4. Coral Reef Debrief



Coral reefs host an astounding amount of life, making them one of the most important ocean habitats. However, they are at risk of dying before our very eyes. We’ll be learning all about the reef’s crucial links with other plants and animals. Join the brief to save the reef!

Blue Planet Oceans from BBC America and GIPHY

What did we do today?

Learned what coral is and the impacts it has on ecosystems

Understood what symbiosis is and how other animals and plants work together

Got to be hands on and design protection for eggs! Eggs also are made of the same material as reefs and can be just as fragile!

Questions to ask your junior biologist

Did your team’s egg lander work? Did your egg crack?

What are some types of symbiosis? Which one do you like the most? Mutualism (where both benefit), commensalism (One benefits, and the other is relatively unaffected), and parasitism (One benefits, other one is harmed)

Is coral a rock, animal, or plant? Animal! Coral reefs are colonies of tiny little animals with a hard rocky skeleton!

The coral debrief

Corals reefs and the corals that make them up are one of the most famous marine ecosystems. It’s usually one of the first images you think of when you’re thinking about the ocean. And of course, it would be! The reefs are colourful and teeming with life, and your immediately think of all the fish, turtles, and sharks. But have you given thought to the corals themselves?

Turtle GIF from GIPHY

Corals may look like rocks, but they’re actually colonies of tiny animals. They’re called polyps! They’re in the same family as jellies and anemones. Called cnidarians because of their stinging cells, all of them use stingers to trap prey and to defend themselves. Unlike their jelly cousins though, corals prefer to stay rooted to the ocean bottom, and making a hard skeletal base.

coral polyps from DK Find out!

Most corals start life out as free swimming larvae. They find a source of light and will slowly drift to the bottom to attach. Once they found their spot, they will slowly deposit a substance called calcium carbonate to form a base. It will then slowly divide itself to make copies of itself, which will add more to the base. As the polyps divide and add to the base, they will slowly build up the skeleton, eventually becoming the beautiful corals we see. As different corals build themselves up, a reef is formed!

A frequently asked question about corals is about the colours. Corals have all sorts of colours, from dazzling blues to deep greens. On their own, corals are actually white, since their skeletons are made from the same stuff as limestone and chalk. The colours come from little pockets of algae called zooxanthellae that live inside the corals. The corals provide the algae with a safe habitat, while the algae provide food for the coral via photosynthesis. This important relationship benefits both parties, allowing the coral to get food and the algae to have a safe place to live. Plus, they make the coral reefs so beautiful! 

Lots of organisms in nature will work together or impact each other. This is called symbiosis, Greek for living together. Animals and plants can have specific relationships with each other that are fascinating to see. These relationships can be broken down into three types.

Mutualism: Both parties benefit

Mutualism is a win win for both parties. Both animals will gain something from the relationship. The benefits can be in the form of shelter, food, or something unique. It’s cool to see animals working together in nature and is great fuel for popular internet content! Here are some examples.

Cleaner shrimp with groupers: Even though a shrimp would usually make a tasty snack for most fish, these cleaner shrimps have a special relationship with most. Fish of all sizes will come from all over to line up orderly to wait for the shrimp to clean them up. The shrimps will eat up all the dead skin and parasites from the fish. The shrimps get food, and the fish get a clean up.

They'll clean divers too!
Cleaner shrimp GIF from GIPHY

Greater honeyguide and humans: Most birds would love to get into a beehive to get up all the fat bee larvae, but of course, bees will defend their hives at all cost. These clever honeyguides will find a hive, and then fly and alert a human. The human will go in and open the hive and subdue the bees, and the birds will be able to eat up all the baby bees and beeswax that they want. The humans get honey, and the birds get a feast!

Honeyguide picture from Audubon

Commensalism: one benefits, the other isn’t affected

Burdock and mammals: Burdock makes seeds that stick to fur. Lots of animals like dogs and deer will walk by these plants and have seeds stick on to the fur. Eventually the seeds will fall off and plant themselves in a different area, helping the burdock spread across the habitat. The animal is unaffected at all.

Burr seeds from Kuhn Photo

Golden jackals and tigers: This one is pretty odd, some jackals are left out of their pack. In order to survive, they will shadow a tiger, following it at a safe distance. Once the tiger has made a kill and finished eating it, the jackal will go up to the carcass and eat what’s left. The tiger is largely unaffected by this arrangement and will tolerate a jackal following them.

Tigers practice surprising their prey from a young age
Tiger GIF from GIPHY

Parasitism: One benefits, the other is harmed.

Parasitism is a scary one to see. A lot of the parasitic relationships often involve nasty insects and worms that can leave us feeling uncomfortable. But they are the coolest to study. The fact that one animal has evolved to specialize on parasitizing off one or two species is amazingly complex and fascinating to study.

Green banded broodsac, snails, and birds: The broodsac is a crazy parasite.  They start out as eggs in bird droppings. Snails come along and see the droppings and eat it, ingesting the eggs as well. Inside the snail, the broodsac will hatch and grow inside the snail. Eventually, it’ll need to move onto the next stage. They need a way to get from snail to bird.

The broodsac will move inside the snail to the tips of the snail’s eye stalk. Once inside the eye stalk, the broodsac will start pulsating and moving up and down, causing the snails to look like fat little grubs. The worms also make the snail walk towards sunlight, exposing them to potential predators. Now the snail is in broad daylight, with pulsating brightly coloured eyes. Easy meal for a bird, which will snap it up for an easy lunch. Once inside, the worms will start to lay eggs and repeat the whole cycle over again.

Broodsac from GIPHY

Coral Threats

The natural world is full of crazy animals and all sorts of amazing interactions. Coral reefs support a lot of this and are a natural treasure for everyone. However, humans are not doing a great job at preserving them. We are contributing a lot to the decline of coral reefs worldwide. You’ve probably seen news articles about the great barrier reef bleaching and even being dead.

Coral bleaching is the phenomenon where stressed corals begin to turn white, taking on a bleached appearance. It happens when stressors like temperatures changes and pollution is prevalent in the ocean. When this happens, the algae that lives in the coral will start to produce chemicals that can harm the coral polyp. To avoid damage, the polyps will expel the algae. Once expelled, the corals lose their brilliant colours, become white. This is meant to be a temporary measure, since the algae provide about 90% of the food for the polyp. However, as ocean temperatures are affected more and more and pollution is only increasing, the corals lose their ability to recover. Leading to mass coral die offs, and the collapse of several ecosystems.

coral bleaching GIF from GIPHY

Coral reefs are crucial to worldwide ocean health, since the support up to 25% of all marine species on earth. We need to do all we can to help preserve coral reefs around the world! Here’s what you can do to help!

Explore responsibly! Lot of us Canadians want to escape the cold of the north in favour for some tropical heat once in a while. If your junior biologist has enough say, you might even get a chance to go swimming near corals. It is breathtaking to see corals up close, but remember to stay a respectful distance and to minimize contact. Even an accidental kick to a fragile coral can take years to recover from!

We haven’t seen the sun in a bit, but sun screen is a must once summer comes back. When making your sunscreen choice, look for reef safe sunscreens. Most are labelled, but if you’re willing to venture to the ingredients list, look to avoid oxybenzone and octinoxate. These have been found to cause damage to reefs, so avoid them if you can!



Check out the factors that can cause coral bleaching on NASA climate kids 

Learn more about reef safe sunscreens here

Watch this video to see the incredible event of coral spawning!

Learning Objectives

Corals are complex animals that take many years to form reefs along with others

Animals and plants interact with each other in various ways with winners and losers

Coral bleaching is happening around the world and our actions can affect the reef ecosystems

Continue to 5. The Great Invertebrate Debate »