On 'Nature,' how 2 species intertwine The rapidly disappearing red knot depends on the increasingly popular horseshoe crab.

Posted: February 08, 2008

A ripple disturbs the water.

An eye appears.

It is a horseshoe crab on Delaware Bay, a helmet-shaped relic of the dinosaurs, coming ashore to spawn.

"For 350 million years, they've answered to the call of the moon," begins award-winning filmmaker Allison Argo as she narrates a PBS Nature special airing at 8 Sunday night on WHYY TV12. "They've survived ice ages, asteroids and cataclysmic forces . . . While thousands of species came and went, this humble creature endured."

Good thing. It has a modern mission - saving lives, both of humans and of a small bird called the red knot, which is headed toward extinction.

Crash: A Tale of Two Species is a loving portrait of both the crab and the bird, an achingly poetic exploration of nature's fragility and tenacity, not to mention its sheer audacity.

Every spring on the bay, as the crabs begin their spawn, the robin-size red knot is beginning one of the longest migrations on the planet, headed from the tip of South America to Arctic breeding grounds.

It lands on the shores of the Delaware Bay, exhausted and emaciated, with about two weeks to fatten up before continuing north. There is but a small window of opportunity for it to breed before the snows begin again.

It needs the crab eggs.

The creatures are linked by an astonishing synchronicity.

But a few decades ago, humans discovered other uses for the crab. Its blood, which clots in the presence of bacteria, is used in medical tests. "Each day, we're finding more ways the crab can help us, from sutures to contact lenses," Argo notes.

The crabs are released alive after donating some of their blood. But beginning in the 1990s, millions have been harvested to be used as bait for eel and conch, suddenly in high demand in the Asian food market.

As the crabs have declined, so has the bird.

Argo tells their story with clarity and passion, aided by gorgeous photography.

At one point, we see tiny crabs in their eggs deep under the sand, each greenish animal tumbling in its "watery nursery."

Argo takes viewers with her as researchers net the birds to gather data. She visits a pharmaceutical lab, talks to a waterman who feels crabbers are being unfairly targeted, tags along for full-moon crab counts.

In the Arctic, the researchers search and search, but find no red knots.

"We're getting in touch with what this decline really means," says Larry Niles, a New Jersey biologist who has studied and championed the bird for more than a decade.

The population data, he acknowledges as the camera sweeps across a desolate rocky landscape, "just sounds like a bunch of numbers. But you come up here, and you can see what that feels like."

Niles' wife, biologist Amanda Dey, provides some of the most eloquent commentary.

"If you've ever held a bird or a small animal in your hand," she begins, but then her voice breaks with emotion. "How could you, how could you not want them to continue to exist?"

It would be "extraordinarily selfish" to allow the red knot to disappear, she says.

But it's happening.

Weeks ago, researchers in Chile documented another setback. The red knot population has fallen from 29,000 in 2004 to 14,800 - a 50 percent decline in four years.

Yesterday, Niles pleaded the case of the bird before the Atlantic States Marine Fisheries Commission, an interstate regulatory body that has limited the crab harvest in New Jersey and Delaware to males only. He thinks stronger action is needed.

New Jersey has a two-year moratorium on taking any horseshoe crabs and wants to extend it. Monday, a state fisheries commission may decide to endorse it, or nix it.

Computer models have predicted the red knot could go extinct by 2010, and Niles worries the bird is on track.

"I always had hope," he said recently. But now, "this is the first time I've felt the species could really go under. Unless there's decisive action taken, it could go bad fast."

Argo's film concludes with baby crabs swimming through the water, headed toward maturity 10 years from now, and red knots winging south.

"It's only a little bird, and a strange-looking creature called a horseshoe crab," she says as the camera lingers on a flock silhouetted against the moon. "But the implications might be profound.

"Their story will play out in the years to come. It may be too late for the red knot, but the next time a story like theirs begins to unfold, perhaps we'll write a different ending."

Contact staff writer Sandy Bauers at 215-854-5147 or sbauers@phillynews.com.

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