How coral reefs help create surf perfection

Coral reefs are exciting for surfers and not only due to the waves they help shape. Of course, they only occur in tropical parts of the planet so they come bundled with the full package of tropical joy. For example, either the winds are light due to the equatorial doldrums, or they're consistent trade winds. One way or another it means that wherever coral reefs grow the atmospheric conditions are conducive to great surf.

Surfing photographers, magazines, and filmmakers all love coral reef waves as, not only is the wind often good, but the water is invariably clear and blue. This is not an accident - reef-forming hard corals will only grow in warm clear waters. Thankfully tropical seas have a way of keeping it just so. The hot tropical sun warms the surface waters and they become less dense than cooler deeper waters, developing a strong thermocline. This layering of the water column is due to decreasing temperatures and increasing density with depth. Cool waters are usually denser and richer in nutrients, so the warm surface layer actually blocks nutrients from entering the sunlit surface waters. This means that not only is the water boardshorts warm, but the lack of nutrients minimises algal growth, keeping the water clear and ideal for coral reef growth. 

Surprisingly the lack of nutrients is no limitation to abundance and diversity of life forms. Coral reefs have unlocked the key to an extraordinary bloom of life, based on cooperation and recycling in spite of the limitation of nutrients. The utopian world of the coral reef holds many examples and concepts that could easily cross from ecology to economy. For example a sustainable steady-state of diversity and productivity is based on harvesting energy and resource flows, with little or no waste or loss. Energy and nutrients are not ‘consumed’ then thrown away as waste. Rather energy and nutrients are incredibly valuable and what's leftover by one organism becomes the nourishing basis for the next life form - and so on. 

The coral reef ecosystem is also self-equalising, constantly adapting to changing conditions so as to optimise function. For example, islands are constantly subsiding as their weight depresses the oceanic crust. As a result the water gets deeper and the coral grows up toward the light, building the reef to the perfect depth. Extend this process over a few million years and a fringing reef becomes a barrier reef. Then the island sinks below the waves entirely, leaving an atoll.

The atoll may persist for a geologically long time however it is the pace of change in sea level rather than the overall change in depth that eventually overwhelms the atoll. For example, when an island subsides, or sea level rises faster than the reef can grow upwards, it sinks below the surface to become a flat topped sea-mount called a ‘guyot’. Even millions of years after the island has formed, grown reefs, subsided, and then disappeared below the waves, they still remain highly productive fisheries hidden below the surface.

Corals are best known for the stunning and intricate structures of limestone (aragonite) they secrete when forming a home for the colony. But the living organism is a small colonial animal with tentacles, a stomach and a mouth that also doubles up as an anus when required!

Amazingly, these tiny coral polyps don't just filter feed, they do a little symbiosis on the side. The cooperation - that is, the symbiotic relationship - occurs between coral polyp animals and primitive photosynthesising zooxanthellae, a microscopic organism that is not plant but not really animal either, they are a type of photosynthesising bacteria. The coral build a home in a zone of optimum sunlight and clean water. The coral also generates proteins helpful to their microscopic tenants. The zooxanthellae pay the rent by using sunlight to photosynthesise (like plants) and create carbohydrate (food) from sunlight, water, and carbon dioxide. The bright colours of a healthy reef are actually the colours of the zooxanthellae. Giant clams have also locked onto this winning strategy, hosting brightly coloured zooxanthellae in the lips of the clam.

With the work of photosynthesising taken away from those slimy green algae, the coral reef food chain requires a different basis. The coral polyps and the limited things that grow on the coral exoskeleton provide this basis, but it is magnified by opportunity. Thankfully not only do corals create food and biomass, they also create incredibly diverse yet attractive habitats. From deep, dark, and low wave energy reef walls to bright shallow lagoons and back reefs, there are incredible opportunities for organisms to find a niche that suits them.

In the second point of recycling, you can consider a coral reef as a large and dynamic city, and each process generates some wastes. Thankfully the recycling team are so effective that the very limited nutrients are kept cycling through the ecosystem with little or no loss. The result is an ecosystem of staggering diversity, abundant biomass, and strong flows of energy and nutrients throughout. If you have ever snorkelled on a healthy reef you have probably seen an example of this in action, with parrotfish grazing, biting off small chunks of coral and algae, then pooing out the limestone creating a pile of sand. Bigger fish will eat the parrot fish and shrimp will feed around the poo/sand pile. These then are part of the food chain and the nutrient cycle.

The end result of this virtuous cycle is a long-lived, resilient, adaptable living structure. The best thing for surfers is these coral reefs are extremely effective at building broad reefs with slightly convex profiles and curved plan shapes oriented at ideal peel angles amongst a low wind or predictable trade wind climate. And they do it in warm, gin-clear tropical waters, usually in developing countries that are both stunning and exceptionally good value for the travelling surfer. 

What’s not to like?

In next week's article we look more closely at the process affecting reef growth and structure and how this can be applied to understanding good waves.

Coastal Creationsim is an eight part series written by Chris Buykx. Chris is a geologist, traveller and lifelong surfer. Specialising in eco-tourism, his passion is interpreting nature and the environment. Chris is a resident of Sydney’s Northern Beaches though he's currently doing a lap of Australia with his family. Read past articles:
Part 1: Basic reef shapes
Part 2: Complex curves
Part 3: The good, the bad, and the ugly of coasts
Part 4: Sedimentary sequences and superior shapes
Part 5: Sand dunes and limestone
Part 6: Slabs!