By SYLVIA EARLE
When I first met a horseshoe crab, technically Limulus polyphemus, on a New Jersey beach many decades ago, my 3-year-old mind sympathized with what appeared to be the animal’s struggle to find water. I picked it up and returned it to the sea, then realized there were more, dozens, apparently stranded and in need of my assistance. Fortunately for them, my mother intervened, explaining that they needed to come high on the beach to lay their eggs and that — much like sea turtles — on the next very high tide, baby horseshoe crabs would emerge from buried eggs and be released into the sea.
By the light of the full moon in May, as oblivious to humans as most humans are to them, legions of wondrous, glossy-brown horseshoe crabs will be emerging from the sea within sight of New York skyscrapers and on a few special sandy beaches from Maine to Yucatán, repeating their ancient rhythms of regeneration. Females the size of half a soccer ball, with slightly smaller attendant males, will take advantage of higher-than-usual tides to lay millions of jade-green eggs in moist sand, much as their ancestors are likely to have done for hundreds of millions of years.
Icons of antiquity, with fossil relatives dating back nearly 500 million years, they are one of only four species that hold the genetic codes for an entire class of organisms, the class Merostomata, a category of life comparable to the class Insecta, with at least a million individual species.
The current populations of Limulus must overcome extraordinary challenges if they are to continue to make a place for themselves in a rapidly changing world. In the past century, horseshoe crab nurseries have largely been displaced by the many ways people have transformed coastal beaches and marshes with landfills, sea walls and marinas.
Loss of critical habitat tops the list of concerns, but human predation is a close second. Although not targeted as food by American consumers (after all, they are related to spiders and scorpions and have astonishingly blue, copper-infused blood), the rare Asian species are prized as a tasty specialty in certain markets. Horseshoe crabs are valued for use in certain medical tests, and for this thousands are gathered and their blood collected before they are released. Many more thousands of females are taken by the truckload to be quartered for bait to attract eels and conchs that are mostly destined for export.
Numerous sea birds owe their prosperity to the seasonal appearance of horseshoe crab eggs, a vital source of sustenance at a midway point for migrations from South America to Arctic nesting sites. Concern for declining populations of at least nine species of egg-eating birds, especially the red knot, motivated lawmakers in several states to enact protective measures, mostly aimed at limiting the number of horseshoe crabs that can be taken, for the birds’ sake. But what about the fate of the horseshoe crabs themselves? In the past century their numbers have declined sharply, a trend that puts them in the company of much of the natural world, from coral reefs and blue fin tuna to pangolins and pandas.
Species come and species go, but never since a mighty asteroid struck the earth has the magnitude of loss come close to what is now occurring to the only place in the universe that is just right for horseshoe crabs — and humankind.
We have a chance to shift from the present trend of consuming wild places and wildlife for shortsighted short-term use to an era where our actions are aimed like a laser at securing an enduring place for ourselves within the natural systems that make our lives possible. With care, in the next million years or so, horseshoe crabs and human beings may still be sharing space on earth.
Sylvia Earle is an oceanographer and president of the nonprofit environmental group Mission Blue.