How Coral Reefs are Formed?

Coral reefs sometimes referred to as the “rainforests of the sea,” are home to about 25% of all known marine species.

More than 4,000 different fish species, 700 different coral types, and countless other plants and animals call reefs home.

Hard corals are the master builders of coral reefs.

Hard corals, in contrast to soft corals, have rocky skeletons formed of limestone, which is created by coral polyps.

The skeletons of dead polyps are left behind and used as the building blocks for new polyps.

Layers of skeletons covered by a thin layer of living polyps make up the actual coral branch or mound.

If a coral reef is compared to a busy city, a coral colony would be like a single apartment complex with numerous rooms and halls that are home to various marine animals.

The only coral barrier reef in North America can be found in the Florida Keys.

The Soldier Key in Biscayne Bay and the Tortugas Banks are both parts of the Florida reef tract.

The property is approximately four miles wide and almost 150 miles long.

Seen the popularity of these unique creatures one might begin to ask how coral reefs are formed?

Before we look into how these unique animals are formed let’s know, what is a coral reef?


What is a Coral Reef?

Large underwater structures known as coral reefs are made up of the coral-like skeletons of colonial marine invertebrates.

The coral species that form reefs are referred to as hermatypic, or “hard,” corals because they draw calcium carbonate from saltwater to make an exoskeleton that is strong and resilient and shields their soft, sac-like bodies.

Polyps are the individual corals that make up a coral.

Coral polyps build their exoskeleton to the existing coral structure by living off the calcium carbonate exoskeletons of their ancestors.

The coral reef progressively expands over the years, gaining one little exoskeleton at a time, until they are enormous components of the aquatic ecosystem.

Types of Coral Reefs

According to Coral Reef Alliance, the four basic classes of coral reefs commonly accepted by scientists are:

  • Fringing Reefs
  • Barrier Reefs
  • Atolls
  • Patch Reefs

1. Fringing Reefs

Source: Fringing reef – Wikipedia

Fringing reefs develop close to the shorelines of continents and islands.

There are small, shallow lagoons separating them from the shore.

The most prevalent kind of reef is one that is fringed.

2. Barrier Reefs

Source: Barrier reef (geology) – Britannica

Barrier reefs also run parallel to the coast, but deeper, larger lagoons divide them.

They can constitute a “barrier” to navigation at their shallowest locations, where they can even touch the surface of the water.

3. Atolls

Source: What Is An Atoll? – WorldAtlas

Atolls are coral rings that form safe lagoons and are typically found in the middle of the ocean.

Atolls typically develop when islands with fringing reefs collapse into the sea or when the surrounding sea level increases.

4. Patch Reefs

Source: Patch reefs – Capricorn Bunker Group (aerial photo of patch reef) – Flickr

Patch reefs are tiny, solitary reefs that emerge from the continental shelf or island platform’s exposed underside.

They typically exist between barrier reefs and fringing reefs.

They come in a wide range of sizes and hardly ever break the surface of the water.

Importance of Coral Reefs

Coral reefs are incredibly intricate ecosystems that, because of their stunning and distinctive architecture, offer crucial habitats for fish and other species.

Numerous creatures that are essential to the coral reef ecosystem, including fish, marine worms, clams, and many other animals and plants, find shelter in these structures.

We will go through some of the reasons why coral reefs are significant below.

Source: Coral Outcrop Flynn Reef by Toby Hudson via Wikimedia [CC by 2.0]

  • They provide habitat and refuge for a variety of marine creatures.
  • They provide a source of nitrogen and other crucial nutrients for marine food chains.
  • They shield coastlines from the destructive effects of wave action and tropical storms.
  • Coral reefs are a biodiversity hotspot because they are home to over 4,000 species of fish, 700 types of coral, and thousands of other plants and animals.
  • They also aid in fixing carbon and nitrogen and recycling nutrients.
  • Coral reefs serve as a natural barrier between coastal cities, towns, and communities and the ocean’s waves. Coral reefs provide about 200 million people with protection from storm surges and waves.
  • People who live close to coral reefs depend on them for a major portion of their protein and they are essential to global fisheries.
  • The coral reef holds the potential to hold even more of the chemicals that are already employed in human treatments.
  • Coral reefs support fisheries and tourism, which together account for billions of dollars in revenue and countless employment in more than a hundred nations.
  • Coral reefs are important to the fishing business because many fish spawn there and young fish hang out there before venturing out into the open sea.

Fishing and tourism at the Great Barrier Reef bring in more than $1.55 billion annually for Australia’s economy.

To provide a precise, verifiable record of climate occurrences during the last million years or so, coral reef research is crucial.

This includes information about recent powerful storms and the impacts of humans as seen in changes in coral development patterns.

How Coral Reefs are Formed?

When free-swimming coral larvae cling to submerged rocks or other hard surfaces along the margins of islands or continents, coral reefs are first formed.

Reefs develop one of three basic characteristic structures when the corals swell and grow.

The most frequent type of reef, a fringe reef, extends immediately out to sea from the shore and creates boundaries for the coastline and nearby islands.

Barrier reefs abut shorelines as well, but farther off.

They are isolated from the nearby land mass by an open lagoon of water that is frequently deep.

An atoll develops when a fringing reef surrounds a volcanic island that entirely submerges while the coral continues to grow higher.

Atolls typically have an oval or circular shape with a central lagoon.

Gaps in the reef allow access to the central lagoon, and portions of the reef platform may form one or more islands.

Barrier reefs and atolls are not only some of the most stunning and biologically varied environments in the ocean but also the oldest.

A coral reef can take up to 10,000 years to form from a group of larvae, with growth rates of 0.3 to 2 centimeters per year for large corals and up to 10 centimeters per year for branching corals.

Barrier reefs and atolls can take anywhere from 100,000 and 30,000,000 years to fully build, depending on their size.

The biogeographic profiles of the fringing, barrier and atoll reef types are similar to one another.

Characteristic horizontal and vertical zones of corals, algae, and other species are created by the interaction of the bottom topography, depth, wave, and current energy, light, temperature, and suspended particles.

Depending on the location and kind of reef, these zones change.

The reef flat, reef crest or algal ridge, buttress zone, and seaward slope are the four main divisions that most reefs share as they extend out to sea from the shore.

Threats to Coral Reefs

Globally, coral reefs are in decline. Many experts now think that unless we step up our efforts to safeguard coral reefs, their very survival may be in danger.

Threats to coral reefs come from both local and global sources.

  • Local Threats to Coral Reefs
  • Global Threats to Coral Reefs

1. Local Threats to Coral Reefs

The majority of coral reefs are found nearby in shallow water.

Due to this, they are particularly susceptible to the negative consequences of human activity, both directly through the exploitation of reef resources and indirectly through the effects of nearby human activities on land and in the coastal zone.

The social, cultural, and economic fabric of local coastal communities is intricately woven with many of the human activities that harm coral reefs.

Coral reefs face many threats from local sources, including:

  • Physical Damage or Destruction
  • Pollution
  • Overfishing
  • Overharvesting
  • Algae And Bacteria
  • Irresponsible Tourism

1. Physical Damage or Destruction

Damage from recreational overuse, damaging fishing methods and equipment, dredging, quarrying, and coastal development (touching or removing corals).

The deliberate harm some individuals cause to corals is another aspect of this.

It has been reported that visiting divers have carved phrases and patterns into the cherished corals, further harming their already fragile bodies.

Additionally, travelers have been known to tear off chunks of coral to bring back as gifts.

This, sadly, serves as a reminder of how many individuals like inflicting violence on animals for amusement.

2. Pollution

There are many types and sources of pollution from land-based activities, for example:

  • Sedimentation
  • Nutrients
  • Pathogens
  • Toxic Substances
  • Trash
1. Sedimentation

This happens as a result of human activities like agricultural practices, stormwater runoff, and coastal development.

Coral is in danger because when it is deposited, it smothers the coral, preventing it from growing, reproducing, and feeding.

2. Nutrients

Residential and agricultural fertilizer, pet waste, and sewage all leach nutrients into the water.

Even though nutrients are normally important, this hazard is too nutrient-rich for reefs, leading to an excess of bacteria and other microorganisms like algae.

This keeps the reefs’ sunlight from reaching them, depleting their oxygen.

3. Pathogens

Contaminants including improperly handled sewage and stormwater contribute to this concern.

Bacteria and parasites from these pathogens have been found to infect corals with illnesses, however, it is a rare occurrence.

4. Toxic Substances

These including as metals, organic compounds, and pesticides, which are present in industrial discharges, sunscreens, urban and agricultural runoff, mining activities, and landfill runoff.

Pesticides may have an impact on coral growth, reproduction, and other physiological functions.

Particularly herbicides can harm symbiotic algae (plants).

This may harm their relationship with the coral and cause bleaching.

Polychlorobiphenyls (PCBs), oxybenzone, and dioxin are only a few examples of the organic compounds and metals that are thought to have an impact on coral reproduction, growth rate, eating, and defensive responses.

5. Trash

The trash from improper disposal, microplastics from stormwater runoff, and other debris.

Marine debris, which includes trash like plastic bags, bottles, and abandoned fishing gear, can entangle and kill reef creatures as well as break or damaged corals.

It can also snag on corals and block the sunlight essential for photosynthesis.

Coral, fish, sea turtles and other reef creatures might ingest degraded plastics and microplastics (such as beads in soap), which could obstruct their digestive processes and introduce hazardous substances.

3. Overfishing

Overfishing can change the structure of the food chain and have a cascade effect by, for example, lowering the population of grazing fish that keep corals free of algal overgrowth.

Corals can also be physically harmed by blast fishing, which involves killing fish using explosives.

4. Overharvesting

Overharvesting of some species, habitat degradation, and decreased biodiversity can result from the removal of coral for the aquarium trade, jewelry, and curios.

The cumulative effects of these stressors can make the reef less resilient overall and make it more vulnerable to disease and invasive species.

A reef ecosystem’s biological checks and balances may become unbalanced as a result of invasive species.

5. Algae And Bacteria

The enormous growth of toxic marine algae, which blocks sunlight and depletes the water’s oxygen supply, is sparked by nitrogen-rich fertilizers, animal waste, human sewage, and untreated industrial effluents.

This imbalance in the marine ecosystem is the outcome.

The extra nutrients also encourage the growth of potentially lethal bacteria or fungi, which can be harmful to corals and increase their susceptibility to illness.

Similar to how hot water emitted from thermal plants and oil spills may be extremely harmful to coral reef health.

6. Irresponsible Tourism

If tourism is not properly regulated and managed, it adds to the hazards to coral reef health. Photograph courtesy of ChameleonsEye/Shutterstock

Numerous tourists are drawn to the coral reef ecosystems by their dazzling and vibrant colors.

Tourists frequently engage in sailing, fishing, diving, snorkeling, and other outdoor pursuits close to coral reefs.

The activities that harm the reefs and disrupt the organisms that live there include touching the reefs, agitating the sand and silt on the seafloor, and collecting corals.

2. Global Threats to Coral Reefs

The greatest global risks to coral reef ecosystems are rising ocean temperatures and shifting ocean chemistry.

These dangers are brought on by rising ocean carbon dioxide levels and warming air temperatures.

  • Climate Change
  • Ocean Acidification

1. Climate Change

Bleached Coral Reef – Source: Image credit: buttchi 3 Sha Life/Shutterstock

Since the earth’s atmosphere has been heated by human-caused global warming and the surface temperature of ocean waters has increased, coral reefs all over the world are being affected.

Zooxanthellae, the small algae that reside in coral polyps and support coral health, are susceptible to higher temperatures.

Thus, a minor rise in ocean temperature causes corals to expel their zooxanthellae, revealing their limestone skeleton and causing the coral tissues to whiten or bleach.

These bleached corals will eventually perish and the reef will become a lifeless environment when they are repeatedly exposed to warmer ocean waves.

The ideal water temperature for promoting coral growth is thought to be between 20 and 28 degrees Celsius.

However, the majority of the corals will get bleached if the water temperature drops below 18°C or rises beyond 30°C.

Coral bleaching is anticipated to worsen as long as global warming keeps the globe from cooling.

2. Ocean Acidification

Coral reefs are more susceptible to illness as a result of ocean acidification.

Ocean acidification is the term used to describe the process by which ocean waters become more acidic as a result of an increase in carbon dioxide levels brought on by the excessive burning of fossil fuels.

The ocean water’s pH is consequently lowered as a result, which has an impact on coral reefs all around the world.

The carbonic acid produced by this process of acidification prevents corals from constructing their calcium carbonate exoskeletons.

Coral reefs are more susceptible to illnesses, which can lead to the structure of the reef being destroyed.

Studies have also shown that an increase in acidity causes a loss in coral reef biodiversity, which results in the extinction of crucial species needed for the development of robust reefs.

The coral reefs are also negatively impacted by other effects of climate change, such as increasing sea levels, stronger and more frequent tropical storms, and changing ocean circulation patterns (El Nino).

The coral reefs are expected to become substantially deeper underwater as a result of the rising sea levels, receiving significantly less sunshine, and developing more slowly.

Stronger tropical storms produce waves that are significantly bigger and more forceful, which can break coral branches, turn coral colonies upside down, and destroy the structure of the reef.

Coral Reefs Around the World

The following are some of the best coral reefs around the world

  • Maldives
  • Great Barrier Reef – Australia
  • New Caledonia Barrier Reef – New Caledonia
  • The Red Sea Coral Reef – Red Sea
  • Rainbow Reef – Fiji
  • Tubbataha Reefs Natural Park
  • Raja Ampat – Indonesia
  • Palancar Reef – Cozumel, Mexico
  • Great Chagos Archipelago – Indian Ocean
  • Wakatobi Islands – Indonesia
  • Lord Howe Island – Australia
  • Belize – Belize Barrier Reef
  • Apo Reef – Philippines
  • Bonaire Reef – Dutch Caribbean
  • The Grand Central Station and Chimneys – Fiji

1. the Maldives

Source: Scuba Diver on Coral Reef, Felidhu Atoll, Maldives | © Mauritius images GmbH / Alamy Stock Photo

The Maldives consist of 1,200 islands and 26 atolls; the seas have a stunning coral reef environment and a diverse range of marine life.

However, over the past few years, there have been optimistic signs of recovery.

Unfortunately, with the warming of the ocean waters, particularly the El Nio weather event of 1998, the majority of coral suffered from heavy bleaching and died off.

2. Great Barrier Reef – Australia

Source: Great Barrier Reef, Australia | © WaterFrame / Alamy Stock Photo

The Great Barrier Reef in Australia is not only the largest and one of the most stunning reefs on the planet.

The reef consists of more than 3,000 distinct reef systems, together with 400 different varieties of coral and an abundance of colorful marine life.

The reef, which sits off the coast of Queensland, is home to hundreds of islands, many of which have stunning beaches that draw both locals and visitors each year.

The Great Barrier Reef is one of the Seven Natural Wonders of the World and a UNESCO World Heritage Site.

3. New Caledonia Barrier Reef – New Caledonia

Source: A green sea turtle underwater on a shallow coral reef with fish, New Caledonia, South Pacific ocean | Courtesy of Damocean / Getty Images

The UNESCO World Heritage Site New Caledonia Barrier Reef, the second-largest double barrier reef in the world, is a wonderful example of Mother Nature at her best, complete with stunning blue waters in various tints.

This double-barrier reef, which can be found in the South Pacific off the northeast coast of Australia, is home to a wide range of marine life, many of which are still being identified and categorized.

The Green turtle and 1,000 different kinds of fish have already been identified. This beautiful habitat, like the majority of them, is always in danger because of human activities.

4. The Red Sea Coral Reef – Red Sea

Source: Red Sea coral reef, Safaga, Egypt, Red Sea, Indian Ocean | © Jane Gould / Alamy Stock Photo

The Sahara and Arabian deserts are two of the world’s hottest and driest deserts, and the Red Sea Coral Reef is an incredible underwater habitat sandwiched between them.

This 1,200-mile-long reef, which is more than 5,000 years old, is home to more than 1,200 fish, 10% of which are unique to this region, and 300 hard coral species.

This coral reef is sturdy and can survive a wide range of factors, including drastic temperature variations, which is something to keep in mind.

5. Rainbow Reef – Fiji

Source: Colorful Soft Corals (Dendronepthya sp.) and small Anthias fish (Psedanthias sp.), Rainbow Reef near Taveuni Island, Fiji, South Pacific | © Danita Delimont Creative / Alamy Stock Photo

Rainbow Reef is the ideal name for this location since it boasts a kaleidoscope of vivid hues under the water, produced by the hard and soft corals and marine creatures that call the area home.

It is situated between the second and third largest islands of Fiji, Vanua Levu, and Taveuni.

A visual feast is provided by close to 1,200 different fish species and 230 different hard and soft corals.

It’s not surprising that this is one of the best diving locations in the world given its incredible beauty.

6. Tubbataha Reefs Natural Park

Source: © RooM the Agency / Alamy Stock Photo

The Philippines’ Tubbataha Reefs are renowned as one of the world’s best diving locations because of their breathtaking underwater landscape that is made up of colorful corals and marine life.

The reefs, which consist of two coral atolls, are home to 600 different species of fish, 360 different types of coral, 11 different shark species, 13 different species of dolphins and whales, birds, and Hawksbill and Green sea turtles.

The “pristine coral reef” of the Tubbataha Reef Natural Park, together with the “vast lagoons and two coral islands,” led to its designation as a UNESCO World Heritage Site in 1993.

7. Raja Ampat – Indonesia

Source: Bioluminescent seafan surrounded by a halo of reef fish, Raja Ampat, Indonesia | © Howard Chew / Alamy Stock Photo

Given the size of the region, the Raja Ampat Islands have the most coral reef biodiversity, with 450 species of reef-building coral present in its waters.

When scientists discovered this fact, they put a plan into motion to protect this underwater habitat, as so many reefs around the world are at risk.

Located in the heart of the Coral Triangle, an area with 75 percent of all identifiable coral species, the area also has an impressive 1,427 species of fish.

With the abundance of biodiversity, it should come as no surprise that Raja Ampat is a favored spot among divers.

8. Palancar Reef – Cozumel, Mexico

Source: Green Sea Turtle, Palancar Reef, Cozumel, Quintana Roo, Mexico | © Cultura Creative Ltd / Alamy Stock Photo

Divers return again and again to this beautiful hidden gem off the coast of the island Cozumel in Mexico.

Divers frequently return to this stunning undiscovered treasure off the Mexican island of Cozumel.

Even while it may not be as big as other reefs, this one is just as stunning thanks to its marine life, which is abundant and multicolored (think vivid pinks, greens, oranges, and yellows).

The region, which contains 1,427 different kinds of fish, is in the center of the Coral Triangle, which is home to 75% of all known species of coral.

It should not be surprising that Raja Ampat is a favorite diving location given the region’s rich biodiversity.

9. Great Chagos Archipelago – Indian Ocean

Source: Chagos Information Portal

The Great Chagos Archipelago, which consists of 55 islands, is situated in the center of the Indian Ocean.

The Great Chagos Bank is the world’s largest coral atoll and is also the least polluted and most protected.

Here is where half of the world’s coral may be found, including indigenous species like the brain-shaped coral Ctenella chagius.

The abundance of fish, along with turtles, dolphins, whales, and other animals, should also be considered.

Researchers don’t even use sunscreen to maintain the water as pure as possible.

10. Wakatobi Islands – Indonesia

Source: Coral reef thrives in Wakatobi National Park, Indonesia | © Stocktrek Images, Inc. / Alamy Stock Photo

With 1.39 million hectares and 750 of the 850 coral reef species in the world calling its blue-green waters home, the stunning Wakatobi National Park in the Coral Triangle is a breathtaking site to explore.

This undersea wonder, which is a potential World Heritage Site, is situated off Sulawesi, Indonesia.

The presence of numerous fish species—a total of 942 different species—adds to the already spectacular sight.

11. Lord Howe Island – Australia

Source: Norkeller underwater with fish and corals, North Bay, Lord Howe Island, NSW, Australia | © Suzanne Long / Alamy Stock Photo

Beautiful Lord Howe Island is situated in the Pacific Ocean.

Even if the sea is incredibly beautiful from above, diving beneath its pristine, blue waves may reveal even more attraction.

Its marine biodiversity is exceptional, with over 90 coral species and 500 distinct fish species, making it a marine park and UNESCO World Heritage Site.

You can approach dolphins, humpback whales, and even sharks up close (the harmless ones, of course). It truly is heaven.

12. Belize – Belize Barrier Reef

Source: Image by Keith Levit via Alamy

The entire Belize Barrier Reef Reserve System was added to the list of UNESCO World Heritage Sites in 1996.

It also boasts several other attractions like coastal lagoons and mangrove forests in addition to having the largest barrier reef in the northern hemisphere.

Only around 10% of what scientists anticipate to find, or 106 hard and soft coral types and 500 kinds of fish, are present on the reef itself.

However, due to man-made or natural causes, it’s not certain which, over 40 percent of the coral reefs are damaged, making protection efforts that much more important.

13. Apo Reef – Philippines

Source: Scuba diver in a coral reef with dominating Acropora table corals (Acropora Hyacinthus), Apo- reef, Philippines | © Helmut Corneli / Alamy Stock Photo

The Apo Reef is the second-longest continuous coral reef in the world, stretching 13 miles across the Mindoro Strait in the South China Sea.

A stunning variety of blue and pink corals, as well as marine life including triggerfish and sea turtles, may be found below the surface of the deep blue waters.

To save this gem from destruction, Apo Reef is currently on UNESCO’s preliminary list for World Heritage Site classification.

14. Bonaire Reef – Dutch Caribbean

Source: Stoplight parrotfish (Scarus viride) at Stove-pipe sponge (Aplysina archeri), Bonaire, Netherland Antilles | © Helmut Corneli / Alamy Stock Photo

Known as ‘The Diver’s Paradise’, the Bonaire Reef is home to a dazzling display of hard and soft corals in bright blues, greens, yellows, purples, and pinks, like an artist’s palette.

Located in the Dutch Caribbean, the waters are crystal clear, allowing divers to see the rich marine biodiversity.

Some of the marine life that call this reef home are angelfish, groupers, sea turtles, and seahorses.

15. The Grand Central Station and Chimneys – Fiji

Source: A diver examines the dive location at Namena Island known as “Chimneys or Thumbs” | Michael Greenfelder / Alamy Stock Photo

The “soft coral capital of the world,” The Grand Central Station and Chimneys in Fiji, is home to an abundance of corals and marine life.

The Bonaire Reef, also known as “The Diver’s Paradise,” is a spectacular display of hard and soft corals that come in vivid blues, greens, yellows, purples, and pinks, like a painter’s palette.

The waters of the Dutch Caribbean are so clear that divers may view the diverse marine life there.

Angelfish, groupers, sea turtles, and seahorses are a few of the marine species that reside on this reef.

Both the Chimneys and Grand Central Station are noted for the abundance of marine species they draw, including manta rays, marble rays, hammerhead sharks, and many others.

The Chimneys have two coral towers that are ornamented with soft coral in a variety of colors.

400 corals, 445 known marine plants, and more than 100 invertebrate species can be found in the vicinity.

Facts about Coral Reefs

  • Coral reefs are home to 25% of marine life.
  • Corals, not plants, are animals.
  • Coral reefs provide food for half a billion people, but they require sunlight to develop, and too much heat can be dangerous.
  • When storms occur, they serve as a barrier.
  • Reefs of coral purify the water they are in.
  • They are a significant source of tourism.
  • There have been coral reefs for 240 million years.


Having known some mind-blowing details about coral reefs, we must seek to protect this biodiverse resource.

Some things are better left to themselves for continuous existence, that’s the case of coral reefs.

Also, having known quite well that climate change adversely affects coral reefs, we should be careful as little actions that go against the climate affects these our water creatures.


Why are coral reefs important?

Coral reefs are important because they offer chances for recreation as well as storm and erosion protection for beaches. They also provide new treatments and food as well. More than 500 million people rely on reefs for safety, income, and food.

What causes coral bleaching?

Climate change is the main factor causing coral bleaching. A warming globe results in a hotter ocean, and coral can drive away algae with a shift in water temperature of as little as 2 degrees Fahrenheit. Other factors, such as incredibly low tides, pollution, or too much sunlight, can also cause coral to bleach.


Editor at EnvironmentGo! | | + posts

A passion-driven environmentalist by heart. Lead content writer at EnvironmentGo.
I strive to educate the public about the environment and its problems.
It has always been about nature, we ought to protect not destroy.

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