With approximately 400 different species of coral belonging to 80 genera and 17 families, the coral ecosystem of Vietnam can be compared to some of the most diverse coral regions in the world.
Summary Information about Corals:
- Corals are extremely fragile yet highly resilient.
- Corals are considered a delicacy for whales and many other marine animals.
- Corals are related to jellyfish.
- Most corals are found in warm tropical and subtropical waters, although many soft corals also thrive in colder regions around the world, even in Antarctica.
- In recent decades, over 35 million hectares of coral reefs have been destroyed.
- Coral reefs are now one of the most threatened ecosystems on our planet. If the current rate of destruction continues, 70% of the world’s coral reefs will be destroyed in our lifetime.
What do Corals Look Like?
Corals resemble plants, and naturalists have historically described coral reefs as gardens. In some parts of Vietnam, corals are referred to as stone flowers. But upon closer inspection, you will see that corals are made up of tiny creatures called coral polyps.
Each coral polyp resembles a sea anemone with a bag-like body and a single mouth that takes in food and expels waste. Surrounding this mouth are tentacles with stinging cells.
A coral colony is not just a group of individual polyps living together for mutual benefit, but rather the result of the growth and budding of a single base polyp.
The polyps in a coral colony share a common fluid and nervous system. They are genetically identical, and the polyps are connected by a thin layer of tissue.
Where Do Corals Live?
Coral reefs form on solid surfaces in warm, shallow, and clear marine waters.
The seawater there must have:
- a temperature of 22–29°C (average annual temperature)
- clear water with low turbidity
- low nutrient levels
- stable salinity
– Coral reefs grow around the continental slopes or coastal edges. They are known as fringe reefs.
– Atolls are formed from fringe reefs surrounding extinct volcanic islands.
– Platform reefs are usually found on the continental shelf.
– Ribbon reefs (also known as barrier reefs) are long, narrow structures that grow along the edge of the continental shelf.
What Do Corals Eat?
Coral polyps capture food. Each polyp has a mouth surrounded by tentacles with stinging cells that immobilize tiny organisms swimming in the water.
The tentacles push the polyp’s food into its mouth and can also sting predators!
The mouth connects to a tubular gut that contains digestive tissue.
During certain months of the year, the digestive tissue may also contain developing reproductive organs. Some polyps have both male (sperm sacs) and female (egg ducts) reproductive parts.
How Do Corals Reproduce?
Corals reproduce sexually or in various other ways, such as splitting into two organisms or releasing polyps to grow elsewhere. Corals have fascinating reproductive methods, and many species utilize more than one.
Fragmentation: pieces of branching or plate-like corals can break off and attach themselves to the reef surface where they continue to grow. Branching corals tend to fragment in turbulent waters or where many organisms come to feed or rub against them.
Binary fission or ‘budding’: coral fungi can split into two or more organisms.
Polyp bailout: when bumpy corals become stressed, they can release polyps to live elsewhere.
Polyp balloons: during the day, corals release small balloon-like tissues onto the reef surface to grow near their parents and form new coral clusters.
Asexual reproduction: some flower-like corals and bumpy corals have very young individuals that grow on their tissue. They are produced from a single egg rather than from a union of sperm and egg. Once released, the small polyps settle and grow near the parent.
Sexual Reproduction: there are two types of sexual reproduction:
- Internal larval production within polyps: this method is similar to asexual reproduction, except the small polyps are produced from the union of sperm and egg.
- Mass spawning: at least 100 species of reef-building corals in the Great Barrier Reef release egg and sperm bundles into the water during several nights at the start of summer. The eggs and developing larvae swim with the current a few days later. Mass spawning occurs over 3 to 6 nights after a full moon and when the seawater warms up after winter. After rising to the surface, the egg and sperm bundles burst, allowing egg cells and sperm cells to meet and fertilize. Among the millions of eggs and sperm produced, only a few eggs may fertilize, settle, and survive until maturity. The rest become a delicious meal for fish!
Corals, with their rainbow colors and varied shapes and sizes, are a unique and essential part of marine life in Vietnam.
Coral reefs are among the oldest and most biodiverse ecosystems on Earth. They also support a symbiotic (mutually beneficial) relationship among organisms in the natural world. Although formed by very small creatures, corals create beautiful reefs along the coast of Vietnam and serve as habitats for many diverse marine species.
Each coral organism is part of this reef ecosystem and also plays a role in the gradual formation of a new reef. Some corals grow very slowly, less than 1 cm per year, while others can grow as much as 15 cm per year. However, the size of the coral reef does not indicate its sustainability.
Corals are very sensitive to disturbances, and damage from human carelessness can severely impact the health of the entire reef ecosystem. The condition of a coral reef is closely linked to the surrounding mangrove and seagrass ecosystems. Mangroves and seagrasses filter nutrients from land sources and provide shelter and nourishment for many organisms residing in the coral reef.
Corals are currently under threat, with damage reported in 93 countries, and corals could disappear in the next 20 years. The threat to coral reefs is no longer just a national issue but a global concern. With approximately 20% of the world’s coral reefs irreversibly damaged, 24% threatened, and 26% facing long-term threats, the international community must do more to protect them. If we allow coral reefs to die alongside rising sea levels, thousands of islands worldwide will disappear, along with their communities and cultures.
Coral reefs are found in over 100 countries and cover approximately 285,400 km² globally. They are the most diverse ocean ecosystems, with the only rival being terrestrial tropical rainforests. 25% of all marine species, including thousands of wonderful fish, mollusks, sea urchins, and more, live within them. Due to overfishing, fish populations in coral reef areas have significantly decreased in some regions of the world. This has led to an imbalance in the coral ecosystem, allowing other organisms like algae to thrive. As a result, algae, which were once controlled by fish, have become overwhelming in many areas. Furthermore, many fishermen use drag nets to scour corals and sponges on the seabed in search of economically valuable fish.
As the human population increases and economic and social activities develop, the amount of wastewater entering the oceans also rises. Wastewater can carry large amounts of sediment from deforested areas, nutrients from agricultural regions, and pollutants like oil products and pesticides. All these pollutants increase the turbidity of the seawater, reducing the amount of light that reaches the corals, thereby causing coral bleaching.
Coral is also a popular decorative item among humans. Often, when vacationing in tropical regions with beautiful coral reefs, some people wish to purchase coral souvenirs to bring back home. To satisfy the demand of tourists, locals have been exploiting coral on a commercial scale, selecting specimens that can yield the highest profits. This situation is also occurring in Vietnam.
Oil spills, oil leaks into the sea, ship anchors, and large ships running aground have severely damaged significant portions of coral reefs. Researchers have discovered that the paint covering the bottoms of many ships contributes to the formation of toxic Tributyl tin, along with other harmful chemicals to corals. Surveys indicate that pollution, overfishing, rising temperatures, coastal development projects, and diseases pose major threats to coral reefs.
Approximately 70% of the world’s coral reefs are being destroyed or are at risk due to human activities. However, some reefs are exhibiting remarkable resilience to global warming. Countries around the world should take more action to reduce pollution, limit fishing, and cut greenhouse gas emissions (such as CO2) to protect corals. To save coral reefs, governments need to urgently reduce CO2 emissions. Global temperatures have increased by 0.6°C since the late 1800s.
In Vietnam, since late 2003, fishermen in coastal areas have been freely harvesting black coral, which has severely impacted the marine ecosystem. Since late 2003, Chinese merchants have been coming to these areas each month to purchase hundreds of tons of black coral as raw material for crafting decorative items. The average purchasing price ranges from 150,000 to 200,000 VND per kilogram, while this price can soar to 2 million VND per kilogram when exported to China.
Applications of Coral in Bone Treatment:
– In cases of eye enucleation: Since 1998, coral products have been introduced for use at Ho Chi Minh City Eye Hospital. As of now, coral beads have been used in over 100 cases. For patients who unfortunately suffer from traffic accidents, trauma, or diseases requiring eye removal, immediately after the enucleation, doctors implant a coral bead into the scleral sac to reshape the eye socket, maintaining the position of the eyeball and preventing atrophy. After healing, doctors can place a prosthetic eye, allowing patients to have some degree of movement.
– In dentistry and maxillofacial surgery: When extracting teeth, doctors can use coral grafts to fill in the jawbone, preventing atrophy, which makes it easier when placing dentures later. In cases where tooth roots are decayed or inflamed, creating cavities known as periapical cysts, treatment requires the removal of the infected bone, leaving a void that needs graft material for healing. Previously, expensive HTR materials from France were used. Now, using Vietnamese coral, bone will start to grow in and replace the coral after about three months, integrating almost normally.
In 2003, the use of coral began for reconstructing bone defects in patients with jaw, cheekbone, or eye socket injuries. These patients previously had to accept a deformed face due to bone loss or were required to use expensive materials like cement or titanium, which do not resorb after grafting.
In grafting coral material, in addition to creating the initial shape, it will gradually be replaced by the patient’s own tissue. The treating doctor will create initial molds for the patient using plastic or plaster, and then fabricate coral pieces using manual techniques. The Jaw and Facial Surgery Department at the Ho Chi Minh City Dental University has performed six such cases.
– In conditions causing spinal cord compression due to spinal stenosis (from degenerative bone or disc issues compressing the spinal canal): The treatment method involves widening the spinal canal using coral as graft material to expand the canal. Ho Chi Minh City Orthopedic Hospital has applied this method in 10 cases, while the neurosurgery department at Chợ Rẫy Hospital has carried out over 30 cases.
Le Thi Thu Nga
(Third-year student, Faculty of Natural Sciences, University of Science)
