In his article, I take a look at horseshoe crabs, the challenges they face, and our interdependency with these animals. It contains an introduction into the species and its endangerment, an interview with Dr CHEUNG Siu Gin, a horseshoe crab researcher of The City University of Hong Kong, and a concluding outline of ways you can support horseshoe crabs.

Horseshoe crabs are benthic animals, meaning they live on the ocean floor. Humans encounter horseshoe crabs mainly on sandy shores, in mangroves, on muddy bottoms and in other intertidal zones. There are several subspecies with varying diets, consisting typically of small invertebrates such as worms. They congregate in large numbers on the shore during spawning season. Following their first to second moulting, they enter the ocean and inhabit progressively deeper waters as they mature.

Horseshoe crabs, members of the marine chelicerates family, have been around since the Ordovician Period (485.4 to 443.8 million years ago) [1], which means they have been present on Earth since before the dinosaurs and, accordingly, have survived multiple global extinction events. Whether or not they will survive our environmental impact, however, is unsure. This is not only due to our pollution and destruction of wildlife habitats in general, but also because horseshoe crabs are overfished as a culinary specialty and as a biomedical resource. Both these threats mainly target female horseshoe crabs, which has particularly negative effects on their population dynamics.

In some parts of the world, horseshoe crabs are considered a novelty delicacy and some people believe that their consumption can cure ailments. They do not, however, offer any particular nutritional value, and some subspecies are even poisonous. Thailand and China in particular are large culinary consumers of horseshoe crabs. In some provinces of Mainland China, the harvesting of horseshoe crabs is regulated. These regulations, however, are not always enforced effectively.

A greater threat to horseshoe crabs stems from the biomedical use of their unique, blue-coloured blood. It is the only currently-approved source of Limulus Amoebocyte Lysate (LAL), a reagent sensitive to the liposaccharide toxins produced by Gram-negative bacteria, which are responsible for 80% of cases of life-threatening sepsis in humans. For this reason, medical manufacturers use horseshoe crab blood to assure that their products – vaccines in particular – do not contain liposaccharide toxins. [2]

The harvesting of horseshoe crabs for pharmaceutical purposes is especially common in the US, where they are caught during mating season, and then “milked”, typically of one third to half of their blood by puncturing their hearts. The mortality rate resulting from this procedure is 15% to 30% [3][4], which accounts for the killing of several tens of thousands of horseshoe crabs every year. Harvesting usually takes place during mating season and it targets females, which are larger than males. As a consequence, crabs that are set free after milking are disoriented and exhausted and lack the desire to mate. The practice of biomedical bleeding also takes place in Asia, where it mostly results in the horseshoe crabs being killed afterwards.

There is a synthetic alternative to horseshoe crab blood on the market, the so-called rFC test. It can be produced sustainably and in far greater quantities than the LAL test [5] but it is not FDA-approved. Therefore, it cannot replace LAL tests based on horseshoe crab blood in the US and in other countries that recognise FDA approval. Recently, there is much concern about this in the animal rights community due to the great demand for Covid-19 vaccines, and the related need for LAL tests. [6][7]

I conducted the following interview with international horseshoe crab expert Dr. CHEUNG Siu Gin in June 2020 in his lab at The City University of Hong Kong.

Q: How does commercial horseshoe crab harvest work in Hong Kong? Are they targeted directly or mostly bycatch?”
A: Well, it depends on the policy. Of course, trawling is now banned in Hong Kong which means there is less bycatch, but you can still find horseshoe crabs on the market. According to some fishermen, these are caught in Mainland-Chinese waters instead of Hong Kong waters. In the US though, fisheries are allowed to specifically target horseshoe crabs while trawling/fishing because horseshoe crabs are used for medical purposes. The local fishermen on the US Eastern coast, however, also catch horseshoe crabs and chop them into pieces for bait. They then use this bait to catch eels and conches, which are exported to Asia. There is a limiting quota for every state to regulate how many are used for bait or medical purposes. This demand for medical use of horseshoe crabs will only increase because more and more countries are getting better and better health care. Of course, the endangerment to Asian species is even worse because of a lack of enforcement by the government to protect these animals.

Q: Why are horseshoe crabs caught in Hong Kong?
A: We surveyed some of the markets and found out that most Hong Kong people do not eat horseshoe crabs. The reason most fishermen put horseshoe crabs on display is for tourists. The main reason people in Hong Kong buy and catch horseshoe crabs is because of the Buddhist tradition of setting things free for good karma. Buddhists buy the horseshoe crabs from the fishermen and set them free on random shores. Oftentimes this means that the pollution from boats and other waste in these locations are so bad that they kill the horseshoe crab, so the point of setting them free again is defeated.

 
Q: Are there any government regulations that protect horseshoe crabs, or are there any petitions one could sign to put pressure on governments and/or organisations?
A: Well, there are four species of horseshoe crab world-wide, with only the Chinese horseshoe crab being on the list of endangered species. This is because the populations of horseshoe crab are hard to observe, so even with the horseshoe crab populations declining rapidly, they aren’t listed as being endangered because of insufficient data. This means it is hard to fight for protection of these species. At the moment, the only thing Hong Kong is doing is to consider putting three beaches under protection as sanctuaries.

 
Q: Is there a lot of demand in Mainland China for horseshoe crabs?
A: Yes, actually. They are consumed a lot. In this case it is not for Chinese medicine, but actual food. This is because the more exotic and rarer an animal is, the higher the demand in the Chinese market. In addition, the demand for vaccine test kits is also very high in China.

 
Q: Is there a way to farm horseshoe crabs?
A: Well, horseshoe crabs take a long time to grow and mature into a size where it would be possible to milk them. It usually takes more than ten years for them to reach that stage. I do not think there is any laboratory in the world that would have the time or resources to farm these animals for such a long period of time. Horseshoe crab farms could not be operated industrially with our current means because it would not be profitable. There is an idea right now that they want to catch the mature adults from the sea, and just milk them indefinitely, without ever releasing them. I personally think it is possible to hold them for a number of years, if you feed them regularly, and let them live in good conditions, but if you want a good supply of blood you have to hold many horseshoe crabs. This idea wouldn’t work with just a few crabs. There are also other problems to this idea, for example that horseshoe crabs get infections and parasites very easily.
 
Q: Is there anything people can do even if they are not in Hong Kong to spread awareness about the horseshoe crab?
A: Well, there are a number of things. You could participate in the World Horseshoe crab Day for example, which is held on June 20th, by posting about horseshoe crabs on the internet, or by joining online meetings. The best thing you can do is educate yourself, and learn more.

Q: What would you say is the demographic that consumes horseshoe crabs the most?
A: Mostly people in Asian countries such as Thailand and China. Many other countries that have local populations of horseshoe crab such as Malaysia, Vietnam and Indonesia harvest their horseshoe crabs and export them to Thailand and China where they are eaten in large amounts. They especially target females during breeding season because of their eggs, which are considered delicious.

Q: What are things we need to do in the future?
A: We need more laws to protect horseshoe crabs and we need to enforce them better. We need to be more careful with the construction of new infrastructure such as coastal development that may interfere with their habitats, and we should push for the acceptance and development of alternative vaccine test kits. We should also inform people about the importance of protecting these species of wildlife.

To help protect horseshoe crabs and other species, there are various things that we can do. We need to be aware of the impact of our choices and our actions and stay informed about environmental issues affecting both our local surroundings as well as our planet in general. Here are some of the things you can do:

Research current laws regulating the use of rFC tests, and organise or join related petitions. Tell your friends and family members about horseshoe crabs and the dangers they face. You can also organise or join beach clean ups and be more environmentally friendly in your daily life, for example by using a reusable cotton bag and by avoiding single-use plastic. Participate in the World Horseshoe Crab Day on June 20th and post about it on social media. Please also remember that how you eat can change the world. Most importantly, do not stop learning because the more you learn, the more responsibly you will act and the less damage you will cause. The more you learn, the more you can help. The more you learn, the more you can contribute to the animal rights discourse and activism. 

Acknowledgements:

Thank you very much to Dr. CHEUNG Siu Gin, for his great support towards this project and especially for showing me the baby horseshoe crabs in the lab at The City University of Hong Kong.

References:

[1] britannica.com/animal/horseshoe-crab

[2] genengnews.com/news/new-method-for-sustainable-harvesting-of-horseshoe- crabs-for-limulus-amebocyte-lysate

[3] tandfonline.com/doi/abs/10.1080/10236241003786873

[4] journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2006607

[5] usp.org/news/rfc-horseshoe-crabs-statement

[6] euronews.com/living/2020/07/20/crab-blood-used-to-make-covid-19-vaccine-outrages-animal-rights-activists

[7] nhm.ac.uk/discover/horseshoe-crab-blood-miracle-vaccine-ingredient.html