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
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
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
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
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,
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.
Distribution: widespread primarily among aquarists
in the United States.
These are the zoanthids, Zoanthus sociatus. They are
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,
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
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
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