IX. Feeding Coral - Increasing Colony Growth
This article discusses Coral Diets, Appropriate Foods & Feeding
When thinking of coral growth it is easy to focus on factors such as water chemistry and waste levels, while these play a considerable role in a corals ability to grow, they alone will not assure good growth and you will often see a coral added grow very little if at all only to die later due to rapid tissue necrosis or bleaching, two of the most common "unexplainable" losses in a reef tank. While the research is not yet there to confirm this, I would suspect a large portion of these occurrences are due to the coral colony itself depleting all energy reserves and simply shutting down systematically by first expelling zooxanthellae and then attempting to absorb and digest its own tissues in an attempt to reclaim energy and survive.
Coral Diet
This is often spurred by neglect of coral feeding. When first introduced to coral, many people struggle to classify them as animals in the first place. To make this distinction more difficult, most corals have algae that live within their tissue that aids in absorbing nutrients through photosynthesis. I heavy focus will then be put on lighting the tank under the assumption that the algae have enough to photosynthesize, thus the coral must be able to obtain sufficient energy through natural means. We usually fail to properly observe that photosynthetic symbiosis is only one form of nutrient absorption and that form routinely follows function.
All coral consist of polyps, small mouths lined with tentacles. These tentacle house nematocysts, tiny harpoon-like structures meant to ensnare prey and hold it to the tentacle while it is transported to a mouth in the center and digested by a stomach. With such a high amount of energy requirement from the coral to reproduce these polyps, and for entire colonies to be more or less one large polyp we are perhaps correct to assume that there is more to the equation than light levels.
Coral, like any other animal, needs to derive its energy from food sources. This goes against the logic of Autotrophic corals if we dogmatically defined. However, if we loosen our assumption of autotrophic coral to understand that photosynthesis and the symbiotic relationship with algae is an ancillary system to standard digestion then we begin to see a clear need to feed our coral and not to rely on photosynthesis alone to provide adequate nutrients.
Appropriate Foods
Unlike fish who may have complex mouthparts used for mastication and swallowing, coral is more of a stomach with an opening. Incapable of breaking down large fare into smaller portions any food consumed by coral is consumed whole. If a food source activates the nematocysts, an instinctual process takes over. The coral will move the food fare to its mouth, open it and deposit the food into its stomach using the tentacles. This requires the coral to stretch and pull and otherwise exert energy to digest food. If a coral attempts to eat food that is too large it may instead simply swallow it, holding it for some time attempting to digest it and then eventual regurgitate this into the water column taking very little nutrients from the projected food mass. Repeated occurrences of this may lead to malnutrition, slowed growth, or excessive nutrients in the water column. To avoid this it is best to consider the size of the polyp and the size of the food you are offering. Small polyped stony coral may readily accept zooplankton in the form of copepods or brine shrimp eggs. Large polyped stony coral may consume larger zooplankton like Mysis or adult brine shrimp. Anemones, on the other hand, may greedily store an entire fish in its stomach until all that remains is the bones is expels later.
Feeding
With a variety of foods to be fed out to our reef fish and corals, it is paramount that we adhere to a clean tank policy or we could inadvertently pollute our tanks with noxious waste, ultimately resulting in losses. To reduce the amount of uneaten food resulting from feeding coral it is best to treat coral feeding as a separate matter from feeding your fish. I do however recommend feeding your fish to satiation first as they may attempt to steal food from your coral.
With your fish happily fed and more or less ignoring the new food being offered, we can begin feeding our corals which should begin by cutting power to the circulation pumps and any affected equipment. Using a modified turkey baster or pipette depending on food size gather a portion of foodstuffs for your coral. Hovering several inches above the target coral slowly release food allowing it to fall onto the target coral. You should never attempt to "Hand feed" coral by putting food directly in its mouth, additionally, great care should be taken to not "squirt" food and water at the coral. Most corals have a built-in reflex to this action. Before a large fish like a Porcupine Puffer lobs off a branch of stony coral, the force of its beak opening creates a vacuum and a short pulse of water. Coral react to this by retracting their polyps to minimize damage. Your turkey baster feels the same way to a coral as a greedy predator when used incorrectly.
At first, if you make this mistake and the coral you are attempting to feed closes up I recommend simply moving to other coral and allowing that specimen time to relax and for its polyps to reopen. As time goes on if you have a specific coral that you are having a hard time avoiding this with, either due to the size of the food offering or other circumstances related to pressure and volume, you may choose instead to purchase stainless steel feeding tongs or forceps-like those sold for feeding reptiles. Carefully pick up a piece of food, slowly position the tongs above the coral polyps and release the food, it will fall into the polyp and the coral will begin to feed naturally.
In all the articles I write there is not a single topic that I hold to a higher importance than the topic of coral feeding. As a hobbyist and later as a business owner there is no other advice I can give to so drastically influence the health and beauty of a reef tank. While there are plenty of hold-outs that remain convinced that autotrophic coral capable of symbiotic relationships with algae are well-equipped to fend for themselves with adequate lighting, I feel a glaring level of ignorance is taken when we compare our lighting rigs to that of the 1.989 X 10^30 kg plasma ball we are emulating.
Do to several physical limitations, lighting in our aquariums will never, or at the very least probably should never approach the intensity of natural sunlight on the equator at noon time. Unless you can only view the tank through protective lenses, or, large parts of the ceiling in an equatorial based domicile have been removed, my recommendation is to take heed of anyone who claims success based purely on a lighting decision, it is often more complicated than this and there is usually more to their success then they are willing to divulge.