SpongeBob SquarePants is probably the most famous sponge in the world, and for many children he is the first sponge they ever hear about. That is no bad thing. The show has introduced generations of kids to the idea that the ocean is full of strange animals. But it also leaves a lot of people with the impression that sponges are yellow, square and full of personality. Real sponges are none of those things, though some are yellow. This page sets the record straight in a friendly way, and explains why the real animals are even more interesting than the cartoon.

I have a soft spot for any show that gets people curious about the reef. Having spent decades keeping reef tanks and diving reefs from the Caribbean to the South Pacific, I know how much there is to discover once you start looking. If SpongeBob is the gateway, that’s fine with me.

Why SpongeBob is square

SpongeBob is square because he is modelled on a household kitchen sponge, not a sea sponge.

Stephen Hillenburg, who created the show, studied marine biology and worked as a marine science educator in California before becoming an animator. He has said in interviews that he considered drawing his main character as a natural sea sponge, which would have looked more like a lumpy, irregular blob, but chose the shape of a rectangular kitchen sponge because it was funnier and easier to animate, and gave the character a neat, slightly nerdy look. The square pants completed the joke. Kitchen sponges are made from synthetic materials such as polyurethane foam or cellulose and are cut into blocks in factories. They have never been alive. Natural bath sponges, which are the real skeletons of sea sponges, are irregular and rounded; see our page on natural bath sponges.

What real sea sponges look like

Real sponges come in an extraordinary range of shapes, none of them square.

On Caribbean reefs you can see giant barrel sponges taller than a person, clusters of purple and yellow tubes, cup-shaped vase sponges, long rope sponges trailing from walls, branching tree-like sponges and bright orange or red crusts spreading over rock and wrecks. In the deep sea, glass sponges form delicate lattices and vases. A sponge’s shape depends on its species, the current, the light and the space it grows into, so the same species can look different in different places. Look for small pores over the surface and larger round openings called oscula, where water comes out. Our guide to what sponges look like underwater covers the main forms, and sea sponge symmetry explains why most have no regular shape at all.

Some reef sponges are bright yellow, which is probably the closest anyone will get to a real SpongeBob. The yellow tube sponge of the Caribbean, Aplysina fistularis, grows as clusters of yellow tubes on reefs, and many encrusting sponges are yellow; see yellow sea sponges.

The real-life SpongeBob and Patrick

In 2021, a deep-sea expedition filmed a scene that went viral as “SpongeBob and Patrick in real life”.

During a NOAA Ocean Exploration dive with a remotely operated vehicle on a seamount in the North Atlantic, the cameras recorded a bright yellow sponge with a roughly blocky shape sitting next to a pink sea star. The sea star expert Christopher Mah shared the image, noting the resemblance to the cartoon characters, and pointing out the real biology: the sponge was a deep-sea species and the sea star was not a friendly neighbour but probably a predator, since many sea stars feed on sponges. The image is a lovely example of how deep-sea exploration keeps producing surprises, and of how the cartoon gets the relationship backwards.

What SpongeBob gets wrong

SpongeBob is a cartoon, so nobody expects realism. But it is fun to compare him with the real animal.

Sponges cannot move. Adult sponges are fixed to rocks, coral or the seabed for life. Only their tiny larvae swim, for a short time before they settle. Sponges have no eyes, mouth or brain. They have no nervous system at all; see does a sea sponge have a brain? They feed by pumping water through pores and catching bacteria and particles with special cells. Sponges have no limbs or organs. There are no arms, legs, heart or stomach, just specialised cells working together. Sponges are not square, as covered above. And sponges do not cook or flip burgers, though plenty of animals eat them, including hawksbill turtles, angelfish and some sea stars; see what eats a sea sponge.

What SpongeBob gets right

Hillenburg’s marine biology background shows in some details.

SpongeBob absorbs water and can soak up liquids, which is exactly what a sponge skeleton does. In the show he can regenerate after being torn, which is a nod to the real ability of many sponges to regrow from fragments; some sponges can even reassemble from separated cells. He is porous, full of holes, which is the defining feature of the phylum Porifera, the “pore bearers”. And he lives on the seafloor in a warm, shallow lagoon among other reef animals, which is where many sponges really do live; see where do sponges live? For a scientist turned animator, these were small, clever touches. Even his habit of soaking up water and swelling, then drying out and shrinking, mirrors what a real spongin skeleton does when you take a bath sponge out of the cupboard and run it under the tap.

How a real sponge spends its day

If you could follow a real sponge for a day, you would see very little happen, and yet it would be working the whole time.

A living sponge is a water pump. Thousands of tiny cells called choanocytes beat whip-like flagella that draw water in through pores all over its surface, push it through a maze of internal canals and out through larger openings at the top. Along the way, the same cells catch bacteria and tiny bits of organic matter for food, and the sponge absorbs oxygen and releases waste. A large sponge can filter an enormous volume of water every day; see how much water sponges filter. Inside the sponge, wandering cells carry food around and build new skeleton. Many sponges also host huge communities of bacteria inside their bodies. All of this goes on silently, with no movement you can see, which is why most people swim right past sponges without noticing them.

Sponges also provide homes. Small shrimp, crabs, brittle stars, worms and gobies live in and on sponges, and some fish hide in the oscula of large tube and barrel sponges. In that sense, a real sponge is more like a block of flats than a resident: it is part of the furniture of Bikini Bottom rather than one of its citizens.

The real setting is worth a word too. The fictional town takes its name from Bikini Atoll in the Marshall Islands, a real coral atoll in the Pacific, best known as the site of US nuclear tests in the 1940s and 1950s. Its reefs have since recovered to a surprising degree, and scientists study them to understand how coral reefs respond to extreme disturbance. That is a far more serious backstory than the cartoon suggests.

Using SpongeBob to teach real ocean science

Teachers and aquariums often use the show as a starting point, and it works well.

Asking children “Is SpongeBob a real animal?” opens the door to discussing what makes something an animal, how sponges eat, why they don’t move and how they fit into the reef. Comparing Patrick to real sea stars leads to predators and prey; Squidward leads to octopus intelligence. Many children are surprised to learn that sponges are animals at all; our page is a sea sponge an animal or a plant? explains why. Hillenburg himself saw education as part of what drew him to the ocean, and it would be a fitting legacy if his square sponge led more people to discover the real ones. For more surprising facts, see 15 interesting sea sponge facts.