Coral reef facts: 10 amazing facts worth knowing

1. How do coral reefs form?

Coral reef facts - The formation of coral reefs

The formation of coral reefs start when when drifting coral larvae attach to submerged hard surfaces, such as rocks surrounding the edges of islands.

The larva grows into a coral polyp and begin to secrete a calcium carbonate to form a skeleton.

This skeleton protects the coral polyp from predators, and in turn gives other coral polyps a place to attach themselves.

When thousands of these coral polyps connect to one another, they create a colony that acts as a single organism.

As these colonies grow over thousands of years, they join with other colonies and become reefs that can grow to hundreds of miles long.

The corals that form reefs are known as ‘reef-building’ these are hard corals, such as Brain and Staghorn Coral.

Soft corals, such as Sea Fans and Sea Whips, do not form reefs.

2. How old are coral reefs?

Most established coral reefs are between 5,000 and 10,000 years old.

However the oldest coral reefs lived around 450 million years ago, long before the Dinosaurs which clock in around 240 million years ago.

Size is often a good indication of the age of coral reefs, but not always.

3. What is the largest coral reef?

Satellite view of entire great barrier reef

The largest coral reef is the Great Barrier Reef, located in the Coral Sea, off the coast of Queensland, Australia.

The Great Barrier Reef spans over 2,600 Kilometers (1,615 Miles), and has been growing for about 20,000 years.

This reef system is composed of around 3,000 individual reefs and approximately 900 islands.

4. How many different species of corals are there?

There are at least 2,500 different types of corals in the world. These species are split into two major groups; hard corals and soft corals.

Around 40% are hard corals (building-corals) and 60% are soft corals.

Almost all species of coral can be found in South Pacific Ocean, compared to only about 60 different kinds found in the Caribbean.

Coral reefs are the largest structures on earth of biological origin.

5. How do corals reproduce?

Staghorn coral reproduction with sperm and eggs

Most coral species contain both a male and a female coral, however some will be hermaphrodite (male and female). Regardless, they each produce eggs and sperm.

At certain times, often triggered by the moon or temperature, corals will spawn in sync.

This synchronization leads to contact between sperm and eggs, which then leads to fertilized eggs.

The fertilized coral eggs float on the water surface and hatch into larvae.

The larvae are then carried off in the ocean currents, and in time develop and land on another coral reef or sometimes even form their very own reef.

6. Are corals plants or animals?

Coral reef animal statistic fact

Many people often mistake corals as plants, even scientists once had them incorrectly labelled as plants.

However, this mistaken identity was understandable, given that there are so many similarities between the two; corals permanently attach themselves to the ocean floor, much like the way plants root themselves.

Another similarity between corals and plants is that we cannot recognize them by their faces or other noticeable body parts, like we can with other animals.

However unlike plants, corals do not make their own food. They have very small arms which are used to capture food from the water to feed their mouths.

So although coral reefs may look like fields of colorful plants, they are in fact made up of tiny animals.

7. How fast does coral grow?

Corals rely on their skeleton to grow, and raise themselves up higher to get more sunlight and food.

Different species of coral grow at different rates which are influenced by water temperature, turbulence, salinity and the availability of food.

Massive Corals are the slowest growing of all species, only increasing in size by approximately 5 to 25 millimeters per year.

Branching corals, such as Staghorn often grow much faster, adding up to 20 centimeters to their branches each year.

8. Coral reefs are the most biodiverse ecosystem

map of coral triangle and marine protected areas

If we were to travel back in time 40 million years, the most diverse place on earth would be somewhere between London and Paris. Today the coral triangle in South East Asia holds that claim.

This area supports more than 7,000 species of fishes, from small marine fish like seahorses to giants like manta rays, and invertebrates such as octopuses and other marine mammals.

An estimated 25 percent of all marine life are dependent on coral reefs at some point in their life cycle.

9. What do corals need to survive?

sunlight shining on brain coral in shallow water

Corals need 4 things to survive:

Sunlight: Corals depend on the algae that grow inside of them for oxygen, and these algae require sunlight to survive. Hence why you will mostly find coral reefs in shallower waters and rarely below 50 meters.

Clean and clear water: Corals are sensitive to water pollution. Sediment creates cloudy water and can be deposited onto corals, blocking out the sun they require.

Salt Water: Corals need salt water to survive, hence why they grow poorly near river openings where there is excessive freshwater runoff.

Warm Water: Corals are generally confined to tropical waters as they need warm water. Many species of coral grow optimally in water temperatures between 73° and 84° Fahrenheit (23°–29°Celsius).

10. Growing threats to coral reefs

Since the 1980s, the worlds tropical coral reef coverage has diminished by an estimated 30-50%.

The drive behind this massive decline is attributed to four major causes; Pollution, habitat destruction, overfishing and our increasingly changing climate.

Rising water temperatures continue to increase the frequency of mass bleaching events and disease outbreaks.

Help coral reefs

Coral Reef Jewelry

Shop our Coral Jewelry and help save our coral reefs. A percentage of all Citrus Reef orders go towards coral reef conservation efforts.

Or read our guide "How to help protect coral reefs" for more ways to contribute to coral conservation.

Sources of information

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