Rock + Plant + Animal = Coral?

As a junior high science teacher, I teach a wide variety of scientific subjects. This year, we have already covered plants, animals, and rocks. When we learned about plants and their unique ability to perform photosynthesis (a process that converts Carbon Dioxide and water into food for the plant using sunlight as its energy source), students brought up corals as plants that use photosynthesis. When we learned about rocks, students brought up corals of examples of pretty sedimentary rocks found underwater. But whenever we talk about animals, students never bring up the fact that corals are tiny gelatinous animals mere millimeters long with tentacles that reach out for waterborne food at night. Indeed, it is always a shock when students learn that corals are actually ANIMALS!

A close up look at fossilized coral. Thousands of coral polyps could have lived on this small section of coral. Photo was taken with my phone camera using a macro lens attachment.

A single coral animal is called a “coral polyp” and is simply made of tiny tentacles attached to a round gelatinous sac all protected by a hard skeleton known as corallite. The tentacles of the coral polyp reach out at night to try and snag microscopic food floating by. They can also shoot paralyzing darts from their tentacles to catch prey or to attack other corals in an ongoing coral territorial war. But most corals only get about 2 percent of their food this way. The vast majority of their food and nutrients come from a symbiotic relationship they share with microscopic algae called zooxanthellae (but its friends simply call it “zoox”). The algae produces food for the corals by using energy from the sunlight to drive a process known as photosynthesis. The algae is also responsible for creating the rocky, hard, gorgeous calcium carbonate fortress the coral polyps live in. Algae produce calcium carbonate as a waste product. In return, the coral polyps offer the algae shelter and food in return (the algae eats the waste products from coral polyps metabolism. Nothing spells ‘friendship’ like eating each other’s biological waste products!).

Again taken from my phone camera using a macro attachment lens. Multiple polyp tentacles would come out of the small openings of this fossilized coral.

Basically coral reefs are coral polyp animals sharing a beautiful rock home with tiny algae. But corals are quickly losing their roommates. “Coral Bleaching” is the process of algae leaving their coral home due to a lack of nutrients and protection from the polyps and the environment. Coral bleaching is mostly due to pollution in the water and the air. Once the algae leaves, the corals die. Coral reefs are known as the rain forest of the sea. They support more than 25% of marine life. However, corals are quickly fading away. For example, elkhorn and staghorn coral populations have declined by about 95% since  1970.

A huge item on my bucket list is to go scuba diving at the Great Barrier Reef and explore this magical alien world of corals for myself. By the time I save up enough money for that trip, it is very likely the corals will have declined significantly in that area of the world, or perhaps even die off all together. How do we stop this tragedy from occurring? It starts with an awareness of how we handle our own garbage and waste as well as how we choose to live in and treat this beautiful yet fragile planet we live on. Please help me accomplish my dream of experiencing one of the most beautiful ecosystems on Earth.

clownfish under water
Photo by Tom Fisk on

Thanks for reading! Most the information I gathered for this blog post were from an excellent book I read (and one I highly recommend if you are interested in the fascinating animal known as coral) called “The Enchanted Braid” by Osha Gray Davidson. I also used some conservation information from this website:

Science Words of the Week: Symbiotic–Denoting a close, long-term biological relationship between two different organisms.

Photosynthesis–The process by which plants and other organisms use sunlight to synthesize foods from carbon dioxide and water. The oxygen we breathe is a product of photosynthesis.


If you read this whole blog post, you are my hero! Thanks for reading. Please feel free to leave me a comment and feedback below. Also, let me know if there is any particular science topic you would like me to look at “through green tinted glasses” and I will write about it.

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