Coral reefs are the largest living structures on earth, and provide the backbone for some of the planet’s most spectacular ecosystems. Like underwater forests, coral reefs provide a nurturing habitat for an astonishing variety of marine life. In fact, despite only covering a tiny portion of the ocean’s surface area, coral reefs are home to a quarter of all the species that live in the ocean!
For this reason, coral reefs are sometimes referred to as the rainforests of the sea.
In addition to sheltering so many of the ocean’s creatures, coral reefs are also visually stunning. Filled with colour, shape and texture, they resemble nothing so much as an underwater fairyland. Naturally, the backbone of a coral reef is coral.
A coral reef is composed of “living stone,” made up of thousands upon of thousands of individual coral organisms, called polyps. Coral polyps are small, soft-bodied creatures that create limestone skeletons for themselves using calcium and carbon dioxide from ocean water.
The intricate branches and colourful ridged shelves that make up a coral reef is actually a colony of tiny organisms that attach to each other and form these characteristic shapes as they grow. When old coral die, they leave their skeletons behind. Young coral attach themselves to the skeletons of the old, and begin building up another layer of calcium carbonate.
Over many generations, a coral reef can build itself up to immense proportions, even forming small islands!
Fun facts about Coral
- Coral are closely related to jellyfish
- Coral have a symbiotic relationship with a type of algae called zooxanthellae. The algae lives with coral, converts the sun’s energy to nutrients via photosynthesis, and uses these nutrients to feed the coral.
- Coral polyps are actually colourless-the incredible colours we see in a coral reef are actually created by zooxanthellae.
- The coral reefs that exist today started forming 5,000 to 10,000 years ago.
Threats to Coral Reefs
Unfortunately, these “rainforests of the deep” are disappearing almost as fast as the real rainforests are. Although it’s natural for some colonies of coral or even some reefs to die off for various reasons, coral are usually able to recover over time. However, human activities have unnaturally increased the rate at which coral colonies die off, and made it harder for them to grow back.
In fact, some scientists have predicted that if current trends continue, we will lose over 60% of the world’s coral reefs by 2050. Many reefs have been directly and purposefully destroyed by humans. For example, the trade in exotic fish has made it profitable to dynamite entire coral reefs to catch the fish that live inside. Also, some fishermen catch fish for the exotic pet trade using cyanide, which poisons the entire reef.
However, the biggest threat to coral may be global warming. Coral are only comfortable in a narrow range of water temperatures, usually between 23 and 29 degrees Celsius. As ocean temperatures rise, coral become stressed out. When they are experiencing environmental stress or disease, coral evict their zooxanthellae and become ghostly white skeletons, a process known as bleaching. Bleached coral almost always die.
A 2007 study by the Coral Disease Research Team found that the growing amount of carbon dioxide produced by human activity is threatening the existence of coral reefs the world over, by making the oceans too warm and too acidic to support them. If we can’t get our CO2 emissions under control, these spectacular ecosystems may be lost forever!
What can you do to support coral reefs?
- Do your part to try to reduce the amount of carbon dioxide being pumped into the atmosphere. Plant trees, drive less, and support clean energy-and no, clean energy does not mean “clean coal!”
- Don’t buy tropical fish collected from coral reefs in the wild. These are sometimes collected using destructive methods such as dynamite or cyanide. Incidentally, fish collected using these methods are likely to go belly-up soon after you get them home.
- If you are lucky enough to visit a coral reef, be a good guest. Don’t touch the coral-even though they have limestone skeletons, they are still easily damaged by human touch.
If you are swimming in the ocean in or around a reef, be careful what kind of sunscreen you wear. A recent study found that some common sunscreen ingredients kill coral by activating a dormant virus that kills the zooxanthellae. Read the label, and avoid using a sunscreen that contains any of the following ingredients: butylparaben, ethylhexylmethoxycinnamate, benzophenone-3 and 4-methylbenzylidene camphor. Instead, look for natural sunscreens that use titanium dioxide to block UV rays.
All of the creatures in a coral reef are interconnected. Plankton and zooxanthellae support the coral, and the coral in turn provide a home, protection and sometimes food for fish and many other sea creatures. All the different sea plants and animals in a reef have evolved to be dependent on each other.
Where do we fit in? It might be tempting to think that humans exist on another plane, above the ecological web that ties everything else on the planet together. However, that’s just not true. We need coral for more than just the beauty and colour that it adds to the sea floor. Coral reefs protect and nurture many of the fish we consume as food. Barrier reefs help protect low-lying coastal areas from the ocean.
Finally, coral form an important part of the carbon cycle, by incorporating carbon dioxide dissolved in the ocean into their limestone skeletons. We are dependent on coral, too, which once again goes to show that protecting the environment is not just a matter of morality or aesthetics.
When we protect nature, we are actually protecting ourselves.