Name: 【TED-Ed】為什麼要採集鱟血？- 伊麗莎白-考克斯 (【TED-Ed】Why do we harvest horseshoe crab blood? - Elizabeth Cox)
Uploaded: 2021-01-14T07:05:24.000Z
Duration: 4 min 46 s
Description: 【看影片學英語】數萬部 YouTube 影片，搭配英漢字典即點即查，輕鬆掌握單字發音與用法，長久累積看電影不必再看字幕。

During the warmer months, especially at night during the full moon,

horseshoe crabs emerge  from the sea to spawn.

Waiting for them are teams of lab workers

who capture the horseshoe crabs by the hundreds of thousands,

Oddly enough, we capture horseshoe crabs on the beach

because that's the only place we know we can find them.

A female horseshoe crab lays as many as 20 batches of up to 4,000 eggs

the juvenile horseshoe crabs often stay near shore,

periodically shedding their shells as they grow.

they don't return until they reach sexual maturity ten years later.

Despite our best efforts, we don't know where they spend those years.

Though we've spotted the occasional  horseshoe crab

as deep as 200 meters below the ocean's surface,

we only see large groups of adults when they come ashore to spawn.

Horseshoe crab blood contains cells called amebocytes

that protect them  from infection by viruses,

Amebocytes form gels around these invaders

to prevent them from spreading infections.

All animals have protective  immune systems.

But horseshoe crab amebocytes are exceptionally sensitive

Endotoxins are molecules from the cell walls of certain bacteria,

Large amounts of them are released when bacterial cells die,

and they can make us sick if they enter the blood stream.

Many of the medicines and medical devices we rely on can become contaminated,

so we have to test them before they touch our blood.

We do have tests called Gram stains that detect bacteria,

which can be there even when bacteria aren't present.

produced from harvested  horseshoe crab blood

They add LAL to a medicine sample, and if gels form,

that millions of people who've never seen a horseshoe crab

If you've ever had an injection, that probably includes you.

How did horseshoe crabs end up with such special blood?

the horseshoe crab has an open circulatory system.

This means their blood isn't contained in blood vessels, like ours.

Instead, horseshoe crab blood flows freely through the body cavity

and comes in direct contact with tissues.

If bacteria enters their blood, it can quickly spread over a large area.

with the horseshoe crab's bacteria-filled  ocean and shoreline habitats,

and it's easy to see why they need such a sensitive immune response.

Horseshoe crabs survived  mass extinction events

that wiped out over 90% of life on Earth and killed off the dinosaurs,

And the biggest disruptions they've faced in millions of years come from us.

Studies have shown that up to 15% of horseshoe crabs

die in the process of having their blood harvested.

And recent research suggests this number may be even higher.

Researchers have also observed fewer females returning to spawn

Our impact on horseshoe crabs extends beyond the biomedical industry, too.

Coastal development  destroys spawning sites,

and horseshoe crabs are also killed for fishing bait.

There's ample evidence that their populations are shrinking.

to synthesize horseshoe crab  blood in the lab.

For now, we're unlikely to stop our beach trips,

but hopefully, a synthetic alternative will someday eliminate our reliance

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【TED-Ed】為什麼要採集鱟血？- 伊麗莎白-考克斯 (【TED-Ed】Why do we harvest horseshoe crab blood? - Elizabeth Cox)

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immune

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vulnerability