9 Corals Facts: They Are Animals, not Plants

Corals are one of the most important species of the ocean. Making up less than 1% of the ocean, but coral reefs support up to 25% of marine life. The coral facts below will help you understand the crucial roles of this species.

1. Corals are animals

Anchored on the seafloor, with branchlike structures or hard-rock looks, corals are usually mistaken as plants or rocks. However, they are animals. Coralsare inverbrate and classified under the phylum Cnidaria.

To know more about Invertebrate animals, you may find more related articles below:

There are 2 types of coral: hard corals and soft corals.

  • Hard corals

Hard corals or stony corals have hard skeletons made of calcium. Most hard corals are made up of multiple single polyps that live in colonies. These tiny polyps multiply and divide to create enormous colonies. And those colonies are the foundation of coral reefs.

All hard coral polyps have rings of 6 tentacles. The reefs you’re seeing in the ocean right now are created mostly by hard corals. Their dead skeletons will be used as anchors for other corals, both stony and soft corals.

  • Soft corals

Soft corals do not produce a stiff calcium carbonate skeleton so they do not build reefs, although they are present in a reef ecosystem. Without a hard skeleton, soft corals are very flexible. They are held by spicules, which are small limestone spike-like structures.

Unlike hard corals, soft corals have 8 feathery tentacles and swaying bodies. Moreover, they also have bright colors such as bright pink and mauve which are barely seen on the stony corals. A variety of creatures, including fish, prawns, and sea slugs, prefer to live in the branches of soft corals. These animals usually have the same colors like the soft coral to disguise.

This kind of coral is often threatened by many snails, fish, and crustaceans. They resist by creating substances in their cells that are unpleasant or even harmful to those creatures. Spiky spicules in soft corals operate similarly to thorns on a rose bush.

2. Some corals can take 1000 years to grow

The growing rate of corals depends on the species and the types, nutrition, and water.

– Boulder coral colonies are said to be the longest-living corals on the Great Barrier Reef. And these corals, each year develop about one centimeter in height. And this is not the slowest one. The porites (stony corals with finger-like structures) only increase one to three millimeters per year on average. On the other hand, some branching coral species, Staghorn corals, can grow up to 30 centimeters per year.

Unlike hard corals, soft corals develop quickly and their colonies can double or triple in size in a year.

The oldest coral – black coral

– While the typical growth rate of corals in some areas is 2 centimeters per year, a healthy coral that lives in an environment with no pollution and enough sunlight can develop more than 10 centimeters per year.

Corals need time to grow, which means that they can live for a very long time. Living up to 4000 years, black coral is now the world’s oldest coral.

3. There are different types of coral reefs

You can see different types of coral reefs around the ocean with different structures, locations and formations:

Fringing reefs (Shore reefs) grow close to the shore and develop in shallow water. You can see them near the coastline for kilometers along the shore. They grow from the shore and expand outwards to the sea.
These corals grow at a consistent depth until the continental plate is reached. They also cause bordering lagoons to form as the coral near the shore erodes over time, forming a bowl-like depression. The Red Sea corals are a well-known fringing reef.

Barrier reefs grow near the end of a continental plate. You can find them in the place where the sea bed abruptly lowers. Barrier reefs are rare and they are in charge of the formation of lagoons near the shores of the Caribbean, French Polynesia, New Guinea, Indonesia, and the Louisiade Archipelago.

The Australia great barrier reef

Platform reefs are usually found in shallow areas and are wider at the top and near the seafloor. They develop on the continental shelf and can be far from the shore. They expand outwards from the primary polyp and can often cover many kilometers in width. Erosion in the midst of the platform reef develops lagoons in the middle of the open ocean over time. These reefs are most typically seen within atolls and grow in a variety of shapes depending on wind and water flow.

There are more than 3 types of coral reefs above, such as atoll, Habili, apron, bank, cays, patch, ribbon, and Guyot reef.

4. Diet

Corals acquire their food in various ways:

– From sunlight

As you know that corals are not plants, they can’t be photosynthesis. So how can they get energy from the sun? The answer is algae.

Most coral reefs have a symbiotic relationship with small algae known as zooxanthellae. They live within coral polyps. Zooxanthellae, like plants, use the light to generate energy for themselves and the coral. This is why corals need to live in clean and shallow waters to get more sunshine. The algae supply corals with the necessary nutrition, energy, and oxygen. In exchange, coral polyps provide carbon dioxide and a safe home for algae.

The zooxanthellae not only provide energy for corals but also give them a gorgeous color spectrum. These algae will have various colors depending on their type and the presence of chlorophyll. Their primary colors are usually green and brown, but they can have other brilliant colors as a result of environmental changes.

When the light and temperature change, the color of zooxanthellae will change throughout a wide spectrum to protect themselves from UV rays. It’s like the sun cream. Coral reefs growing close to the surface are more colorful because the algae can absorb more sunlight.

– Fish and plankton

Corals consume tiny fish as well as plankton which are small animals or plants that float around in the ocean. How can they catch the prey?

At night, coral polyps emerge from their skeletons to find food. Like their jellyfish and sea anemones cousins, corals use their tentacles to paralyze their prey with specialized stinging cells called nematocysts. They then draw the prey into their mouths and eat them. They also eat microscopic plants or the zooxanthellae that locate within their cells.

These species have quite a few predators in the ocean where they live. Fish, sea stars like the crown-of-thorns starfish, corallivorous snails, marine worms, barnacles, and crabs feed on the delicate inner tissues of coral polyps. When predator populations surge to excessive levels, they can cause severe devastation to entire reefs.

5. Reproduction

Coral reproduction can be sexually through eggs and sperms or asexually through fragmentation or budding.

a. Reproduce asexually

Fragmentation: When a piece of a larger colony is split off from the main colony, a new colony that is genetically similar to the original colony is formed. This can be caused due to groundings, storms, or the damaged reef by humans. The new fragment, on the other hand, will only stay and expand if it is exposed to suitable growth conditions.

Budding happens when young polyps develop from a dividing parent polyp, resulting in the expansion of a coral colony. Like fragmentation, budding also creates new polyps which have the exact same genetics as the parent polyp.

b. Reproduce asexually

Broadcast Spawning: When the time comes (depending on the moon and temperature), corals will deliver significant amounts of eggs and sperm at around the same time. Because corals are sessile and cannot swim, timing is highly essential.

The fertilized eggs will be floating freely and are carried by water currents until they settle on a suitable surface to grow. This type of sexual reproduction produces offspring that are distributed throughout a large area.

Brooding: Brooding coral species, on the other hand, have internal fertilization within the polyps and release settlement capable larvae. Those huge larvae already have zooxanthellae, as opposed to broadcast spawners larvae, which pick up their zooxanthellae immediately after settling. The reproductive seasons of this coral species last from a few months to throughout the year.

To compensate for the massive loss of offspring during the early embryonic phases, many coral species, particularly broadcast spawners, produce massive amounts of gametes. Beaches in some areas become red after a night of coral spawning from washed-ashore gametes.

Over millions of years, this strategy has helped corals maintain their vitality. Today, however, coral reproductive success is restricted by stressed and damaged spawning colonies, inaccessible distances between spawning colonies, and intolerable climate conditions for larval development and survival.

6. White corals are stressed corals

Corals can be stressed by changes in conditions such as light, oil spills, changes in water temperature and salinity, nutrients, pollution, disease, increased sedimentation, oxygen depletion, and predators. When corals are stressed, they will expel the symbiotic algae (zooxanthellae) that live in their cells, causing them to turn pale or entirely white. This is known as coral bleaching.

Bleaching corals

Bleached corals are still alive. If environmental conditions improve quickly enough, the corals may be able to recover or rebuild their zooxanthellae and withstand the bleaching event. However, if the corals keep being stressed or the stressors are worsen, corals might die as a result of bleaching. Because they lack their principal energy source, bleached corals are more vulnerable to illness, predators, and death.

Colony-specific bleaching has been documented for over a century. But the last 25 years, we’ve seen widespread bleaching events with a diverse range of coral species over a vast area of reef. These events are caused by high sea temperatures combined with enhanced UV exposure. Just an increase of 1oC – 2oC above the average can cause mass coral bleaching. They are one of the endangered species right now.

7. They’re home to millions of marine flora and fauna

Known as the “rainforests of the sea”, coral reefs are home to millions of species, including fish and seabirds, turtles, crustaceans, or even sharks, and dolphins. They maintain a huge underwater ecosystem.

The “refuges” that dot a coral reef are the reason why so many creatures come here. Refuges are fissures and niches within which fish might hide to avoid predators. They provide a perfect hiding place for different creatures at any time.

Corals are home to many species

Furthermore, the marine life in and around the reef promotes a healthy exchange of nutrients, ensuring a steady flow of essential minerals and vitamins. The reefs filter the water, allow nutrients to move through while protecting marine life from toxic chemicals, particle pollution, and other contaminants.

Fish, seabirds, algae, reptiles, and many creatures thrive because the coral reef protects them and filters the water. They allow nutrients to move through while safeguarding marine life from toxic chemicals, particle pollution, and other contaminants.

Algae, sponges, fish, seabirds, reptiles, sponges, and marine invertebrates use them to establish a stable biosphere.

8. Have huge benefits to the environment and human

a. Coral reefs keep the seafloor stable

The sea bed has become increasingly unstable over the last few decades as a result of extensive sand mining. Human activities have also started to cause erosion. Developing throughout the seafloor, coral reefs can control erosion. They aid in the stabilization and prevention of big swaths of land from moving.

The coral’s core is made up of polyps that attach their pedal discs to the substrate surface. Calcium secretion also securely embeds the entire coral reef over millions of years. Even after corals die, they still protect the seafloor from erosion. However, because the deceased polyp no longer generates its shell, the reef will disappear over time.

Coral reefs prevent beach erosion by stabilizing the ocean floor and also provide as a bedrock for the formation of islands. Some coral reefs can absorb more than 95% of incident wave power. They serve as a buffer or natural barrier for the beach, protecting shorelines from erosion caused by wave action. Thus, coral reefs protect people and property by supporting the seafloor.

b. Filter and improve the quality of seawater

Polyps are extremely sensitive to even little environmental changes. Changes in pH, temperature, salinity and particulate matter concentration can all kill a polyp. As a result, corals have an internal filtration system. To eliminate particle matter, they use microscopic sieves that line the coral shell. They also adapt to slight temperature and salinity changes.

This ability helps to improve the quality of water, which benefits organisms within coral reefs by providing them with clean, filtered water. The more corals in the reef grow, the more they can digest water and enhance filtration. Even after a polyp is dead, the coral skeleton maintains to provide some filtration.

The disadvantage of this filtration is that creatures within the reef become more vulnerable to major environmental changes. They get used to the comfortable water, but they may not be able to adapt if the temperature changes. The polyp suffers the same fate, being dependent on substantial filtration for survival.

c. Support 25% of ocean life

People call corals with the names of ecosystem engineers or architect species for their roles in designing the physical environments in which animals live. Coral reefs are like a marine forest, the nooks and crevices of a coral reef provide a habitat and a home for a vast, bio-diverse community of ocean life.

Corals provide food and income for humans. They provide sandy beaches and protect coastlines from up to 90% of potentially harmful waves and flooding. The value of the advantages provided by coral reefs is approximately valuable to be $10 trillion each year.

d. The red sea coral reef is resistant to temperature changes

The Red Sea is famous for its red coral reefs and the bacteria Trichodesmium Erythraeum within the corals is responsible for this brightly red color. The coral reefs of this sea are nearly 2 kilometers long and are estimated to be between 5,000 and 7,000 years old. The Egyptian government had to establish the Ras Mohammed National Park to safeguard these coral species.

The coral reefs here are famous for their tolerance to extreme temperatures and diseases. Thalassomonas Loyona is a bacterium recognized for causing white plague, a devastating sickness exclusive to corals of the species Favia Favus. It bleaches the corals, causing them to die.

While most other reefs across the world have significant rates of coral bleaching, the infection rate of the Red Sea corals is only 9% – an astonishingly low number. The reason for this is the presence of BA3 which can kill the bacterium.

Currently, research is being performed to determine the viability of employing BA3 to prevent bleaching on other coral reefs.

e. Coral reefs help to mitigate hurricanes

Coral reefs have an important role in reducing the effects of hurricanes and storms. Scientists have directly tracked the relationship between coastal protection and coral health in the region. During the sequence of storms that hit the Eastern coast of North America and the Caribbean in the 2000s, areas with coral reefs resisted the storm better.

Tsunamis and storms can be managed because Coral reefs can reduce energy by roughly 97%. You can easily recognize with the water within a lagoon is always calmer than the water beyond the reef.

Surprisingly, corals play the same roles as breakwater embankments constructed outside of ports. Countries in hurricane and storm-prone areas can lessen the damage by 30% by extending a few tens of meters of corals from the shoreline.

f. Can be used for medicinal properties

Since ancient times, corals have been utilized for medical purposes. Scientists have discovered that they have therapeutic benefits.

The coral calx first appeared in Indian medicine, where it was known as Praval Bhasma in Sanskrit. It was frequently used to treat bone diseases, calcium deficiency, and metabolic abnormalities. In other civilizations, calcium carbonate obtained from coral shells was powdered and used to treat ulcers and other digestive tract diseases.

Coral shells are being employed in bone grafting to offer a foundation for the body’s healing of complicated fractures. It is also used to treat symptoms of diseases and medical disorders such as AIDS and cancer.

Because corals are facing extinction due to climate crisis, pollution near the shoreline, and effluent dumping, the use of corals in medicine is subject to strict laws.

9. There’re hundred of Coral species

There are around 6,000 coral species worldwide, with some flourishing in warm shallow seas near coasts and others surviving on the dark, cold bottom of the open ocean. They come in a wide range of shapes, sizes, and colors. Mound and boulder corals are as their names, they’re big and spherical mounds on the seafloor. Brain corals have the shape of a human brain, with maze-like patterns running over them.

Branching corals can grow upwards and outwards like tree branches or flatten out like a table top. Sea fans, a type of soft coral, have large flat fans that softly move back and forth with the current of the water. Sea pens and sea whips resemble trees, which make them look like an underwater forest. Pillar corals form tall columns that, when grouped together, can resemble a city skyline.

Colorful Sea Whip (Leptogorgia virgulata) is a colonial soft coral found along the Atlantic Ocean’s western coast. They have long, branch-like arms which can grow no more than 60cm tall (24 inches). This colorful coral provides critical habitat for a variety of other species, such as the Atlantic wing oyster and several varieties of shrimp.

Clubbed Finger Coral (Porites porites) is one of the tiniest coral species. It has tiny lobes with a white or blueish-grey tint that resembles thick fingers. Some clubbed finger corals can live for an astonishingly long time.

Finger Coral (Montipora digitata): Despite having the same common name as the clubbed finger coral, this coral is an entirely different species. They grow in the form of little bush-like clusters with large, finger-like branches. Nonetheless, unlike many of its neighbors, the finger coral appears to be remarkably unharmed by bleaching.

Mushroom Coral (Fungia fungites), also known as Plate Coral, prefers to live in very peaceful reefs with little activity. They will only connect to a reef in the early stages of their lives. When it grows large enough, it will break loose from the reef and live on the bottom by itself.

Elkhorn Coral (Acropora palmata) is one of the most common corals in the Caribbean Sea. Elkhorn coral likes to develop in big groupings known as thickets, which are typically found in shallow waters.

Leaf Coral (Pavona decussata): As the name, it usually has the form of a leaf that is just 3 to 10 millimeters thick.

Carnation Coral (Dendronephthya) is a popular home aquarium species. They are, however, difficult to care for. The carnation coral, unlike most other corals, feeds solely on phytoplankton, therefore it needs a steady source of food to thrive.

Open Brain Coral (Trachyphyllia geoffroyi) is a popular coral species for home aquariums. It has an unusual figure-eight shape and a plethora of fantastic colors. They can change into a variety of bright colors as they age.

Grooved Brain Coral (Diploria labrynthiformis) resembles a human brain. It contains deep grooves that resemble the folds of the human brain, and it frequently has a grey tint that adds to its brain-like appearance.

Organ Pipe Coral (Tubipora musica) is a soft coral found in the central and western Pacific. Interestingly, although being categorized as a soft coral, this species has a hard calcium carbonate skeleton. It is well-known for its lengthy polyps, which resemble organ pipes. When dying, it frequently leaves behind a calcium carbonate skeleton. This skeleton can be brilliant red.

Vase Coral (Montipora capricornis), commonly known as Monti from its Latin name, is found naturally across the Indo-Pacific, particularly in the Red Sea. It prefers to reside in the upper half of the reef, where the water is warmer.

Precious Coral (Corallium), sometimes known as red coral, is the common name for a genus of corals called Corallium. What distinguishes these corals is that when they die, they leave behind a hard skeleton of calcium carbonate. Because these skeletons are frequently red, they are popular as a raw material among jewelry producers. This also makes them in danger of being fished to make jewelry.

Bubble Coral (Plerogyra sinuosa) features bubble-shaped tentacles that can expand and shrink depending on the feeding schedule of the coral.

Sun Corals (Tubastraea) are a genus of distinct cup corals found across the Caribbean. They have been observed in areas as far north as the Florida Keys, but prefer deep waters, particularly near shipwrecks.

Boulder Star Coral (Monstastrea annularis/Orbicella annularis) is a type of coral that is generally known as the boulder star coral. They develop small boulder-shaped clumps composed of dozens of individual polyps. They are frequently found in colonies resembling mounds of green or golden rocks.

Staghorn Coral (Acropora cervicornis) has a more tubular shape than elkhorn coral, giving it the appearance of adult male deer horns.

Massive Starlet Coral (Siderastrea siderea) forms large dome-shaped structures made up of dozens of smaller individual corals.

Lettuce Coral (Agaricia agaricites) is a widespread coral in the Atlantic and Caribbean oceans. As the name implies, lettuce coral has a characteristic lettuce-like look.

The Venus Sea Fan Coral (Gorgonia flabellum) is a well-known variety of soft coral. The Venus sea fan forms gigantic fan-like formations that grow vertically upward from the ocean floor.

Smooth Cauliflower Coral (Stylophora pistillata) likes to move around a lot because it attaches itself to floating items like shipwreck debris. This coral then follows these objects as they drift around in the ocean.

There’re many more species of corals like Sarcophyton, Lobophyllia, Orange cup coral, Ricordea florida, Acropora millepora, Euphyllia corals, Pocillopora, Fire coral, Goniopora coral, Turbinaria, Gorgonian coral…


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