Source | SELFtalks
"In the future, we hope that through our efforts, we will gradually increase and restore the resources of the tropical sea cucumber population in the South China Sea, improve the marine environment through sea cucumbers, and build a beautiful home for marine life."
Luo Peng · Researcher, South China Sea Institute of Oceanography, Chinese Academy of Sciences
Gezhi Dao No. 59 | November 28, 2020 Guangzhou
I'm sure you're no stranger to sea cucumbers because many people have eaten them.
I first came into contact with sea cucumbers more than a decade ago, and when I first saw it, I thought it was a huge flesh worm in the sea, soft and soft, and full of flesh thorns, which looked particularly disgusting and ugly, and I did not dare to touch it.
In fact, sea cucumbers are not meat worms in the sea. From a taxonomic point of view, it belongs to the echinoderm phylum and the sea cucumber family.
Left: Map of the distribution of sea cucumber resources in the world
Right: Imitation ginseng (top) California ginseng (bottom)
| Bruckner et al., 2003
There are more than 900 species of sea cucumbers in the world, and as can be seen from the large map on the left, most of the sea cucumbers are distributed in the tropical waters of the Indian and Pacific Oceans, and only a small number of sea cucumbers are distributed in temperate waters. On the west coast of the Pacific Ocean, the species of sea cucumbers are mainly imitation ginseng, and on the east coast of the Pacific Ocean, the species of sea cucumbers are mainly California quasi-thorn ginseng.
In China, there are 140 species of sea cucumbers, the vast majority of which are distributed in the South China Sea on the mainland. There are 40 species of edible sea cucumbers in the world and 20 species on the mainland, of which 10 have high edible value. There is currently only one species of sea cucumber on the mainland– the imitation ginseng in the north that can form a large-scale aquaculture industry.
Rough thorn ginseng Flower thorn ginseng Rough sea cucumber Green thorn ginseng Black sea cucumber Jade foot sea cucumber (from left to right from top to bottom)
The above pictures are several tropical sea cucumbers commonly found in the Waters of the South China Sea.
Source | Yutube
When we study sea cucumbers, we first start with how sea cucumbers eat, which is its feeding habits. This video shows the sea cucumber eating process.
We can see that there are many flexible tentacles around the mouth of the sea cucumber, the ends of the tentacles are sticky, it can adhere to particles of fine organic matter in coral reefs and sediments, along with sand swallowed in the mouth. After food is digested, it can expel inorganic ammonia nitrogen and phosphate, which can become nutrients for algae and plants in the ocean.
Let's take a look at the body structure of the sea cucumber.
The body structure of the sea cucumber | Zhang Yu
The body structure of the sea cucumber is very simple, including two parts: the body wall and the internal organ mass. The thickness of the body wall of different species of sea cucumbers is relatively large, some are very thick, some are very thin, and its internal organs are mainly composed of stomach, intestine, anus, reproductive glands and respiratory trees.
There are two very magical places in the body structure of the sea cucumber, the first of which is its reproductive glands. The opening of its reproductive glands is located in the center of the back of the head, so the sea cucumber spawns not on the abdomen, but on the head.
The other is the breathing tree, which is its respiratory organ, but also the excretory organ, and the opening of the breathing tree is near the anus, so the sea cucumber does not breathe with its mouth, but with its anus.
When we saw this structure, we felt that the body structure of the sea cucumber was indeed a bit "against the sky" and "unscientific".
What is the way to survive the deliciousness of walking?
The sea cucumber moves slowly, the body is soft, and it does not have the armor of a crab. Crabs can also run rampant, but not sea cucumbers. In the crisis-ridden ocean, sea cucumbers can live well, and there must be its superiority.
In fact, there are very few types of natural enemies of sea cucumbers in the ocean, mainly because the body of sea cucumbers emits a special smell, and its body carries toxins. So, with these two factors, other marine animals are reluctant to go near sea cucumbers.
How does a sea cucumber escape if it encounters an enemy creature or danger? Let's introduce the three survival skills of sea cucumbers.
The first survival stunt is poisoning.
In the video, the sea cucumber is being harassed by a small fish that excretes something like noodles, which is an organ of the sea cucumber's body called the Cuvi tube.
When the sea cucumber encounters predators or dangerous situations, it can discharge the Cuvi tube, which has a special odor and toxins. Usually, it is white, and some species are red or pink. Once this noodle-like thing is discharged and encounters other animals in the ocean, it immediately becomes very sticky, able to entangle and trap the attacker. But strangely enough, the sea cucumber itself is not stuck to this white noodle-like thing.
In the process of transporting sea cucumbers, we often find a phenomenon that the sea participants spit out all their own internal organs. The feeling for us is: Is the sea cucumber too prone to motion sickness? Is it dizzy and spit it out to you?
In fact, the sea cucumber is not motion sickness, which involves its second survival stunt - defiling.
When a sea cucumber encounters predators, dangerous situations, or extremely unsuitable environments, its body contracts violently and then drains the entire visceral mass out of the anus. When an enemy creature enjoys the toxin-laden offal mass it excretes, it can take the opportunity to escape.
Many friends will have questions: will the sea cucumber die after excreting its own internal organs? The answer we give is: it won't die.
In the process of evolution for more than hundreds of millions of years, sea cucumbers have cultivated a set of magical stunts, which is "regeneration".
Figure | Okada etal, 2019
From this picture, we can see the regeneration process of the sea cucumber intestine. Under normal circumstances, it only takes 20 days to give birth to a complete, new intestine.
We also studied the "regeneration" of the South China Sea tropical sea cucumber, the rough ginseng, and we cut the rough ginseng in two, and we found that each segment of the rough ginseng can grow into a brand new sea cucumber.
But the process is relatively long, it takes about 3 months, and during this stage, the sea cucumber does not eat or drink, and does not move. This regenerative mechanism of sea cucumber has become a hot topic of research, and scientists hope to provide some enlightenment for human regenerative medicine by studying the regenerative mechanism of sea cucumber.
Sea cucumbers have another great skill, called autolysis. However, this time, it is not for its own survival, but for the sake of leaving no corpse after death, and returning the ocean to a pure land.
图 | Liu et al, J. Food. Process.Pres.,2020
This image shows the autolysis process of sea cucumbers. When sea cucumbers are too far out of water, exposed to oil, or die naturally, self-dissolution is triggered. Usually, in 6-8 hours, it can become a very thin, glue-like thing. Studies have shown that the autolysis of sea cucumbers is caused by a series of autolyzymatic enzymes, but the specific mechanism is not very clear.
The body of the sea cucumber carries toxins, and it also has a special smell, and many marine animals do not like it, but the radish cabbage has its own love. For example, in this video, this slender, soft fish called the hidden fish, it likes to be with the sea cucumber.
This video shows the process by which hidden fish enter the intestines of sea cucumbers.
Sea cucumbers provide shelter for cryptosclaves, while food scraps from the intestines of sea cucumbers also provide a partial food source for cryptosystems. But is the presence of hidden fish valuable to sea cucumbers? There have also been some studies on this issue, but it is still unclear whether it is beneficial for sea cucumbers.
Protect the marine ecological environment
Sea cucumbers silently guard the hidden fish, but also silently guard the marine ecological environment.
Biological agitation (left) Substance circulation (middle) Acid-base equilibrium (right) | Purcell, et al. 2016; Conand, et al. 2018
First, by crawling, moving, and hiding, it can stir up sediments on the seafloor and promote the release of nutrients from the sediments on the seafloor.
Second, sea cucumbers feed on organic matter particles and many tiny organisms in the ocean into invisible inorganic nutrient salts, which are then absorbed by algae and plants, promoting the circulation of marine material.
Third, sea cucumbers expel inorganic ammonia, which is alkaline and can neutralize the acids of carbon dioxide dissolved in the atmosphere that dissolves into the ocean.
Biodiversity (top) Energy transfer (bottom) | Purcell, et al. 2016; Conand, et al. 2018
Fourth, sea cucumbers symbiotically or accompany a lot of marine life inside and outside the body, so it also promotes the biodiversity of coral reef ecosystems.
Finally, sea cucumbers can convert marine animals, plants and organic debris into inorganic nutrient salts that can be used as fertilizer for algae and marine plants.
So it plays an important role in the ecosystem food chain of the ocean and is an important part. Through this ecological process, we can see that sea cucumbers are an important maintainer in marine ecosystems.
For most people, we care about sea cucumbers because we eat them. Indeed, sea cucumber is a high-end food, so it is also called "ginseng in the sea".
Large-scale fishing and processing of sea cucumbers (left) The distribution of damaged sea cucumber resources (right) | Erikssonetal et al., 2015
The huge consumer demand for sea cucumbers has directly stimulated the expansion of the sea cucumber fishing industry. Nearly 100,000 tonnes of wild sea cucumbers are reportedly fished worldwide each year, and in tropical waters, 70% of tropical sea cucumber populations are threatened by overfishing. As a result, the entire wild sea cucumber resources have been seriously damaged, and the situation on the mainland is similar.
Artificial breeding of sea cucumbers
When the sea cucumbers in the sea are fishing less and less, and there are more and more foodies, can we increase the number of sea cucumbers in the ocean through artificial breeding, and also meet everyone's consumption needs? To accomplish this work, we first conducted research on artificial breeding of sea cucumbers.
Shoot | Zhao Yu
Let's take a look at the breeding habits of sea cucumbers through this video.
These are two tropical sea cucumbers— jade-footed sea cucumbers are draining sperm, and throughout the entire sperm evacuation process, they are shaking their heads and shaking their heads, while their heads are spitting out something like smoke rings. Notice that this is not the sea cucumber that learns to smoke, it emits smoke-like things that are semen.
Our team began researching the artificial breeding of tropical sea cucumbers in 2009, and so far, we have taken the lead in the world to break through the artificial breeding technology of rough ginseng, flower ginseng and jade foot sea cucumber.
The following takes you to see the scene of tropical sea cucumber jade foot sea cucumber breeding.
The picture below is of the male ginseng of the jade foot sea cucumber in the drainage.
The picture below shows the female ginseng of the jade-footed sea cucumber laying eggs, and the eggs are orange-red.
Sea cucumbers are divided into males and females, but before ovulation and sperm, it is difficult to distinguish between males and females. In general, a male sea cucumber can produce hundreds of millions of sperm at a time, while a female sea cucumber can produce 1.3 million eggs at a time, which is a very large number.
Now to give you a brief introduction to the process of sea cucumber breeding, first of all, we have to choose a high-quality father and mother for the baby of sea cucumber, the technical term is called pro-ginseng. We put these ginseng in a large bucket called the ginseng bucket. Around 6 p.m., we drain the seawater out of the bucket and let the sea cucumbers dry here for 15-30 minutes. Then we add seawater to the bucket and create a stream of water to impact these sea cucumbers, a process called yin dry water stimulation.
With such measures, we can let the sea cucumbers produce more sperm and spawn. Usually after this operation for about a few hours, the sea cucumber begins to release sperm and lay eggs. At this time, we must pay attention to observation, when we find that the sea cucumber begins to shake its head, we must be particularly careful, we must be quick with our eyes, and quickly fish out such sea cucumbers and put them in buckets one by one. After such an operation, it will soon release sperm and lay eggs.
After getting the eggs and sperm, we have to perform artificial insemination, we mix the eggs and sperm together, of course, the egg and sperm mixing should pay attention to the ratio, the ratio of sperm and egg number is about 3-5:1.
Juvenile and juvenile ginseng development of jade-footed sea cucumber
This image shows the development of sea cucumbers from fertilized eggs to larvae, which takes about 22 days. The survival rate of sea cucumbers on days 17 to 20 is very low, with a mortality rate of 50%.
Developmental morphology of jade foot sea cucumber at 60, 80, and 120 days
These pictures show the development process of naïve ginseng, which generally takes 60 days of development to reach 2 cm, and after 100 days of development can reach 4-7 cm.
Left: Rough Ginseng - Big Ear Juvenile Right: Rough Ginseng - Juvenile Ginseng
These are two close-up photos of the large-eared juveniles of the sea cucumber larvae and the sea cucumber of the juvenile stage, which can be said to be the peak of the two appearances in the life of the sea cucumber.
As the sea cucumber grew, its body became no longer transparent, and the body was covered with various pigments, and it became what we see the sea cucumber now.
A baby of a sea cucumber will go through many levels in his life. The baby of the sea cucumber is weak and vulnerable to enemy attacks, and this video shows three copepods attacking the baby sea cucumber. Therefore, copepods are the most important enemies in the artificial breeding process of sea cucumbers, and we must focus on prevention and control.
When the specifications of the sea cucumber reach more than 2 centimeters, we have to multiply and release it, that is, put it back into the sea, and the following video shows the process of putting the sea cucumber seedlings back into the sea.
In addition to the release of sea cucumber seedlings, we can also transplant the adult ginseng of sea cucumber, or we can say that we can move it from a place with high density to a place with low density. Through such measures, the rapid growth of sea cucumber populations can be promoted.
This is the video we transplanted the sea cucumber.
Sea cucumbers are the scavengers of the ocean, which convert organic particles into inorganic nutrient salts. So we use this feature to polyculture sea cucumbers and other marine economic animals, including fish, shrimp, and shellfish.
These pictures show how we polyculture jade foot sea cucumber, rough ginseng and shrimp.
Sea cucumbers are the maintainers of marine ecosystems and are also marine organisms with high fishery economic value. In the future, we hope that through our efforts, we will gradually increase and restore the resources of the tropical sea cucumber population in the South China Sea, improve the marine environment through sea cucumbers, and build a beautiful home for marine life.
At the same time, we also hope that through hard work, sea cucumber is no longer a precious ingredient, but like fish and shrimp, so that everyone can eat it often.
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This article is reproduced with permission from the Theory of Objects (ID: SELFtalks), originally titled "Boo... These sea cucumbers, which do not eat or drink and are motionless, are "reborn" | Luo Peng", if you need to reprint it for the second time, please contact the original author.