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  • 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,

  • take them to labs,

  • harvest their cerulean blood,

  • then return them to the sea.

  • 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

  • on her annual visit to the beach.

  • When the eggs hatch,

  • the juvenile horseshoe crabs often stay near shore,

  • periodically shedding their shells as they grow.

  • Once they leave these shallow waters,

  • 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,

  • fungi,

  • and bacteria.

  • Amebocytes form gels around these invaders

  • to prevent them from spreading infections.

  • This isn't unusual.

  • All animals have protective immune systems.

  • But horseshoe crab amebocytes are exceptionally sensitive

  • to bacterial endotoxins.

  • Endotoxins are molecules from the cell walls of certain bacteria,

  • including E. coli.

  • 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,

  • but they can't recognize endotoxins

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

  • So scientists use an extract called LAL

  • produced from harvested horseshoe crab blood

  • to test for endotoxins.

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

  • bacterial endotoxins are present.

  • Today, the LAL test is used so widely

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

  • have been protected by their blood.

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

  • How did horseshoe crabs end up with such special blood?

  • Like other invertebrates,

  • 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.

  • Pair this vulnerability

  • 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,

  • but they're not invincible.

  • 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

  • at some of the most harvested areas.

  • 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.

  • Some researchers have started working

  • 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

  • on the blood of these ancient creatures.

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

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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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    osmend 發佈於 2021 年 01 月 14 日
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