Volume XI, Issue 24 ~ June 12-18, 2003

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~ Bay Life ~

Who Could Love Such a Face?
For eons, horseshoe crabs have linked together the great chain of being. Now, they’re a weak link.
by Steve Carr

When I was a boy growing up along the shores of the Severn River, my friends and I used to have a daily ritual. Every afternoon we would walk along the beach in front of Ferry Farms and see what the tide had delivered. The river coughed up arrowheads, historic bottles, boat cushions and an endless stream of plastic garbage. My friends and I each had a grand collection of river trash that we proudly harbored in our garages and bedrooms back home.

The find that seemed almost magical was the shell of a horseshoe crab. None of us had ever actually seen a live horseshoe crab. We had no idea what to make of this beast. Where did it come from? Heck, it didn’t even look like a crab. It obviously wasn’t from around here.

Yet every once in a while, as we patrolled the beach, one of us would spot a dark brown shell drifting lazily at the edge of the tideline, and we’d rush to be the first to lay claim to one of these natural treasures. We’d triumphantly hoist it above our heads like a trophy and try to make some sense of the curious beast.

How can you tell a boy from a girl? What are all those goofy legs for? Can it sting you with that tail? Where is its mouth? What does it eat? Does it walk or does it swim? How does it see where it’s going? Which is the front and which is the back? Why does it need such a big shell? What eats horseshoe crabs? What do you think killed this one?

Very Curious Beasts
In later years, I learned some of the answers to those questions. The horseshoe crab isn’t really a crab. It’s related to spiders and scorpions. Horseshoe crabs do, however, molt like a blue crab about once a year, until they reach sexual maturity when they are three or four years old. From then on they wear the same shell.

The horseshoe crab has been found in the fossil record going back hundreds of millions of years, making it one of the oldest marine animals on earth.

One way to tell the males from the females is their size. The girls are about 75 percent bigger than the boys.

They like to eat marine worms, razor clams and soft-shelled clams, which they dig out of the mud.

Horseshoe crabs can swim or crawl along quite rapidly. They travel great distances during their lives, which usually span about 12 years. They call the ocean home, but they come into the Delaware and Chesapeake bays to spawn each year between early April and late June.

Surveys conducted on the Saturday closest to the full moon in late May or early June have verified several spawning beaches along the Severn and South rivers.

But as with so many species in the Bay, recent surveys have begun to show a dramatic decline in the numbers of horseshoe crabs.

What Good Is Such a Beast?
Some might wonder why we should care about something so ugly and worthless. What good are horseshoe crabs? You can’t eat them, so who cares whether there are fewer of them to go around?

The answer is perhaps the most intriguing aspect of the horseshoe crab.

In late April, when millions of horseshoe crabs line the Delaware Bay beaches to spawn, something happens the likes of which can rarely be seen on this planet. It is the biggest feeding frenzy on the East Coast — bar none. Because, at the same time the horseshoe crabs are literally covering the beaches and making love by the light of the moon, millions of sea birds are leaving their wintering grounds in Central and South America.

These plovers, sanderlings and a zillion sandpipers begin their long trek north to their breeding grounds in the Arctic, flying non-stop to Delaware Bay. They have chosen their departure date to coincide with the full-moon cycle, which in turn is connected to the breeding cycle of the horseshoe crab. That means the shorebirds arrive at the same time each female horseshoe crab is digging a hole in the sand and depositing her eggs.

Each nest contains about 4,000 eggs, and a crab will dig about 20 of these nests. You can do the math, but that translates into tons and tons of high-protein eggs lying beneath the Delaware beaches like buried treasure.

When the birds arrive, they go nuts. They are literally starving, half-dead from flying over 2,000 miles. Studies show that they have lost over half their normal body weight by the time they land in Delaware. Imagine losing half your weight! So the stop in Delaware is crucial to the survival of the vast majority of shorebirds flying up the Atlantic Coast each year. Without all of those horseshoe crab eggs to chow down on, many birds would not be able to fly north and breed.

In 1986, horseshoe crab numbers reached a high of 1.2 million. By 1996, the surveys recorded an all-time low of 400,000. To show the obvious connection between the crabs and the birds, Delaware census figures of shorebird populations also reached their zenith in 1986, only to be halved a decade later.

Why Does Everybody Want This Beast?
The loss of horseshoe crabs corresponds directly to over-harvesting. Fishermen from New Jersey, Delaware and Maryland use trawlers, dredges and scrapes to catch the crabs. In the last few years, the harvest levels in Delaware have gone up 410 percent, in New Jersey 210 percent, and in Maryland they landed an additional 1.2 million pounds.

Who eats horseshoe crabs, you might ask? If you’ve ever looked under the shell of a horseshoe crab, you couldn’t help but notice that there isn’t much there. It’s all spindly legs and very little meat. So why would there suddenly be a booming market for horseshoe crabs?

The answer to that question leads us to the fishermen who go after eels and conch and who use horseshoe crabs for bait. As the Western Europeans eat more eel and conch, the demand for horseshoe crab bait goes up. A conch fisherman can use over 500 horseshoe crabs each day.

The other thing that’s driving the demand for horseshoe crabs is the medical industry. The blood of the horseshoe crab is like no other blood on the earth. It has certain rare qualities that make it a favorite for eye research, as a clotting agent in surgical dressings and in detecting infectious bacteria. Medical labs from Virginia to Massachusetts catch about 200,000 crabs a year and remove about 20 percent of the blood from each crab before returning it to sea. In the process, about 10 percent die.

The final factor — and the one that we who live along the Bay can actually impact — is the loss of habitat. Horseshoe crabs have been coming to every one of our local rivers to spawn since before the time of dinosaurs. But they need a sandy beach to do their thing.

As we continue to bulkhead and rip-rap the entire length of each waterway, we are making it impossible for any living creature to leave the sea. When the beaches are gone, we will have also lost this remarkable underwater spider known as the horseshoe crab.

Our children will never get the chance to find the Bay’s oddest of shells, hold it in their hands and wonder where in the world it came from.

About the Author: Steve Carr owns an environmental consulting business and is a past president of the Severn River Association. An avid birder who enjoys canoeing, hiking, and bicycling, he has written extensively about the Bay for many years and has lived along the Severn River his whole life.


© COPYRIGHT 2003 by New Bay Enterprises, Inc. All rights reserved.
Last updated June 12, 2003 @ 1:22am