular have a very sensitive clotting factor that engulfs certain bacteria, called gram negative bacilli, and deactivates the toxins they release. The metabolic products of gram negative bacteria are toxic to us, and cause fevers in even very small amounts. Their presence indicates bacterial contamination of medical products, so it is important that every IV kit, every serum, vaccine and other injectable medication be tested. Once there was a "rabbit test", but now the clotting factor in the blood of horseshoe crabs is used; it works ten times better.

Horseshoe crabs are captured, bled of about 1/3 of their blood, and returned to their native waters. A product called LAL is isolated from the blood, which is blue because rather than the iron in our kind of blood, theirs contains copper. Every time you've had a needle stuck in you for any reason, somewhere along the way the IV or hypo kit, and probably the medication also, were tested with LAL. Without it, about a third of the time the treatment itself would cause a fever lasting a day or two, and possibly a deadly reaction.

Female horseshoe crabs are bigger than their mates, so you can get more blood from them. But a crab that has been bled will be disoriented for days or weeks when she is returned to the sea, and will usually produce fewer eggs that year. A certain number are known to die before they are returned. Even more must be dying after return. A century ago, the usual sight was that each female crab was accompanied by one or sometimes two males as she came ashore to lay her eggs. Now it is common to see four to six males surrounding each female.

States such as North Carolina have banned the taking of horseshoe crabs for any reason other than this medical one. Nobody really needs them for bait any more, but some fishermen find it\\they are easier to gather than other bait fish, so there is legislative resistance to similar bans elsewhere. Researchers have devised several ways to use LAL that are from four to twenty times more efficient. But until the FDA (and similar bodies in other nations) rules upon the new tests, it is illegal to use them.

We soon may have no choice. Horseshoe crabs' numbers continue to decrease throughout the western Atlantic. A similar Asian crab species apparently cannot be used to produce LAL because of other toxins in its blood. And the birds? They are of no use to the crab. But they are of use to us. Their abundance, or scarcity, is a signal we had best not ignore. As the population of crabs declines, so does that of many species of shore bird, not just the Knots. And other populations are also affected. Large fish and seals that eat horseshoe crabs have turned in desperation to other prey, such as the famed Delaware Blue Crab. The price of Blue Crabs is increasing as a result. So it the price of your medicine, as it gets harder to gather enough crabs to meet an ever increasing demand for LAL, particularly as China Westernizes its economy and culture.

Doing something the cheapest way is not always, or even usually, the right way. Horseshoe crabs may be OK as a bait fish, but there are numerous alternatives. When the health of every human depends on them, is it permissible to use them for bait? Researchers find it hard to synthesize LAL, but it ought not be impossible. Sure, it'll cost a few millions to produce the first gram of synthetic LAL, but once the method is known, the price will drop and drop until it is cheaper than drawing blue blood from crabs. But will that price cutoff be reached because technology improves, or because crab capture and bleeding become so costly that natural LAL drives the cost of an IV kit to $1,000 and a flu shot is not $35 but $350?

And what of the birds? Will the loss of the Red Knot matter? Did the loss of the Passenger Pigeon matter? After 1914, when Martha the pigeon died, this marvelous bird species was lost forever. What else happened? At one time, they ate so many acorns and other forest nuts that there were fewer mice and other seed-eating small mammals. Now instead of millions of pigeons, we have billions more mice. One critter that inhabits mice is the "deer tick". So there are many, many more of them. Young ticks feast on mouse blood. Then they drop off and molt a time or two. Next they look for a larger host. They usually find deer, but a human will do. Then what happens? Lyme disease! Lyme disease was almost unknown before 1970. That shows that the burgeoning mouse numbers are only part of the equation. More and more suburbs being built into forests is another.

We don't know what other links are in the chain that includes Red Knots and Horseshoe Crabs. It is more of a mesh, anyway, like chain mail. Life is an unending Tetris game. Blocks drop and we fend them off. So does every other species. Eventually the stack fills the box and it is "Game Over". For many species, we are part of that Tetris game, not only adding extra falling blocks, but throwing them down faster and faster. Every species lost is irretrievable. You may not see the beauty in the horseshoe crab, but to the right kind of eye, the crab and the bird have equal beauty, and they are both of great value.