The number of Chinese horseshoe crabs has plummeted over the past 30 years, in large part because of demand for the animal’s copper-based blood. This is used to make the most sensitive indicator of bacteria ever discovered.

The horseshoe crab is a 450-million-year-old creature that predates the dinosaurs. In March this year, the International Union for Conservation of Nature (IUCN) listed the Chinese horseshoe crab (also known as the tri-spine horseshoe) as endangered. But few people in China are aware of the plight of the animal, and experts are calling for stronger measures to protect it.

Precious blue blood

The Chinese horseshoe is found across Southeast Asia, but 95% of its numbers are concentrated in China’s waters, especially along the coast of the southern region of Guangxi. Two of its relatives, the mangrove horseshoe and the Indo-Pacific horseshoe, are also native to Asia with some presence in China. The fourth species, the American horseshoe, is found in the Gulf of Mexico and along North America’s Atlantic coast. All have a similar appearance with a hard shell covering most of the body and a long sword-like tail. Despite the name, they are more closely related to spiders and scorpions than crabs.

In the 1950s, US scientists discovered that the blood of the horseshoe clots when it comes into contact with bacterial endotoxins. This led to the development of LAL, a processed extract of the blood used to test for bacterial contaminants during the manufacture of anything that might enter the human body, from surgical equipment to vaccinations.

Demand for LAL and the lack of better alternatives make it one of the most expensive liquids in the world, with an oft-cited price tag of US$60,000 per gallon (4.55 litres).

Increasing demand in China

With its own native species to exploit, China’s developing biomedical industry started to produce its own version of LAL in the 1980s, during the country’s reform and opening up period. The largest of the four species, the Chinese horseshoe is easier to work with and provides more blood than its American cousin.

Increasing demand from the biomedical industry has seen a corresponding decline in Chinese horseshoe numbers. There were 600,000-700,000 breeding pairs on the Guangxi coast prior to the 1990s, according to a 2015 paper. By 2010, there were only 300,000.

Chen Ruifang of the Guangxi Ocean Institute says current numbers are likely to be significantly lower. Based on its research, the institute estimates the current population of Chinese horseshoes in Guangxi to be only 40,000 breeding pairs.

