[Narrator] For hundreds of millions of years, horseshoe crabs have been crawling around
the ocean floor. Coming ashore to mate in the spring, these living fossils are synched
to the rhythms of the tides.
Today, migratory shorebirds, sea turtles, and other ocean animals
depend on horseshoe crabs for food.
They are a keystone species at the heart of many coastal ecosystems
in Asia, and along the east coast of North America.
Despite having survived ice ages and asteroids, these long-lived
animals might finally be on their way out.
And if they disappear, the consequences could be lethal. Not just for the many
species that depend on them, but for humans too.
The horseshoe crab has evolved a powerful mechanism for protecting itself from infection.
When bacteria sneaks past a horseshoe crab's shell, cells in the crab's blood
send out a chemical that clots around the invader, stopping it in its tracks.
And it's this property that makes horseshoe crab blood invaluable
to the medical industry, and to just about every human alive today.
[Win Watson] It's used by the biomedical industry to test things that go into
your body, whether it be blood or heart valves, to make sure that
they're not contaminated.
[Narrator] It's currently the only FDA approved method that insures vaccines,
various drugs, and medical devices are free of toxic bacteria that
might otherwise harm or kill us.
[Win Watson] And as a result, thousands of horseshoe crabs are bled every year to
get this, and then they're released.
[Narrator] It's estimated that over half a million crabs are bled every year in the
United States. Each one contributing about a third of their blood, before being
returned to the ocean.
This catch-and-release system supposedly leads to few crab deaths, so while
American fishermen who harvest horseshoe crabs as bait have to limit
their catch, the medical industry hasn't been subject to quotas.
[Win Watson] What we don't know is whether there's some sublethal effects that may cause
mortality later on, or sublethal effects that may affect their behavior in such a
way as to alter their population magnitude.
[Narrator] In recent years, people have noticed that horseshoe crab numbers are
dropping. In fact, the Atlantic horseshoe crab is currently listed as vulnerable by
the International Union for Conservation of Nature. One step down from endangered.
And the three other species of horseshoe crabs have started to disappear from many
of their usual haunts in Asia. Global warming and habitat loss are probably at play here,
but there's a growing concern that the practice of bleeding the crabs might also
be a factor in their declining numbers.
While the race is on to create an FDA approved synthetic alternative, some
scientists are exploring how the bleeding process might be stressing
horseshoe crab populations.
[Meghan Owings] So we are looking at the industry standard procedures and trying to
replicate them as close as we can, and then returning these animals into their
natural environment with transmitters to see if there's any impacts to these
horseshoe crabs and then we're looking at it in the laboratory to try and isolate
which variables they are.
[Win Watson] Our goal is to make sure that this is a sustainable process, so that for
years to come we can use this valuable product without harming the population.
[Meghan Owings] So throughout the biomedical bleeding process, horseshoe
crabs are exposed to three different big variables.
[Win Watson] What we call stressors. They're out of water for a while,
they're at high temperatures, and they remove some blood. And so we're trying to
examine each of these stressors independently.
[Meghan Owings] We went and collected about 28 horseshoe crabs through
scuba diving in Great Bay Estuary in New Hampshire.
[Win Watson] Half of them we bled the way the industry does it and half of them we
did not. They were the controls.
[Meghan Owings] And then the next day we actually put on our ultrasonic transmitters
and we released them back into the bay, where we can keep track of their behavior.
[Narrator] Dr Watson and Meghan Owings have identified a few key findings. They saw a 14%
death rate among their horseshoe crabs. A rate similar to earlier studies. When it comes to
the three main stressors, they found that it was the combination of two or three that
had the biggest impact on the surviving crabs' activity levels. And though the
effects were more pronounced in the lab, in the field, they were most pronounced in
females, and within the first month after release.
[Win Watson] We also discovered early in the season, their hemocyanin levels seemed
to be very low, because they really haven't eaten all winter long. Hemocyanin being
the respiratory pigment they use for transporting oxygen.
[Narrator] Lower hemocyanin levels mean the crabs are at a more fragile state.
[Win Watson] And so if you were to capture these animals, and bleed them in the
spring which is when it's most convenient because that's when they're breeding, it
might have a more negative impact on them, than later in the summer. Because during
the summer they're feeding and making more hemocyanin.
[Meghan Owings] So we are starting a new experiment and seeing how feeding them
different dietary supplements might be able to boost their hemocyanin concentrations.
[Narrator] Dr Watson and Meghan Owings also plan on studying the crabs recovery
of their blood volume over time using radiography to peer inside the animals.
Ultimately, they hope to share their data with bleeding facilities to help them
work in a more sustainable way.
[Win Watson] There's something that makes you want to preserve these animals,
because they've been around so long. I'd hate to see them disappear after
being here for 450 million years.