Rare! The explosive "blue tears" shocked the screen! What are "blue tears"?

Experts in this article:

Sun Xueqiong, Master's student at the School of Oceanography and Earth Sciences, Xiamen University

Luo Hao, Postdoctoral Fellow, School of Environment and Ecology, Xiamen University

This article was reviewed by Lin Xin, Associate Professor of Xiamen University

Blue Tears, just the name sounds romantic. In fact, people who see it will feel more romantic.

Recently, the spectacle of blue tears once again flashed in the eyes of Xiamen people, and many people came to Haicang Bay Park, Haiwan Park and other major places where blue tears occurred in Xiamen to check in.

Some friends who like it directly touch it with their hands, and even want to take it home. However, the truth behind the blue tears is not as beautiful as imagined...

What are blue tears and why does the sea cry?

The essence of blue tears is the luminescence phenomenon of a type of marine organisms (such as fireflies and Noctiluca scintillans).

Under suitable environmental conditions, when the Noctiluca scintillans cells grow to a certain density, they will emit blue light at night due to disturbances and other stimuli.

The higher the cell density, the stronger the blue light. This type of blue light will rise and fall with the waves, like tears flowing from the sea, so it is called "blue tears".

Source: See watermark

The blue tears discovered in Xiamen this time are caused by the luminescence of Noctiluca. When Noctiluca gathers in large numbers, the sea surface will appear pink or red during the day. When night falls and the sea water surges or hits the reefs, it will emit blue light, which is the blue tears we see.

Why do blue tears glow?

Noctiluca scintillans is a marine dinoflagellate that includes red heterotrophic types and green mixotrophic types (with symbiotic green algae in the body).

Red Noctiluca is widely distributed and has been found in major tropical and subtropical waters around the world. The one that appeared in Xiamen is red Noctiluca.

In contrast, green Noctiluca is concentrated, mainly appearing in tropical waters such as the Arabian Sea and the Gulf of Thailand.

Here, red and green Noctiluca are used to distinguish the different lifestyles of Noctiluca (heterotrophic and mixotrophic), while blue is the bioluminescence stimulated by biochemical reactions within the cells of Noctiluca, which are different concepts.

Single Noctiluca scintillans cell

The diameter of Noctiluca scintillans generally ranges from 200 microns to 2 millimeters, which is visible to the naked eye. It can be called a "giant" among single-cell algae, and its round body can be clearly seen under a microscope.

In the ocean, their growth rate is not very fast, but when the environmental conditions (temperature, salinity, light and food, etc.) are suitable, they can reproduce in large numbers in a short period of time. When they reach a sufficient concentration, they can produce the visual feast of blue tears.

The reason why Noctiluca scintillans glows is because there are luciferin and luciferase in the cells of Noctiluca scintillans, which will react and emit blue fluorescence when disturbed by external factors.

For a cell, the luminescence phenomenon is fleeting, and the blue tears can only be formed by the power of countless cells gathering together. However, this luminescence requires energy, so the Noctiluca scintillans cannot glow all the time.

Can I take the blue tears home?

The algae cells that form blue tears will absorb a large number of invisible bacteria, viruses and other pathogenic microorganisms during the aggregation process, which may infect humans.

Therefore, when viewing blue tears, it is not recommended to directly touch the blue tears with naked limbs, especially for friends with wounds on their limbs.

Blue tears are so beautiful that many friends want to take them home.

But this may not work, as Noctiluca scintillans needs suitable water environment conditions to grow and reproduce, and these conditions can only be provided by professional laboratories.

If you take some seawater home from the sea where blue tears occur, you may be able to see a little blue light that night, but the Noctiluca scintillans will die after 2-3 days and you will no longer be able to see the blue tears.

The Noctiluca scintillans cultured in the laboratory emits blue light when shaken; Photo provided by Professor Ji Nanjing of Jiangsu Ocean University

Will blue tears cause harm to the ecological environment?

The prerequisite for the formation of blue tears is that the Noctiluca cells gather and reach a certain density. When the density reaches 3,000 or more Noctiluca cells per liter of seawater, blue tears can be regarded as a type of red tide caused by Noctiluca (a common ecological disaster in my country's coastal waters), which may have an adverse impact on the local seawater quality and marine ecology.

Because during the disappearance of the red tide of Noctiluca scintillans, on the one hand, a large number of cell death and rupture will release high concentrations of ammonium salts and other nutrients into the water, causing the nutrient concentration in the water to increase and damaging the water quality.

On the other hand, the intensified decomposition of microorganisms will consume a large amount of oxygen, causing hypoxia in the water, which will harm fish, shrimps, crabs and shellfish.

Scientific reports have shown that red tides of Noctiluca scintillans can cause mass deaths of fish and other marine life.

In addition, during the outbreak of Noctiluca, it may block the condensate water inlets of nuclear power plants and seawater purification plants, causing harm to social production. ③After testing, the density of Noctiluca that caused the Xiamen Blue Tears did not reach the level of red tide.

The blue tears phenomenon has swept the world and received widespread domestic and international attention.

While we appreciate its beauty and magic, we should also pay attention to the other side of blue tears' impact on the marine ecological environment.

I hope that you who read this article can recognize the true face of blue tears and have a new understanding of blue tears.

References:

[1] Harrison, PJ, Furuya, K., Glibert, PM, Xu, J., Liu, HB, et al. (2011). Geographical distribution of red and green Noctiluca scintillans. Chinese Journal of Oceanology and Limnology, 29(4), 807-831.

[2] Gomes, H., Goes, JI, Matondkar, SP, Buskey, EJ, Basu, S., et al. (2014). Massive outbreaks of Noctiluca scintillans blooms in the Arabian Sea due to spread of hypoxia. Nature communications, 5(1), 1-8.

[3] He Liyan, Song Xiuxian, Yu Fan, Wang Kai, Song Shuqun, Yu Zhiming. 2019. Characteristics of algae blooms that may affect the cooling system of Fangchenggang nuclear power plant and its monitoring and control technologies. Oceanology and Limnology, 50(3): 700-706.

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