What Do Coral Eat? | Beyond Fish Waste

For the full breakdown, see our best Coral Food guide.

The short answer to what coral eat is more varied than most aquarists expect. Most corals are mixotrophs: they capture and ingest food from the water column while also hosting symbiotic algae called zooxanthellae that supply sugars. The mix depends heavily on the species, but the target is always small, organic, and drifting — never flakes made for fish.

Understanding that balance matters because it changes how you feed a reef tank. Knowing what your specific coral needs is the difference between a thriving polyp and a slowly starving one.

What Corals Eat In The Wild

In natural reef systems, corals capture a broad range of organic material. The most consistently documented wild foods are:

• Zooplankton — tiny drifting animals like copepods and rotifers, which most corals actively capture
• Bacterioplankton — free-floating bacteria that many corals filter from the water
• Phytoplankton — microscopic plant-like organisms, especially important for non-symbiotic tropical species
• Dissolved organic matter (DOM) — the invisible soup of organic compounds in seawater
• Detritus and particulate organic matter — fine organic debris that settles or drifts past
• Small crustaceans, invertebrate larvae, and fish eggs — larger prey items for species with bigger polyps

Some large-polyp corals occasionally catch small fish, though this is the exception rather than the rule. The coral’s stinging cells, called nematocysts, immobilize prey before it moves to the mouth.

How Much Do Corals Rely On Light Versus Food?

Reef-building corals get sugars from their zooxanthellae, but those sugars come with a catch: photosynthesis alone doesn’t supply everything. Most other nutrients, especially nitrogen and phosphorus, must come from captured prey.

The balance varies dramatically by species. Soft corals and gorgonians often depend almost entirely on ingested particulate food rather than photosynthesis. Non-symbiotic tropical species, which lack zooxanthellae entirely, favor phytoplankton and weakly swimming zooplankton. Octocorals typically rely more on weakly swimming mesozooplankton, particulates, dissolved organic matter, and picoplankton.

This is why treating corals like underwater plants fails. A photosynthetic coral can survive on light alone for a while; many soft corals and non-photosynthetic species will starve without regular feeding.

Feeding Corals In A Home Aquarium

Most corals feed at night when prey is more available and light levels are low for zooxanthellae-driven photosynthesis. In a reef tank, hobbyists commonly use live plankton, rotifers, brine shrimp, copepods, mysis shrimp, phytoplankton, amino acids, and prepared coral foods.

If you’re setting up a feeding routine, the practical route is matching food size to polyp size: small-polyp stony (SPS) corals take fine particulates and bacterioplankton, while large-polyp stony (LPS) corals grab mysis and larger chunks.

Common Mistakes Reef Keepers Make

Three errors cause most coral nutrition problems. The first is assuming all corals eat the same way — a gorgonian and an Acropora have almost nothing in common at feeding time. The second is overfeeding, which spikes nutrients and fuels algae outbreaks. The third is relying only on fish waste, which provides some nitrogen but lacks the balanced nutrition corals need from live prey.

A coral that catches food is visible — you’ll see tentacles extended and prey disappearing toward the mouth.