The coral reef recipe

Coral Reefs are the most complex and productive of all eco-systems on earth. As divers, we often marvel at the incredibly beautiful and complicated coral reef structures we see and maybe wonder how how they came to be. They have been created over many thousands of years using a complex, unique combination of ingredients and circumstances.

Here is nature's incredible recipe...

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Building blocks

The first crucial ingredient are coral polyps from hard coral species. These small invertebrates - or spineless animals - that are related to jellyfish, are the primary reef-builders that are mainly responsible for the beautiful coral reefs we see today.

Then you would need to add thousands of Zooxanthellae to each coral polyp. Zooxanthellae are special, tiny algae or plant that lives inside the coral polyp and use photosynthesis to convert the sun's rays into create energy, which the coral polyp then feeds on. All plants you see on land also use photosynthesis to create energy from the sun.

For this photosynthesis to work, you will also need plenty of sunlight, such as a nice tropical location. Then you will need clean, clear water that allows plenty of the sun's light to pass through it to the coral reef. Water with lots of sediment or other matter will prevent sufficient light reaching the coral and halt its development.

It is also important that the water is warm, between 21 and 29 degrees Celsius is just perfect. If the water is lower than 20 degrees Celsius, then the corals will die. To warm, and they will bleach.

The water also needs just the right amount of salt - the levels of salt in today's sea-water are just about perfect. Add a little too much freshwater though and the corals will not take hold.

Now, you must be very patient and provide a stable environment to allow the coral reef to take hold. The fastest corals can grow up to 20cm per year. Other reef building corals only grow two or three centimetres per year. A fully-fledged coral reef may take hundreds, if not thousands of years to grow.

Taking hold...

Once the reef starts to take hold, you will need to add some marine life. Fish such as Parrotfish & Rabbitfish are important as they scrape certain types of damaging algae off the corals, allowing them to stay healthy and keep growing.

It's worth mentioning here that there are many different types of algae, some which help corals to grow and some which can harm coral. If too much of the wrong type of algae is allowed to grow, it will smother the corals and they will die.

Ideally, you will also need some marine life with hard skeletons living in the reef, such as Shells, Giant Clams and even Sponges. Their remains will become part of the reef when they die, supplementing the structure and helping to build a stronger and better reef. Then you will need Zooplankton - microscopic larvae or animals floating past in the current. At night, coral polyps filter this Zooplankton out of the water to supplement the food supplied by their Zooxanthellae in the day.
If you can get all these ingredients together in a stable environment, for a long enough period of time, you are well on the way to building a coral reef.

The thriving coral polyps will build a skeleton around them to protect themselves from predators. This skeleton is made of Calcium Carbonate, otherwise known as Limestone. Over time, they will build numerous protective skeletons each on top of one another, creating coral reefs (the stunning limestone karsts that dot the landscape of Asia today are actually old coral reefs built in exactly this way).

You can see this very process taking shape if you look closely at a Staghorn Coral. In the tip, you will see a slight coloration - this is where all the many coral polyps live - their colour provided by a pigment within their Zooxanthellae. The branch of Staghorn Coral stretching back from the tip is their skeleton & is made of Calcium Carbonate, or Limestone.

To gel the whole reef together though, you need one more crucial ingredient - a special kind of algae that is beneficial to corals called Coralline Algae. This algae is a little like cement. It fills in the gaps in the reef structure, binding the reef together and making it stronger, so that it can grow larger and is more structurally secure. Without this crucial last ingredient, the reef would more than likely thrive for a while, before collapsing under it's own weight.

If you are able to get all these ingredients together and mix them in the right way, and in the perfect environment, for enough time, you should have a beautiful coral reef. There is no doubting that it is a very tall order indeed though.

Never-the-less, this is what mother Nature has been doing for a very long time now. The first evidence of coral reef structures dates back an astonishing 4 million years. The species of corals that you see today have been in evidence for 25 million years, while many of today's living coral reefs have been growing for up to 5000 years.

Sadly, all this great work is in the balance thanks to the damaging influence of mankind. It is our responsibility to make sure that these beautiful coral reefs, which are responsible for so much life, will be there for the next generation, and the generation after that to enjoy.