Article\Hainan Weekly special contributor Liu Yi
Like many marine creatures, my knowledge of hòu began at the dinner table as a child. Fujian people have a history of eating horseshoe crab (Chinese horseshoe crab, also known as Chinese horseshoe crab, Oriental horseshoe crab, three-spined horseshoe crab). Probably by the time I was in middle school, the resources of Chinese horseshoe crab were getting less and less, and it had become a key protected wild animal in Fujian Province, and it was illegal to catch, sell and eat Chinese horseshoe crab, and there was no trace of chinese horseshoe crab on the brine stall.
A Chinese horseshoe crab in Danzhou Bay. Photo by Chen Zhengping
Strange-looking "sea monster"
Horseshoe crab, because of its slightly horseshoe shape, commonly known in English as horseshoe crab, in Chinese folk often known as "husband and wife fish", in fact, the horseshoe crab is neither a crab nor a fish, belonging to the arthropod phylamentosaurs orthophea, there are 4 species in existence, including the American horseshoe distributed on the east coast of North America, distributed in the Asian coast of the Chinese horseshoe, southern horseshoe and round-tailed scorpion horseshoe (also known as round-tailed horseshoe). Among them, there are two kinds of Chinese horseshoe crab and round-tailed scorpion crab in China.
The horseshoe crab looks strange, similar to a large gourd with vines, so that many people mistakenly recognize its head and tail upside down, and it is also called "sea monster".
Horseshoe crabs have a typical three-segment structure, divided into cephalothorax (covering the meniscus-shaped cephalothorax), abdomen (covering hexagonal nails), and tail (swordtail). The front end of the cephalothorax has a pair of small eyes that can only sense light, while on both sides of it there is a pair of symmetrical large compound eyes, with the function of imaging, which can strengthen the contrast of the images seen, people have studied the principle of the compound eye of the horseshoe, and applied it to the research and development of some televisions and cameras. In addition to these 4 eyes, the horseshoe also has 6 eyes; there are 6 pairs of appendages under the cephalothorax, the first pair of which becomes a claw, which is the "tableware" for eating, which is used to catch food, and the other five pairs are walking feet, and in the center of these appendages is its mouth, like the face-hugging insect in the series of science fiction movies "Alien", which is also the origin of the name of the "limb mouth" to which the horseshoe belongs; there are 6 pairs of marginal spines on both sides of the dorsal carapace, the main function is defense; the ventral surface of the dorsal carapace is like a page of 5 pairs of book gills, which also assist in swimming through the fan breathing of the book gills. This is quite similar to the early popular blinds with flattened and cascading blades, which are flexible up and down, so the Xiamen people called the blinds "Hundred Pages". The tail is a long sharp sword tail with a triangular cross-section, and its main function is defense, but when the horseshoe rolls over and falls on its back, it must rely on the support of the sword tail to turn over.
In addition, there is often a common-sense mistake in thinking that the blood of the horseshoe crab is "blue". In fact, the blood of the horseshoe crab is colorless, because it contains copper ions, and it will only appear blue after encountering oxygen.
A "living fossil" that travels through 500 million years
Wenchang Huiwen Wetland two round-tailed scorpion horseshoe crabs hugging each other. Photo by Liu Yi
Horseshoe crabs are often referred to as "living fossils".
The earliest known fossils of E. bream were unearthed in Morocco, about 485 million years ago, in the early Ordovician fezouata biota. In 2008, paleontologists found a 445 million-year-old fossil of the late Ordovician "moon shield horseshoe crab" in Canada, North America, which already had a three-stage body structure like modern horseshoe crabs. Since then, the fossils of the horseshoe crab have been distributed until the Mesozoic Jurassic Period, about 200 million years ago, and the appearance of the horseshoe crab has been basically consistent with the living species.
In the early stages of evolution, suitable habitats and ecological niches have been found, and the corresponding morphologies and physiological functions have been evolved, during which the evolutionary process has been continuous, but the early evolutionary results have hardly been changed, and they have been maintained for 500 million years, which is a very successful case of species evolution. From the beginning of the species, the horseshoe has evolved a three-stage body structure combination (efficient breathing, movement and feeding organs) and adaptable physiological functions (to cope with low oxygen and large temperature spans), thus once and for all.
The geological record shows that the horseshoe crab has always been a creature of shallow waters (estuaries, shallow seas and continental shelves), and the evolution has been more than half successful by choosing the right habitat and ecological niche. Among them, the estuary is the breeding area of the horseshoe, the shallow waters (shallow sea) are the living areas of the great horseshoe, and the shallow sea of the continental shelf provides a channel for the distribution and spread of the horseshoe crab in different estuaries.
China's Beibu Gulf coast is one of the most important distribution areas of the horseshoe crab, from the Beilun River mouth in Guangxi to the Leizhou Peninsula in Guangdong to the west coast of Hainan, you can see the traces of Chinese horseshoe crab and round-tailed scorpion horseshoe crab. Where did the earliest horseshoe crabs on Hainan Island come from? It is clear that it cannot be a separate species evolution event, nor is it likely that Hainan Island migrated after it separated from the mainland, because although the horseshoe crab has a certain swimming ability, it seems impossible to cross the long and deep Qiongzhou Strait. The only possibility is that before Hainan Island separated from the Leizhou Peninsula (at least 2.5 million years ago), the horseshoe crab had spread to Hainan through a connected continental shelf passage. The distribution of the horseshoe crab also fully confirms the history of Hainan Island and the mainland.
Hainan's horseshoe crab resources
The ventral surface of the round-tailed scorpionfish. Photo by Huang Haiyan
Due to the needs of mangrove macrobenthic research, I have traveled almost all over the mangrove distribution areas of Hainan in the past ten years, and have also encountered horseshoe crabs or their carcasses in Haikou Dongzhai Port, Wenchang Huiwen, and Danzhou Xinying Wetland many times. Once, while conducting an investigation in the mangroves at high tide, a pair of round-tailed scorpion horseshoe crabs swam by my feet, and I was so excited that I almost threw the camera into the sea.
Ancient books often have records of Hainan Island related to horseshoe crabs. For example, the Qing Dynasty Daoguang "Qiongzhou Fuzhi Tuchanan" wrote: "The horseshoe crab, shaped like a panel, has eyes on the back and mouth under the abdomen; its blood is blue, the skin shell is very strong, the male is small and the female is large, and the female is often negative and male." However, it is difficult to fully answer "where Hainan's horseshoe crab is distributed, how much is it, and what problems it faces", and the previous literature does not have more comprehensive data.
Fortunately, from 2020 onwards, with the support of the competent units of various protected areas in Hainan, the Haikou Haolan Wetland Research Institute (hereinafter referred to as "Haikou Haoyu") has jointly carried out a census of the young crab resources on Hainan Island, and I was also fortunate to participate in the first round of investigation of Danzhou Xinying Bay. According to the survey report released by Haoyu, the round-tailed scorpion crab is mainly distributed in Huiwen Wetland and Chengmai Bay in the east of Hainan Island, and has a sporadic distribution in Dongzhai Port and Xinying Bay; Chinese horseshoe crab is mainly distributed in Danzhou Xinying Bay and Xinying Bay, and there is a sporadic distribution in Chengmai Bay and Dongzhai Port, of which the Chinese horseshoe crab in Danzhou Xinying Bay is superior to several other distribution areas in terms of number, habitat density and distribution range, and is the most important distribution area of Chinese horseshoe crab in Hainan, which is of great conservation value.
Horseshoe crabs in need of protection
Illegal fishing gear such as ground cages is an insurmountable gap in Hainan, and a joint survey organized by Haoyu has been found at various survey points in Hainan. In addition, the pollution discharge of breeding ponds, the invasion of alien species, illegal fishing and consumption are also the reasons for the decline of Hainan crab resources.
At present, habitat destruction and overfishing are the two major reasons for the significant decline of horseshoe crab resources, including coastal zone reclamation, coastal infrastructure construction, sea sand extraction, mariculture, illegal fishing and overuse. Among them, reclamation projects and coastal infrastructure construction have caused direct loss of habitat for horseshoe crabs, and sea sand extraction is considered to be an important cause of the degradation of spawning habitats of horseshoe crabs along the southeast coast of China.
Take the Chinese horseshoe crab, for example. They were once widely distributed along the southeast coast of China, of which the Beibu Gulf is the most ideal habitat for Chinese horseshoe crabs. In the 1980s, many domestic and foreign experts saw flocks of Chinese horseshoe crabs spawning on the North Sea coastal mudflats in the Beibu Gulf, and the scene was spectacular. Chinese horseshoe crab has also flourished on the west coast of Taiwan Island, Penghu Islands and Kinmen Island in China, which can also be reflected in some folk sayings and vocabulary. There is a saying in Kinmen: "Water head crab, ancient gang stink." It refers to the fact that the water head of Kinmen is rich in horseshoe crabs, so much so that the smell drifts to Gugang, which is 3 kilometers away.
However, in less than 30 years, China's horseshoe crab resources have undergone tremendous changes. A set of survey data shows that the population of Chinese horseshoe crab in the Beibu Gulf area has declined by more than 90% in the past 20 years.
In recent years, in the face of the increasingly serious destruction and degradation of horseshoe crab resources, the international community, government departments, protected area management agencies, scientific research institutions, social welfare organizations, etc. are all working hard to reverse this situation. In 2012, the World Conservation Congress adopted a proposal to protect three species of horseshoe crab in the Asia-Pacific region; in March 2019, the International Union for Conservation of Nature (IUCN) listed Chinese horseshoe crab as an endangered species; in June 2019, the Fourth International Symposium on The Science and Conservation of The International Horseshoe Crab published the Declaration on the Conservation of the Beibu Bay of the Global Horseshoe Crab, which designated June 20 of each year as the International Crab Conservation Day, and in 2020 the iucn Expert Group launched the "Asia-Pacific Regional Horseshoe Observatory Network Program", which was piloted in China in 2021. Danzhou, Hainan is also included in one of the 17 horseshoe crab observation sites; in February 2021, the adjusted List of Wild Animals under National Key Protection was officially announced, and the Chinese horseshoe crab and round-tailed scorpion horseshoe crab were upgraded to national second-level protected animals.
Just as the raw materials of turtle shells in turtle paste can be replaced, the raw materials of horseshoe crabs in the vinegar are not necessary, and the capture, sale and consumption of national second-level protected animals will also bring prison. It is hoped that the public can consciously protect the horseshoe crabs and let them freely and happily write a string of "Chuan" characters on the beach, which will continue endlessly.
May the tides not stop, the "river" will not stop, the ends of the earth, and the horseshoe crabs will have periods.
Original title: The end of the world, the horseshoe crab will have a period