Blowing bubbles during the day, waking up at night, that is coral?

Today is World Oceans Day and National Oceans Publicity Day. This year’s theme is “Protecting the Marine Ecosystem, Harmonious Coexistence between Man and Nature”. In the mysterious, magnificent and dynamic blue realm of China’s coastal waters, there are all kinds of marine creatures, about 20,000 species, accounting for about 10% of the global marine species. Nutshell, the Publicity and Education Center of the Ministry of Natural Resources, and the People’s Daily jointly created and released a marine version of cancan dance – “You You You You You You”! The song was composed and sung by the “Nutshell Science Choir”. Through the joyful and magical singing, everyone dived into the seabed and felt the wonder and beauty of the ocean.

Diverse and fascinating creatures have always been the driving force for people to explore the ocean. Among them, coral reefs formed by animals such as reef-building corals shelter 25% of the creatures in the ocean.

The so-called “reef building” means to form a reef. The branch-shaped staghorn coral, the small spherical “Oriental Pseudohorn coral”, the ganoderma-shaped “shizhi coral”, the honeycomb-shaped “honeycomb coral”… Reef-building corals of various shapes together build a “tropical rainforest in the sea” – Coral reefs. The world’s coral reefs cover less than 0.1% of the ocean, but more than 25% of marine life live in them.

‘Rainforest in the Sea’ coral reef, renowned for its diversity

The world of coral also is cuteness

Reef-building corals often have a common feature of forming large calcareous skeletons within their bodies. It is these calcareous skeletons that provide complex habitats for other creatures. It is precisely because of these calcareous skeletons in the body that reef-building corals have a certain hardness to the touch and were once called hard corals.

Do you think it’s time to watch some “tough guys” today? Don’t worry, let’s take a look at this animation first:

This is not enoki mushroom, it is also reef-building coral! Taken at the National Maritime Museum in Nha Trang, Vietnam, 10 times faster.

Surprise! What we want to introduce today is a soft reef-building coral that subverts people’s perception – Plerogyra sinuosa. It looks like a bunch of grape-sized bubbles that can be broken by blowing bombs. The Chinese name “bubble coral” and the English name “bubble coral” are also vivid. It is precisely because of this interesting image that it has also been moved from the sea into their own aquariums by aquarium enthusiasts at home and abroad, calling it “bubble coral”.

A large group of vesicular corals

Different in day and night

The vesicular corals are distributed in the Pacific-Indian Ocean and have also been found in the South China Sea. It has a special image of “underwater grape bunches”. If you encounter it during diving during the day, I believe it will be unforgettable at first sight. Night diving, but not necessarily. Because, sac corals are not the same during the day and night.

Daytime appearance of sac coral

During the day, vesicular corals blow bubbles, which are lovely. At night, they not only put away their bulging sacs, but also stretch out their fleshy, stinging tentacles, reappearing as predators, preying on plankton in the seawater.

deflated sac coral

The tentacles of a saccular coral.

night owl blowing bubbles

If you want to know why the sac coral has two faces of a little angel during the day and a little devil at night, you have to talk about the reef-building coral group to which it belongs. In addition to the formation of large calcareous skeletons, most reef-building corals have one feature in common—they have two metabolisms at the same time: autotrophic, which photosynthesizes in symbiosis with zooxanthellae, and heterotrophic, which preys on plankton.

The researchers found through experiments that more zooxanthellae were present in the bulging cells of vesicular corals than in tentacles. During the day, the vesicular coral blows bubbles, allowing the zooxanthellae to fully receive sunlight, and the photosynthetic efficiency reaches the maximum; the photosynthesis of the zooxanthellae also shares a large amount of energy with the symbiotic coral for its normal life and the production of limestone. skeleton. For tentacles covered with cnidarians, night is a more relaxed and pleasant time; rather than crowding between bulging sacs during the day, the tentacles can eat at night when the sun is lost and the corals put away the sacs. Swing freely, the predation efficiency is greatly increased.

It’s not easy to get tentacles out of this pile of orbs during the day.

Figuratively speaking, vesicular coral is like a little night owl who basks in the sun during the day, blows bubbles and sleeps, and wakes up when night falls.

Bubble coral and its friends

Different from the image of human night walkers who are often hidden in the night and sparsely socialized, the sac corals in the vast sea usually have small friends who can play with them – symbiotic coral shrimp or coral crabs.

Achaeus japonicus in symbiosis with vesicular coral

Between the bulging small sacs, the small coral shrimp and coral crabs can enter and exit freely, and their survival in the crevices keeps them away from the danger of being swallowed by predators. At the same time, the protein-rich mucus secreted on the surface of the vesicular coral, the algae on it, and even the “night supper” residue left by the vesicular coral are also the food of these symbiotic friends.

Coral shrimps and coral crabs enjoy the protection and delicacy provided by corals, while sac corals also enjoy the cleaning services of their friends-coral shrimps and coral crabs eat other algae, so as not to block the sunlight needed by the symbiotic algae. And coral crabs can even provide some sort of security service — driving away predators of vesicular corals.

There are also unwelcome guests, such as the acoelomates that inhabit saccular corals, which are beautiful and harmful to corals.

Today’s story is just a microcosm of the colorful coral reef ecosystem, the very existence of which is vital to marine ecology. At present, the country is gradually increasing the legal protection of coral reefs, and more researchers and volunteers are devoted to coral research, protection, popularization and publicity. There are also biologists who help corals carry out assisted evolution, find varieties with strong adaptability in the wild, select them in the laboratory, and then put them back into the wild for strict cultivation.

As people explore deeper and deeper, the magic and beauty of the ocean continue to emerge, and people’s ideas for ocean protection are gradually becoming clearer.

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