The outstanding appearance of corals is largely due to these “green pearls”!

Zooxanthellae are yellow-brown single-celled algae that coexist with coral polyps and were discovered by Japanese biologists in the 1940s. In 1962, it was first formally proposed that zooxanthellae belong to the genus Symbiotic Dinoflagellate. Zooxanthellae are widely distributed and can be found in almost all tropical and subtropical coral reef ecosystems. From the Indian Ocean to the Pacific Ocean and then to the Caribbean Sea, in my country, they are mainly distributed along the southern coast of Fujian and the Nansha Islands. They are one of the most spectacular underwater landscapes in the world. Their existence not only enriches marine biodiversity, but also helps regulate the carbon cycle in coral reef areas and maintain the health of the entire marine ecosystem.

Zooxanthellae have a unique skill - photosynthesis. Through this process, they are able to convert sunlight into chemical energy, producing sugars and oxygen. This energy conversion mechanism driven by green pigments provides corals with essential energy supplies. In return, corals supply zooxanthellae with inorganic nutrients, including carbon dioxide, phosphates, nitrogen and nitrates, which are indispensable raw materials for zooxanthellae to carry out photosynthesis. Moreover, in the process of reef-building corals and stony corals forming reefs, zooxanthellae have the effect of promoting calcification.

Zooxanthellae not only provide energy to corals, but also give them rich colors. In fact, corals themselves are not naturally brightly colored; it is the pigments in zooxanthellae, such as carotene and chlorophyll, that give corals a gorgeous coat. These pigments not only attract potential mates and protect corals from UV damage, but also enhance the overall beauty of corals, making them a beautiful sight in the ocean.

Zooxanthellae not only provide energy to corals, but also give them rich colors. In fact, corals themselves are not naturally brightly colored; it is the pigments in zooxanthellae, such as carotene and chlorophyll, that give corals a gorgeous coat. These pigments not only attract potential mates and protect corals from UV damage, but also enhance the overall beauty of corals, making them a beautiful sight in the ocean.

Corals provide a stable living environment for zooxanthellae, a home away from external dangers. In this safe haven, zooxanthellae can photosynthesize without worrying about the risk of being devoured by predators. At the same time, the hard skeletal structure of corals also provides a physical barrier for zooxanthellae, protecting them from changes in the external environment. Bacteria play the role of intermediary and bridge in the symbiosis. They participate in the metabolic process of corals, help deal with waste, and even synthesize certain vitamins, which are essential for the growth of corals. Some bacteria also have defensive functions, fighting against pathogen invasion and maintaining the immune system of corals.

However, this perfect symbiosis is not without its hidden dangers. When environmental conditions change, such as when sea temperatures rise, corals may not be able to withstand the heat stress and begin to reject the zooxanthellae in their bodies, leading to "coral bleaching". Without the zooxanthellae, corals lose their colorful luster and turn pale, becoming more susceptible to disease and environmental damage, and even eventually die. The frequent occurrence of coral bleaching events is a major warning sign of global climate change on the marine ecosystem, reminding us that we must pay attention to and protect this fragile symbiotic system.

"Bacteria-zooxanthellae-coral" is a classic triangle relationship in the ecosystem, which contains complex material flow, information flow and energy flow. The balance and stability of the three are important guarantees for maintaining the health of the coral reef ecosystem. Faced with the challenges brought by global warming, the importance of protecting the symbiotic system of coral reefs and zooxanthellae has become increasingly prominent. Maintaining this fragile and precious partnership means protecting the future of the marine ecology and the well-being of countless human societies that rely on coral reef ecosystem services. Let us work together to contribute our part to this beautiful blue planet, protect every inch of coral, every tiny zooxanthellae, and jointly maintain the balance and prosperity of the earth's ecology.

References

[1]Xu Lintong, Zheng Yankun, Hao Jun, et al. Research progress on coral symbiotic zooxanthellae[J]. Hebei Fisheries, 2018, (08): 56-59+62.

[2] Wang Tao, Cheng Keke, Cai Zhonghua, et al. Communication in the triangular relationship of “bacteria-zooxanthellae-host” in coral symbiosis[J]. Chinese Journal of Applied Ecology, 2022, 33(09): 2572-2584.

[3] Lin Qiang. The story of corals and zooxanthellae[J]. Nature, 2016, (03): 30-35.

[4] Zhu Xiaoou, Chen Xiaofeng. The role of zooxanthellae in coral reef construction[J]. Bulletin of Biology, 1993, (08): 19+27.