How Corals Feed | Beyond Zooxanthellae

Corals are not passive rocks or underwater plants. They are living animals with mouths, stomachs, and clever ways to capture food. While the famous algae inside their tissues (zooxanthellae) make sugars from light, corals also eat in many other ways you can support in a home aquarium. Understanding these feeding strategies will help you grow healthier, more colorful corals and avoid common mistakes like overfeeding or starving certain species. In this beginner-friendly guide, we’ll explore how corals feed beyond zooxanthellae and turn that knowledge into simple, practical steps for your reef tank.

The basics: corals are animals with algae partners

Corals are cnidarians, related to anemones and jellyfish. Each coral polyp has tentacles with stinging cells (nematocysts), a mouth, and a simple stomach. Many reef-building corals host symbiotic algae called zooxanthellae (family Symbiodiniaceae). These algae live inside coral tissues and use light to produce sugars and other compounds. The coral uses this energy for growth, mucus production, calcification, and daily life.

In bright, nutrient-poor tropical seas, photosynthesis can supply a large part of a coral’s energy—often 50 to 90% for many shallow-water species. But the percentage is not fixed. It changes with light, water quality, flow, and species. Some corals rely far less on light and far more on catching food. Non-photosynthetic (NPS) corals lack zooxanthellae entirely and must eat to survive.

Beyond zooxanthellae: the other ways corals eat

Particle capture: zooplankton and meaty foods

When you picture a coral grabbing food, this is the classic method. Tentacles extend, nematocysts fire, and the coral reels in prey. In the wild, corals catch zooplankton like copepods, crab larvae, worms, and tiny jellyfish. In aquariums, this translates to foods such as rotifers, copepods, baby brine shrimp (nauplii), finely chopped mysis, and specialized coral foods. Many corals can also take small fish eggs or reef-safe micro pellets if the particle size matches their mouths.

Filtering tiny life and detritus

Corals also capture very small particles suspended in the water: microzooplankton, protozoa, marine snow, and fine detritus. Mucus and cilia help guide these particles to the mouth. Some soft corals and gorgonians are excellent at this style of feeding, and a steady supply of fine suspended food can make a big difference in their health.

Dissolved organic matter and amino acids

Not all “food” is visible. Corals can absorb dissolved organic matter (DOM), including small peptides, amino acids, and simple carbohydrates, directly through tissues. This does not replace solid food for all species, but it can boost growth, pigment production, and repair. In tanks, carefully dosed amino acid supplements can mimic this source. Use moderation and observe your corals’ response.

Bacteria as food

Corals can capture and digest bacteria. A rich microbial soup feeds many reef animals, and corals are part of that web. Some corals even prefer bacterioplankton-sized particles. In aquariums, a balanced nutrient level supports bacterial populations, which indirectly feeds corals. Over-sterilizing water can reduce this subtle food source.

Mucus nets and ciliary conveyors

Some corals produce mucus sheets that trap particles, then move the sheet to their mouths using tiny hairs (cilia). This method is common in certain LPS and soft corals. It is a low-energy way to harvest a constant rain of micro-food. You may see a coral “sliming up” after a feeding; this can be normal feeding behavior rather than stress, especially if the mucus contains captured food.

Mesenterial filaments: external digestion

When food is too big or when competing with neighbors, corals can extend digestive filaments from their mouth or body wall. These release enzymes that digest tissue or trapped prey outside the body. In tanks, this sometimes appears as white stringy threads during aggressive encounters or after feeding. It is a reminder that corals are active predators, not passive plants.

Day vs. night: when do corals feed?

Many corals feed more at night. Zooplankton swarms rise in the dark, and corals extend tentacles to match. In bright light, some species retract to avoid predators and protect their delicate tissues. However, corals can “learn” your schedule. If you feed at the same time each day, many will show a feeding response—tentacles extend, mouths open—even during the light period.

For best results, try feeding in the evening or early night when polyp extension is naturally strong. If your schedule only allows daytime feeding, create a routine and reduce flow briefly so food stays near the coral. Over a week or two, you will often see stronger feeding behavior as the coral adapts.

Flow, light, and polyp behavior

Flow that delivers food, not a fire hose

Corals need flow to bring oxygen and food while carrying away waste. Turbulent, variable flow is best for most reef tanks. As a rough guide, aim for enough flow to gently bend polyps and keep food suspended without ripping tissue or blasting food away instantly. If a coral cannot hold onto food, the flow is too strong during feeding. Many aquarists lower pump speed or switch to a gentler pattern for 20 to 40 minutes while target feeding.

Light changes the feeding equation

Brighter light boosts photosynthesis but can reduce daytime polyp extension for some species. Corals often extend more at lower light levels or at dawn/dusk. Also, corals that get plenty of light still benefit from feeding. Heterotrophy provides nitrogen, phosphorus, lipids, and essential compounds that light alone cannot fully supply. In short: more light does not mean zero feeding, and more feeding does not replace all light. Balance both.

Matching foods to coral types

SPS corals (Acropora, Montipora, Pocillopora)

SPS corals have small polyps and generally prefer very fine foods. Think bacterioplankton, rotifers, copepod nauplii, and high-quality powdered coral foods designed for small polyps. They benefit from frequent small feedings and stable water quality. Broadcast feeding of fine foods works well. Too large particles (like whole mysis) usually get rejected. Some SPS respond strongly to amino acids, but dose conservatively and watch nutrients.

LPS corals (Euphyllia, Micromussa/Acanthastrea, Trachyphyllia, Scolymia)

LPS corals have larger mouths and can take bigger pieces. Finely chopped mysis, small clam or fish meat, enriched brine shrimp, and small pellets are often accepted. Target feeding every few days can speed growth and improve flesh fullness. Watch for aggressive sweepers in species like Galaxea and Favites after feeding; space corals accordingly to avoid stinging.

Soft corals and zoanthids

Most soft corals (like Sinularia, Sarcophyton, and some gorgonians) and zoanthids benefit from fine suspended foods and stable dissolved nutrients. Phytoplankton supports the food web and feeds some filter feeders, but many photosynthetic soft corals prefer small zooplankton and dissolved organics more than phyto alone. Broadcast feeding of a fine mix works well. Target feeding zoanthids can help colonies take off, but avoid smothering polyps.

Non-photosynthetic (NPS) corals (Tubastraea, Dendronephthya, many gorgonians)

NPS corals must be fed to live. Sun corals (Tubastraea) take meaty foods during nightly target feeding. Delicate NPS gorgonians and Dendronephthya require continuous or very frequent feeding of very fine plankton, often several times per day. These corals are beautiful but challenging. If you are new to reefing, learn coral feeding basics first before committing to NPS species that demand constant foods and stable export.

Feeding methods for reef tanks

Broadcast feeding

Mix fine foods in a cup of tank water and pour or gently disperse into a high-flow area. This spreads tiny particles across the reef, which is ideal for SPS and soft corals. Use small amounts to avoid nutrient spikes. Let pumps distribute the cloud, then after 15 to 30 minutes resume normal filtration if you reduced it.

Target feeding

Use a turkey baster or coral feeder to place food near coral mouths. This is perfect for LPS and sun corals that accept larger pieces. Turn down flow so food is not blown away. Aim for light puffs that let the coral grab the food voluntarily. Avoid blasting the tissue or burying the coral in food.

Continuous or frequent micro-feeding

For NPS and some finicky feeders, dosing small amounts of micro-food several times a day can mimic natural plankton drift. An automatic doser or slow drip of a refrigerated plankton mix is useful. This method demands solid nutrient export and close monitoring of nitrate and phosphate to avoid algae problems.

Pre-soaking and particle sizing

Rinse frozen foods in clean saltwater to remove excess juices that can spike nutrients. Chop or select particle sizes that match the coral’s mouth. Small-polyp SPS prefer tiny foods; large-polyp LPS can handle larger bites. Pre-soaking dry powders ensures they sink and disperse instead of floating to the overflow.

What to feed: practical options

Live and frozen zooplankton

Copepods (live or concentrated), rotifers, enriched baby brine shrimp, cyclops, and finely chopped mysis are great staples. Live foods trigger strong feeding responses and are less likely to foul water if consumed quickly. Frozen options are convenient. Rinse and portion carefully.

Phytoplankton

Phytoplankton mainly feeds filter feeders like feather dusters, bivalves, some gorgonians, and the microfauna that corals may later consume. It supports a healthier plankton web in the tank. While most stony corals do not eat phyto directly, adding phyto a few times per week can still benefit the system as a whole.

Powdered coral foods

Many powdered blends include tiny zooplankton, marine proteins, and carbohydrates. They are excellent for SPS and small-mouthed corals when broadcast fed. Start with small amounts. If you see a positive feeding response and better polyp extension, you are on the right track.

Amino acids and carbohydrate supplements

Amino acid dosing can enhance color and growth, especially in SPS, by providing building blocks that light alone cannot supply. Use conservative doses and observe. Too much can fuel bacterial films, browning, or cyano. Carbohydrate-rich foods can boost mucus production and microbial food chains but carry similar risks if overused.

How much and how often?

For most photosynthetic corals in a balanced reef, feeding 2 to 4 times per week is a good starting point. SPS often prefer smaller, more frequent feedings of fine foods, while LPS may enjoy a larger meal once or twice per week. NPS corals need daily or multi-daily feedings according to species.

Let the coral’s behavior guide you. A clear feeding response looks like tentacle extension, sticky capture, and swallowing. If food blows past, the polyp retracts, or pieces sit uneaten, reduce flow, resize the food, or feed less. Stop adding food when capture slows or leftovers begin to collect on the sand. It is better to feed small amounts consistently than to dump in a huge meal.

Balancing nutrients: nitrate, phosphate, and export

Feeding adds nutrients. Corals need nitrogen and phosphorus, but too much fuels nuisance algae and cyanobacteria. Too little starves both corals and their symbionts. A practical target for many mixed reefs is nitrate between about 2 and 15 ppm and phosphate between about 0.03 and 0.10 ppm. Avoid bottoming out to zero, which can stress corals and promote dinoflagellates. Also avoid very high levels that smother tissue or promote algae blooms.

Use export tools to balance your feeding. Protein skimmers remove dissolved organics and boost gas exchange. Refugia with macroalgae absorb nutrients steadily. Mechanical filters and filter rollers trap particles before they rot. Water changes reset trace elements and dilute waste. Activated carbon polishes water and reduces odors from heavy feeding. If you use UV or ozone, consider pausing them briefly during targeted feedings to avoid stripping plankton instantly.

A simple routine is: lower the flow or switch to a gentler mode, feed, allow 20 to 40 minutes of contact time, then restore normal filtration. Monitor nutrients weekly and adjust feeding or export accordingly.

Troubleshooting common feeding problems

Corals will not open

Check light intensity (too strong can keep polyps withdrawn), flow (too harsh), or pests. Feed at dusk when polyps naturally extend. Try a small amount of a favorite food to “train” a response at the same time daily. Stable alkalinity, calcium, and magnesium also support feeding behavior. If fish or shrimp pick at the coral, use a temporary feeding guard or cup to give the coral time.

Food blows away

Reduce pump speed or switch to a gentler mode during feeding. Use thicker foods for target-fed LPS or pre-soak powders so they sink. Aim the feeder so food drifts slowly across the polyp, letting tentacles grab it naturally.

Algae or cyanobacteria bloom after feeding

Cut feeding amounts, increase export, and ensure you are not pouring in cloudy food water from thawed cubes. Rinse frozen foods in clean saltwater. Maintain stable nitrate and phosphate within the target ranges rather than chasing zero. Consider shorter photoperiods for refugia or increasing macroalgae harvest.

Brown jelly or bacterial films

Overfeeding, damaged tissue, or stagnant spots can allow harmful bacteria to bloom. Improve flow around the coral, reduce heavy foods, and ensure clean tools. Remove decaying food promptly. Healthy, steady feeding in clean water is safer than large feast-or-famine cycles.

Shrimp and fish steal food

Feed the fish first to distract them, then target feed corals. Use a feeding dome or cut plastic bottle as a temporary cover for slow eaters like Acanthastrea or Scolymia so they can swallow undisturbed.

Myths and misconceptions

“Corals are plants.” Corals are animals that host algae. They have mouths, digest food, and can hunt.

“Strong light means no feeding needed.” Light provides energy, but feeding supplies nitrogen, phosphorus, lipids, and essential compounds. Many corals grow and color better with both.

“All corals eat the same foods.” Particle size and preference vary widely. Match food to polyp size and species.

“Phytoplankton feeds all corals directly.” Most stony corals prefer animal plankton or dissolved organics. Phyto is still useful for the system and certain filter feeders.

“More food is always better.” Overfeeding causes poor water quality and pests. Aim for small, consistent feedings and watch nutrient levels.

The hidden helpers: microbiome and nitrogen fixers

Corals host bacteria and other microbes that aid digestion, nutrient cycling, and disease resistance. Some bacteria can fix nitrogen from the water and make it available to the coral-algae partnership. Healthy microbial communities come from stable parameters, moderate nutrients, diverse foods, and avoiding unnecessary sterilization. Think of your reef as an ecosystem: your feeding supports not just corals directly, but also the tiny life that feeds them in turn.

Putting it all together: a sample beginner routine

For a mixed reef with SPS, LPS, and soft corals, try this simple plan. Two to three evenings per week, broadcast a fine powdered coral food or live/frozen micro-zooplankton with pumps on a gentler flow for 20 minutes. Once or twice per week, target feed LPS small meaty foods after feeding your fish. Add phytoplankton two or three times weekly to support the microfauna. Optionally, dose a conservative amount of amino acids on nights you are not adding other foods. Test nitrate and phosphate weekly and adjust feeding or export to keep them in range. Observe polyp extension, feeding responses, and growth to fine-tune the schedule.

Measuring success

Look for consistent polyp extension at feeding times, clear capture and swallowing of food, fuller tissue on LPS heads, steady skeletal growth on SPS, and stable coloration. Keep a simple log: what you fed, how much, and how corals responded. Small adjustments week by week will bring you to a sweet spot for your unique tank.

Advanced notes: energy budgets and trade-offs

In shallow, bright conditions, many corals can meet most of their energy needs from light, but heterotrophy remains valuable for nutrients and resilience. In deeper or lower-light tanks, heterotrophy can become a larger fraction of the coral’s energy. Different species lie along this spectrum. Acropora may thrive with fine particulate foods and strong light; Trachyphyllia may prefer fewer, larger meaty meals; NPS gorgonians require nearly continuous micro-food. Your job is to place each coral in the right spot, offer the right food sizes, and keep water clean but not sterile.

Conclusion

Zooxanthellae are only part of the coral story. Corals are active animals that feed in diverse ways: capturing plankton, absorbing dissolved organics, harvesting bacteria, and even digesting on the outside. In your aquarium, success comes from matching food size and method to each coral, timing feedings with natural behavior, providing smart flow, and balancing nutrients with solid export. Start small, watch closely, and let the corals teach you what works. With a steady routine and a light hand, you will see better growth, richer colors, and a reef that looks alive because it is—feeding, breathing, and thriving beyond zooxanthellae.