Coralmania by Eric Borneman

Mything the Point: Part One


With several labor intensive and complex subjects looming in my mind for future articles, and yet another research cruise looming even sooner, I focus this month on something a bit simpler and more practical for reef aquarium enthusiasts. In particular, I am offering a narrative version of the presentation I gave at the IMAC conference in Chicago several months ago, with a few additions thrown in for good measure. Considering the rate of information I threw at the audience during that lecture, I would imagine even those present might be pleased for a more slowly digestible version.

Without question, one of the more frustrating aspects in the hobby is the perpetual flow of misinformation that awaits both the novice and advanced aquarist at every turn. The amount of misinformation sometimes seems more like an avalanche, and with each new "crop" of aquarists comes a new "oral tradition" of myths passed around the campfire. It is my hope that, at the very least, we can eventually eliminate some of the current myths and at least replace them with a whole new group of myths if not only for the novelty of new material to debunk.

For each myth, I have created two analytical terms. First, the "Potential" is the degree or potential to which the myth can cause harm, either to the aquarist or the organisms in the tank. Second, the "Distribution" is how pervasive the myth is in the aquarium hobby, whether it occurs in isolated sectors or is widespread throughout the hobby.


Two words seem important to define, in order to set the stage for the multitude of topics that encumber the experience and language of aquarium husbandry. The first of these is the word, "unsubstantiated."

Unsubstantiated is an adjective meaning unsupported by evidence. To make sure this is clear, the word evidence means, "the data on which a judgment can be based or proof established." Evidence requires data. Unfortunately, not all data are equal, and thus evidence may at times be circumstantial or flimsy. However, I am going to assume that at least some degree of evidence based on data exists for the discussion of the topics that follow.

The second term is one that is used often in reef aquarium circles, and the word to which I refer is "anecdotal." Anecdotal means, "based on casual observations or indications rather than rigorous or scientific analysis." This is an important concept for two reasons, seemingly diametrically opposed. The first is that anecdote can be inherently valuable information, and often leads to hypotheses to be tested and thus provide data for evidence. Unfortunately, anecdote is also often taken as de facto knowledge that something has occurred based on observation alone, without separating variables, without controlled conditions, often without replication (or even multiple observations).

As an example, consider the following: An aquarist does a 10% water change with a new brand of salt, and makes the observation that his other corals bleached soon thereafter. The anecdotal observation is that the salt caused bleaching. This leads the aquarist to the hypotheses: "Replacement of 10% or more of tank water volume using Salt X leads to coral bleaching." The null, or alternative, hypothesis would be that replacement of 10% or more of tank volume using Salt X does not lead to coral bleaching." To make this anecdote become evidence, one would set up an experiment. Replicate tanks would be used, and at least two treatments would be done. One set of tanks would replace 10% of the water volume with Salt X, and the other set would be a control, without replacement of any water. To be valuable, the number of replicates should be high enough that a statistically significant event occurs. For example, see Ron Shimek's article on experimental design. In other words, having only one tank with an observed effect could very likely be due to random chance, rather than a real cause and effect relationship.

However, even if fifty treatment tanks were set-up and fifty control tanks, and in each case the treatment tanks bleached, one is left with the very real possibility that other factors were involved. Perhaps it is not only Salt X that causes an effect, but also Salts A, B, C, and D. Separate treatments would be set up for those salts, to see if the effect was due to Salt X, or all of the salts, or some of the salts. Other explanations are also possible. Perhaps Salt X needs to be mixed for a longer period of time. Perhaps there is an interaction with Salt X and another aspect of the treatment tank such that Salt X does not directly cause bleaching under different conditions (lower water temperature, lower organic content in the water, etc.). Each alternate hypothesis is tested, and eventually, with more and more possibilities included, the evidence for the hypothesis becomes stronger and stronger until it can be said that, statistically, it is extremely likely that addition of a 10% or more water change using Salt X causes coral bleaching.

After reading the above paragraph, perhaps it is apparent why, even when a very large number of anecdotal observations are made, that it is not possible to say the evidence supports a hypothesis, only that the number of anecdotal observations point towards what may be a very good hypothesis to test.

With this information at hand, I now turn to several myths that are pervasive within the aquarium hobby and which, in my view, are in need of careful examination in order that we progress forward in a helpful and meaningful manner.

Myth 1: Aquarium organisms are often correctly identified and sold by their correct species.

I think few persons who have ever bought corals would disagree with this idea. Misidentified species are common, if not the norm. Still, websites abound with species levels names attached to corals. As I have written a whole series on this subject (Part 1, 2, 3), and those articles are readily available for examination, I will treat this subject only briefly.

As most aquarists know, the identification of corals depends on skeletal features. One cannot look at a photo in a book and say, "it looks like the one on page xx of the book." Yet, that is what most aquarists, stores, and all people in the trade are doing. I would ask how many people (including the vendors selling corals) even have a microscope with which to do identifications were the coral's skeletal material removed and analyzed. Moreover, even analysis of skeletons is tentative in many cases, is extremely difficult, and cannot generally be done without many references (a very good one is the Coral ID compact disc). Many animals we keep, besides fish, do not even have skeletal material to examine. Identification of most invertebrates requires a tremendous amount of expertise and knowledge. Shimek's monthly column, A Spineless Column, on Reefkeeping should make this apparent to anyone reading about the anatomical parts of many such organisms.

Apparently, a lot of hobbyists consider me to be fairly proficient at the identification of corals, judging by the number of "what is it?" requests I receive on The Coral Forum. I'm probably better than the average person at this task, and I may have the facilities, abilities, and references to accomplish true identification. Nevertheless, in many cases, I cannot identify skeletons I have in my own collection. What I cannot do, what no one can do, is look at a photo of a coral and say with any degree of certainty (with the exception of a very few) anything beyond a genus level identification. I have never received any sort of training on coral identification, am completely self-taught, and am in general very unskilled in this area. I wonder, then, given my relative abilities in this field, how so many aquarists seem to be able to identify living corals by a photo.

The crux of this matter, of course, lies in the fact that living corals have tissue that covers the very features required to even attempt to identify them. To conclude this myth, I offer the following: one of the more common Acropora in the hobby is the species, Acropora millepora. It is also among those most likely to have a species affixed to it within the hobby, and most people I talk to imply that the scale-like radial corallites make it easy to identify and unmistakable. The following 14 images are of some of the seven different species in the Acropora aspera group that includes A. millepora. I am curious how many who think they can recognize A. millepora can do so using these images. As far as I am aware, there are no colors, or growth forms, or polyp features (hairy, etc.) that would do anything but add more species to the identification possibilities. It should be relatively easy since there is no tissue obscuring the skeletal features.

In summary, it is very difficult to distinguish species in all but a few stony corals, and aquarists should not feel the need to do so. To even be able to identify to a genus level for the many organisms in reef tanks is a skill to be admired (photos from Wallace, CC. 1999. Staghorn Corals of the World, AIMS, Townsville).

Potential: relatively harmless; may be harmful if there is a wide difference in the care requirements between the real species and the incorrectly applied name.
Distribution: widespread; exists throughout all levels of the aquarium trade on a global scale.

Myth 2: Aquarists commonly keep zooanthids.

There is a group of genera that are very popular with aquarists that includes Zoanthus, Palythoa, and others. This group belongs to the Family Zoanthidae of Order Zoanthidea. As you will note, there is but a single "o" following the "z" in all the taxonomic names. Stony corals maintain symbioses with dinoflagellates called zooxanthellae. There is a stony coral genus called Zoopilus. Small animals in the water column are called zooplankton. In these examples, two "o's" follow the "z." Unfortunately, popular aquarium books and magazines have allowed writers to send the "Zoo-anthids" word out to the masses. By logic, then, zoanthids are not referred to in the vernacular by the terms "zoo's" as short for zoanthids.

Potential: harmless.
Distribution: widespread primarily among aquarists in the United States.

These are the zoanthids, Zoanthus sociatus. They are not zooanthids.

Myth 3: Corals do not need to be fed. They get all they need from light.

For more information on this myth, I refer to my coral feeding series: Part 1, 2, 3, 4, 5, 6, 7.

Among other possible groupings, corals may be divided into two groups: those that contain symbiotic photosynthetic algae (zooxanthellate) and those that do not (azooxanthellate). Of those zooxanthellate types, algae provide energy to their host coral. The amount of energy they provide varies, but is mostly dependent on the amount of light available. Without knowing the exact species and the exact amount of photosynthetically active radiation available, or the densities or pigmentation of the algae, and the position of the coral in the tank, it is exceedingly difficult to say if a coral is receiving adequate light. It is as possible to provide too much light to some species, as it is to provide not enough to others. Because corals can acquire energy from other sources, the amount of light considered to be "enough" could vary with the availability of these other energy sources.

In all cases, the energy provided by photosynthesis in zooxanthellate corals is rich in carbon and much of it is lost in the production of mucus. Other compounds are used in metabolism or stored mostly as lipids and wax esters. Under ideal conditions, which are rare, photosynthesis can provide 100% or more of the carbon needs of many corals. For many others, even ideally, photosynthesis alone cannot provide all of the carbon requirements. In all cases that I am aware of, corals require additional energy and materials in the form of nitrogen to build tissues and proteins. This nitrogen requirement is met from acquisition of prey, ingestion of particulate material and bacteria, and/or from absorption of dissolved nitrogen compounds.

Potential: serious. Modern aquariums appear to be limited in the amount and types of material available for absorption or heterotrophic acquisition. The relatively rare production of gametes by aquarium corals is probably indicative of this shortage of material. However, more aquarists seem to be aware of this myth than have been in the past. Without question, many organisms in reef tanks starve to death, including corals.
Distribution: widespread. In general, aquarists in the United States may be more aware of the feeding requirements for reef aquariums, and the implicit shortages of many food sources in tanks, than aquarists in other countries.

Corals in shallow water may acquire all their carbon needs from light alone.
However, many cannot, and must gain both carbon and nitrogen from other sources.

Myth 4: SPS corals have requirements that include high light and water flow.

Corals with small polyps are the most abundant corals in all reef habitats. Some species require high light and water flow, and some do not. Growth form, however, is a fairly good indicator of where corals with small polyps were collected. Delicate and fragile growth forms are from areas of reduced water flow while robust, encrusting or massive growth forms are likely from areas of stronger water flow. In terms of lighting, Myth 3 provides a summary of information regarding the amount of light corals require. Corals with small polyps do not necessarily require more or less light than those with larger polyps. The only real difference between corals with small polyps and corals with large polyps is the size of the prey they can consume. Many small polyped corals, such as Pocillopora damicornis and Stylophora pistillata, are highly photoadaptive and can be found in very deep water. The genus Acropora has more species than any other coral and, as might be expected, can be found in similarly varied locations. Species of Acropora are found in deep water and shallow water, high water flow and low water flow. Furthermore, corals with small polyps have been found in many studies to consume more prey than corals with large polyps (see Borneman's article on feeding corals in Reefkeeping 2002 for pertinent references). The belief that large polyped corals need to be fed more than small polyped corals is just wrong. The requirement of light and food depends on the species and the availability of the resources.

Potential: harmless to serious. How harmful this myth is to a species depends on the requirements of the species. As many aquarists soon discover, many small polyped corals will bleach or do poorly if they are placed in very high light or water flow.
Distribution: widespread. The term "SPS" corals have become almost standard nomenclature among aquarists around the world. The coined term carries with it great misconceptions, and its use shows no signs of abating.

This Acropora species is found in very deep water and is exposed to low water flow in
its natural evironment. Not all "SPS" corals need strong light and flow. The growth form
shown here, delicate branches, can serve as a clue as to the habitat in which a coral is found.

Myth 5: The "K" rating of aquarium lamps plays an important role in the coloration of corals.
Myth 6: Corals are colorful because of their symbiotic zooxanthellae.

Zooxanthellae are golden brown to deep brown in color, depending on their pigment content and the light/temperature environment in which they are found. The bright colors in corals arise from either animal-based or skeleton-based pigments. Many gorgonians, soft corals, and a few stony corals incorporate pigments into skeletal elements. Others have animal based pigments that are either biosynthesized or acquired through diet. Many zooxanthellate corals have their bright colors because of a family of multi-hued fluorescing proteins. These pigments seem to be produced in response to a given light environment. The primary control on their production appears to be total irradiance level, and little evidence exists to suggest that the "k" rating of bulbs will influence their production. There is also a strong genetic component, although the specific aspects of fluorescing proteins and their respective genes have not yet been worked out. The color temperature of light bulbs most likely influences the perceived color of corals in a tank, with ultraviolet components enhancing highly fluorescent pigments. Certain bulb temperatures may have enough of their spectrum skewed in relative distribution that total irradiance with a given wattage may be affected, and thus total irradiance influencing the relative production of fluorescing proteins.

It is notable that some pigments appear to be formed as a result of low light, while others appear to be formed in environments with high irradiance levels. For more information, see the article and references located here.

Potential: varied. If a brightly colored coral is producing fluorescing proteins in response to low light, placement in high light environments may result in bleaching. Other aspects of fluorescing protein production may be related to bleaching resistance in high light environments. Otherwise, coloration is largely aesthetic for reef aquariums.
Distribution: widespread. It is becoming more widely recognized in aquarium circles that coral coloration does not arise from the colors of zooxanthellae. However, many articles in the lay press still wrongfully propose this notion. The belief that the k-rating of bulbs is important to coral coloration is widespread among the hobby populace, and appears to be a common misconception in all countries.

Even though brightly fluorescent, colorful corals such as this Trachyphyllia geoffroyi
are often from low light areas, they may bleach (as in the specimen shown) when
exposed to strong tank lighting.


Aquarium myths are widespread and are often based entirely on anecdote. Myths are perpetuated in a sort of modern oral tradition, whereby one aquarist learns and believes information without proper evidence or investigation. The need to read and act skeptically is a good skill to learn when dealing with aquarium information sources. This article will be continued as Mything the Point, Part 2, in the next issue.

Link to Part Two

If you have any questions about this article, please visit my author forum on Reef Central.


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Mything the Point: Part One by Eric Borneman -