The Coral Reef – Cancer

Image of coral reef

General Facts about Coral Reefs.

Enjoyed by scuba divers and sea creatures alike, Coral Reefs represent ocean vitality. Bright colours and shapes adorn these rocky structures with endless textures and designs. Some stand strong against ocean tides, while others dance in the current. They are truly a work of natural art. Among these seascapes, you will see schools of small fish camouflaging and standing out with bright neon tones. But these fish are not the only living organisms in this bountiful seascape. Corals themselves are animals! They are colonial animals that consist of super organisms and small organisms. Today we will explore all of the ways Corals grow and thrive like all other sea life!

It was 485 million years ago, when Coral Reefs first appeared. The fabric of these living, breathing reefs is a calcium carbonate skeleton, and from there sea anemones, corals, and polyps grow to catch sunlight and nutrients. Most Coral reefs thrive in sunny, warm, agitated water that’s close to the surface. They belong to the same family Anthozoa, which includes sea anemones and jellyfish. Thousands of Corals have been discovered over time, in what is known as the “Rainforest of the Sea”. They earned this name by housing 25% of all marine species. In places like Hawaii, their coral reefs house 7,000 species of fish, plants, turtles, and marine mammals.

Image of coral reef
Photo by Francesco Ungaro on

The Coral Reef: Out of the Blue! 

What are Corals?

Corals are colonial organisms, as they are built from colonies of thousands of individual organisms. The animals that comprise Corals are known as polyps. Each polyp has tentacles, a mouth, and a stomach to capture small animals. Their mouth is the only opening and is used to consume and excrete food matter.

Corals inhabit much more than tropical reefs, they have also been found in the depths of dark, cold water. Most Corals rely on dark water to feed. Much like their jellyfish cousins, they use their nematocysts or “stinging cells” to capture zooplankton. These nematocysts release toxins into their prey, killing them on contact!

Corals are also omnivores. They capture organic matter in their mucous film which makes for excellent nourishment.

Coral characteristics.

Geologists have found that Corals and their reef ecosystems date back 240 million years. Most of today’s reef systems are between 5,000 and 10,000 years old. The age of Coral can be calculated like trees on land, where age is measured by growth spurts.

Coral comes in many shapes and sizes. In fact, there are 2,500 species of Coral. The shape and texture of the Corals depend on their location. In reefs with strong currents and waves, the coral will be more robust and flatter, while softer tides produce delicate and detailed patterns and branches.

Hard Corals.

The two main differences between coral species are whether they are Hard Coral or Soft Coral. Hard Corals are the foundation of the coral reef. With all of their alcoves and intricate designs, they make an excellent habitat for fish and invertebrates. This is a symbiotic relationship, where the sea creatures aid the Corals in functioning.

These colonies of Hard Coral are made from calcium carbonate (limestone), which over time becomes rock. Hard Corals are the more prolific and dominant species of Coral. Some examples of Hard Coral are: Staghorn Coral, Table Coral, Brain Coral, Pillar Coral, Great Star Coral, Tube Coral, and Elkhorn Coral.

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Soft Corals.

Soft Corals are another vital part of the reef environment. They do not aid in the building of reefs, but they aid in providing habitats for small fish and invertebrates. Soft Corals have wood-like cores and fleshy rinds to aid them in swaying with the current. While these colourful friends resemble plants and trees, they are animals! Some examples of these animals include:

Sea Whips, Sea Fingers, Sea Feathers, and Sea Pens.

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Reef Characteristics.

Reefs can be divided into 4 categories: Fringing Reefs, Barrier Reefs, Atolls, and Patch Reefs.

Fringing reefs.

These Reefs are the most common. They are found hugging coastlines of tropical landmasses, usually separated from the shore by a lagoon or inlet. This lagoon is always shallow and more integrated into the ocean. It peeks out from under the Island as a continuation of the landmass, giving it that “Fringe” appearance.

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Barrier Reefs.

Barrier Reefs share the proximity to landmasses as Fringe Reefs, but their lagoons are much wider and deeper. The Barrier Reef in Australia is the most dramatic and famous in the world. Barrier Reefs give many landmasses a vast supply of shallow waters, allowing fish and sea life to thrive

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Atolls are more remote Reefs. They consist of ring-shaped inlets protecting a lagoon. These are caused by small islands becoming absorbed by the ocean. They can also be caused by underwater volcanoes. This is why many Atolls are found on continental shelves where tectonic plates see a lot of action!

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Patch Reefs.

Patch Reefs can be the most remote and isolated of all Coral Reefs. This is because they line continental shelves and grow from the bottom of the open ocean. They can also be easily spotted lining continental Barrier reefs. The diversity and unpredictability of these make for interesting shapes, sizes, and locations, with many never reaching the surface. They can be spotted from the air as scattered collections of dark and light patches.

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How do Coral Reefs grow?

In order for a Coral Reef to expand, eggs must be released by a Coral polyp nearby. These free-swimming coral larvae search for rocks and landmasses to cling to. From here, like many organisms, they will spread across the surface and harden. This involves them slowly secreting skeletons made from calcium carbonate. Once the Coral has developed its skeleton, it can offer a substrate for other new polyps to attach.

All Corals grow at different paces. This depends on many factors in the water such as salinity, turbulence, temperature, and food. Massive Corals grow much slower, at a maximum of 1 inch per year (3cm). Branching Corals can grow much faster, achieving 8 inches a year (20cm). The best temperature for Coral growth is 70°F (21°C). Corals must be in pure saltwater without any proximity to runoff water in order to maintain their temperatures and salinity. It can take up to 10,000 years for Corals to form a group!

Size and Weight.

Coral polyps are extremely small, measuring 1.5cm wide. Polyps can grow much larger depending on the Coral, such as Mushroom Corals spanning 13cm. As the Corals grow, they can span for miles. Once they are fully grown, the collective of Corals can weigh several thousand kilograms.

What and How do Corals eat?

Shallow water Corals rely on photosynthesis to produce food. This is accomplished with algae called zooxanthellae, which produces carbohydrates and oxygen. The Corals and algae have a symbiotic relationship where the algae consume Coral waste. Deepwater Corals do not have the algae to aid their survival. Instead, their energy comes from food such as plankton and organic matter.

Most Corals hunt by night, where their polyps come out of their skeletons to catch floating debris with their tentacles. This is especially useful in catching slow-moving phytoplankton.

In addition to these food sources. The Corals feed on debris called “reef snow” which consists of bacterioplankton, mucous, and floating eggs. Many Corals with larger polyps are able to feed on small fish occasionally, but they rely more on dissolved organic material.

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The Colour of Coral.

There are some fabulous colours in Coral. The colours include green, brown, pink, yellow, red, purple, blue. In fact, the association is iconic enough to have a colour named after Coral, which is a deep peach shade. These colours are due to three things: Photosynthetic pigments. Fluorescent proteins. Non-fluorescent chromoproteins

Chlorophyll also causes green to appear in Corals; however, this is due to the symbiotic algae. The exact colour of Coral will depend on a combination of algae and its 3 naturally occurring pigment chemicals.

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Corals can reproduce in many ways. Depending on the species, they can accomplish this asexually or sexually. Polyps can use both methods and switch between male and female within their lifetime. Furthermore, this fertilization can happen internally or externally!

Coral reproductive cells are in membranes called mesenteries. These membranes are within the polyp’s stomach tissue. Fertilized eggs develop here from days to weeks, and once they are ready the polyps will disperse their planulae all at once.

This can happen all year round but usually happens 3-6 days after a full moon in the springtime. The release of eggs also happens at nightfall and can last several days.


Coral Reefs grow best in low-current tropical waters. Due to this, you will not find them in abundance along the west coast of America. They will also not be found along the west coasts of South America due to the freshwater release from the Amazon river. They are estimated to cover 284,300km (under 0.1% of the ocean’s surface). 92% of Coral Reefs are found in the Indo-Pacific region, with 41% of that surrounding Australia.

The Great Barrier Reef is by far the largest Coral Reef on the planet. It covers 348,700 km² of the ocean. It is located off the coast of Queensland, Australia, in the Coral Sea.

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Why should you care? 

Over half a billion people depend on Coral Reefs. They protect coastlines, provide abundant food, and supplement the livelihoods of fishermen, tourism companies, and marine biologists. They also offer significant recreation opportunities for scuba divers and snorkelers. The economic value of Coral Reefs is 375 billion USD per year. This biodiversity has become a large part of the world economy and without it, countless people would lose jobs and livelihood.

Threats to Coral Reef ecosystems.

The most significant threat to Coral Reefs is pollution. Runoff from land filled with chemicals and waste, coastal development, and agriculture are partially responsible.

However, 8 million tons of plastic currently occupy our seas. When Corals come into contact with plastic waste, it increases their chance of disease by up to 89%. This pollution, combined with destructive fishing practices that utilize dynamite and cyanide, means that the environment for Coral has become hostile. Many attempts have been made to create artificial reefs to combat the loss. But the construction process of these manmade reefs causes additional pollution and harm.

Corals have natural threats as well. This includes disease, predators, and storms – all of which contribute to coral bleaching. This bleaching happens when the polyps expel the zooxanthellae from stress. Without the algae, the Coral has a difficult time retaining colour and eventually turns translucent. Coral bleaching does not mean they’re dead, but by the time we notice the process it is too late. When zooxanthellae are not present to provide food, the Corals will starve and eventually die.

El Niño from 2014-2017 caused a bleaching event that affected 70% of coral reef systems worldwide. This was a significant change in water temperature, and it will take our oceans many years to fully heal from that event.


As previously mentioned, bleached Corals are not dead Corals. Many of them are able to recover from bleaching. It is very easy to assume that when Corals are not vibrant, they are dead. But they are simply recovering and awaiting new algae to grow. In fact, the algae have been expelled by the coral because it has become chemically destructive to the polyps, and only when the water returns to the right temperature is it safe to grow on Corals. Bleached Coral is simply algae-less.

Image of coral reef
Photo by Lachlan Ross on

What can you do to help?

  1. Ethical Consumption:  It’s very common for brands of sunscreen to contain Oxybenzone and Octinoxate. These chemicals are known to contribute to coral bleaching and affect the PH levels of seawater. To protect coral from this damage, research sun care brands that don’t use these chemicals.
  1. Spread the word! Talk to family members and friends about what they’re doing to help the cause. Inform people on how they can help keep ocean water healthy and free from chemicals.
  1. Get Involved: Lastly, spend time signing petitions and getting involved in online spaces. If you can, join a local ocean clean-up to stop microplastics and other debris from polluting the waters.

If there is a public demand for change, then change will come. With everyone’s help we can create new standards for the ocean and all of its inhabitants! With safer oceans we will continue to see the health of our coral reefs stabilize.


Some of the most beautiful Coral Reefs in the World.


The Maldives are made up of 1,200 islands and 26 atolls. The waters feature a beautiful landscape of corals and a vibrant array of marine life. Unfortunately, with the warming of the ocean waters, particularly the El Niño weather event of 1998, a majority of coral suffered from heavy bleaching, dying off; however, over the past few years, there have been encouraging signs of recovery.

The Great Barrier Reef.

Not only is Australia’s Great Barrier Reef one of the most beautiful reefs in the world, but it’s also the largest one on Earth. The reef comprises over 3,000 individual reef systems, complete with abundant colorful marine life and 400 types of coral. Situated off the coast of Queensland, the reef also features hundreds of islands, many of which have pristine beaches that locals and tourists alike flock to every year. One of the Seven Natural Wonders of the World, the Great Barrier Reef is also a UNESCO World Heritage Site.

New Caledonia Barrier Reef – New Caledonia.

The second-largest double barrier reef in the world, the UNESCO World Heritage Site New Caledonia Barrier Reef is an example of Mother Nature at her finest, complete with incredibly blue waters in varying shades. Located in the South Pacific off the northeast coast of Australia, this double-barrier reef is home to a variety of marine life, many of which are still in the process of being discovered and classified, with the Green turtle and 1,000 fish species already documented. As with most of the stunning habitats, this one is constantly under threat due to man-made causes.

The Red Sea Coral Reef – Red Sea.

The Red Sea Coral Reef is an amazing undersea world located in between two of the hottest and most arid deserts in the world: the Sahara and the Arabian. Approximately 1,200 miles long, this reef, which is over 5,000 years old, is home to 300 hard coral species and about 1,200 fish, of which 10 percent are found only in this area. One thing to note about this coral reef is that it is strong, able to withstand a variety of elements including extreme temperature changes.

Rainbow Reef – Fiji.

Located between the second and third largest islands of Fiji, Vanua Levu, and Taveuni: Rainbow Reef is the perfect name for this locale. It features a kaleidoscope of vibrant colors under the water, provided by the hard and soft corals and marine life that call the area home. Indeed, there are 230 hard and soft corals and close to 1,200 fish species, creating a feast for the eyes. With the fantastical beauty, it’s no wonder that this is one of the top diving destinations in the world.

Tubbataha Reefs Natural Park.

A stunning underwater landscape made up of vibrant corals and marine life, Tubbataha Reefs in the Philippines is recognized as a top diving site in the world. Comprising two coral atolls, the reefs feature 600 species of fish, 360 species of coral, 11 species of sharks, 13 species of dolphins and whales, birds, plus Hawksbill and Green sea turtles. The Tubbataha Reef Natural Park was declared a UNESCO World Heritage Site in 1993 due to its ‘pristine coral reef’ along with the ‘extensive lagoons and two coral islands.’

Raja Ampat – Indonesia.

The waters of the Raja Ampat Islands have 450 species of reef-building coral, making it an area with the largest coral reef biodiversity based on its size. 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.

Palancar Reef – Cozumel, Mexico.

Divers return again and again to this beautiful hidden gem off the coast of the island Cozumel in Mexico. While it may not be as large as other reefs, it is just as beautiful with its multicolored (think bright pinks, greens, oranges, and yellows) marine flora and fauna. The Palancar Reef is part of a bigger reef system, the Mesoamerican reef system, the second-largest on Earth. The dazzling array of coral serves as homes for seahorses, butterfly fish, sea fans, squirrel fish, parrot fish, and many others.

Wakatobi Islands – Indonesia.

A stunner located in the Coral Triangle, the Wakatobi National Park is 1.39 million hectares, and its blue-green water is home to 750 coral reef species out of the world’s 850, making it a spectacular place to explore. A tentative World Heritage Site, this underwater gem is located off the southeast portion of Sulawesi, Indonesia. Adding to the already impressive scene is the diverse fish presence; indeed, the collection of fish equals 942 species.

Great Chagos Archipelago – Indian Ocean.

Located in the middle of the Indian Ocean, the Great Chagos Archipelago comprises 55 islands, and the Great Chagos Bank happens to be the largest coral atoll in the world and also the least polluted and the most protected. Half of the world’s coral is located here, with endemic varieties such as the Ctenella chagius, coral that resembles a brain. Add to that the rich fish population, along with turtles, dolphins, whales, and more. In order to keep the water as pristine as possible, scientists conducting research don’t even wear sunscreen.

Lord Howe Island – Australia.

Lord Howe Island is a gorgeous island located in the Pacific Ocean. There is much beauty above the sea, but once you dive into the crystal-clear blue waters, there might be even more allure beneath. A marine park and UNESCO World Heritage Site, its marine biodiversity is unique with over 90 coral species along with 500 different species of fish. It’s possible to get close to dolphins, humpback whales, and even sharks (the harmless ones, of course). It is a true paradise.

Belize Barrier Reef – Belize.

Another UNESCO World Heritage Site, the entire Belize Barrier Reef Reserve System was inscribed in 1996. It has the largest barrier reef in the northern hemisphere, plus several other highlights like coastal lagoons and mangrove forests. The reef itself contains 106 hard and soft coral species plus 500 species of fish, only about ten percent of what scientists hope to find. However, due to man-made or natural causes, it’s not for certain which, over 40 percent of the coral reefs are damaged, making protection efforts that much more important.

Apo Reef – Philippines.

At 13 miles long, the Apo Reef, located in the South China Sea on the Mindoro Strait, is the second-longest continuous coral reef on the planet. Underneath deep blue waters are a smashing array of corals in blues and pinks along with marine life such as trigger fish and sea turtles. Curreny, on UNESCO’s tentative list for World Heritage Site status, Apo Reef also has National Park sttlatus in order to protect this treasure from any undue harm.

Bonaire Reef – Dutch Caribbean.

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

The Grand Central Station and Chimneys – Fiji.

The Grand Central Station and Chimneys, located in Fiji, known as the ‘soft coral capital of the world’, is home to an abundance of corals and marine life. The Chimneys feature two coral towers adorned with soft coral in various colors, while the Grand Central Station is known for the plethora of sea life the area attracts, including manta rays, marble rays, hammerhead sharks, and many others. The area features 400 corals (that scientists know of) 445 documented marine plants, and over 100 invertebrate species.

Bethany MacDonald

Bethany MacDonald

Bethany MacDonald has contributed articles since 2020. As their Blog Lead, she specialises in informative pieces on culture, education, and language learning

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