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What's Coral? By Emlyn Mackenzie

03/06/2018 01:06PM ● Published by Nancy Babin

“What is a coral?” is a question I often get asked while guests are staring at our main aquarium, a 40,000-gallon Indo-Pacific reef ecosystem called the “Living Sea.” They are often shocked when I tell them that coral is actually an animal! Although they may look just like colorful rocks, corals are invertebrates: animals without a backbone. If you look closely at a piece of coral you will notice hundreds or even thousands of small soft-bodied polyps that look like little upside-down jellyfish. All of these individual polyps form a coral head, or colony. These colonies form reef structures because of the polyps’ ability to absorb calcium and carbon from the seawater, making a “limestone” skeleton. These skeletons house the tiny animals and connect them all together. These skeletons also make excellent platforms for new corals to settle and grow on top of. This process eventually leads to the building of coral reefs, such as the Great Barrier Reef, found in Australia. The building of reef structures like this can take hundreds of years, however. Coral grows very slowly and depending on the type of coral, some only grow between 1/8th of an inch up to 6 inches every year.

If you think of coral, the first thing that might come into mind is how colorful and bright they are. Ranging anywhere in color from yellow to pink to orange to green, and sometimes blue, corals always look picturesque! This color is made possible by a symbiotic relationship with a type of algae that lives inside the coral tissue. This algae is called zooxanthellae and they play an important role in building reefs by providing coral with food. Through the process of photosynthesis, zooxanthellae use the sunlight, much like plants, to convert carbon dioxide into food, which gets passed along to the coral. The hard coral skeleton provides the algae a safe place to live within its tissue in exchange for this food, creating one of the most important symbiotic relationships in the ocean. This is also the main reason why many corals are found in tropical waters - they need a lot of sunlight to keep their algae happy!

Many people also do not know that these beautiful animals have some very important jobs in the ocean. Coral reefs are known as “rainforests of the sea” due to the wide diversity of animals that call them home. Making up less than 0.1% of the ocean’s surface area, it is estimated that coral reefs give shelter to at least 25% of all marine life in the ocean. This is more than any other type of habitat! Coral reefs also serve as a source of food for people all over the world. Many of the types of fish and other seafood items we like to eat came from a coral reef habitat. These coral reefs are also vital to helping build and protect our beaches. Incoming storms and waves are very damaging to coastlines, but reefs act as natural buffers, slowing down waves before they erode parts of the beach. White sand found on tropical beaches and here on the Emerald coast is actually tiny pieces of coral skeletons that broke off from reefs or was crushed by parrotfish and eventually ended up on the ocean floor.

Coral is definitely my favorite animal in the whole world due to their important role in ocean ecosystems and their complex but beautiful nature.  

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