[Smart Farmers] The Wandering Earth from an Agricultural Perspective: This tiny transparent creature may become the last source of animal protein for humans

Editor’s Note:

The recent hit of "The Wandering Earth 2" has aroused deep thought behind the sci-fi blockbuster: the doomsday scenario assumed in the movie is far-fetched, but if the earth reaches the "doomsday", what will humans eat? Popular Science China Smart Farmers has launched a series of popular science articles, welcome to follow.

"Big fish eat small fish, small fish eat shrimp" refers to the relationship of the food chain in the ocean. In the ocean, in addition to marine mammals such as whales, seals, walruses, sea lions, and cephalopods such as octopuses and squids, which are all carnivores, some big fish and small fish are also carnivores. With so many carnivores, what do they eat?

First of all, there are plankton. There are a lot of plankton in any sea area, including phytoplankton and zooplankton. Phytoplankton, such as dinoflagellates, diatoms, and flagellates, grow in the upper layer of the ocean and dissolve carbon dioxide in the water through photosynthesis to produce organic compounds. Scientific research has found that more than 50% of the world's oxygen is produced by phytoplankton. Phytoplankton is not only a good carbon sink in the ocean, but also the food of many marine organisms.

The second are zooplankton, such as copepods, cnidarians, etc. These zooplankton not only live in the upper layer of the ocean, they can appear in any sea water level.

The most common and densest zooplankton in the ocean is krill. There are 85 different species of krill living in the world's oceans. We know that the largest marine mammals often feed on the smallest marine organisms. Krill is such a "poor" little animal, weighing about 1 gram each, and inevitably becomes the food of most marine carnivores.

In the topic of "If the Earth wanders, what will humans eat?", why is Antarctic krill included in the "hope" list? Let's first take a look at the characteristics of these "little creatures".

Cute mini shrimps

What kind of shrimp is the Antarctic krill? Its scientific name is Euphausia superba, also known as giant krill or Great Antarctic krill. It belongs to the family Euphausiaceae and the genus Euphausiaceae. Strictly speaking, Antarctic krill is not actually a shrimp, but a marine organism that lives in Antarctic waters. Because it looks like a small shrimp, it is also named shrimp. They are mini and cute, only 3 to 5 cm long, and the largest species is only about 7 cm long. What's even cuter is that their bodies are transparent, and you can see the green digestive glands inside from its shell. This is because their food is mainly phytoplankton, most of which are green.

Glowing shrimp

Many marine organisms have bioluminescent organs, and Antarctic krill is one of them. These organs can emit light, and the fluorescence is larger than that of small fireflies. According to research, the light they emit is relatively far away, and the concentrated brightness is even comparable to that of a flashlight.

Can you imagine where these light organs are located? There is a pair on the eyestalk, a pair on the second to seventh thoracic legs, and one on the ventral plate. They can emit yellow-green light every 2-3 seconds. In the ocean, it is also spectacular to see a large group of small glittering creatures. But the function of these lights is still uncertain.

The picture comes from the Internet

However, the beauty and cuteness of Antarctic krill are not the main reason for being on the "wish list". Antarctic krill is a key species in the Antarctic ecosystem, and some studies have said that they may be the most successful animal species on Earth. Its large resources make Antarctica a "granary in the sea".

In the 2015 edition of the IUCN Red List of Threatened Species, Antarctic krill is classified as a species of Least Concern (LC). According to relevant scientific surveys, the reserves of Antarctic krill are about 400 million to 600 million tons. Biologists estimate that if the catch does not exceed 50 million tons per year, Antarctic krill will continue to grow and develop normally.

The picture comes from the Internet

At present, many countries call Antarctic krill resources "offshore gold mines". Why does it have such a reputation? It must have its unique advantages.

Tenacious vitality

The tenacious vitality of Antarctic krill is the basis for their prosperity, especially their ability to resist hunger. Experiments have shown that they can live for more than 200 days without food. One of their unique skills is to use the method of molting growth to grow negatively during the cold and long winter in Antarctica, that is, to shed the old shell and shrink the body quickly before the new shell hardens, so as to reduce the energy required to keep the body floating. In this way, they overcome the challenges of wintering. We can also see this kind of experiment in the aquarium: when the Antarctic krill in the aquarium are not fed, they will molt and shrink their body size, which is a survival skill that other animals do not have. The lifespan of ordinary small invertebrates is very short, but krill can live for about 6 years, which can be said to be relatively long-lived.

The picture comes from the Internet

Strong reproductive capacity

Antarctic krill have a high egg-laying capacity. The spawning period of krill is from January to March, usually in deep sea areas, and up to 100,000 eggs can be laid at a time. These eggs are usually in deep waters of 2-3 kilometers, and then swim to shallow sea areas after hatching. Usually they will grow into juvenile shrimps when they swim to a depth of 100 meters, and when they swim to the shallow sea areas where they live, they will grow up. They will reach sexual maturity in 2-3 years and can reproduce.

Unique lifestyle

As the most numerous creature in the Antarctic Circle, Antarctic krill feeds many creatures in the Antarctic Circle on its own. It is an important food source for blue whales, fin whales, penguins, seals and many fish, and is also the target of human fishing. Every year, a large number of Antarctic krill are eaten by large marine creatures. For example, blue whales that feed on krill need to eat about 3.6 million krill every day, and seals can eat 63 million to 130 million tons of krill every year.

Living in groups is the lifestyle that krill prefer, and their life tracks can be seen in the surface layer less than 50 meters. Antarctic krill mainly form clusters within 200 meters of the surface, but the density varies in different sea areas and seasons. It can be seen that under many threats, the resources of this small creature are still huge. Perhaps they know that unity is strength.

The picture comes from the Internet

Antarctic krill not only has huge reserves, but is also rich in nutrients.

Many people don't know that Antarctic krill is a high-protein food, with a protein content of up to 20%, which is not inferior to beef, eggs, milk, etc. The nutritional content of Antarctic krill is also slowly being discovered by humans. Studies have shown that Antarctic krill has high protein, low fat, high mineral content, and contains a variety of active substances, such as protein digestive enzymes, mycobacterial amino acids, etc.

At first, humans caught Antarctic krill mostly for the production of feed and bait. Later, it was discovered that Antarctic krill has high content of chitin, astaxanthin and krill oil, and they are easy to extract, so they are used to make medicines and nutritional products.

Since Antarctic krill has so many advantages, why can't we vigorously develop this resource?

This is about biodiversity conservation and the balance of the marine food chain and ecological health. In the ocean, all creatures, big and small, are important to the balance of the marine ecosystem. Current studies have shown that Antarctic krill fix a large amount of carbon to the seafloor through feces excretion, providing a "biological pump" for the ecosystem.

Although the current reserves of Antarctic krill are relatively high, climate change still has a great impact on the reproduction and survival of Antarctic krill. As human demand for protein increases, Antarctic krill has gradually become a target of fishing. The demand for Antarctic krill in many fishing countries is increasing year by year. For example, Norway catches up to 400,000 tons of krill from Antarctic waters every year. If the fishing industry develops in an unorderly manner, it will also lead to resource scarcity and even endanger the survival of other animals in Antarctica, and bring catastrophic consequences to the fragile ecosystem of Antarctica.

Currently, the international community is also paying attention to the effective and sustainable use of Antarctic krill and the healthy maintenance of resources, and has set annual fishing limits for the Antarctic and Atlantic regions: once 625,000 tons are reached, fishing is prohibited.

Another little bit of knowledge is that not all aquatic products with high nutritional value are easy to prepare and taste good. After Antarctic krill are caught, they need to be processed quickly, otherwise the fluorine content in their bodies will increase rapidly, and the taste will be difficult to guarantee, and they may become unpalatable.

In addition, it is difficult for this tiny creature to appear in its original form after processing, that is, it is no longer so "beautiful". Therefore, it is better to leave these small shrimps for the big fish to eat. If the environment really becomes very bad, the earth needs to "wander", and the big fish are gone, we will have to fish for these small Antarctic krill to "save our lives".

Finally, although Antarctic krill has a strong reproductive capacity and extremely rich reserves, it may become the largest protein resource for humans in the future. However, for now, we still need to pay attention to ecological balance, the health of krill resources, scientific protection, and reasonable development. Otherwise, if the earth wanders, this tiny creature may not be able to become "the last source of animal protein for humans."

Produced by: Popular Science in China to Benefit Farmers

Producer: Guangming Online Science Department

Author: Liu Yadan, Researcher, former Assistant Secretary-General of the Chinese Society of Fisheries and Chief Scientific Communication Expert of China

Planning: Wu Yuetong, Xie Yun