Ask the WWM Crew
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Though lights/lighting and filtration get the most attention (as they are very profitable items to sell), more than feeding, the actual nutrifying of stony corals is indeed a major factor in their successful husbandry. The old axiom, "an animal that feeds is an animal that lives" definitely applies to Scleractinians, and many organisms/colonies are lost, or better put, could be salvaged had they received sufficient useful food.
Here is my big chance to make plain, simple
statements of worth to hobbyists, relating what is actually of use in
captive systems. It will surprise some; if not many folks to find that
what they have been told is incomplete to outright misleading on the
subject. Which ways are advised too often pass as "knowledge"
in the ornamental field that will not bear up on close inspection; and
there has been a huge amount of scientific investigation on what these
colonies feed on in the wild. I've reduced a good deal of this
science into practical suggestions.
Diversity in Feeding:
There is a very wide range of feeding types amongst the stony corals, and a similar variety in adaptability to changing these moda by species, even individual colonies. Some Scleractinians derive more than half their nutrition via photosynthesis, and there are some that are entirely azooxanthellate, getting their nutrition mainly by eating other organisms. Know that all stony corals use more than one mode of feeding, and that they can switch to degrees what type/s they employ, depending on prevailing conditions.
Also be aware that many of these animals can go w/o food for considerable periods of time, or as alluded to, utilize other sources to extents. Your success in optimizing their growth, color and perhaps reproduction, is dependent on their nutrification.
Science: Foods & Feeding Methods:
Photosynthesis; Making Your Own Food:
There is a common misconception that "corals" are entirely autotrophic, "self-feeding"; that they derive all their nutrition from making it from sunlight, and absorbing it chemically from their environment. This is not the case. All stony corals are mixotrophic; using photosynthesis through using the production of autotrophs (internally symbiotic algae) and consuming other organisms that eat autotrophs and their predators (heterotrophs) for a good part of their nutrition. No stony coral is entirely photosynthetic.
The majority of the stony corals hobbyists keep are to degrees also zooxanthellate, that is, they internally house symbiotic algae with which they have mutually beneficial relations. The algae utilized carbon dioxide and other materials the coral polyps are better without, and in turn produce sugars and oxygen that are of use to the coral.
Of course the light-production here is dependent on you providing intense light/ing, the availability of minerals (e.g. Calcium, Magnesium, Strontium), sufficient Alkalinity and other macro- and micro-nutrients (including some Nitrate and Phosphate).
Very few stony corals consume any (most eat zero) phytoplankton. Most all outright reject it. How to put this in another way? Hardly any Scleractinian species eat any phyto. There may well be indirect benefits of your applying said material to your system'¦ perhaps feeding other life that in turn itself or its reproductive products feed your stonies, but you are not feeding your corals thus.
Rest assured, all viable systems produce some modicum of indigenous phytoplankton'¦ and this, along with what you add is mostly removed by skimming and mechanical filtration.
Zoo- et al. plankters of Many Types, Sizes, Motilities:
Taking a look at the oral disks of Cnidarians gives good clues as to their prey acquisition. Some with very short tentacles utilize a type of "fly trap" mechanism of exuding sticky mucus to trap small life, passing this into the mouth at intervals. Polyps with medium tentacles generally feed on small crustaceans and planktonic worms, typically at night in the wild, though they can/do adapt to daytime feeding in captivity. Those polyp-like animals with very large tentacles can feed on larger organisms, including fishes.
Such feeding is absolutely essential. Essential nutrients like Vitamins and long-chain fatty acids are not made endogenously. They are derived from the consumption of other organisms.
Marine Snow and Poop:
Yes, many stony corals are to extents scatophagous, detritivorous, bacteriophagous and scavengers on the dead.
Unlike the soft "pulsing" corals of the family Xeniidae, there are no largely chemosynthetic stony corals; however, all stony corals derive essential molecules via heterotrophic feeding and directly from the surrounding water. This material is often labeled as Dissolved Organic Media (DOM), and comprises a very large group (and growing) of chemical species.
Practical Matters: Providing Nutrition for Your Stony Corals:
A not-often spoken of topic in consideration of
photosynthetic efficiency is light transmittance, and factors that
discount same. I would refer you to the paper by Monroe (1994) below.
The gist of this work points to a very sizable loss in useful light
energy as a function of general accumulation of dissolved organic
carbon (DOC). Among other casual factors as dirty cover glass and
reflectors, dissolved color and particulates, tens of percent of energy
costs are lost in reflection and absorption of light before it ever
gets to your photosynthetic life. All would do well to add routine
cleaning (weekly) of tops, reflective fixtures, even lamps (only when
cool!), and pay attention to water clarity period. The measure of
RedOx, ozone use is exemplary here.
Unless you have other Cnidarian life present,
providing phytoplankton is at best an expensive means of indirectly
boosting real food production by feeding possibly other life that your
stony corals will eat. Many soft corals and Zoanthids/Sea Mats, most
gorgonians/sea fans do consume phytoplankton, but not stony corals to
any real extent.
Other plankton of Many Types, Sizes, Motilities:
Depending on the size of organisms your particular corals can ingest, utilizing live or frozen defrosted foods may be advantageous. In an ideal setting, one might have a sufficiently large and vibrant refugium, with a deep sand bed, rubble live rock, macro-algae'¦ enough to culture useful organismal foods that would over time get swept up and pumped into the main display, serving in part as foods for your stonies. In actual practice, there is hardly ever enough space dedicated in live sumps to provide such forage, and aquarists are faced with ancillary feedings.
Examples: LPS and SPS
Many foods are available for these feedings; Cyclops, Copepods, Artemia/Brine Shrimp, even the freshwater insect larvae called Bloodworms. Additionally, a fave of mine, a "bag" of frozen seafood intended for human consumption can be purchased, and processed (removing shells of bivalves and crustaceans, skeletons of fish flesh), diced into small pieces (a blender or chopper is very handy here), and any of these delivered to the colonies via a syringe. This last can be a "turkey baster" to a veterinary type of large diameter opening. Turning off regular recirculating pumps in addition to mechanical filtration is a good practice during these feeding bouts. It may take a few trials to educate your corals to your feeding method, and often the release of just some juice in a system will stir LPSs in particular, into opening up their tentacles to the carnivore mode.
"Other" smaller plankton plays a huge part in nutrifying stony corals in the wild, but to a much lower extent in our captive systems, due to the almost universal use of skimming and mechanical filtration. Consolidate organic material is classed in a few ways; by biological group make-up for instance, and size. A good deal of detritus is comprised of bacteria and other suspended organic matter (POM). A typical size-range description series is "Macro-, Micro-, Nano-, and Pico- plankton". Only the first category (macro) can be seen w/o the use of a microscope.
Some Special Cases:
Some examples of Large Polyp Stony Corals: Some require individual feeding of polyps, one needs large food items on a punctuated basis.
Genus Tubastrea Lesson 1829:
Azooxanthellate branching, tree-like corals found in many places in the tropical and Indo-Pacific. Due to feeding nature they require little light (non-photosynthetic), but the aquarist must take care to see that each polyp is individually fed as they are separate.ã'' About their biggest downside is the mess keeping Tubastrea can entail. With heavy feedings of meaty foods comes concurrent high nutrient levels. Often found in the wild in caves, but also in direct sunlight. Most species are palm-sized, composed of tubular polyps, with T. micrantha being the large exception. Easily encouraged to produce new polyps by regular feedings, especially when these foodstuffs are pre-soaked in a vitamin preparation (like Selcon, Microvit...).
Provision of foods as wastes, principally from fish livestock is an important component of stony coral nutrition. Beyond digested media, fishes stir up the bottom, pick and loosen materials from hard substrates, and provide micro-currents that bring foods to and wastes away from corals. For all's sake, smaller, more frequent feedings are better for providing food for all. Colonies that are basically flat and expansive, opening directly upward are principal feeders on such "detritus".
Dissolved organic material is variably important, but necessary to an extent for all coral growth. Aquarists would do well to leave off with absolute removal of all inorganic nitrate and soluble phosphate, as these materials are critically important, particularly for SPS metabolism. Too-efficient continuous skimming and the over-use of chemical filtrants are especially damaging, often removing all measurable DOM. It won't go w/o my mentioning that sufficient and proportional biomineral (principally calcium and magnesium) and alkalinity (bicarbonate, carbonate) concentration are critically important as well. Some culturists endorse the purposeful addition of simple sugars (hexoses) and other sources of carbon (e.g. Vodka) to boost bacterial growth as well as increasing dissolved organic matter. Carbon can indeed become a/the rate-limiting factor in coral growth/metabolism.
Feeding Times & Methods:
On natural reefs stony corals use cues such as light, tides, currents, temperature, oxygen concentration and food presence to gauge when they feed. As you might assume, conditions that optimize the likelihood of food availability, and conversely an absence of polyp predators (i.e. night), are when these animals are most likely to "open up". Situations become a bit more complex in our aquarium systems, with most stony corals learning in time to feed during the day/light periods with some training. Newly arrived/wild-collected colonies may require a few weeks special night time feedings, but almost all learn in time to capture foods during light-time.
Getting food to your corals can be accomplished in a few ways, blasting/squirting preparations with a baster toward the colony after prep.ing with a small bit/smell of food applied a few minutes ahead to give notice, applying to currents made by your pumps and powerheads'¦ But all direct feeding is made more efficient with the use of timers on pumping mechanisms that include skimmers and mechanical/particulate filtration. Cycling these off (with the timers set to reactivate them <Important!> some ten, twenty or so minutes later will allow the food materials time to settle in and on your corals. For some target feeders that require feeding per polyp (Gonioporas, Alveoporas, Dendrophylliids and some Faviids notably), a chemically inert cage inverted over the colony can serve well to concentrate food during feedings.
How often and how much to feed are matters to be determined through personal experimentation. Most stony corals in most types of settings do well on twice weekly feeding, with "boosted" systems of high light, calcium reactor and ozone use allowing for more often, cooler temperatures and slower-growth philosophy calling for less-frequent feedings. An ideal situation is the use of a large (there is no upper limit) refugium tied into your system. Think about where foods come that feed corals in the oceans. The vast majority "arise" out of the substrate and hard materials above the sand. Having a luxuriant Deep Sand Bed, with live rock, rubble, macro-algae culture, will go a huge way to supply foodstuffs for all your livestock; among many other useful inputs.
I'd like to mention that there are popular groups of stony corals (Acropora, Pavona, Favites, Leptastrea, and others) that derive more than 50% of their nutrition in the wild via capture of bacterioplankton. Though it's not popularized much, I do encourage folks to run their skimmers and UVs on a punctuated basis'¦ As much as several hours off per day, to prevent consistently low bacteria levels and allow this component to build up naturally in their systems. Natural reef water has some 1/5-3 times ten to the sixth bacteria per ml. Such foods are moved to the polyp's mouths via ciliary, tentacular and mesenterial filament action.
Commercial Filter Feeding Foods:
There are several brands of these on the market and they range from worthless pollutants to actually very useful items for folks supporting large numbers of filter feeders. Some are straight out of the bottle, others are powders that require just-prior mixing before administering. Do employ handy timers to temporarily shut off mechanical filtration for thirty minutes or so with your canister filters, skimmers et al. that will otherwise remove the food. And do bear in mind that stony corals do absorb dissolved food molecularly as well as through mucus/net absorption.
I am a big fan of using these supplements on a punctuated (not continuous) basis. Either adding them to foods/mashes soaked for several minutes ahead of offering, or less so, broadcast into the system water along with routine maintenance. There are commercial prep.s as well as good DIY formulations for these materials; use them. Oh, why not apply them on a daily basis? For one, it is easy to have "too much of a good thing" here, and secondly, there is some advantage, widely believed, in starving a system saltatorily; say, once a week.
Though your stony corals may survive on light and decent water quality alone; they will not thrive, grow very fast, or look their best w/o providing supplementary foods. The types of foods, how they're proffered, and taking care of the ensuing wastes are important matters for optimizing your home reefs. The only way to be assured that you are doing your best at providing total nutrient is to study per your specific livestock species, and experiment in providing suitable foods. These foods should be periodically augmented by soaking them or adding vitamins, HUFAs and iodide/ate. Additionally, providing optimized nutrition is of no use w/o other aspects of water quality being addressed.
Stony Coral Foods/Feeding/Nutrition, Rationale, Science. http://www.wetwebmedia.com/corlfdgrat.htm
Borneman, Eric. 2001. Aquarium Corals; Selection, Husbandry and Natural History. TFH/Microcosm. 464pp.
Fatherree, James. 2001. The Cnidarian's Recommended Daily Allowance'¦ Feeding Corals and Anemones in Your Aquarium. TFH 4/01.
Monroe, Allen. 1994. The effect of dissolved organic carbon on light transimittance and implications for the maintenance of hermatypic corals. Journal of Aquariculture and Aquatic Sciences V. VI, No. 4.
Riddle, Dana. 1994. Coral Nutrition; Pt. 1 Notes, Thoughts and Theories, Pt. II Proteins, Pt. III Calcium and Biomineralization, Pt IV Minerals and Metals, Part V. Trace Elements and the Reef Tank. FAMA 4,5,6,7,8/94.
Riddle, Dana 1995. Life, Light & Lipids; Pt. I & II The Importance of Lipid in Coral Diets. FAMA 6,7/95,
Sebens, K and K. Heidelberg, 2000. Effects of water flow and prey behavior on coral feeding. http://www.uncw.edu/aquarius/archive/2000/7_2000/expd.htm
Stepanov, Dmitry. 1994. Coral Feeding in Nature and in the Aquarium. FAMA 1/94.