英語聽力：自然百科 馬蹄蟹與人類（一）

As the water is warm and tides grow high, horseshoe crabs leave the ocean floor and make their way to the shores and estuaries of the Atlantic Coast. Here in the sheltered waters of South Carolina, they suddenly emerge by the thousands in the spawning ritual they've performed for hundreds of millions of years. On the highest tides, they drag themselves to shore to lay their eggs. Crabs don't mature till they are nine or ten. By then, they've molted for the last time and their permanent shells can host an ecosystem of hitchhikers. Horseshoe crabs are safest on the ocean floor, but the only way to carry on the species is to take a risk.

We see the ones that see us come and turn and take off to the water. We caught him before he knows us. You know.

Jerry Golt and his father Bob have worked these waters for decades.

We work the moons. The horseshoe crabs come up and spawn on the moons in the springtime.

If you actually get into the water, you can feel them swimming and sometimes you can't even catch them because they'll get to swimming so fast. A lot of people seem to be scared when they first see them on the beaches. They do look a little scary but what I do is put them right up against my face and as you can see they do not hurt. Their pinchers are all very light. These are harmless. I just like them.

Mine is bigger. Mine is younger. Huh...

For 15 years, South Carolina has been collecting horseshoe crabs for fishing bait. Now, only fishermen with special licenses are allowed to gather crabs for biomedical use and only if they return the crabs alive. Few of us realized just how valuable the horseshoe crab is.

When I first started 37 years ago, we were allowed to harvest them. There was no recording; there was nothing. And they became fair game and I was involved with selling them for bait. And then a doctor came down and he said that if I didn't sell bait crabs anymore, he would be interested in the laboratory.

Normal fishing is, as you know, you catch it, you ice it, and you deliver it to the table, and you eat it. The horseshoe crabs we actually catch them, take them to the lab, and they bleed them and we bring them back and release them. So we are borrowing the crabs, this is what we are doing.

Crabs that are borrowed end up a couple of hours away at the Endosafe Laboratories in Charleston. Here in this alien world, they are given a rigorous cleaning to prep them for the process ahead. For the past 30 years, the biomedical industry has been mining the medical equivalent of gold. Endosafe is one of the only four labs in the world that produces a derivative of horseshoe crab blood. Their blood has a clotting agent that's used to detect minute levels of bacteria. But what's truly surprising is the color. The crab's blue blood is an evolutionary gift that's helped them survive the eons.

Male or female? A small male would be good. OK!

Doctor Norman Wainwright has been working with horseshoe crabs for most of his career, studying the remarkable properties of their blood.

The beautiful blue color is a result of its blood containing copper as an oxygen carryingpigment instead of hemoglobin which contains iron. I am adding a suspension of E. coli bacteria.

At the first sign of bacteria, the crab's blood forms a protective clot.

Look at that, this is perfect. This is the horseshoe crab cells protecting the animal from infection. Any type of leakage of seawater into their blood system will trigger this response, seal the wound and they actually are proteins in the clot itself that kill the bacteria. They are almost theprimitive antibiotics.

The phenomenon caught the attention of the biomedical community in the 70s, they've been putting it to work for us ever since. Up to a third of the crab's blood is removed during the process, yet most of them survive. One quart of horseshoe crab blood is worth about 15,000 dollars. It's a multi-million-dollar industry. The clotting agent called Lysate is used to test intravenous drugs for bacteria. No IV drug reaches the market without being tested on horseshoe crab blood. It's an FDA regulation.

Years ago, the only way to screen for toxins dangerous to humans was to use live rabbits.Feverish bunnies revealed contamination and the test was slow. Horseshoe crab blood takes an hour tops and most of the crabs survive the process. Scientists are exploring alternatives that would make bleeding crabs unnecessary. But each day we are finding more ways the horseshoe crab can help us with everything from sutures to contact lenses.