Without doubt, some of the most perfect waves in the world break over coral reefs. The natural shape and topography of coral reefs are inherently good for creating long, peeling, hollow waves. In addition, coral reefs are located in areas where several other factors contribute to creating perfect surfing conditions.
For example, the fact that coral reefs can only survive in certain water temperatures means that you will probably be surfing in boardshorts. The tropical areas where coral reefs are found are a long way from the storm centres, so the swells arrive clean and lined-up; and you generally get consistent local wind patterns, so if it’s offshore today, it will be offshore tomorrow.
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So, where do coral reefs come from? To start with, we need to know a bit about the coral itself. Coral is not a plant, even though it looks like one. It is made up of animals called polyps. Polyps live inside a skeleton of calcium carbonate, which is continually being manufactured by the animal. When a polyp dies, it leaves its skeleton behind, and, as more and more polyps die, their skeletons accumulate over time, layer upon layer, while the living polyps stay on the surface.
In summary, a coral reef basically consists of a surface layer of live coral above a substrate of calcium carbonate skeletons accumulated over thousands of years.
The polyps have a certain interdependence, or symbiosis, with a small algae species called zooxanthellae. The zooxanthellae lives in close proximity to the polyps and is responsible for giving coral reefs their amazing colours. If the zooxanthellae die, the reef loses its colour – a phenomenon known as coral bleaching. This is now happening big-time due to the climate crisis (more about in a moment).
The evolution of the coral reef itself goes through several different stages, over timescales of thousands of years. At any given time in history, including the present, there exist coral reefs around the world at every different stage of evolution, just like there are people of every different age existing at the same time. These different stages have been identified and named by scientists, with an ever-more confusing array of reef types and sub-types. Here, I’m going to keep it simple and just describe the classic three:
— Fringing reefs, which are directly attached to the land, similar to volcanic or other rocky reefs;
— Barrier reefs, which are further away from the land and separated by a lagoon;
— Atolls, which simply consist of a ring of coral around a central lagoon, no land.
As the reef evolves, it goes from a fringing reef to a barrier reef to an atoll. The original land mass in the middle is continually sinking relative to the sea level (the land might be sinking or the sea level rising). As the relative water level rises, a lagoon starts to appear between the land and the reef, which gradually gets wider and wider until the land in the middle is completely inundated.
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Now, here is the clever bit. As the sea level rises, the coral keeps growing just under the sea surface. Since the live coral on the top of the reef can only exist in shallow water, the top of the reef must remain the same distance from the surface. And, with the skeletons continually accumulating underneath the top layer of live coral, the reef grows upwards, staying just under the surface all the time.
This process takes a long time: typical coral reef growth rates during the recent geological past have been about three to five metres every 1,000 years, in other words just a few millimetres a year.
If there is some factor that keeps the water uncharacteristically warm, you might find coral reefs outside the tropics.
Importantly, if the sea level increases too quickly and the coral can’t grow fast enough to keep up, it will end up too far under the surface and die. With sea levels projected to rise thousands of times faster than normal over the next few years due to the climate crisis, this is another nail in the coffin for coral reefs.
Coral reefs are typically found off oceanic islands in the Pacific, Indian and Caribbean, and less frequently in the Atlantic. They can also exist off the coast of large continents, Australia being the obvious example with the Great Barrier Reef. The principal factor that determines a coral reef’s location is the water temperature: coral can only normally survive between about 20° and 34° C. If the water temperature isn’t between these two values, you won’t get much coral, and you certainly won’t get many large coral reefs.
This temperature dependency means that most coral reefs are found in tropical zones. However, if there is some factor that keeps the water uncharacteristically cold for the latitude, you won’t get coral. For example, upwelling (see my article here) such as in Peru, or massive river outlets, such as in northeast Brazil. Likewise, if there is some factor that keeps the water uncharacteristically warm, you might find coral reefs outside the tropics.
Bermuda, for example, which is nine degrees north of the Tropic of Cancer, has coral reefs due to the warm Gulf Stream which passes close by.
In some places, entire civilizations have been built on small, low-lying sandy islands formed on the top of coral reefs. These are known as cays, sometimes called keys (think Florida Keys), cayes or motus depending on the location and the material making up the island.
Cays are formed a bit like the way a rivermouth sandbar is formed. Firstly, an ocean current flowing over the top of the reef encounters something that slows it down. This could be a current flowing in the opposite direction, or some obstacle sticking out of the reef. If the current is carrying sediment, that sediment will no longer be able to remain suspended in the water column, so it drops to the sea floor.
As a result, the sediment accumulates on the reef until an island is formed. The island is then maintained by processes such as sediment being brought onshore by waves breaking around the periphery.
Coral reefs have serious environmental problems, and are suffering tremendously due to our actions as humans. This is a vast subject, so I’ll just be brief and outline a few of the most relevant issues:
— FISHING: Overfishing can unbalance the ecosystem and threaten the coral, and fishing with cyanide or dynamite is nothing less than collateral murder;
— POLLUTION: The coral can be poisoned by chemicals that enter the sea from agricultural runoff and other human sources, including plastics;
— DREDGING: Physically destroys the coral, almost as bad as dynamite fishing;
— CORAL MINING: Taking coral from the reefs so that it can be ground up and used as cement for building: anybody found guilty of doing this ought to have their bones ground up and used as cement for building;
— CORAL BLEACHING: Excessively-high sea surface temperatures due to climate change kill the zooxanthellae, which takes away the coral’s energy supply and eventually leads to the death of the coral;
— OCEAN ACIDIFICATION: Excessive atmospheric CO2 absorbed by the ocean reacts with seawater to produce carbonic acid, which poisons the coral and kills it.
So please, next time you are surfing perfect tropical barrels over a coral reef in Fiji or in the Maldives, at least be conscious of how fragile that coral reef is. If we don’t start to seriously address all the ways we are abusing our environment, those waves will disappear forever.
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