What are hundreds of thousands of horseshoe crabs exploited for?

2024 Author: Seth Attwood | [email protected]. Last modified: 2023-12-16 15:55

Are we ready to at least sympathize with them, or will we soon finally destroy animals, the history of which goes back hundreds of millions of years?

Megan Owins fishes a horseshoe crab from the water and folds its hard shell almost in half, revealing a soft white membrane. He puts a needle under it and takes some blood: "See how blue she is?" - she shows the syringe to the light. Indeed, blue: the liquid shines with a deep azure. After finishing the demonstration, Megan squeezes the blood back into the container.

I almost catch my breath: "You just threw away a few thousand dollars!" - and this is not an exaggeration. The cost of blood (more precisely, hemolymph) of these arthropods on the American market reaches 15 thousand dollars per quart (0.9 liters). This blue liquid is widely used to detect potentially harmful bacteria in pharmaceuticals, medical devices and implants. Whether it is an insulin solution, an artificial knee or a surgical scalpel, the hemolymph of horseshoe crabs allows an infectious agent to be detected almost instantly.

This provides it with a large and unquenchable market demand. Every year, about 575 thousand arthropods are caught from the ocean for its collection. This number cannot grow indefinitely, and among specialists, the voices of those who are concerned with such barbaric exploitation of animals, which are already threatened with extinction, are louder and louder. Usually, about a third of the blood is pumped out of them, after which they are released into the water to recover. The approach is considered humane, although in reality no one knows how many animals survive after such a forced donation.

This problem is being addressed by Megan Owins, along with animal physiology specialists Vin Watson of the University of New Hampshire and Christopher Chebot of the University of Plymouth. They are trying to assess the challenges and difficulties that come with collecting blood for horseshoe crabs. The experiment, which was carried out by three scientists, replicates the "production process" as closely as possible.

28 horseshoe crabs caught in the Atlantic, near the mouth of the Piscataca River in New Hampshire, were placed in containers and "forgotten" in the sun, shaken for a couple of hours in a car and left overnight, then they took blood and left in containers again until morning - so, as workers of enterprises do, collecting hemolymph on an industrial scale. However, before releasing the unfortunate animals into the wild, biologists fixed acoustic beacons on their shells.

Acknowledgments

Bacteria are divided into two large groups according to the method that the Danish microbiologist Hans Christian Gram proposed at the end of the 19th century. The main difference between them lies in the structure of the cell wall. Gram-negative bacteria (for example, E. coli) do not stain according to Gram: their cell wall has an additional protective membrane that contains complex lipopolysaccharides and does not allow aniline dyes to pass inside. But the walls of gram-positive bacteria (for example, staphylococci) are simpler. They do not have a membrane, the dye penetrates into the cell wall and "gets stuck" in it. When stained according to Gram, such cells acquire a purple color.

When the gram-negative cell dies, the lipopolysaccharides are released, turning into endotoxins that are hazardous to health. These compounds are indestructible, almost like zombies. They can even withstand extreme heat and other harsh conditions under which the production and sterilization of medical products and instruments takes place. Once in the body, endotoxins are able to launch the immune system at full capacity, causing hyperactivation up to septic shock. Therefore, it is so important to find them in advance.

Here the hemolymph of the horseshoe crabs Limulus comes into play: the amoebocyte lysate (Limulus amebocyte lysate, LAL) obtained from it coagulates at the slightest contact with endotoxins. And while many market participants believe that $ 15,000 per liter is too much, the high cost of LAL can be described as a form of appreciation for the value it plays in saving lives. In the words of one conservationist, "every person, every child, every pet on our planet - everyone who resorted to medical help owes one way or another to horseshoe crabs."

Hidden threat

With animals, land is easier: it is often possible to assess the impact of humans on them with the naked eye. How the inhabitants of the seas feel, we often do not see, or even do not want to know at all. We dump garbage into the sea, we also pour wastewater there: what happens at a depth remains at a depth. It is the same with horseshoe crabs. No one knows how traumatic it is for them to take blood, whether the animals are capable of undergoing several such procedures, or at least one. However, there are reasons for concern.

The International Union for Conservation of Nature, which maintains a list of threatened species of animals and plants, in 2012 organized a special subcommittee to assess the state of horseshoe crabs. As a result of his work, these animals were found to be in a vulnerable position. Compared to the previous 1996 estimate, they have taken a step towards extinction. The next stop is “in jeopardy,” and the subcommittee's report pointed that out. According to the forecast of scientists, by the middle of the century the number of horseshoe crabs will fall by a third.

And this applies not only to the animals of the American coast. Common in the Asian Pacific Ocean, the horseshoe crabs Tachypleus are also widely fished for the production of amoebocyte lysate (TAL). Due to the massive catch, they are already disappearing in the waters of China, Japan, Taiwan, Singapore. Experts fear that if Tachypleus disappears altogether, lysate producers will turn to horseshoe crabs living in other regions of the ocean, carrying death to these populations.

Data catch

Every 45 seconds, the beacons installed by Megan Owins give out a series of acoustic signals that the sensor can notice from a distance of 300-400 m. Each signal allows you to identify a specific individual, determine its depth and activity during the previous 45 seconds. Once a week or two Owins and Watson venture out into the bay, taking recorded readings and moving the sensors to follow the slow migrations of horseshoe crabs.

In the center of the bay, the depth reaches 20 m, but the animals try to stay closer to shallow water. After a few minutes of swimming, scientists pull out a cable overgrown with algae, on which one of the sensors is fixed. Megan connects a laptop to it via Bluetooth and starts downloading data. Since the last visit, the device has recorded about 19 thousand signals. The device closes and goes back into the water: the scientists only need information. But this cannot be said about fishermen.

Quotas for the production of horseshoe crabs off the Atlantic coast of the United States are allocated by the Marine Fisheries Commission (ASMFC). However, her strict guidelines only apply to animals, which are then butchered and used to catch eels for food. Biomedical enterprises can harvest as much as they want, and the horseshoe crabs catch for these purposes is growing rapidly - from 130 thousand in 1989 to 483 thousand in 2017. In addition, LAL producers also receive the blood of arthropods, which are used to feed eels: the number of such animals in 2017 was, according to various estimates, another 40.6 to 95.2 thousand.

The ASMFC Fisheries Commission is not authorized to regulate such mining. This area has a direct impact on public health and requires the involvement of the powerful Food and Drug Administration (FDA) to intervene. However, LAL manufacturers are doing their best to prevent this from happening.

No control

“We managed to free ourselves from quotas,” admits Thomas Nowitzki, former head of LAL manufacturing company ACC. - We lobbied for our position in ASMFC, convincing them that no harm is done to horseshoe crabs. We are bringing them back, we are extremely important to medicine, so leave us alone with your regulation. However, even very moderate ASMFC recommendations are not always followed, and the committee itself does not have enough resources to monitor their implementation.

The ASMFC admits that after blood collection and return to the sea, a certain number - no more than 15% - of the animals die. However, in recent years, more and more data have accumulated that this figure is greatly underestimated. According to new data, the mortality rate of horseshoe crabs after taking hemolymph is at least 29%. Bloodless animals are weakened, less active and less oriented, and females produce on average half of eggs. "Industry representatives, of course, chorus, say that the relevant experiments were carried out in laboratories and their results may not apply to animals in the natural environment," says Nowitzki, "but these arguments do not hold up to scrutiny."

Synthetic alternatives to LAL using recombinant factor C (rFC) have been known for over 15 years, but have not yet become widespread. The same FDA still considers LAL tests the "gold standard" for the detection of endotoxins. Therefore, manufacturers of medical equipment and pharmaceuticals try to rely on them so as not to have unnecessary problems when obtaining approval from an influential agency. Eli Lilly's Emgality (galanezumab) migraine drug is still the only remedy to receive FDA approval using rFC tests in place of LAL.

According to Kevin Williams of bioMerieux, a company that promotes rFC tests, the problem is that LAL manufacturers are actively trying to sabotage new methods by convincing officials and the public that they are not effective. “I've seen whole streaks of anti-advertising rFC claiming the technology isn't working,” he says. - But the data show the opposite. They are simply ignored."

Stress factors

Losing a significant amount of blood is not easy for any animal. But the tests are not limited to this: catching and transporting also greatly stress horseshoe crabs. Vin Watson notes that these arthropods can survive in the air longer than fish or crabs, but this ability plays a cruel joke with them. The catch volumes are so large that it is not always possible to place all horseshoe crabs in containers filled with water, and they are simply thrown on the deck: they will survive.

But exposure to air in itself reduces the content of hemocyanin in the hemolymph of animals, an analogue of the oxygen-carrying hemoglobin of our blood. Its replenishment is more difficult and takes longer than recovery from direct loss of a noticeable amount of blood. “Imagine that every time you milk a cow, it takes a month for her to recover,” explains Watson.

Finally, it is worth remembering about the strict adaptation of horseshoe crabs to successive ebb and flow, followed by animals moving in search of safe shelter and food. Even in the laboratory, they exhibit a urge to move every 12.4 hours, and the loss of this natural rhythm for the horseshoe crab can be extremely difficult. All these discoveries should be taken into account when developing new, already more stringent requirements for the extraction of hemolymph. Unfortunately, so far LAL manufacturers are not even inclined to listen to the arguments of biologists.

Weak signal

Several dozen sensors are installed in the bay near the mouth of the Piskataka River. Horseshoe crabs move underwater and can travel several kilometers in a day, so scientists regularly carry their tools after them. In some still poorly understood way, the animals navigate the bay perfectly. By spring, they move to shallow water, where they collect benthic mollusks and worms.

The same individuals regularly return to the same places, where they again become the prey of the same fishermen. Shouldn't they be releasing them somewhere else? Or so we will further disrupt the natural, habitual life of marine animals? And is it possible to hunt in winter, when horseshoe crabs go to the depths, barely surviving the months of cold weather? So far below the surface, the sensors no longer distinguish acoustic signals. After catching one of them, Owins listens for faint beeping sounds. The signal reminds of warnings about the battery ready to go flat.