Range: Tropical and subtropical oceans worldwide Habitat: Shallow reefs Size: 0.5-12 inches (1.27-30.48cm) long Diet: Plankton and fish Threats: Fish, climate change, and habitat destruction Life span: Thousands of years as a colony

Transcript:

Today on Animal Fact Files we’re talking about coral. For more facts on animals, don’t forget to subscribe! Coral was a request from Yan Hui Zeng - we hope you learn a lot with this episode! I feel like I can hear some of you thinking on the other side of the screen, “I thought this was Animal Fact Files,” and indeed it is.

Corals are animals, they just don’t look like the animals with which we’re most familiar. Heck, some of them straight up look like plants. But there’s a lot more to coral than meets the eye. There are more than two thousand different species of coral, and most of us either think of this or even this when we hear that name. Really, though, coral at its most basic stage looks more like this. No, that’s not an anemone or an upside down jellyfish, thought you’d be a smart cookie for thinking along those lines.

Corals are Cnidarians like jellyfish and they belong to the Anthozoa class along with anemones. Now the whole jellyfish thing makes sense, right? This is called a coral polyp. They’re translucent creatures that are typically no more than half an inch (1.27cm) in diameter, though certain species can be as large as twelve inches around (30.48cm). Coral polyps are tube-shaped with six to eight tentacles surrounding what’s called their mouth. The tentacles adorn one end of a coral polyp while the other, tubular end attaches to the seafloor.

For the most part, corals are confined to tropical and subtropical seas between 30 degrees north and 30 degrees south latitude that are less than 200 feet (60.96m) deep - though some corals can live in deeper waters. Nearly all coral polyps are sessile meaning they don’t move once they’ve settled into a favorite spot, and choosing the right spot is kind of important because coral can live for a long, long time. To be fair, not the individual polyps will live forever, but the clones that they produce that form a coral colony can live thousands of years. Yes, clones - see, corals have two ways of reproducing, and that’s where the cloning comes in.

Fully established coral colonies are usually ready to mate after a few years of growth. At this point, they will undergo sexual reproduction. Of course, not being able to move and all sort of makes this interesting. There are two ways corals reproduce sexually. The first is called brooding and the other is called broadcast spawning. In the process of brooding, eggs will be fertilized inside female polyp after being taken in from the water column.

Developed coral larvae will then be spat out into the ocean where they will drift until they find the perfect spot to start growing. In broadcast spawning, females and males will release sperm and eggs into the water in a synchronised fashion that would put any water dancing troupe to shame. The fertilized eggs will float to the top of the surface where they’ll remain for anywhere from days to months until they sink down to the seafloor. Once positioned on the seafloor, they metamorphose into polyps and will eventually undergo the second form of reproduction observed in corals: asexual reproduction. In this case, the coral polyp will bud a clone that remains attached to the parent. These buds will also bud and within a few years a coral colony has formed.

As the coral polyps grow, they will excrete calcium carbonate which creates the hard structure that surrounds and protects the soft polyps inside. Well, at least in the case of hard corals - there are soft corals, too. Soft corals don’t have the same hard structure as hard corals... go figure. Their bodies are made up of strong tissues called sclerites. These are the more plant looking coral formations and they are not part of the hard structures that form coral reefs, although they can be found in coral reefs. Speaking of which: coral reefs are formed via the congregation of large amounts of hard coral colonies.

Coral reefs form as fringes, barriers, and atolls, and they are some of the most diverse ecosystems on our planet which is amazing since they cover less than one percent of the earth’s surface. Coral reefs help to protect nearby land by reducing erosion and acting as a storm buffer. They’re also important because they provide homes for nearly 25% of the animals found within the ocean. Fish such as parrotfish consume coral colonies as well as sea stars and snails.

On the flipside, coral colonies consume plankton and can even eat fish caught with the tentacles of the polyps. They also have a mutually symbiotic relationship with an algae called Zooxanthellae. These algae live within the coral colony which gives the algae protection while the coral gains the excess nutrients created by the algae. This allows coral colonies to grow faster, a rate which can be anywhere from half an inch (1.27cm) to more than 7 inches (17.78cm) per year depending on the species. The Zooxanthellae also give coral colonies some of their color which would appear white without the algae.

When under stress, coral will release the algae into the water and turn white, a process called bleaching. Unless the stress is resolved, this can kill a coral colony. Stressors can include changes in water temperature, lack of sunlight, and pollution. We can actually drill into long established coral colonies and use the cores extracted to learn about the environment of the ocean in the past and any stressors they may have faced. Some scientists go so far as to call them the history books of the ocean. It’s amazing that these tiny creatures are so valuable to life on earth!

For more facts on coral, check out the links in the description - there is so much more to learn that we weren’t able to fit in a single episode. Thank you for watching and give a thumbs up for more Animal Fact Files!