A lot of our readers have asked for a brief history and background on coral reef formations. I’ll try not to bore everyone. Believe me it makes a better discussion when we are sailing or diving on the reef. The Great Barrier Reef is that like every other ecosystem in world. It’s life-cycle is far greater then man’s living history and we are only just starting to understand this complex underwater world. Most research only dates back 30 years and many data points are close to shore and don’t cover the full extent, depths and variety of coral reefs.
As far as the history of the world goes, reefs appear to be a fairly new phenomenon, only one million years old, a bit older than all of us. The earliest signs of the Great Barrier Reef appeared just over 500,000 years old. Just some background here that a lot of people are unaware of, regardless of what the press etc have been reporting, seas rise and fall naturally and have been doing so since time began. During the rising phase, without human interaction, seas rise about 10m every thousand years. Over the last 500,000 years we have undergone the rise and fall of oceans just under 20 times. The current Great Barrier Reef started growing between 6 and 9,000 years ago, that is when sea levels rose over old underlying reefs and corals started growing. Sleepy yet?
So when the sea level rises the coral reefs take full advantage and often the grow faster then the sea level rises. The coral keeps growing towards the surface, like a plant towards the sun, until the reef flat is exposed at low tides (sea level). When the coral reefs reach the surface, the growth stops or slows and the battle between mother nature and the reef continues. Strong winds, storms, predators, the summer heat, as well as numerous other factors are continually impacting the reef.
So how does the reef survive this continual attack? Well, corals have evolved over thousands of years to survive this delicate ecosystem. So a couple of things:
-When coral spawns it can only successfully seed and grow if the spot it comes to rest on is clean. That means no algae or live coral. So all the damage above actually makes way for the next generation of corals.
– These cycles are natural and the Great Barrier Reef has survived these impacts for hundreds of thousands of years.
– We know from core samples taken around the world that reefs are very resilient to natural events. Only a few species have become extinct over the last 100,000 years.
– Different types of corals grow at different rates so reefs have the ability to reclaim themselves very quickly and then diversify over time as long as there is “seed” coral remaining or another reef nearby.
Coral Reefs build up slowly towards the surface, building upon the growth of previous generations as well as dead coral caused by the impacts above. This is how snorkellers and divers get to enjoy the reefs everyday around the world. By minimizing our impact on the reef we can make sure that this cycle continues.
-Follow reef safe diving and snorkeling practices.
-Reducing major pollutants that have impact on coral growth to ensure that we do not wipe out entire reef systems.
Comparing samples from older reefs to the newer reefs we see that much more damage is happening with much more frequency and to date most reefs have proven resilient. Reefs closer to major human population centres have suffered the most impact. As long as we minimize our impacts, we can be pretty sure that these amazing ecosystems will continue to inspire generations to come.
Quick and Fast Facts
• The Great Barrier Reef is the largest structure built by living organisms on the Earth today.
• The Great Barrier Reef region is the world’s largest group of coral reefs.
• There are three main types of reefs found on the Great Barrier Reef: Ribbon, Platform, and Fringing reefs.
• Tiny masses of coral polyps are responsible for building coral reefs.
• Coral Reefs make up 6% of the entire Great Barrier Reef Marine Park by Area.
• Reefs are masses of limestone made from skeletons of millions upon millions of tiny marine animals and plants.
• Main threats to coral reefs include human activities, coral bleaching and crown-of-thorn starfish outbreaks.
The Continental Shelf provides the platform from which the reefs of the Great Barrier Reef develop. In the north, the continental shelf lies close to the coast and gradually widens as it extends south.
How Reefs Protect Themselves
Most reefs have a side protected from the prevailing wind and swell. The exposed face of a reef endures the constant battering of powerful waves generated by high winds. Here, corals and coralline algae grow and bind together to form the limestone breakwater of the reef behind which everything else is sheltered. In these sheltered areas, hard corals, soft corals, algae and sponges inter grow to form gardens that are home to thousands of species.
How Coral Reefs Form
Reefs are masses of limestone made from skeletons of millions upon millions of tiny marine animals and plants. Coral polyps, the main reef builders, grow in colonies on a reef’s surface. They extract dissolved limestone from the water and, with the help of single-celled plants (called zooxanthellae) living inside them, they lay it down as hard limestone around the lower half of their bodies. Over time, polyps slowly multiply to create a coral formation, which varies in size and shape depending on where it lives. People refer to these coral formations by their shape or appearance, for example, staghorn, boulder, vase and plate coral. As a coral grows, new polyps replace old polyps. When coral polyps die, their limestone skeletons and the remains of other animals and plants are added to the framework of the Reef.
Threats to Coral Reefs
Coral reefs in the Great Barrier Reef are under pressure due to a number of threats, from both human and natural impacts. Activities such as diving, boating, anchoring and fishing can affect reefs by damaging corals and impacting on other animals and plants.
Coral bleaching is a natural threat to coral reefs. It occurs when corals are over-stressed and can be caused by extreme sea temperatures, high levels of sunlight, low salinity, diseases, pollutants and exposure to air and rain at low tides.
Crown-of-thorns starfish can destroy entire reefs by feeding on coral polyps. Outbreaks occur and reefs are destroyed when the number of crown-of-thorns starfish on a particular reef is high enough that they are able to consume coral polyps faster than corals can grow.
Types Of Reefs
• Fringing reefs are coral structures that are attached to the mainland or to continental islands. In the Great Barrier Reef most fringing reefs are found around islands. Fringing reefs are probably the reef type most commonly seen by visitors.
• Platform reefs are also known as patch reefs and are scattered in the calm, shallow waters between the mainland and edge of the continental shelf. They are usually round or oval patches and often tend to be broken up.
• Ribbon reefs only occur in the northern part of the Great Barrier Reef. They form along the edge of the continental shelf and can grow so high they form narrow walls.
In keeping with the season another part of the ecosystem of the Great Barrier Reef and one of my favourites is the Christmas Tree Worm. So name because of the shape of the extruding part of the worm. The trees are the mouths of the worm. Christmas tree worms feed primarily by filtering the food from the water around it. Each spiral is actually composed of feather-like tentacles which allows any prey that are trapped in them to be transported straight towards the worm’s mouth. they also use the trees as gills. Any sudden movement or sounds near the worm and it retracts immediately into it’s tube.
One of the most brightly coloured species of the reef the Nudibranch, is a strange and beautiful creature. Nudibranch literally means “naked gill”. They have no hard bones or shells to protect their gills. They are often refered to as sea slugs, although a lot more beautiful then the commmon garden variety. They feed on soft corals and are immune to the toxins that some of these corals produce. They come in a large variety of bright colours and forms. these colours help them blend in with the corals in their surronding environment.
They have the sex organs of both sexes but do not normally fertilize their own eggs.