Coral Sponge: The Guide to Recognizing it While Diving

You’re diving, and there it is, just sitting there.
Right in the middle of the reef.
And you think… is that coral? A sea sponge? What the heck is that?
Let me tell you right now: it’s a coral sponge, but you don’t know that yet. Much less how to tell it apart from the coral it’s growing next to.

But it’s an animal.
And it’s alive.
And it does more for the ocean than some people do for their own neighborhood.

• It filters water.
• It provides a home for the tiniest creatures.
• And on top of that, it’s awesome for underwater photography.

You dive through coral reefs, but what sometimes leaves you speechless isn’t coral. It’s a coral sponge.

Want to know how to tell them apart?
Where to find them?
And how to recognize the different types of sponges?
Then this article is for you, curious scuba diver. We’re going to tell you everything about the coral sponge.

1. What is a Coral Sponge?

A coral sponge is not coral. But there it is, motionless, stuck to the reef like it was born just to confuse us.

You see it and start second-guessing.

It’s got a weird shape, like a tube, a vase or a sack. Mind-blowing colors. And it looks more like a Star Wars prop than a living creature.

But it’s alive.

Marine sponges often grow among corals.
Sometimes on top.
Other times, right next to them.
Sometimes… inside.

Sponges have been around since before any coral.
Before dinosaurs.
Before everything.
Literally. Some species of coral sponge have fossil records dating back 600 million years.

Maybe that’s why they have such a simple design.
Corals only live in saltwater.
But sponges can live in freshwater, estuaries… pretty much anywhere.

Corals = complex organisms.
Sponges = very simple structures. No eyes. No mouth. No brain.
But they are water-filtering machines.

And even though they barely move, there’s movement inside:
Thousands of tiny hairs, called flagella, create currents to filter water.
They absorb bacteria. Process carbon, nitrogen, and phosphorus. They convert the dissolved remains of coral and algae into small, nutrient-rich particles.

A sea sponge can move up to 20,000 times its volume in water every day. Can you imagine?
You drink a liter and already feel bloated.
A sea sponge moves oceans.
And while doing it, it cleans and oxygenates the reef.

As if that weren’t enough, it also offers shelter to fish, shrimp, nudibranchs, crabs; whatever you can think of.
And when the reef runs low on nutrients, there’s the coral sponge, releasing “sea sponge poop” packed with carbon that other critters devour like an all-you-can-eat buffet.

Sometimes the food chain starts in the most unexpected places.

Plus, they adapt to everything.
Rocks. Sand. Mud.
Even floating trash, they’re not picky.

It’s not coral, no.
But without the coral sponge, the reef doesn’t survive. Period.

2. Classification and Types of Coral Sponge (and other sponges)

Today, there are around 8,550 living species of sea sponges.
And every single one of them falls under the phylum Porifera.
What does that mean?
That they’re porous. In other words, their bodies are made up of a network of channels and openings that water flows through, which they filter to feed and breathe.

Coral sponges come with different “building designs” for filtering water:

Ascon

The most basic model.
A hollow tube with a central cavity.
Water enters through the pores, choanocytes (tiny hair-like cells) grab the food… and waste exits out the top.
Simple. Efficient. Old school.

Sycon

Now things get a bit more complex.
Instead of being one big hollow space, this structure has channels that direct water to the center.
More channels = more water = more food.
Think of it like upgrading from a glass to a colander.

Leucon

The most advanced design.
Not just channels, rooms!
Each chamber is full of choanocytes working overtime.
More filtration, better results, faster process.

Now comes the tricky part. Sponge classification is so complex, we’re going to focus on one key trait: their skeleton. Based on that, they’re divided into four main classes:

Calcarea

Their skeletons are made of calcium carbonate spicules with 3–4 rays.
They can have any of the structural types: ascon, sycon, or leucon.

Hexactinellida

Also known as glass sponges.
All marine, all deep-sea dwellers.
Their skeletons are made of silica spicules with six rays.
Delicate, translucent, and stunning, they’re true wonders of nature.
Some can live for hundreds, even thousands of years.
They’re built in sycon or leucon form.

Demospongiae

The queens of the reef, 90% of all living sponge species.
These are the ones you usually see when diving.
Their skeletons are made of six-rayed silica spicules reinforced with a mesh of spongin.
They follow the leucon design and can grow quite large.
Most are marine, but one family lives in freshwater.

Homoscleromorpha

The simplest and rarest class, only about 117 known species.
Their skeletons may have silica spicules, or none at all.
They usually live hidden in caves and dark crevices.

3. Fun Facts and Fascinating Tidbits About Coral Sponges

Get ready to have your dive mask blown off, these sea sponge facts are next level.

They’re not plants
For years, people thought they were just sea veggies stuck to a rock.
Nope. They’re invertebrate animals.

They move. Slowly, but they move.
They look like underwater statues, but some coral sponges actually crawl, creeping in search of food or a better spot to chill.
They move so slowly, scientists didn’t even notice until much later.

No organs.
No eyes. No brain. No heart. And yet, they work.
They rely on specialized cells:
Choanocytes catch food.
Amoebocytes distribute nutrients, clean house, and even help with reproduction.

They’re regeneration masters
Cut one into pieces? No problem, each chunk can grow into a brand-new sponge.

They’re like floating chemistry labs
Sponges produce compounds that can treat diseases.
Antibiotics, antivirals, anticancer agents…
Yep, scientists are drooling over these ocean creatures.

They can live pretty much anywhere
Tropical oceans. Icy abyssal depths. Even freshwater.
If there’s water, there might be a sponge.

They reproduce however they want
Sexual? Sure. Asexual? Absolutely.
Budding, fragmentation, and genetic parties with eggs and sperm in the water.

They have symbiotic buddies
Algae, cyanobacteria, call it underwater mutualism or friends with benefits.
Some coral sponges form win-win partnerships. They give shelter; the microorganisms return the favor with nutrients through photosynthesis.

They communicate.
No mouth, no brain, but coral sponges talk chemically.
“Hey, danger nearby.”
“Hey, food over here.”

Humans have used them for centuries
Before synthetic sponges, we used natural ones for bathing and cleaning.
Soft, absorbent, and totally natural, why wouldn’t we?

Some glow in the dark
Yep, bioluminescent sea sponges are real. They light up like underwater fireflies.

They survive anywhere
Some thrive around hydrothermal vents.
Extreme heat, acidic water, no big deal.
They’re just there, totally unbothered.

4. Where to Dive to See Huge Coral Sponges?

We’ve already mentioned that you can find sponges almost anywhere, but Caribbean sponges are something else entirely.
If coral sponges blow your mind, let me tell you something: Dressel Divers is your direct ticket to the best spots. And when it comes to Cozumel? Well, let me just say, you’re in for a treat.

Why? Because the reefs there are teeming with coral sponges that look like they’ve been plucked straight out of a nature documentary. Seriously!
Here are the best spots to see them:

• Santa Rosa Wall: This place is incredible. We’re talking about vertical coral walls, packed with life. And of course, amidst all this reef, the coral sponges are at their finest. Some are huge, others smaller, but all of them are awe-inspiring. Plus, since it’s about 25 meters deep, it’s perfect for divers who are already comfortable underwater.
• Palancar Reef: Here, coral sponges are everywhere. You dive in, and it’s a world of sponges! They seem to float between the corals, and if you’re quick, you might even catch a glimpse of the currents moving them. It’s like witnessing an underwater garden in motion.
• Columbia Reef: This reef is another place to marvel at.

While Cozumel is the undisputed king of coral sponges, Dressel Divers also has several other locations that could surprise you with their own marine sponge spectacles. Contact us!