Coral Foods: the Ultimate Nutrition Guide

Small polyp stony (SPS) and large polyp stony (LPS) coral tissue contain zooxanthellae (zo-zan-THEL-ee) species of dinoflagellate algae, specifically Symbiodinium microadriaticum.

Some zooxanthellae can swim in the water by moving a pair of whip-like flagella. Zooxanthellae living inside the coral lack flagella. In fact, they spend their entire lifecycle inside the coral tissue.

There are different types of Zooxanthellae algae responsible for the bright coloration of coral tissue. The photosynthetic pigments, fluorescent proteins and non-fluorescing chromoproteins are inside the algae. There are at least nine symbiotic species along with subspecies called “clades.” The coral host provides protection, exposure to light and nutrients like carbon dioxide and nitrogen waste products.

These algae, living inside the coral, supply a portion of the energy the coral needs to survive. Through photosynthesis, the algae “feed” the coral host glucose, amino acids and glycerol. These substances are used by the coral to produce fats, carbohydrates and proteins.

At one time it was thought all corals fed on was the nutrition provided by the algae. But today biologists estimate that reef-building corals obtain about 60% of their energy from Zooxanthellae, 20% from planktonic foods and 20% by adsorbing dissolved organic compounds.

It was previously believed that all you had to do was bathe your corals with a lot of light to keep them alive and thriving in the reef aquarium. The thinking was natural reef corals live in ultra-clean water with very little nutrients and are exposed to bright sunlight. This was the paradox.

How can massive coral reefs thrive in nutrient-poor tropical waters? Marine biologists thought corals were solely powered by the nutrients released by their internal algae. But there are a number of newer studies showing reef-building corals need more energy than their algae can supply.

The nutrients supplied by the Zooxanthellae are low in nitrogen and phosphorous. Because the algae produce substances high in carbon and low in nitrogen, some marine biologists have referred to this energy source as “junk food” for corals. This is because the algae use or store most of the nitrogen (ammonium and nitrate) they absorb from the water and coral host.

Nitrogen is especially important since it is a critical component of amino acids and proteins that are used for growth and disease resistance. Phosphorus is required for building new tissue.

On the reef and in the aquarium, SPS and LPS corals capture zooplankton, algae, fish eggs and other solid foods that can be caught with their tentacles. SPS and LPS corals also send out sticky mucus “nets” that gather pieces of particulate organic matter and bacteria. These “solid foods” are ingested, digested and used to fuel new tissue growth, repair damaged tissue and form new skeletal mass.

Before continuing with our deep dive into coral feeding, it’s important to discuss the issue of artificial lighting on reef aquariums. In the early days of reef-keeping no one knew how much light was necessary to keep corals alive in captivity.

Since the algae rely on sunlight for photosynthesis, aquarists tried to duplicate the sun’s intensity above their aquariums. The approach most took to lighting was “more is better.” The thinking was many reef corals live in shallow water and with long hours of intense sunlight. So why not hit your tank with as much light as possible, right? Turns out this is wrong!

Studies of wild and captive corals under different levels of light revealed that too much light can inhibit coral growth. In fact, some corals develop bright coloration to protect themselves from excess light.

We now know that PAR (photosynthetic active radiation) are the specific light wavelengths the Zooxanthellae algae need for photosynthesis. If an aquarium light has high output but doesn’t produce photosynthetic active radiation, it’s not a good light for a reef aquarium. It won’t stimulate coral growth and can even slow down coral metabolism.

The point is, giving your corals all the right trace elements and food won’t have any benefit if there is too much light or the wrong lighting over the tank.

PAR is measured with a PAR meter. The light sensor is placed under water and sends the reading to the meter’s display. Keep in mind PAR levels are relative to the distance from the aquarium light. PAR readings are often taken at the bottom of the reef tank to get measurements at the lowest part of the aquarium.

It is also helpful to measure PAR at different locations on in the tank. The ideal PAR for reef-building corals is in the range of 100 to 400 PAR. The key point is that too much light can have a negative affect on coral growth, even with using good feeding practices.

In nature corals feed on a variety of live foods. Using their tentacles, polyps capture microscopic crustaceans, called zooplankton, algae and even bacteria. Live zooplankton are rich in essential trace elements, enzymes and essential fatty acids. LPS and SPS corals capture plankton and other organic particulates from the water.

Several experiments have been conducted to find out how feed in captivity and in the ocean. Nearly all the studies used newly hatched brine shrimp (Artemia) nauplii as the experimental prey. “Baby brine shrimp” are easy to culture and feed to corals, so they were used as a plankton substitute.

The brine shrimp nauplii cause corals to go into feeding mode, making it easy for scientists to observe prey capture behavior. But brine shrimp alone are not an adequate long-term food source for captive corals. Nutritionally they have adequate protein but are low in essential fatty acids. To offset this imbalance, brine shrimp can be “fortified” with fatty acids by a process called “enrichment”.

Under proper conditions brine shrimp will hatch in about 24 hours. The enrichment process takes place during the next 24 hours. First, the nauplii are netted and rinsed with clean brine and placed in a new container. Next, a commercially prepared enrichment product is added to the enrichment container. After about a day the live brine shrimp must be fed to the corals. While enrichment increases omega-3 fatty acids, essential amino acids, vitamins C and B12, it is a time consuming and labor-intensive process.

The brine shrimp culture must be kept free of contamination or the culture will foul. Even the culturing equipment must be sanitized after each use.

Rotifers and copepods are also popular live foods for captive corals.

These tiny crustaceans are captured and eaten by corals and other filter-feeders. Aquarists have had success adding them to their reef tanks as a perpetual live food source.

But if you want to culture them in great numbers for intensive coral feeding, you’ll have to grow a separate microalgae culture to feed to the rotifer culture. It’s not hard, but the cultures take up counter space and a lighting to maintain the live algae plus the rotifer grow-out tank.

Commercial coral farms, labs and public aquariums have the room and labor force to keep live zooplankton cultures alive. Some reef aquarists really enjoy the live food culturing process. It adds a new dimension to reef keeping.

But many aquarists don’t have the time, space or desire to maintain live food cultures in addition to keeping one or more reef aquariums in their home or office. But you can buy live plankton food products for your corals.

Reef aquarists will often supplement their corals feeding program with live plankton. Plankton products can be purchased from online suppliers and direct from aquaculture facilities.

Tisbe copepods are a favorite for SPS and LPS corals. They’re the perfect size range (0.7-1.0 micron) for all filter feeders including corals, clams and a variety of small “finicky” reef fish like pipefish, blennies, gobies and seahorses.

Tisbe copepods are naturally high in essential fatty acids and enzymes that boost the adsorption of nutrients and stimulate growth. They’ll also clean up the aquarium as they graze of algae and other pieces of organic debris. The liquid culture is added to the aquarium as a food source and to establish a background culture of live food.

Beware of foul-smelling live plankton products! When you open the bottle, the liquid should have an earthy or seawater odor. This is normal. If it has a rotten egg or other foul smell, the product is dead and should not be used.

Fans of large polyp stony (LPS) corals will sometimes take a piece of fresh or frozen shrimp and place it directly onto the coral. The large fleshy types will respond to a piece of shrimp or other meaty food placed directly on the polyps.

The polyp will extend its tentacles and pull the piece of meat into its mouth. LPS corals have even been known to eat a whole fish! Large chunks of seafood are too difficult for SPS corals to consume. They would never be able to filter out a “large” chunk of meat as it flowed past the colony.

There are a growing number of commercially prepared coral foods. Some brands provide a list of ingredients while others hide their proprietary formulas.

Typically, the foods contain essential vitamins, amino acids, trace elements, algae and zooplankton. Fish meal powder may be included to boost protein levels.

Some coral foods contain a single natural food source like oyster eggs or plankton, like copepods, rotifers or brine shrimp. These natural marine foods may be dried and ground into a powder. This can be fed as-is or blended with other ingredients like vitamins, color enhancers and trace elements.

Some products further process the powder into a refined particle or pellet. This allows the manufacturer to control the size of each particle. It also creates a food particle that is a complete diet. The pelletizing process can also help reduce the dissolution of water-soluble ingredients into the aquarium water. Instead, it increases the chances of the micro pellet reaching a coral polyp, before it has a chance to “melt” in the water.

For the longest time aquarists wondered if feeding corals in the reef aquarium was necessary and if it made a difference. We all know aquarium products use marketing techniques to hype their products and get attention in the highly competitive reef hobby.

An experiment with Porites compressa, Montipora capitata and Pocillopora damicornis corals tested several commercial coral foods for growth enhancement. The study demonstrated that feeding corals can cause a significant increase in growth. But the study also showed that not all coral foods produce the same level of tissue growth.

The study also used newly hatched brine shrimp nauplii as a food source. Some corals grew better on Artemia nauplii while others put on more tissue mass with a prepared food. Other feeding studies appear to confirm that there is no one ideal coral food.

These observations seem to line up with what thousands of successful aquarists and coral fraggers have been saying. The key to feeding corals in the aquarium is variety. It is a good idea to use several corals foods instead of relying on one food to fed them all.

Corals can sense or “taste” food that comes in contact with their polyps. This response is easy to see with LPS corals. A piece of food placed on a LPS results in the coral extending its tentacles to move the food into its mouth. Liquid foods disperse throughout the water and can cause SPS corals to extend their polyps.

But coral feeding involves more than just dumping food into the tank and seeing your corals react. Since our reef tanks are closed ecosystems, we don’t want to add excess nutrients that could cause a bacteria or algae bloom.

As reef-keepers, we strive to add the right amount of light, water movement, skimming. Too much of a good thing is a waste of energy, space and money. With food we want to add just enough to satisfy the coral’s needs but not enough to foul the aquarium.

Target feeding

Target feeding is a method of putting the food right at the surface of the coral polyps. A liquid suspension of food is sucked up into the feeding tube and aimed at the coral polyps. A small amount of food is released onto each polyp or coral colony.

Target feeding greatly reduces the amount of food bypassing the polyp. This will reduce nutrient loading in the reef aquarium. Some foods are thick and viscous, making it easier to place a drop of food onto the corals.

Broadcast feeding

Many reef aquarists use the broadcast method of feeding their corals. It also feeds other reef organisms including resident live foods like copepods.

Broadcast feeding is simply pouring coral food into the water stream. The water movement in the tank carries the food particles to the coral polyps, just like plankton in the ocean. Some of the food reaches the coral. But the some gets caught in rock crevices or filtered out by the skimmer. If you’ve got a refugium, some food will end up there too.

Looking at the big picture, this “lost” food will be eaten by bacteria and even copepods and rotifers living in the tank and refugium. That’s not a bad thing. It may even help develop a thriving population of live foods within your tank. Broadcast feeding is great, as long as you don’t over-do it.

Hand feeding corals

Feeding LPS corals sometimes requires hand feeding. You can use a pair of tweezers to place a pellet or piece of fish directly onto the coral polyp. Some target feeders can be used to drop food onto the corals too.

It is helpful to reduce the flow rate inside the tank when hand feeding. It allows the LPS coral time to move the food into its mouth and not fight against water flow.

There are lots of opinions on when to feed corals. Based on years of hobbyist and commercial fragging experience, there does not seem to be one particular “best time” to feed.

Corals do develop a daily biological rhythm. Reef-building corals synchronize feeding and symbiotic algae activity based on lighting cycles. It makes sense to work with and not against these biological clocks.

One commercial coral grower likes to feed a few hours before the lights begin to dim in the evening. The feeding starts off with a light broadcast feed to alert the corals it’s close to feeding time. Then the staff target feeds the frags. While water flow is normally strong, it’s cut back during the feeding period. The lower flow helps the food stay close to the polyps instead of being washed away.

You’ll have to develop a feeding regimen that works for your personal schedule. One of the benefits of automated aquarium controllers is that you can automatically regulate lighting and flow rates in preparation for feeding time.

Coral feeding is both art and science. The amount of food added is relative to the size and number of corals in your aquarium. You may have a large tank with a lot of water but only a few corals. Feeding by tank size does not make sense in this case.

Adding more food than the corals can eat is a waste and can have negative effects on water quality. As the food decomposes it release nutrients into the water. This will stimulate algae blooms and nitrate spikes. Some aquarists feed several times a month, others feed every day.

A good approach is to feed small amounts once or twice a week and see how your corals respond. Test the water for nitrate and phosphate to keep an eye on nutrient levels. The aquarium water should always remain clear. You should see no sudden algae growth on the rock or glass. The protein skimmer may make more foam and skimmate after the food is added to the tank. There’s also a chance the increased metabolism of the corals will release more organics into the water and cause a boost in skimmer activity.

The answer is “It depends.” Some coral foods make the skimmer produce excess foam. If this is the case, its best to shut the skimmer down during feeding. Here’s where aquarium automation really shines.

If you feed at the same time every day, an automated system will turn off the skimmer for a set time then turn it on again. Many foods have no affect on the protein skimmer at all. Some reef aquarists leave the skimmer run all the time. Experiment and see what works in your tank.