For most of us, the image of vibrant coral reefs teeming with colorful fish is synonymous with golden beaches and tropical holiday destinations.
Sometimes referred to as the “rainforests of the sea,” coral reefs resemble the most vivid vegetation we see on Earth. These curious organisms are, however, animals rather than vegetables or minerals.
Known as “colonial organisms,” different coral species grow together, relying on one another for their collective survival.
The individual organisms that make up these coral colonies are known as polyps. With a mouth at one end, surrounded by tentacles, these cylinder-shaped coral polyps draw food into the mouth. Once digested, the polyp releases its waste products through that same orifice.
There are an estimated 6,000 different species of coral in the world, and more are being discovered all the time. Some prefer the warmth of shallow, tropical seas, while others flourish in the darkness of the deep ocean.
How Many Types of Coral are There?
There are three main types of coral: hard, soft, and deep-sea.
Hard Coral
Hard corals have external skeletons, or exoskeletons made up of a type of calcium carbonate called aragonite.
These coral species rely on a specific type of algae to survive, and it’s only through establishing a symbiotic relationship with zooxanthellae algae that they can survive.
Not only do zooxanthellae keep hard coral alive, but they also give it the vibrant colors celebrated by divers, snorkelers, and underwater photographers.
Hard corals are the foundation of the world’s coral reefs. As individual coral polyps attach themselves to the seafloor or other solid structures, like rocks or sunken ships, they start to divide, creating thousands of clones.
As these attach to one other, their calcareous skeletons slowly build a coral colony.
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Soft Coral
Without the stony skeletons of the hard coral, soft coral move and bend with the sea’s currents, much as trees and grasses twist and turn in the wind.
Instead of using calcium carbonate to form exoskeletons, soft corals construct small, supportive elements known as sclerites.
They also have stabilizing cores made up of the same structural proteins found in the horns and hooves of terrestrial animals.
Although soft corals can’t build coral colonies like hard corals, their fast growth rate means they can “quickly recolonize a disturbed area.”
Soft coral doesn’t rely on zooxanthellae algae for its survival but does house these organisms in their tissues in a similar way to hard coral.
Deep-Sea Coral
Researchers only discovered the first species of deep-sea coral around 250 years ago.
Before that, scientists had no way to access its habitat, which is situated some 20,000 feet below the ocean’s surface.
It survives with little to no sunlight and without the symbiotic relationship, other coral types have with zooxanthellae.
Some of the oldest organisms in the world, some deep-sea coral reefs have been living and growing for nearly 40,000 years.
They survive by trapping microscopic organisms as they drift past on the ocean’s currents.
Since their discovery, scientists have identified almost as many deep-sea species as they have shallow-water corals.
15 Types of Coral: Pictures and Names
It would be impossible to explore every one of the 6,000 or so different types of coral in a single article.
Instead, we’ve selected the most common and colorful species you’re likely to encounter.
Many of these you’ll recognize if you’ve ever been snorkeling on a coral reef or owned a saltwater aquarium.
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5 Types of Hard Coral
#1 Boulder Star Coral
This reef-building coral is abundant in the warm waters of the western Atlantic Ocean.
It lives in shallow waters less than 260 feet deep and forms a variety of shapes, the most predominant being a dome-like mound or boulder.
The name Boulder Star may refer to three different types of coral, all of which share similar “star-like corallites.”
#2 Brain Coral
This unmistakable hard coral bears a startling resemblance to the human brain.
Although it looks like a single organism, it’s actually a complex coral colony consisting of numerous individual polyps.
Brain corals can reach heights of up to two meters and, scientists believe, may live for several hundred years.
#3 Bubble Coral
Although it looks soft and bubbly on top underneath the Bubble coral is hard and stony. The grape-like “bubbles” contain water-filled tubes known as vesicles.
These expand during the day, absorbing sunlight that the coral then converts into energy using photosynthesis. At night, these vesicles deflate, exposing the coral’s tentacles.
Bubble coral has a global distribution, but climate change and habitat destruction have left this stony coral species struggling to survive.
#4 Lace Coral
Lace corals, also known as stylasterids, vary widely in color and form. Many have a delicate, lace-like appearance that belies their role as reef-builders.
Unlike other reef-builders, Lace corals don’t rely on a symbiotic relationship with zooxanthellae, which means they’re not susceptible to coral bleaching.
Many of the 330 different types of Lace coral live in deep water habitats, but a study conducted in Australia in 2019 identified 11 distinct shallow-water species.
#5 Staghorn Coral
Image source: https://en.wikipedia.org/wiki/Staghorn_coral
Arguably “the world’s most successful coral,” scientists believe the Staghorn coral evolved some 55 to 65 million years ago. It has been a dominant feature on reefs for the past 500,000 years.
Reliant on the zooxanthellae algae for its survival, the Staghorn is highly susceptible to coral bleaching.
Climate change is also threatening their existence by reducing their ability to recover from the threats presented by human activity and disease.
5 Soft Coral Species
#1 Snowflake Coral
The Snowflake coral’s delicate appearance contradicts its aggressive tendencies. Native to the tropical waters of the Atlantic Ocean, ranging from South Carolina to Brazil, it has since spread throughout the Atlantic and Pacific Oceans.
Its determined colonization of varied coastal habitats has put coral reefs and other tropical ecosystems at risk.
Preferring sheltered caves and crevices, snowflake coral inhabits shipwrecks, pier pilings, and deep-water reefs.
#2 Organ Pipe Coral
Although the Organ Pipe is a soft coral, it gets its name from its hard skeleton of pipe-like calcium carbonate tubes.
A series of polyps decorate the end of each tube, extending feather-like tentacles into the sea.
The distinctive bright red color of the Organ Pipe coral comes from the presence of carotenoids, which also give carrots their bright-orange hue.
#3 Venus Sea Fan Coral
A surprisingly robust species of coral, the Venus Sea Fan grows in shallow water less than 30-feet deep.
Once cementing its small base, its branches and sub-branches form a complex coral colony.
A true soft coral, the Venus Sea Fan has no hard skeleton. Despite that, it can still reach heights of nearly a meter tall.
#4 Carnation Coral
The Carnation coral may resemble a tree but can’t produce food through photosynthesis.
Like the sun coral, it’s a nocturnal hunter that preys on passing zooplankton. To make this process more effective, it inflates itself to double its size at night.
While some species of Carnation coral prefer sunny reefs, most occur in sheltered areas, like caves and ledges, where sunlight rarely penetrates.
#5 Devil’s Hand Coral
Also known as Lobophytum, Devil’s Hands coral enjoys warm, tropical waters where it forms colonies up to three feet wide.
Instead of relying entirely on their symbiotic relationship with zooxanthellae, Devil’s Hand corals also capture food particles as they drift by and absorb organic matter from the water around them.
Scientific studies suggest that Devils’ Hand corals contain anti-inflammatory steroids that may provide effective treatment for some cancers.
5 Types of Deep-Sea Corals
#1 Ivory Bush Coral
Although the ivory bush coral prefers deep-sea environments, it also forms shallow-water coral colonies.
Its environment dictates which feeding strategies it employs, with deep-sea varieties using filter-feeding.
On a shallow-water reef, however, the Ivory Bush coral uses a combination of photosynthesis and zooxanthellae algae.
#2 Lophelia Coral
This delicate-looking coral only lives on deep-sea reefs and is usually found around 3,300 feet below sea level.
Like all deep-sea coral, the Lophelia variety is highly susceptible to climate change. Deep-sea corals all use calcium carbonate to build their hard skeletons.
As the ocean becomes more acidic, this substance becomes increasingly rare, jeopardizing the survival of coral species like the Lophelia.
#3 Bubble Gum Coral
One of the most prolific coral species in North America, the bubblegum coral is bright pink with polyps at the end of its branches.
During the day, these polyps resemble wads of pink bubblegum. At night, however, each one extends its tentacles into the cold water to capture plankton and other small prey as they drift by.
#4 Black Coral
Black coral is a soft deep-sea coral with few predators but many uses. These tree-like colonies provide shelter, food, housing, and protection for numerous animal species, including crustaceans, fish, and mollusks.
There are approximately 280 different species of black coral, or antipatharian, growing on seabeds throughout the world. The oldest of which is thought to be over 4,000 years old.
#5 Bamboo Coral
Inhabiting every ocean in the world except for the Arctic, the slow-growing Bamboo coral is one of the most widespread and cosmopolitan.
Although they grow just a few millimeters each year, they can form tree-like colonies that stand up to five feet tall.
Preferring deep-sea habitats, bamboo coral has been discovered at depths of up to nearly 16,000 feet!
FAQ
What are the Four Types of Coral Reef?
Fringing Reefs
These are the most common type of reef and begin at the shore, growing seaward.
In some circumstances, fringing reefs develop into circular atoll reefs. A prime example of a fringing reef is Australia’s Ningaloo Reef.
Atoll Reefs
This type of reef often grows out of sunken volcanic islands, forming a ring-shaped reef or island around a central body of water, known as a lagoon.
One of the world’s most notable atoll reefs is the Great Chagos Bank in the Indian Ocean, some 500km south of Maldives.
Barrier Reefs
Similar to fringing reefs, barrier reefs grow along the shoreline but are separated from land by an expanse of water.
The Great Barrier Reef is the world’s largest and stretches for 1,429 miles, covering around 133,000 square miles.
Patch reefs
Patch reefs frequently occur between barrier and fringing reefs, growing up from the bottom of a continental shelf or island.
As patch reefs usually form part of a larger reef, they are rarely recognized or recorded as individual reefs.
The most famous patch reefs are probably those on the Virgin Islands of St. John, St. Thomas, and St. Croix.
What are the Most Common Types of coral?
Hard and soft corals are the most common types and often occur in varying depths and diverse habitats.
How Many Types of Coral are there?
Over 6,000 different types of coral have been identified to date, with more emerging as technology enables us to investigate deeper and further into our oceans.
What Types of Animals Live in Coral Reefs
Coral reefs are essential to the ocean’s biodiversity, providing food, shelter, and protection to a wide variety of marine life. These include clams, crabs, numerous fish species, oysters, sea urchins, and sponges.
How is Coral Formed?
Every coral colony starts life as an individual polyp. As these polyps bud or reproduce, they create genetically identical copies of themselves. These adhere to one another, creating colonies as they grow.
Reef-building corals create hard skeletons out of calcium carbonate. These provide a foundation for other polyps and baby corals to settle on. Along with the skeletons of dead polyps and colonies, other animals and plants also contribute to the reef construction.
What is the Impact of Climate Change on Coral Reefs?
Greenhouse gases are causing both the earth and ocean to heat up. Agitated by the increasing temperatures, those corals that coexist with zooxanthellae expel the algae from inside their tissues, exposing the calcium carbonate skeleton beneath.
This process, known as coral bleaching, stunts the coral’s ability to grow and reproduce and makes it more susceptible to death and disease.
Conclusion
Coral may be one of the oldest organisms on Earth, but the likelihood of it surviving another episode of coral bleaching is remote.
Experts predict that, if left unchecked, global and local environmental pressures will have endangered 90% of our coral colonies by 2030.
This would seriously impact the ocean’s environmental diversity and the estimated 275 million people that depend on them for a living.
It would also mean the demise of one of our world’s oldest organisms.
Nicky is a British adventurer and animal lover who spends her time exploring the natural world and writing about her experiences. Whether on horseback, underwater, running, hiking or just standing with a fishing rod in hand, she embraces everything her adopted home of South Africa has to offer.
I am a shell collector, but have a few pieces of Croal, that I cannot identify. Can I send a picture.
Walt