What Do Corals Eat? The Surprising Diet of a Coral Reef

Corals may look like colourful rocks or underwater plants, but they are actually animals.

And like all animals, they need energy to survive.

But corals spend their entire lives attached to the same spot. They can't swim after their dinner, and they certainly don't look like they're hunting.

So, what exactly do corals eat?

The answer is surprisingly complicated because corals have more than one way of getting their food.

First, Meet the Coral Polyp

What we usually call "a coral" is actually a colony made up of many tiny animals called polyps.

Each polyp has a mouth surrounded by tentacles. Those tentacles aren't just there for decoration, they're part of the coral's hunting equipment.

Many corals can use them to capture tiny organisms drifting through the water.

So yes, those peaceful-looking corals on the reef are actually predators.

Just very, very stationary ones.

Corals Can Catch Their Own Food

Many coral polyps feed on zooplankton and other tiny particles of organic matter floating past them.

Their tentacles contain specialised stinging cells called cnidocytes. Inside these cells are tiny structures called nematocysts that can fire and help immobilise prey.

If that sounds familiar, there's a reason.

Corals belong to the phylum Cnidaria, alongside jellyfish and sea anemones, which use similar stinging cells.

Once prey is captured, the tentacles move it towards the coral's mouth.

Many corals extend their tentacles more actively at night, when zooplankton becomes more abundant in the water.

But hunting is only part of the story.

Corals Have Tiny Partners Making Food for Them

Most reef-building corals have another major source of energy.

Living inside their tissues are microscopic algae belonging to the family Symbiodiniaceae, often commonly referred to as zooxanthellae.

The algae photosynthesise using sunlight and transfer a large proportion of the energy-rich compounds they produce to their coral host.

In return, the coral provides them with a protected home and nutrients.

It's an incredibly important partnership, and one of the reasons most coral reefs develop in shallow, clear water where plenty of sunlight can reach them.

So while corals are animals that can actively catch prey, much of their energy can come from tiny photosynthetic partners living inside their own tissues.

Pretty convenient roommates.

Why Do Corals Need Both?

Different coral species rely on these sources of energy to different degrees, and feeding strategies can also change depending on environmental conditions.

Capturing food provides corals with important nutrients and energy that can contribute to growth, reproduction and recovery.

This becomes especially interesting when corals experience stress.

During coral bleaching, corals lose much of the symbiotic algae living in their tissues — and therefore an important source of energy.

Some corals may be able to compensate partly by increasing how much food they capture from the surrounding water. However, this ability varies between species and does not mean corals can simply "eat their way" through prolonged or severe bleaching.

It does show just how adaptable coral feeding strategies can be.

So, What Do Corals Actually Eat?

The simple answer?

Plankton and other tiny organic particles.

But that's only half the story.

Many reef-building corals combine active feeding with energy received from microscopic algae living inside their tissues.

They're animals.

They're predators.

And they have photosynthetic partners helping to feed them.

Not bad for something that spends its entire adult life stuck to a rock.

And this is exactly why coral reefs become even more fascinating once you understand what's actually happening beneath the surface.

Want to Dive Deeper? 🪸

How corals feed is just one small part of their incredible biology.

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