Corals are not

what you think


The coral structure is home to thousands of polyps


Each of these tiny animals is a polyp.

They can range from the size of a pinhead to a bit larger than a basketball.

They are tiny soft-bodied animals that slowly build coral over tens to hundreds and thousands of years.

These are the animals that build an underwater ecosystem supporting a quarter of all marine life.

The polyps are the mega-builders, and the polyps are the ones we’re concerned about.


How Do They Do It?  

Screen Shot 2019-01-08 at 6.30.00 AM.png
save-the-corals-polyp-diagram-outside_coral polyp on the surface.jpg


Polyps only have one opening: their mouth.

They rely on their tentacles with nematocysts (stinging cells) for defense, and to capture food, pulling it into its thin mouth.


Exploring the underbelly

Once they pull their food, such as algae, plankton, small fish, and everything in-between, into their mouth, it enters their large stomach, which comprises most of their tiny, soft bodies.

save-the-corals-coral-polyp-inside-underbelly-diagram_Harken Derm Coral Polyp.jpg


The coral polyps then secrete a calcium carbonate, building themselves a cup-like limestone skeleton to root and rest in throughout their lives.


They Can’t Do It Alone…



Coral polyps can’t live or survive on their own.

Instead, they share.

They’re givers, they’re connected, and they work in colonies.

Connective tissue called coenosarc allows them to share nutrients with the other polyps in their colony.


These tiny polyps then work together, slowly secreting their calcium carbonate skeleton, and building the coral reefs we see today.

The Evolution of Reefs

giant table coral.jpg

Millions of years ago…

Tiny polyps were floating in the ocean.

With only a mouth and tentacles, they don’t have much chance of survival in the open water.

Luckily, they have many superpowers, and other organisms working with them, enabling them to create the underwater habitat supporting billions of species.

The tiny polyps are able to attach to hard surfaces, such as rocks, building a skeleton to stay rooted in their home.

There, the polyp divides, or buds, into thousands of clones, creating a colony of polly’s to work together and build.

Through the coenosarc, the polyps connect to one another, sharing nutrients, and forming a colony that acts as a single organism.

As colonies grow over hundreds and thousands of years, they join with other colonies to become reefs.

Some of the coral reefs on the planet today started growing over 50 million years ago (National Geographic).


How Do They Get All This Energy?


Coral polyps stay in their home, the limestone cup they’ve built, a calyx, throughout their entire lives.

They can’t hunt for food, and have to rely on what comes to them.

How do they get enough food to reproduce, secrete skeletons, and build reefs that are the most ecologically productive and diverse ecosystems in the world?

It’s not from the tiny plankton and fish they are able to pull into their mouths, it’s from the algae.

The special algae that makes all the magic happen…

the zooxanthellae.



Zooxanthellae are photosynthetic algae that live within the tissues of coral polyps.

They provide coral polyps with 90% of their energy through photosynthesis, and give the polyps their color.

(Polyps are naturally translucent)


Zooxanthellae and coral polyps have a mutualistic relationship: they rely on each other for survival.


Coral Polyps

provide the algae with a protected environment, and the compounds needed for photosynthesis: sunlight, carbon dioxide, and water.

That’s why you so often see reefs in shallow waters, more exposed to the energy of the sun’s rays. The algae needs the sunlight to photosynthesize, and provide the energy the coral needs for growth and survival.


Through photosynthesis, zooxanthellae produce the proteins, fats, and carbohydrates needed for the corals to produce calcium carbonate — to secrete their limestone skeletons to build the reefs.

The energy zooxanthellae are able to produce via photosynthesis provides 90% of the corals’ food source

making them essential to sustaining corals’ life, and their growth.


Coral Polyps Are Animals