Feeding Corals

PART-1 of 4

Corals Need More Than A Lot of Light

Contrary to popular belief, a vast majority of corals are not AUTOTROPHIC, requiring only light to survive. AUTOTROPHS produce their own food from inorganic material they extract from their surrounding environment, usually using sunlight to synthesize it with the aid of ZOOXANTHELLAE algae.

In reality, most corals are HETEROTROPIC organisms, depending at least partly on actively feeding, or, obsorbing nutrients from the surrounding water as well as AUTOTROPHIC nutrition. Most corals are MIXOTROPHIC in that they utilize both autorophic and heterotrophic methods of feeding to survive.

Corals are said to be unlike any other critter in that such a large portion of their body is devoted to capturing food. If you think of the world's oceans as "The Big Soup", you would be right. The ocenas are the personification of the term "food Chain". Everything from microscopic bacteria to the fishes in the sea is there. The zooanthellae contained in coral polyps provide a wide range of materials needed by the coral, but coral feeding must supply the balance of the nutrients and vitamins required for metabolism and growth.

It is now believed that symbiotic (AUTOTROPHIC) corals, as a group, obtain from 20 - 50% of their food from heterotrophic feeding on plankton and dissoved organic materials. Some hard corals can obtain 200 - 300% of their basic energy needs from heterotrophic feeding while most meet more than 100% of their needs in this manner. Octocorals and Zoanthids can meet 10 - 100% of their needs in this manner. Not only is intake in excess of basic energy needs required for reproduction and growth, it also increases the respiration rate of the entire colony, leading to an even greater increase in growth rates.

(CONT. PART-2)

CORALS ARE PRETTY SELECTIVE FEEDERS

Corals, for the most part, are carnivorous, feeding mostly on small animals (zooplankton), suspended in the water column. Copepods, polychrates, chaetognaths, and larvae are the more commonly consumed zooplankton items in a coral's diet. A vast majority (up to 85%) of theis food emerges from within the reef (where it is produced) in the evening and at night.

Most soft corals, zooanthids and gorgonians depend almost exclusively on phytoplankton, (small water-borne plants or algae) for their nutritional needs as well as floating plankton, detritus and slow moving invertebrate larvae, rather than zooplankton (which can actively propel itself).

The third important source of food for corals is bacterioplankton, which consists of free-living bacteria as well as the bacteria associated with various materials in the water (mucus, dead pLant material, and other particulate matter) which are commonly called detritus or reef snow. Almost all corals feed heavily on bacterioplankton. Material which includes detritus, floating eggs and other material is also known as pseudoplankton.

The fourth category of food utilized by corals is dissolved organic matter (DOM) which is absorbed across cell membranes directly into the coral.

Many of the corals with larger polyps (i.e. Cynarina and Catalaphyllia) are capable of capturing and eating larger food items, including the occasional small fish. Many corals (particularly gorgonians and soft corals) may select their food based more on the size of the plankton, than its composition.

In the past, it was believed that the large polyped corals, with their more efficient tentacle formations, obtained a large portion of their nutrition from active feeding on the food that floats by, rather than from their zooxanthellae algae. It has since been discovered that many of the small polyp corals are acturally more aggressive feeders than their larger cousins.

If you have live corals in your aquarium, you are probably wondering what foods your corals eat to supplement the nutrition provided by their resident zooxanthellae algae. You could just make a slurry of a variety of different foods which cover the entire spectrum (the "shotgun method" approach) and load it into your tank, allowing the corals to select what they want form the mix. The uneaten food in the mix is guaranteed to increase your nitrate levels in a short period of time, or, you can fine tune the supplement to the requirements of your specific corals.

It is difficult to generalize the food Requirements for groups (LPS, SPS or Soft) of corals as there are always a few renegades in each group which have a more selective diet. It is highly recommended that you obtain a good book (reference source) on corals to determine what your specific corals feed on. One very good book is "Aquarium Corals-Selection, Husbandry, and Natural History" by Eric H. Borneman. The sections devoted to each coral provide detailed information on what the corals feed on in the wild. There is also an excellent chapter devoted to feeding corals in your aquarium.

(CONT PART-3)

WHEN DO CORALS EAT?

Corals derive their nutrition in several ways, all of which required that the polyps be open, either for the zooanthellae algae to gather light, or for the active feeding from the environment.

Corals are stimulated to expand their polyps to feed by a number of influences. Temperature, the time of the day, oxygen content of the water, water movement, and the presence of food or sediment are the influencing factors. Coral polyps will expand and contract throughout the day and night, depending upon how much food is readily available. the Zooplankton contained in the coral polyps release the amino acids glycine, glutathione and proline, which appear to induce a feeding response in most corals.

Each polyp feeds until its appetite has been satisfied. The amount of food required depends upon the individual species, metabolic requirements and the amount of food available. In the wild, corals seem to feed more actively at night rather than during the day. As the sun sets and the reef becomes darker, plankton rises from the reef, providing a food rich environment for the polyps. This is the major food source for most corals.

As the sun sets on the reef and the zooxanthellae reduce their photosynthetic activity (which is used for fueling a high rate of calcification for growth), there isn't much left for the corals to do but eat.

It seems that corals are very adaptable animals. When introduced into an aquarium, where the entire food availability routine is reversed due to the fact that most aquarists feed their tanks during the day (when the tank is lit), most corals change or at least modify their feeding habits.

Corals which normally grow in the lower light (deeper) areas of the reef depend much more heavily on active feeding than do shallower water corals. Shallower depth (high light) corals need to actively feed on zooplankton for most of their nitrogen uptake, since the zooanthellae are already photosynthesizing sufficient carbon and transporting it to the coral animals.

Corals which normally retract their polyps during the day may leave them open longer in low light conditions in the aquarium in order to meet their carbon requriements.

Although some corals actively feed on available plankton during the daylight hours, a majority of corals open their polyps, extend their tentacles with their stinging nematocycts and actively feed during the night.

Ideally, the evironment is which aquarium corals are kept should be as close to those on the reef as possible. A number of coral aquarists have found that feeding their corals at night with the assistance of an automatic feeder and running their mechanical filter and skimmers through timers which turn them off during coral feeding hours has provided good results

The "Complete Coral Food Recipe", inspired by the "homemade Coral Ration" from "Aquarium Corals-Selection, Husbandry, and Natural History", by Eric H. Borneman, provides an ingredient list and preparation instructions for a nutritious, freezable meal for corals.

(The referenced food mix is provided in part 4)

(CONT-PART 4)

A COMPLETE CORAL FOOD RECIPE

As we discussed earlier, all corals require more than light in order to grow and reproduce. Most hobbyist who have corals in their aquariums pay close attention to the level of trace elements and calcium in their tank water. Keeping these levels as close to optimum as possible is an improtant part of a coral's overall health, but they do not provide any actural nutrition.

Since one of the major goals of most aquarists is to keep their tanks as close to sterile as possible (with the exception of beneficial bacteria and trace elements) the average home aquarium provides scant nutrition to their resident corals.

Adding extra food to your tank can be a double edged sword, however. If we try to keep the available food level in a closed aquarium system at thesame level that is availale to corals on thereef, it would't tke long fgor the average tank to crash due to the quantity of uneaten food decomposing in the tank's substrate.

Many experienced aquarists have found that the judicius application of the proper mix of foods and additives to a coral tank is extremely beneficial to the corals. Active water circulation in the tank as well as a powerfull protein skimmer will dispose of the uneaten food and avoid the accumulation of the decaying matter.

Following is a coral food recipe which was inspired by Eric H. Borneman's "Homemade Coral Ration" from his book "Aquarium Corals-Selection, Husbandry and Natural History". It is simillar to what the oceans make available to coral reefs in that it contains a wide variety of nutrients as well as elements and a variety of particle sizes, making it suitable for a mixed coral tank. A key factor for coral foods is that it possess properties which allow the mix to remain suspended in the tank for long periods of time, rather than sinking quickly to the bottom of the tank.

INGREDIENTS:

SEAFOODS:
-6 fresh mussels
-6 fresh clams
-6 fresh oysters
-3 whole shrimp (fresh or frozen)

These seafoods contain blood or blood components, which are rich in nutrients. If one or more of these ingredients are not available, you may substitue simillar items (not precooded, canned or containing additonal additives or other intredients).

FROZEN AQUARIUM FOODS
-1/2 package frozen sea urchins (aquarium pack)
-1/2 package frozen fish roe (aquarium pack)
-4 oz. decapsulated artemia nauplli.

The decapsulated (de-shelled) artemia are readily accepted by most corals as they do not have the shells, which many corals will reject. Frozen brine shrimp may be substituted however, as with the artemia, the shells may cause some corals to reject them. These ingredients are an excellent source of nutritional ingredients.

DRIED SEAWEEDS
-1/4 cup of red, green and brown seaweeds after soaking.

Dried seaweeds can be found in pet shops and health food stores or in the Asian section of most food stores. Do not use roasted or other products which have flavors or other ingredients added to them. Seaweeds are an excellent food for zoanthids and other soft corals which feed on plant matter. Natural sea weeds are also an excellent source of iodine.

AQUARIUM FOODS AND SUPPLEMENTS
-2oz. (1 small container) marine flake food.
-2 oz. (1 small container) tiny food pellets.
-1 tbsp liquid vitamins (seco, or other vitamin/amino acid supplements).

PREAPRATION
1. Soak the seaweeds in fresh (declorinated) water until soft.
2. Thaw all of the frozen ingredients in a bowl.
3. Remove shells from all seafood.
4. Crush all dry ingredients into a powder.
5. Add liquid vitamins to the powdered ingredients.
6. Liquify all of the ingredients in a blender.
7. freeze in ziplock bags in thin flats or in small compartment ice cube trays
(cut pieces in half, or quarters for feeding convenience and store in zip loc
bags after frozen)

FEEDING RECOMMENDATIONS

Start by feeding small amounts (1/2 tsp per 50 gallons of system water per day) to begin with. You can gradually increase the amount, until you start to see water quality problems, then back off on the quantity a bit. the food can be administered at night (when most corals actively feed) or with the use of a turkey baster (dissolve the ration in a container of tank water and inject directly onto the corals).

This coral food is pure, high potency nutrition for your corals. Using a high powered protein skimmer in your tank will greatly assist you in keeping the accumulation of uneaten food to a safe level. (REMEMBER NOT TO OVER DO IT AND GO SLOWLY)(IF YOU DO NOT HAVE THE PROPER FILTER AND SKIMMING EQUIPMENT I DO NOT RECOMMEND THIS FORMULA EXCEPT IN THE MOST MINUTE QUANTITIES.)(WATER QUALITY PARAMETERS WHILE USING THIS FORMULA ARE THE RESPONSIBILITY OF THE HOBBYIST).

END.