Hakai Magazine

Coastal science and societies

Cover image courtesy of Yale University Press, background photo by Lynda Richardson/Corbis

Book Review: The Narrow Edge

When the lives of horseshoe crabs and migrating sandpipers intersect, the past and future are joined.

Authored by

by Daniel Wood

Article body copy

If there’s any doubt about the interconnectedness of all sentient things, The Narrow Edge puts the question to rest. Author Deborah Cramer wanders the coastlines of North and South America pursuing a series of linked scientific mysteries. How does the red knot, a russet-breasted species of sandpiper, manage its annual 15,000-kilometer migration from Canada’s Arctic to Tierra del Fuego, including a non-stop crossing of the entire Caribbean Sea? And what role does the horseshoe crab play in this transit? And, more fundamentally, what are the consequences of the destruction of global coastlines—the “narrow edge” of the book’s title—not only on the horseshoe crabs and sandpipers, but also on humankind, whose medical system, curiously, depends on the extraction of the crab’s extraordinary blue blood? Sandpipers, horseshoe crabs, humankind: linked together and balanced on a precarious narrow edge.

In a detective story with global implications, Cramer follows the clues and uncovers the causes and the impending consequences of what she’s learning. She travels with a Chilean researcher investigating if the migration of millions of shorebirds—including red knots—has succeeded, and what lies behind the huge drop in sandpiper numbers. She struggles through stormy weeks on Canada’s Arctic tundra, but—search as she might—the knots are nowhere to be found. “As the red knots go,” Cramer writes, “so go many other shorebirds.” The knots are, it seems, a sort of “mine canary,” affected by the multiple coastal dangers of declining crustacean populations, rising oceans, shoreline development, hurricanes, and oil spills.

But the story pivots on Delaware Bay, the midway point on the knots’ incredible migration, and the place where the southbound birds encounter—and utilize—the world’s largest concentration of horseshoe crabs. Here Cramer finds some of the 150,000 knots that depend on the high-energy nourishment provided by female crabs’ newly laid eggs. But again, calamity looms. For the horseshoe crabs, which have survived 475 million years and all five of the Earth’s mass extinctions, are succumbing, not only to centuries of use as fertilizer and bait, but also to a recent and bizarre medical discovery. The crabs’ unique blue blood is an endotoxin detector, and clots in the presence of bacteria. Biomedical companies located along Delaware Bay bleed tens of thousands of crabs annually to produce a test that ensures that material in vaccines, IV line flushes, stents, and implant operations is bacteria-free. But 25 percent of the female crabs die during the bleeding process, and with them Delaware Bay becomes ever less capable of providing nourishment for migrating shorebirds.

The Narrow Edge explores geologic, evolutionary, and natural history, but always keeps the scenes and people—dedicated field scientists, defenders of coastal habitats, medical researchers, and Cramer’s own wide-ranging curiosity—central to the story’s trajectory. The book is an elegy for what has been lost and a plea for what needs to be saved.

The Narrow Edge: A Tiny Bird, an Ancient Crab, and an Epic Journey
By Deborah Cramer
293 pp. Yale University Press