They look like "jelly", but they are actually a group of marine creatures that can eat and reproduce!

Produced by: Science Popularization China

Author: Lai Yanjiao (Shenzhen Institutes of Advanced Technology, Chinese Academy of Sciences)

Producer: China Science Expo

Jelly-like things piled up

(Image source: References 8 and 9)

Imagine if you saw this kind of jelly-like thing piled up densely at sea, you would definitely be curious, what is it? If you scoop it up with your hand, you will find that it feels sticky and bouncy, just like a fish made of jelly.

"Jelly Fish"

(Image source: Wikipedia)

But it is not a fish, but a kind of zooplankton called "Zun" ("Zun"), which is a kind of hollow barrel-shaped wine bottle. Like jellyfish, they have a watery and sticky body and are all colloid zooplankton.

The family Neuraminididae belongs to the class Salpae, which is a tunicate zooplankton, a group of colloid zooplankton.

(Image source: self-made by the author)

Big Eater Newgill Thrush : Eats a lot and fast!

The thrush is a big eater! There is a filter structure inside its body. Its muscles constantly contract to allow seawater to flow into the filter. In this way, any phytoplankton, bacteria, or even eggs and larvae of other zooplankton in the seawater that can pass through the filter can be eaten by it.

Left: The green area is the filter position of the salp species. Right: The filter morphology

(Image source: The left image is from reference 1, and the right image is from reference 2)

At the same time, they filter food at an astonishing speed. For example, a salp that is a few centimeters long can filter 200 mL of seawater in one minute, which is thousands of times faster than other zooplankton[3], so they are truly big eaters.

Salmons are still the "upstarts" in the ocean

Newbryons are very fertile! They have a unique life cycle that alternates between sexual and asexual stages.

When their asexual individuals reach sexual maturity, they can undergo three budding reproductions, producing hundreds of chains of sexual offspring at a time[4]. These sexual offspring are female at birth. They are fertilized at birth, and each sexual individual can then give birth to an asexual offspring.

Sexual stage of a hydrilla colony

(Image source: Wikipedia)

An asexual stage of budding of the cypripedium cypris

(Video source: provided by the author)

When the asexual offspring are released from their bodies, these mothers will transform into males and then produce sperm to fertilize the newly born females. This sexual and asexual life cycle of the thrush is very efficient. For example, the two-tailed thrush of the family Nematoda can grow 10% in length within an hour and can reproduce a generation in as fast as 48 hours[5].

Life cycle of the trout

(Image source: self-made by the author)

The high reproduction rate and short life cycle of newt salps mean that they only need to produce a few asexual individuals to form a large local cluster. Therefore, when the environment is suitable, explosive proliferation will occur. Scientists compare them to "locusts in the ocean." However, the frequency of newt salps outbreaks in the ocean is much higher than that of locust plagues on land. In the ocean, newt salps outbreaks occur almost all the time, and some outbreaks can even reach an area of ​​100,000 square kilometers[6], equivalent to the area of ​​13 Guangzhou cities.

So, what impact will the newts have on the ecological environment when they gather together in such a large area?

Salmons play a very important role in natural ecology

Once salps gather in large areas, firstly, they will quickly consume all the food in the sea area, and also eat the eggs and larvae of other zooplankton, which is a devastating blow to other zooplankton. Secondly, if such an outbreak occurs in coastal areas, it will also consume a large amount of dissolved oxygen, pollute the water quality, and even block the water inlet of nuclear power plants, causing huge economic losses to humans.

So it seems that this thrush is actually a "villain"? But don't be quick to dislike it, in fact, they have a very "charming" side and play a very important role in the natural ecology!

Before introducing their importance, let me first introduce you to the marine biological carbon pump. Carbon dioxide in the atmosphere is converted into organic matter by phytoplankton through photosynthesis, and then eaten by marine zooplankton, and then sinks to the deep sea in the form of feces or corpses. In this process, carbon dioxide in the atmosphere is transferred to the deep sea and will not be decomposed for the time being. We call this carbon transfer process the marine biological carbon pump. This process can reduce carbon dioxide in the atmosphere, thereby alleviating climate warming.

A simplified diagram of the marine biological carbon pump

(Image source: self-made by the author)

Because salps are very gluttonous, they can eat a large amount of these plants, which form feces and corpses that sink to the deep sea continuously. Therefore, their role in the marine biological carbon pump is very powerful, and this role is particularly obvious when they have outbreaks. For example, a study in the Southern Ocean showed that the amount of carbon transferred from the atmosphere to the deep sea in areas with outbreaks of salps can be increased by 5 times compared to areas without outbreaks [7]. So when we humans produce a large amount of greenhouse gases, these hardworking animals like jelly use their lives to continuously consume this carbon dioxide for us and maintain our temperature.

Conclusion

The story of the thrush inspires us that the ecosystem is very complex and we cannot simply draw a conclusion about a species as good or bad. For example, termites, which we regard as "pests" because they damage buildings and trees, play an indispensable role in the ecosystem. They feed on wood, leaves and other plant debris, help decompose organic matter, convert complex plant matter into simple nutrients for other plants and microorganisms, and promote the material cycle of the ecosystem. On the contrary, woodpeckers, which we often think are beneficial to the forest, may damage the epidermis and xylem of trees by pecking too frequently, affecting the growth and development of trees and bringing negative impacts to the forest ecosystem. Finally, I want to say that there are too many distant and unfamiliar creatures in this world that play an important role in the ecosystem, and we have not yet known them. We should remain in awe of the world and protect every creature we are not familiar with, because we really don't know what value may be hidden behind it. This is the meaning of protecting biodiversity.

References:

[1] Conley KR, Lombard F, Sutherland K R. Mammoth grazers on the ocean's minuteness: a review of selective feeding using mucous meshes[J]. Proceedings of the Royal Society B: Biological Sciences, 2018, 285(1878): 20180056.

[2] Sutherland KR, Madin LP, Stocker R. Filtration of submicrometer particles by pelagic tunicates[J]. Proceedings of the National Academy of Sciences, 2010, 107(34): 15129–15134.

[3] Paffenhofer G A. Grazing and ingestion rates of nauplii, podids and adults of the marine planktonic copepod Calanus helgolandicus[J]. Marine Biology, 1971, 11(3): 286–298.

[4] Deibel D, Lowen B. A review of the life cycles and life–history adaptations of pelagic tunicates to environmental conditions[J]. ICES Journal of Marine Science, 2012, 69(3): 358–369.

[5] Heron A C. Population Ecology of a Colonizing Species: The Pelagic Tunicate Thalia democratica[J]. Oecologia, 1972, 10, 269–293.

[6] Madin LP, Kremer P, Wiebe PH, et al. Periodic swarms of the salp Salpa aspera in the Slope Water off the NE United States: Biovolume, vertical migration, grazing, and vertical flux[J]. Deep Sea Research Part I: Oceanographic Research Papers, 2006, 53(5): 804–819.

[7] Décima M, Stukel MR, Nodder SD, et al. Salp blooms drive strong increases in passive carbon export in the Southern Ocean[J]. Nature Communications, 2023, 14(1): 425.

[8] Moazzam M, Moazzam N. Some Observations On The Swarm Of Pegea Confoederata(Tunicata: Salpidae) In Mianihor, Balochistan, Pakistan[J]. Fuuast Journal of Biology, 2020: 5.

[9] Al-Yaqout A, Nithyanandan M, Issaris Y, et al. In-situ observations of swarming pelagic tunicate Pegea confoederata (Forskål, 1775) (Tunicata: Thaliacea) in coral reef habitats of Kuwait[J]. Kuwait Journal of Science, 2023: S2307410823001013.