Old-timer ready for another spectacular spring fling

ON THE BAY

May 15, 1993|By TOM HORTON

Today we offer a brief escape from life's pressures; you can travel back to a time when the bones of Earth were still forming, and observe one of the most profound annual events in all the cycles of Chesapeake life.

Mark the weekend beginning Friday, June 4, time of the full moon and of the maximum high -- or "spring" -- tide that occurs twice monthly. If you're already booked, any time a week or so on either side of June 4 is still worth trying.

Find a long, sandy stretch of shoreline, protected from large waves, with a gentle, extended underwater slope. The lower bay and its tidal rivers, from Pocomoke and Potomac south to the sea, is better than the upper half, with the possible, curious exception of the Miles River, a small waterway in Talbot county.

Pick your spot and let the moonlight bathe you, cleansing from your consciousness all but these timeless elements: moon overhead, sand underfoot, the gentle lap of water -- and, if you are fortunate, something else, crawling slowly from the depths with the swelling, ripening tide: Limulus polyphemus, emerging to spawn.

You know it as the horseshoe, or king crab. Chesapeake Indians called it seekanauk, and used its great spike of a tail to tip their lances. A closer relative of spiders than true crabs, the creature is a living fossil, a throwback to an epoch nearly 400 million years ago, when its order, the Xiphosura, or sword-tailed animals, arose.

When helmet-shaped Limulus first crawled, the old Devonian shales of the Appalachians and the marbles we quarry for our finest buildings were just being laid down in the geologic strata, and Earth's land mass had not yet broken into continents.

The early ancestors of trees had just begun to sprout from Paleozoic swamps. The dinosaurs would not begin to appear for another 150 million years, and the earliest birds were still 250 million years in the future. Maryland's state fossil, an extinct snail that flourished 10 million years ago, is an utter infant compared with Limulus.

To witness the horseshoes as they complete their impossibly ancient ritual of creation and renewal is as close as you can get to experiencing primordial time. There is only sand and sea and moon, and these olive-brown, thick-carapaced spiders.

If the gulls that prey on their eggs were pterodactyls, and the foxes that ravage their stranded carcasses were sabretooths, it would not seem out of place to Limulus.

The crabs spawn over a period of several weeks in late spring, but the peak usually occurs around the full moon in late May or early June, and on the high, spring tides associated with it.

Spawning at night runs about three times as heavy as during the daylight.

The larger females, each laden with as many as 80,000 greenish-beige eggs, ascend the beach around the high tide; but hours before that you may see the spiked tails, or telsons, of males just offshore, patrolling to and fro to intercept and attach themselves to the females, who drag their suitors up the beach to fertilize the eggs deposited in the sand.

One scientist, watching the males' frenetic patrols, was moved to write that "cruisin' for chicks can be dated back nearly half a billion years."

The next tide to reach the eggs, the spring tide two weeks after spawning, will wash the hatchling crabs into the water to begin a life that can last more than 15 years.

While the horseshoe crab is common throughout the lower and middle Chesapeake, far greater populations are centered around Delaware Bay. Heavy spawning there can literally cover the beaches for hundreds of yards as the crabs pile up two and three high in their push to procreate.

On such beaches, concentrations of eggs buried in the sand can reach hundreds of thousands per square meter, with excess eggs piled in windrows on the beach several inches deep.

So huge and reliable is the Delaware Bay spawn that massive populations of shorebirds have evolved to depend on it during their spring migration from South America to the Arctic. Arriving famished, they will consume an average of one crab egg every five seconds, fourteen hours a day, for nearly three weeks, before resuming flight in fine-fatted condition.

If you want to see guaranteed, big time horseshoe crab spawning this spring, then seek out Delaware Bay. Some reliable spots include Reeds Beach on the New Jersey side, and Port Mahon and Bowers Beach on the Delaware side. The sandy hook at the tip of Chincoteague National Wildlife Refuge in Virginia is good, too.

But consider, in the interests of contributing to science, seeking old Limulus on the Chesapeake shore. I think there may be more spawning going on than has been documented.

For example, science tells us emphatically that the crabs don't ,, spawn in the marsh, only on beaches. Yet I was at a restaurant on Ocean City's bayside when horseshoes began rising magically on the high tide and soon covered large portions of the parking lot.

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