In keeping with my theme of positive, happy subjects, I again asked Trish to give me an idea for an animal that makes her happy (last time she said Nemo... the clownfish). This time she said, "My happiest happy place is snorkeling in a coral reef! So you should feature coral."
Trish wasn't kidding about this. I enjoy snorkeling, too, but to her it is almost a spiritual experience. She actually tears up when snorkeling among the corals (have you ever tried wiping tears away while wearing a face mask?). So, coral is another excellent suggestion. Besides, some people may not really know what corals are... or that they are even animals. So let's take a look.
What the heck is a Coral?
Corals are invertebrate animals in the phylum Cnidaria, which also includes sea anemones, sea pens, jellyfish, box jellyfish, and hydrozoans such as the Portuguese Man o' War.
Actually, it's kind of silly of me to lump all types of corals together in this email, as corals represent a diverse group of animals. After all, there are about 2,500 species. Of those, about 1,000 species are reef-forming corals. These are the corals that form a hard skeleton by secreting calcium carbonate. Over many years these hard skeletons build up and form massive coral reefs.
Amazing facts about Corals
First let's talk about what a coral is. Corals generally live in large colonies of genetically-identical individuals. Each individual coral is called a polyp.
If you look at an individual polyp, you will see tentacles. In the center of the tentacles is a mouth that leads to a basic stomach, or digestive sac. Each of the tentacles is lined with stinging cells called nematocysts. As you can probably guess, these stinging cells help the coral defend itself and help it capture its prey, which is usually tiny animals swimming in the surrounding water.
The polyp's body secretes calcium carbonate that forms a hard protective shell around the polyp. This cup-like shell is called a corallite. Over time, millions of corallites build up upon each other to form massive coral reefs and outcrops (see the coral outcrop in the photo above). Some coral reefs are big enough to be seen from space!
Below is a simple diagram.
Coral polyps have only one opening. Yep, only one—the mouth. That means food goes in the mouth, and waste goes... well, back out the mouth. Eww. I'm glad I have an anus.
Nematocysts (stinging cells) are pretty awesome. If you've ever been stung by a jellyfish, you know how awesome nematocysts are (awesome for the jellyfish, not for you).
Let's look at how these nematocysts work. Basically, they're like a spear gun shooting a barbed dart, and the dart contain toxins that can be lethal. These tiny darts are contained within a cellular capsule, connected to a thread that is coiled up under pressure. When a prey animal touches the polyp's tentacle, the cellular capsule's covering (called the operculum) pops open, and the thread rapidly uncoils, shooting the dart out at high speed. The dart punctures the prey animal and releases its toxins. Like I said... awesome!
If you've ever snorkeled in a coral reef, you may be thinking, "Wait, I didn't see all those tentacles. All I saw were the hard coral boulders, outcrops, and reefs." Well, that's probably because many corals extend their tentacles mainly at night.
By the way. Snorkeling at night in the ocean or sea can be amazing, but it's also kind of scary. Trish and I have done this twice (while taking marine biology classes together), and I can tell you there is something deeply frightening (but also exhilarating) about not being able to see in the water beyond the range of your waterproof flashlight. It's worth it, though, because the corals are particularly beautiful at night!
Below is what corals usually look like during the day (left) and at night (right).
Corals eat just about anything they can catch, from nearly-microscopic plankton to small fish. Whatever they can kill with their stinging cells is fair game.
But wait! It's not that simple. Many corals also feed in a different way. They have a mutualistic relationship with specialized algae called zooxanthellae. These algae live on and in the coral polyp and can actually be 30% of the polyp's mass.
What does the coral polyp get out of this relationship? The algae are photosynthetic, which means they use sunlight to produce food, and they share that food with the polyp, particularly glucose, glycerol, and amino acids. The algae also help by removing waste particles, and they help with producing the hard shell, the corallite.
What do the algae get out of this relationship? Well, they get a safe place to live, protected by those awesome stinging cells. They also get to feed on the polyp's yummy waste, particularly carbon dioxide, phosphate, and nitrogenous waste.
I should point out that, when water conditions get bad, the internal algae can become stressful to the polyp. When this happens, the polyp will eject the algae in order to give itself a better chance to survive the difficult times. When the water gets really bad, mass ejections can occur, and this is called coral bleaching. Vast areas of coral reefs can turn white, because it was the algae that gave the corals their diverse colors in the first place. Coral bleaching can be caused by pollution or by an increase in water temperature. If the bad conditions continue for too long, the coral polyps will die.
The image below shows the before and after appearance of coral bleaching. Unfortunately, coal bleaching is becoming a big problem, but since this email is all about being positive, I'm not going to focus too much on that.
Here are a few more amazing facts about coral.
Corals have been around for a long time. They originated about 500 million years ago, long before dinosaurs existed. Coral reefs grow very slowly, only about 2 cm per year, and some of today's reefs have been forming for 50 million years.
When coral reefs grow parallel to the coast, they are called barrier reefs. The Great Barrier Reef in Australia has grown to include 900 smaller reefs, and it extends for 2,600 miles (4,184 km).
Coral reefs provide a home for an incredible variety of wildlife. Coral reefs take up only about 1% of the ocean floor, but they provide a home for as much as 25% of all species in the oceans!
White sandy beaches are actually made of coral pooped from fish. Yep, it's true. Some types of fish, such as parrotfish, like to nibble on corals to eat the algae living in the polyps. Once the fish have digested the goodies, they poop out the hard calcium carbonate shell as tiny granules of sand. These sandy poop granules help make up those nice white beaches we all like to lay on. Check out the beak on the purplestreak parrotfish below. That beak can chomp right through the coral shell, and one parrotfish can poop out 200 pounds (90 kg) of white sand per year!
So, Corals deserve a place in the C.A.H.O.F.
(Corking Animal Hall of Fame).
FUN FACT: The word corking originated in about 1890, and is used, particularly in British English, as an adjective to describe something as excellent or fine. Example: "It was a corking celebration." Often it is paired with another word, particularly good, as in "That Bridgers book was a corking good read." Anyway, the word corking came from the word corker. The word corker is a slang term from the early 1800s that originally meant “something that settles and puts a definite end to a discussion or argument,” a reference to how a cork tightly seals a wine bottle. Then corker was eventually used to describe anything as good or excellent: "That was a corker of a joke." Eventually, the adjective corking arose from that.
So, corking is another way to say awesome!
Happy dog - Twitter
Penguin rover - Le Maho et. al via Nature... via Buzzfeed
Giraffe Manor - The Giraffe Manor
Coral outcrop in Australia - Toby Hudson/Wikimedia Commons
Coral anatomy - USGS/Public Domain
Bleached coral - Green and Growing
Parrotfish - metha1819/Shutterstock via Marine Conservation Society
Every human being needs a creative outlet. That's why I write.