On a blustery March morning, I crouch at the Pacific’s edge to inspect a delicate white disc tossed onto the beach by the surging tide. Suddenly a passer-by shouts:
“They call them ‘dollars,’ but they aren’t worth anything!”
The naturalist in me bristles. I want to run after the stranger and make him look—really look—at the remarkable creature in my hand. Even in death, the intricate skeleton of a Pacific sand dollar (Dendraster excentricus) retains its elegance and beauty.
In the ocean, sand dollars dazzle—soft and velvety, in shades of deep purple, lavender-gray or brown. About three or four inches across, their flattened bodies are made of a tough, chalky material called a test, similar to the skeletons of sea urchins, their marine cousins. The pretty five-petaled flower imprinted on its top side—called the petaloid—consists of pores that enable a sand dollar to breathe. On the underside sits the mouth, equipped with Aristotle’s lantern—a set of five calcified jaws with very sharp teeth.
Along the Northern California coast, sand dollars nestle on the sea floor from the nearshore to just beyond the breaker zone. Like savvy human beach-goers, they position themselves strategically. Rooting themselves partly in the sand, they tilt on an edge at a slight angle so the current, with its floating dinner buffet, flows over their bodies. In some places, the sea floor becomes a living mosaic, with armies of sand dollars forming lines that make feeding more efficient. Juveniles tend to remain in shallow water, while adults move to deeper zones offshore.
Their diet consists of whatever tiny organic bits they can grasp. Like a conveyor belt, their spines and tube feet pass the morsels along ciliated grooves toward the mouth. Their mighty jaws grind the “catch” for digestion—a process that can take several hours.
Although they may seem defenseless, sand dollars have evolved subtle protective strategies. When threatened by predatory fish or sea stars, they burrow quickly into the sand. In rough waters, juveniles may ingest heavier sand grains for greater stability.
In summer, these “broadcast spawners” release eggs and sperm directly into the water. In a synchronized spawning event, huge numbers gather, increasing the likelihood of reproductive success. The fertilized eggs develop into transparent larvae that drift in the ocean for weeks or months.
Eventually, the survivors settle on the sea floor and metamorphose into teeny sand dollars, with an average lifespan of six to more than ten years. Marine biologists can calculate how old a sand dollar is in the same way that arborists determine a tree’s age: by counting growth rings—but on a test rather than a trunk.
To us, sand dollars resemble oversized coins exchanged for goods and services. But these unseen, unappreciated workhorses earn their place in the underworld by performing essential tasks: filtering plankton, recycling nutrients, aerating sediment, shaping the seafloor grain by grain and sustaining a far larger ecosystem.
In doing these jobs, sand dollars display traits we value in the people who manage our money. They’re quiet, flexible, efficient, productive—and well equipped to weather storms and shifting currents.
So what’s a sand dollar worth?
In the unforgiving economy of the sea, it may be priceless.
