How Are Coral Reefs Formed? and The Threats They Face.

If you have not yet witnessed the majestic beauty and diversity of a coral reef, then you may not be aware that beneath the waves there exists a living and breathing ecosystem full of extraordinary wonder.

Like the world’s tropical rain forests, which are absolutely critical to the health of the planet, the world’s coral reefs are necessary to the health of our oceans, and, therefore, our own well-being. These marine metropolises are critically important for thousands of species of fish and hundreds of other species. In addition, they protect our shores from erosion, feed millions around the world and even sustain economies in places like Florida in the United States.

Knowing how incredibly important these natural wonders are to a multitude of animals – including ourselves – you may ask: How are coral reefs formed?

As you might expect, these delicate ecosystems have some important requirements needed to grow into vibrant ecosystems. Once the conditions are right, they can grow into one of three types of coral reefs. These are known as fringing reefs, barrier reefs and atolls.

These majestic ecosystems can take many thousands of years to form ( in some cases millions of years), and yet can be destroyed in a relatively short time. Threats include natural and human made factors. The latter is one we have control over and represents the greatest threat to these indispensable habitats.

The United States government has taken steps to protect coral reefs. However, regular folks like you and I can increase the level of protection exponentially. After all, we are among the countless creatures who stand to greatly benefit from their survival or face peril by their demise.

Read on and see for yourself how coral reefs are formed and the many challenges they face.

Settle Down Baby

I’m certain that you are well aware nature operates in cycles; birth and death is probably the one we are most familiar with. When it comes to coral reefs, we can start by focusing on the coral larvae found swimming freely in the ocean waters. These came from the resulting union of male and female gametes released by the adult corals (polyps related to jellyfish and sea anemones) in an attempt redistribute their genes throughout the reef and beyond (NOAA).

These larvae drift about facing many dangers from predators while in search for an adequate hard surface to become attached to, such as a rock or another coral. The few that survive become affixed to a solid surface for their entire lives. They now extract calcium from the water and as a result deposit calcium carbonate – this begins to build a new coral structure or adds to one that already exists.

This process of creation will continue unchecked if it weren’t for bioeroders like the sea sponge. This important member of the reef burrows holes in the coral and converts calcium carbonate (now limestone due to pressure) into fine sand. It serves to enhance the landscape of the coral as well as supply tropical beaches with fresh sand.

I’ve explained to you the general way coral reefs are formed; now I would like to show you what they need to flourish.


Triumphant In The Tropics

Coral reefs are most abundant in the warm waters of the tropics and subtropics. In fact, they are not able to grow in waters below 64.4 degrees Fahrenheit (18 degrees Celsius). For this reason, stony corals become fewer in numbers as they approach 30 degrees latitude north and south. Beyond these latitudes they are usually not found. One interesting exception is located in the waters off of Bermuda, which are located at latitude 32 degrees north. The reason for this is that this location receives the warm waters that come from the Gulf of Mexico called the Gulf Stream.

Corals also require very clear water in order to receive the maximum amount of sunlight. This is why you will find them mainly in the euphotic zone. This level of the ocean spans from the surface to the maximum depth where the sunlight is able to reach.

It’s obvious that coral reefs need salt water since they are only found in the world’s oceans and seas. However, the water they need has to have a salt content between 32 and 42 parts per thousand (NOAA) – this means very salty water.

The water must also be free of suspended sediment; otherwise the coral’s mouth will become clogged making it impossible to eat. Turbid water will be a double edge sword for the coral; it will interfere with their ability to capture and swallow food as well as with their capacity to receive much-needed sunlight. As a result, coral reefs do best in clear tropical and subtropical waters. For this reason they are a main destination for snorkelers visiting the tropical waters of the world.

These underwater paradises grow into three general shapes. One is closer to the shore while the other two are farther out to sea.

Around And Under

All coral reefs are an awesome display of what life can be when left untouched by humankind. Depending on its location in relation to a given landmass, coral reefs can grow into one of three general forms: fringe reef, barrier reef and atoll.

The last time you visited a beach and gazed at the waves, it is likely that just beneath the surf there was fringe reef – if for example you happen to be visiting the eastern United States or the Caribbean. This variety extends from the coastline out into the sea. They form borders along the coastline and also around islands – making them the most popular type of reef.

The barrier reef occurs even farther out to sea; It is usually separated from the land mass by a deep body of water such as a lagoon.

A fringing reef becomes an atoll when the land mass sinks below the water while the reef continues to grow upward. This specific type of reef has a circular shape which surrounds a large body of water.

Regardless of its shape, coral reefs are a haven showcasing life’s splendor. Nevertheless, these invaluable habitats face numerous threats.

With Great Power Comes Great Responsibility

As critically important as coral reefs are to the world’s oceans, they still have to contend with many dangers. Let’s begin with those that arise from nature herself.

As you may have guessed, powerful waves pose a significant danger to the physical structure of these ecosystems. It seems a bit ironic that coral reefs thrive in the part of the world (tropics) which generate the most powerful storms in the world known as hurricanes and cyclones. The force of the waves can break and scatter large parts of the coral leaving wide areas flattened. This undoubtedly will affect many other members of the reef as well, as many species depend on them for their own survival.

Another threat is longer than usual low tide; being exposed to the sun for long periods of time can cause the coral to become stressed and succumb to bleaching and even death.

In 1997 – 1998, El Nino was responsible for higher ocean surface temperature, lower sea levels ( due to unusually low rainfall) and an increase in water salinity. This situation resulted in the death of up to 80% of the shallow-water coral in many parts of the Indo-Pacific.

Coral reefs are also targeted by a variety of predators, including crabs, snails, sea stars, fish, barnacles and marine worms. Although it is unusual, entire coral reefs can be devastated by predators. There have been times, although rare, when a whole reef has be devastated by predators.

As tough as it may be, corals can bounce back from natural assaults. However, when the threat is exacerbated by human-made global warming and/or pollution these ecosystems are pushed to the brink.

Among the many ways we harm these majestic ecosystems include: pollution, over fishing, catastrophic fishing tactics that make use of cyanide or dynamite, mining the coral to extract building material and removing live coral to be sold to the aquarium market (NOAA).

Other human – made hazards include industrial chemical, and sewage runoff into the ocean, as well as deep water trawling which can dislodge corals from their base.

The sad reality is that we pose a far greater danger to coral reefs than nature ever could. Yet, this means that it’s up to all of us to make sure, through our choices of consumption, that these majestic marine cities will be there for our children in the future.


On The Brink

Coral polyps begin their lives as free-swimming larvae in search for a suitable hard surface on which to settle for life. The few that manage to avoid being eaten become part of a new or existing coral. By extracting calcium from the sea water they produce calcium carbonate, which they use to build the foundation of the coral structure.

Coral reefs are mainly found in tropical and subtropical oceans; there the waters are warm, clean and clear. This is very important since corals can’t tolerate water temperatures below 64.4 degrees Fahrenheit; in addition, the water must be very salty and clear of sediment. Clear water allows them to obtain nutrients and absorb the needed sunlight.

Depending on the reef’s position in relation to land they can grow to form a fringing reef, barrier reef or an atoll. A fringing reef extends from the coast out into the sea, while a barrier reef is formed farther out to sea allowing a body of water, such as lagoon, to be between the reef and the coastline. An atoll is formed when the land is submerged under water while the coral reef continues to grow upward; this type of reef has a circular shape. Regardless of the type of reef, they are all a marvel of nature.

Both nature and humanity pose many threats to these marine habitats. Events like prolonged low tide and predators are some natural threats the reef can bounce back from. However, when it comes to human originated dangers such as global warming, pollution and harmful fishing practices, to name a few, the world’s corals reefs are being pushed to the brink.

On the bright side, the fact that we represent the most serious threat to the world’s coral reefs means that we can, if we choose to, bring these essential habitats back from the edge of calamity. We must first realize that we have to live in harmony with nature, rather than simply profit off or it.

It has been said that what one does for another one does for one self. If we don’t care for the world’s coral reefs then we are not caring for our selves. If, however, we decide to protect them, then we will be further ensuring our own survival.

Today humanity is a lot more aware of how our actions affect the environment. Only time will tell if we follow that awareness with concrete action in time to save the planet and in turn ourselves.





What do think we can do to protect the world’s coral reefs? Have you ever seen a coral reef at low tide? Would you like to see one some day? Please leave your comment below.



Thanks for stopping by,








  1. This subject  held me entranced, I found it to be enthralling and totally captivating.  Coral has always fascinated me, whenever I have seen films or television documentaries, it is so beautiful.  It is unlikely that I will ever see it for real, so to read this was for me totally amazing.

    How I could learn so much by just reading this in so short a space of time is beyond my vision, I now know that there are three types of coral or reef, also how they are formed, that alone was fascinating.

    Thank you so very much for sharing with us the beauty of the sponge and the coral, let us hope that man is not allowed to destroy anymore.

    • Hello Stuart, please excuse me for taking so long to respond to your great comment . It’s great to see another person appreciate the magnificent beauty coral reefs hold. There’s hardly anything in the world with such amazing display of diversity. Not only that, what they offer the world can’t be calculated. The world will simply be lost without the coral reefs. 

      Thank you for your awesome comment,


  2. Hi Jose,

    This is a very interesting post. I was not aware that coral is a living set of mini animals!  The definitely do a great job of creating calcium carbonate though.

    As for pollution, I agree that sewage and oil is a great detriment to reefs and other sea life.  The same on the land….

    For example, it was raining near where I live recently.  I glanced at the pavement and noticed that the snails no longer came out to cross it.  Also certain birds no longer frequent our neighbourhood..  Central heating, car fumes and other fumes are killing everything off.

    We may do our best to change these effects, but complete reversal is definitely off the cards….

    Wishing you the best,


    • Hello Stella, please excuse the amount of time it took me to respond to your great comment. I see eye to eye with you. Much of the human progress is being compromised by our lack of care we are showing to mother nature. I can just imagine how mornings used to sound like before humanity began to settle down and build settlements and then cities. Don’t get me wrong. We are a a species that builds and always will be. However, we must understand that the best of what we need has already been built by a higher power. 

      Thank you for your awesome comment, 


  3. I love coral reefs! I’ve had the good fortune to see some in the Caribbean while snorkeling. Great analogy comparing coral reefs and tropical rain forests. Both are very important and conservation awareness is always appreciated. I did not know that these ecosystems can take millions of years to form. In this case they should be protected at all costs. Sea sponges are really important too. If I can I think I’ll start a sea sponge farm some day. I like that there is a bright side and I thank you for bringing awareness to this very important topic.

    • Hello Pentrental, I’m there with you; I think coral reefs are one of the worlds most beautiful creations. They are life at it’s finest. Their impact on the oceans is unquestionable. As a result their impact on all of us is without a doubt critical.

      The funny thing is, maybe not so funny, is that we have a choice on whether we hurt of help these magnificent ecosystems. Why many of us choose, or rather, choose not to care is due to a host of reasons.

      Once we realize that if coral reefs don’t do well, we’re next, then maybe this will be the kick in the pants we need to finally live by the golden rule we speak so much about.

      Thank you for your great comment,


  4. It’s very easy to think that it’s a whole other world down there… but the truth is, we share this planet with the oceans and her creatures, and live and die in concert with each one another. She takes care of us by providing water, moisture, winds, heat, cooling, and atmosphere that combined together makes survival possible for us humans, all land creatures. and vegetation on this planet. What are we doing for her? Great post, thanks for sharing.

    • Hello Elaine, your point is well taken. Even tough coral reefs look like a different world, in actuality it’s all one interconnected world. What affects then, for better or worse, will have an effect on us.

      If we do good by coral reefs, then we will be doing good for ourselves, and vice-versa. The same goes for all of nature. Humanity has to stop shooting itself in the foot. We must see the truth of the matter – we are inseparable from nature.

      Thank you for your great response,


  5. Jose,
    Our oceans are the last frontier on this planet (aside from Antarctica). We must show better stewardship toward them as well as teh creatures that live in them.

    Without coral reefs, we will lose the abundance of teh sea. It may even create a cascade of ecosystemic collapse. There are not enough humans worried about this.
    Anything we can do to preserve and recover our reefs is only to our benefit.

    Thank you for this informative article.

    Gwendolyn J

  6. Jose,
    Our oceans are the last frontier on this planet (aside from Antarctica). We must show better stewardship toward them as well as teh creatures that live in them.

    Without coral reefs, we will lose the abundance of teh sea. It may even create a cascade of ecosystemic collapse. There are not enough humans worried about this.
    Anything we can do to preserve and recover our reefs is only to our benefit.

    Thank you for this informative article.

    Gwendolyn J

    • Hello Gwendolyn, folks like you are the reason why there’s still hope on this planet. I feel hopeful when I meet someone like you.

      We have some big decisions to make; we have been warned by the scientific community about the consequences of maintaining the status quo. We need a new way of doing things that is not only good for us, but also good for other creatures that live on this planet. At the end of the day, however, this is ultimately what is best for us. That is because if they do good we do good and if they don’t.. well, neither do we. It’s as simple as that.

      Thank you for your great comment,


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