Mything the Point: Part Two
In the last article, I began a somewhat in-depth explanation of some of the pervasive myths and misunderstandings in the reef aquarium hobby. That article, and the current one, expands upon a presentation I gave at the 2003 International Marine Aquarium Conference in Chicago. In this part, I will look at other topics that are still in widespread belief despite lacking basis, or with evidence to the contrary. It is by no means an exhaustive treatment, and without question there are many other myths that need (and will need) to be dispelled from this hobby, and industry, for future progress in the field to occur.
Myth 7: Hairy crabs are bad (can eat corals, etc.) and should be removed.
The hairs or bristles on crabs are extensions of various appendages and are tactile and/or chemosensory receptors involved in all manner of behaviors, from feeding to defense to locomotion. Crabs with the stiff bristles called setae on their feeding appendages often use them as filters or combs, and this is equally true of many of the symbiotic crabs associated with corals. Some coral-associated crabs are hairy, and some are not. Similarly, some "non-hairy" and mostly herbivorous crabs, like Mithrax, can and do eat corals (many others, such as the portunids, eat fish). Other extremely hairy crabs may not interact with corals at all, but may be scavengers. It's my experience that most crabs should be watched closely in aquaria as they tend to be somewhat nonselective in their feeding choices, but it is also my experience that crabs found and remaining within the branches of coral colonies are almost invariably symbionts and not predators (though the latter do exist), irrespective of the number of bristles on their appendages.
Potential: relatively harmless, except, of course, to any crab that becomes the victim of a wrongful designation. There is some evidence to suggest that the presence of symbiotic crabs is beneficial to corals, although the relative benefits to corals in aquaria is more questionable. In any event, they are not harmful and are certainly interesting and attractive.
Distribution: Widespread. I have heard this repeated since I began keeping aquariums.
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Click picture for larger image.
Myth 8: The statement, "but my water quality checks out fine."
In his articles here (and elsewhere), as well as in his forum on Reef Central called The Reef Chemistry Forum, Randy Holmes-Farley provides extensive information on the nature of common (and sometimes uncommon) chemicals in reef aquaria. Ron Shimek, and others, have also covered various topics in chemistry and biochemistry over time frames spanning ten years and more. Until relatively recently, only a few chemicals were generally considered in reef aquaria, and the ability to accurately measure those parameters has frequently been called into question.
My point above is that aquarists routinely check a variably complete set of a handful of chemical parameters in variably accurate ways to make the oft-repeated statement, "my water quality checks out fine." As has been discussed elsewhere, there are many difficulties of being assured that such statements are true, and the more recent information concerning more exotic and toxic chemical species including various metals and organometallics virtually ensure that there might be many reasons to suspect that one's water quality might not be "fine," despite routine testing for common parameters.
To take this issue a step further, one must necessarily include the bounty of organic chemicals produced by organisms in aquariums called secondary metabolites. I am both pleased and troubled that the word "allelopathy" has become a regular word in many aquarists' vocabulary. It is almost impossible to describe how varied the products of metabolism can be in the marine environment. In short, virtually every organism in the tank has them, produces them, and releases them. The effects of secondary metabolite chemistry are significant enough to cause real and sometimes dramatic effects in the wild where dilution effects are vast. So common and numerous are these compounds that conferences, books, and journals are devoted entirely to the subject. I would urge readers to look through a copy of the Journal of Natural Products to see the scope of this topic (it is only one of many sources of such information). Each issue consists of several hundred pages (often filled with 1-2 paragraph descriptions) of metabolites derived and isolated from natural sources (organisms) and, sometimes, a brief description of potential effects (usually based on chemical structures similar to those of known function). In any given issue, about 20-50 percent of the chemicals are from marine organisms, and many are from tropical marine organisms. For example, here are the relative feature articles from the past two issues alone:
Novel Oxylipin Metabolites from the Brown Alga Eisenia bicyclis
Isolation and Structure Determination of Lyngbyastatin 3, a Lyngbyastatin 1 Homologue from the Marine Cyanobacterium Lyngbya majuscula. Determination of the Configuration of the 4-Amino-2,2-dimethyl-3-oxopentanoic Acid Unit in Majusculamide C, Dolastatin 12, Lyngbyastatin 1, and Lyngbyastatin 3 from Cyanobacteria
Semiplenamides A-G, Fatty Acid Amides from a Papua New Guinea Collection of the Marine Cyanobacterium Lyngbya semiplena
Komodoquinone A, a Novel Neuritogenic Anthracycline, from Marine Streptomyces sp. KS3
Placidenes C-F, Novel -Pyrone Propionates from the Mediterranean Sacoglossan Placida dendritica
Plakortides M and N, Bioactive Polyketide Endoperoxides from the Caribbean Marine Sponge Plakortis halichondrioides.
New Polyhydroxy Sterols: Proteasome Inhibitors from a Marine Sponge Acanthodendrilla sp.
New Brominated Labdane Diterpenes from the Red Alga Laurencia obtusa
Briaexcavatolides S-V, Four New Briaranes from a Formosan Gorgonian Briareum excavatum
The Synthesis of SO-3, a Conopeptide with High Analgesic Activity Derived from Conus striatus
New Cembrane Diterpenes of the Marine Octocoral Eunicea tourniforti from the Eastern Caribbean
Isolation and Structure Determination of an Antimicrobial Ester from a Marine Sediment-Derived Bacterium
Identification of New Okadaic Acid Derivatives from Laboratory Cultures of Prorocentrum lima
One can imagine what twenty years worth of this type of research has produced. In the feature articles of the past two issues of a single journal, we see novel chemicals derived from sponges, soft corals, dinoflagellates, bacteria, algae, cyanobacteria and mollusks. These are, of course, in addition to those already known from these organisms. Some sponges, algae, and soft corals have been identified that produce in excess of 40 separate chemical compounds.
They are termed "secondary metabolites" because in many cases these compounds do not seem to have a function in basic metabolism. However, many are extremely bioactive, and have diverse effects on other organisms, including being lethal. Of course, the effects are largely unknown and many of these chemicals are not produced to have an effect on organisms that would not ordinarily be encountered by the producer of the compound. Other compounds may have an unintentional effect. Furthermore, various compounds may be very specific in the species they affect, and in how they affect those species. In almost all cases, pairwise tests of one species on another have not been done for any effects. There is little to no information as to what the ultimate fate or reactivity of these organics products might be in any environment, much less in aquaria. Finally, these bioactive compounds are highly concentrated in the closed small water volumes of our aquaria. For some examples of the scope of secondary metabolite chemistry from coral reef organisms, see the boxes below which I have derived from various primary and secondary literature over the years. The listings in the boxes are by no means exhaustive.
I hesitate to make such seemingly alarming statements, for I am concerned that such "unknowns" may become the fuel for more myths. It would be comparatively easy for such information to be used as an excuse on which to blame the death or failure to thrive of various tank inhabitants. However, the fact that virtually every inhabitant in our aquaria is producing variable amounts of novel, uncharacterized, and well-known bioactive secondary metabolites of mostly unknown effects, and may be reactive with a host of other largely unknown organic and inorganic compounds present in our tanks, makes our water a complex soup with no two tanks being alike - or predictable.
The take-home message of this myth is that it is practically not possible to say "my water tests fine." All we can do is recognize certain facts, and act accordingly. In my opinion and experience, the most pragmatic solution is dilution and absorption by the use of water changes, protein skimming, and activated carbon. I fully realize the many issues that might stem from this simple advice, especially in light of the materials provided by authors as mentioned above. However, if nothing else, it seems to potentially simplify the many potential chemical interactions that might be occurring.
Potential: Innocuous to lethal. I believe many inexplicable problems in the survival of aquarium species may be due to secondary metabolites. Some are well known to occur, others are purely speculative. However, there remains the incontrovertible fact that there are effects, and that every reef aquarium has organisms producing a pharmacopoeia of bioactive compounds.
Distribution: Ubiquitous. Every day, aquarists around the world use hobby test kits to measure the levels of perhaps 1-6 variables for which tests are available. There are no tests available for the 4-Amino-2,2-dimethyl-3-oxopentanoic acid unit in Majusculamide C, Dolastatin 12, Lyngbyastatin 1, and Lyngbyastatin 3 from Cyanobacteria that were discovered last month. For all we know, this unit causes 100% mortality in Trachyphyllia geoffroyi. Then again, it might not.
| Box 1 - Tissue hypertrophy |
| Box 2 - Defense against predation |
Myth 9: Lugol's dips or other commercial dips are useful or prophylactic for treating coral ailments.
Myth 10: Bacterial infections are common in aquarium corals.
I have discussed this extensively in other columns, and so I will be very brief here. To date, there is no disease of aquarium corals that has been shown to have a bacterial cause. There are unquestionably bacteria that can cause disease in aquarium corals, and bacterial infections of aquarium corals may be relatively common. However, I doubt it. There is at least one genus of ubiquitous bacteria that has been isolated from corals (Euphyllia species, Catalaphyllia jardinei, and zoanthids) that also causes, or is part of the consortium that causes diseases in wild corals. It is a species of Beggiatoa, and it is often visible as white filaments or webs, occasionally becoming like mats or paste as the colony increases in density. Beggiatoa are gliding filamentous bacteria that tend to form cottony colonies or mats at interfaces between aerobic and anaerobic zones in terrestrial, freshwater, and marine environments. They oxidize hydrogen sulfide produced in the anoxic zones, but can also grow heterotrophically using acetate as a carbon source and some can autotrophically use carbon dioxide. These microbes are found on sediment and substrate surfaces, including corals. They provide a valuable function in nutrient processing, and cannot be "eliminated." Being opportunistic coral pathogens to some species is unfortunate, but I am afraid it must be viewed in terms of the root factors that may have been involved in a coral becoming colonized and infected by Beggiatoa in the first place.
Other bacteria commonly thought to cause disease in aquarium corals are the numerous, and often yet to be described, Vibrio species. Vibrios are common on coral surfaces, and some, but not all, are known to be potentially pathogenic. However, the conditions under which they become pathogenic are largely unknown, and whether or not they are opportunists is similarly unknown. Furthermore, in no case have they been found as a disease-causing agent in aquarium corals.
Even if bacteria were someday found to be a problem for aquarium corals, recognizing the signs that would unambiguously indicate a bacterial infection would be extremely difficult or impossible. Thus, treatment options will be very difficult. After all, if you simply see recession on a coral how is it known if it is due to shading, poor water flow, allelopathy, or bacteria? The answer is that you probably won't.
If this is the case, why not just use antibiotics or antiseptic dips prophylactically? The answer to this question is that both the coral and the normal bacterial flora (some may be symbiotic) growing on the coral surface produce natural antibiotics, mainly to non-native strains. Therefore, anything that kills potentially bad bacteria will certainly also be killing good bacteria. This, in itself, compromises the aggregate of coral and bacterial defenses to colonization by new strains and reduces natural immunity. Additionally, there is little or no information on the effect of various substances and drugs used as antibiotics on the coral itself, and at least some of these products are moderately toxic to corals (see below).
In cancer chemotherapy, the theory behind treatment is that you hope to preferentially kill more cancer cells than healthy cells. In the process, the patient takes a beating. Sometimes it works, sometimes cancer continues, and sometimes the patient dies from the treatment. Based on my own experience, I can say that treating corals with unknown agents results in the same three possibilities. If a coral is recently purchased, it is already likely to be stressed, and further stress of "prophylactic" treatments may result in the mortality of a specimen. Of course, this "theoretical" discussion all operates under the assumption that 1) the substance is actually effective against whatever is being treated and 2) that there is some knowledge of the cause of the disease at all.
In my experience, Lugol's iodine solution is moderately effective at treating corals with brown jelly infections and seems reasonably well tolerated by most (but not all corals). Otherwise, I have not noticed Lugol's solution to be a particularly useful treatment for other problems in aquarium corals. Speaking of brown jelly infections…
Myth 11: Brown jelly is caused by the protozoan, Helicostoma nonatum.
I have found occasional references to the Family Philasteridae of the Ciliophora containing a species named Helicostoma notata. I have browsed books on ciliates, and found no reference to any affiliation between the genus Helicostoma and corals. I have found no reference to support that brown jelly infections are caused by protozoans or ciliates, except those based on a German book on reefkeeping and an article in a German aquarium magazine from the mid 1980's. Since then, this designation has been promulgated throughout the world to the point where an internet search yields only two non-aquarium based references to the genus Helicostoma in total. I can find no valid reference to H. notata or H. nonatum, and one reference to an H. brudderbuckii. In fact, the few volumes I can find that mention Helicostoma consider it to be monotypic, consisting of the species H. oblongum. The characters of H. oblangum do not fit the characters of the ciliates I have found in brown jelly, either, as might be expected since this ciliate is mentioned being found in brackish or salty water of the New York bight. A search of a ciliate database confirms that this is the only valid species. In fact, even an Australian science publication has erroneously called brown band disease as attributed to this ciliate (again, without any reference at all). The point here is that while ciliates are present in the brown jelly material, it is not clear at all what role, if any, they play in brown infections. They might easily be present simply because of the dead tissue. However, the ciliates are mostly of one kind, and there are ciliates present in all samples. What ciliate is anyone's guess at this point, and there may be many. I suppose it might even be Helicostoma nonatum, but I do not believe this ciliate has been accurately identified in corals with brown jelly infections.
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still visible above. The outlines of the branches are still visible in this
amorphous mass of digested tissue and zooxanthellae.
What I have done is examine brown jelly from three affected corals: a Euphyllia ancora, a Pocillopora damicornis, and a Plerogyra sinuosa. The samples were all from different tanks, and collected many years apart. I have also sampled a brown jelly-like material from a reef coral in the Caribbean, and a sample of a brown slimy flocculent material that is relatively common on substrates in the Caribbean, usually from reefs that are not doing very well. I have not yet had a chance to examine the wild material. However, one sample of brown jelly now resides with the Registry of Coral Pathology, and the description by coral pathologist Esther Peters, confirms that there is coral tissue material, both algae and animal, within vacuoles of the protists. The necrotic condition of the coral tissue, and the fact that ciliates are not found digesting nearby corals or even healthy tissue of the affected specimen suggests they may just be opportunists of necrotic tissue rather than causative, or that they are part of an as yet unidentified consortium. I am slowly getting to these other samples, and hope to have more information soon.
Potential: innocuous to very harmful. The use of experimental treatments may have no effect at all, or it may result in mortality of the treated coral. I have watched the polyps of Pocilloporids bail out of their skeleton within an hour of being exposed to experimental treatments, including Lugol's solution. The use of antibiotics may also be harmful, in general, when applied without diligence in the creation of AB-resistant strains. Playing "doctor" with corals may seem compassionate and impressive, but mostly its just irresponsible guesswork, often with the hopes that some miraculous "cure" might result to save corals from unseen and unknown pathogens.
Distribution: extremely widespread, and has been occurring over long periods of time.
Myth 12: Aquariums need supplements from the fish store.
Again, I refer readers to the many articles published by Holmes-Farley and Shimek. It has become obvious we know little about the chemistry of aquaria, and it has long been known we know very little about specific requirements of corals and other reef aquarium inhabitants to exotic elements. It is equally apparent that the use of various foods and salts result in all manner of elevations in water chemistry that are aberrant.
There are a relatively few things that are quickly depleted in aquaria, or that are generally absent, that have numerous and documented functions in many organisms. As far as I am aware, these things consist principally of calcium, carbonate, iron, iodine, oxygen, and plankton. Of these, iodine is of questionable utility as an element in solution to most species of interest to aquarists, although the use of algae in refugia is a perhaps more recent interest and one that may, according the species grown, be of concern.
I will not pretend to guess at the myriad potential requirements of every organism nor the presence or absence of every potential element in a tank. What I can say is that I have not personally added any supplement from a fish store to my tank in six years, and I have not regularly dosed any supplement for eight years, with the exception of calcium, carbonate, and foods. In that time, I have not seen any specimen or population decrease, fail to thrive, or vanish as a result. Admittedly, I have not done any study to confirm my observations, nor am I sure that some ignored or unseen population has not been lost as a result of my omissions. However, I would also say that no evidence exists to show that any aquarium supplement other than those mentioned above has resulted in any specimen or population increase in growth, health or survival.
The aquarium trade is astonishingly fast to react to trends in the market, and to capitalize on the passion and excitement of aquarists' desire for magic bullets. The labeling and claims of virtually all such manufacturer's read like the sound of a broken record, all claiming to produce dramatic results and seeming to require their purchase. The recognition of elevated metals in aquaria, discovered within the past four years and only becoming a major topic of interest within the past two years, has already resulted in manufacturers producing products claiming to address these problems and be equally as miraculous and required as their previously or concurrently produced "high metal" predecessors. I find it funny to imagine how the "research and development" teams that must certainly be sitting behind lab benches in white jackets with corals in research systems never picked up this problem - until now, of course, after the real researchers in the hobby have made the real discoveries (with no credit by the companies of course, but sometimes with criticism in advertisements, I might add) and have adjusted to market demand with the appearance of the "new and improved" products.
Potential: harmless to lethal. Since many supplements are mostly water, the primary harm is to the wallet of the aquarist. In other cases, aquariums may be compromised by the appearance of nuisance species that take advantage of normally limiting nutrient sources. In the worst case, the supplements are toxic additives.
Distribution: global. The purchase of unnecessary supplements may be as much testimony to the effectiveness of advertisement and the international distribution of such products as to the intrinsic nature of humans to desire such things.
Myth 13: The refugium concept.
The now-common practice of maintaining "refugia" is a welcome advance to the reef aquarium hobby. The concept, as far as I can recall, originated with the design of the Smithsonian Caribbean mesocosm in the 1980's. As an offshoot of the technology that was used in that display, algal turf scrubbers were licensed to Inland Aquatics, who soon offered drop-in refugia to retrofit existing tanks not utilizing turf scrubbers. In the 1986 book, Dynamic Aquaria, Adey and Loveland write, "Most of our refugia have been directed towards freeing attached fleshy algae, soft-bottom invertebrate populations, and plankton from severe predation by fish and larger invertebrates (particularly crabs and lobsters)….In general, the semi-stability that is achieved in community and population structure in the wild over large areas, and at time scales of centuries and millennia, is achieved in microcosms, mesocosms, and aquaria by the manipulation of space (refugia) and, when necessary, the populations themselves."
In any case, the rest is proverbial history. Now, do-it-yourself refugia and commercially available refugia exist at every turn and are very common in today's reef aquaria.
As mentioned, the idea behind refugia was to provide an area safe from constant predation for the many small organisms that were quickly eaten in displays housing large populations of fish and predatory invertebrates. Macroalgae were often incorporated into refugia as both food sources and habitat. Soon, the rich flora and fauna that tended to grow in refugia was exploited as a recovery area for sick fish, and could act as a nursery for breeding species in some cases. Of course, the size of the refugium might limit how many predators (as adults or juveniles) might be able to temporarily dwell there.
As more aquarists began to utilize these small, attached tanks, the ideas behind them were both improved upon and also bastardized. Soon, mud- and Caulerpa-filled sumps became commercially developed as a natural filtration method. Aquarists using these systems noted the luxuriant growth of the same populations mentioned above, and likely also noticed how they rather resembled things called refugia. Other aquarists took advantage of a new tank in the system utilizing the same water in which many of their corals were thriving, and the refugia began doubling as coral propagation tanks. Of course, the corals appreciated the extra available food, too. All too soon, photographs of refugia with one or two fish, or some shrimp, began appearing on websites. The refugium had become a low flow, specialized habitat reef tank with predators whose primary purpose was really denitrification through the use of sand beds and large quantities of the toxic algae, Caulerpa species.
The concept that macroalgae and sand beds could be used in refugia as nutrient uptake began in the 1980's. The widespread use of them as such seemed to be a novel concept to many, though it wasn't. However, it was a welcome use and a wise idea to incorporate them to many systems. Yet, refugia by themselves are generally quite small, and the largest fraction of nutrient processing of a tank is probably happening in the larger fraction of the system. In other words, small refugia with sand and macroalgae are supplemental to the processes and uptake happening in the bulk of the tank. Most aquarists keep one to many herbivorous fishes in their tanks, in addition to the many herbivorous invertebrates that are major grazers of algal biomass. Just as in the wild, with low nutrient levels in the tank, algal control is a top-down process where grazing limits algae within the main reef system. If anyone doubts this to be the case, remove all the herbivores from a well-lit reef aquarium and watch what happens. Turf algae will begin growing rapidly. It is not the magical properties of Caulerpa in action, it is just ecology.
I am not in any way condemning the use of macroalgae in refugia. I am very fond of many of them, although many have quite numerous and toxic secondary metabolites, like soft corals and sponges. In particular, I am very unfond of Caulerpa (Figure 5). It is invasive and very difficult to eradicate. It is toxic to fish and has many metabolites - and releases them when the organism degenerates during spawning. Acidic rhizomes etch carbonate (Figure 6) and these algae can kill other more desirable species by overgrowth. I have had it grow right through the stalks of soft corals. Many aquarists say that it has not been a problem for them. My response? Just wait. It will. I guess my big question regarding Caulerpa is why use it at all when so many more desirable species of macroalgae exist, like Chaetomorpha species, or others (Figures 7 & 8).
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that makes it difficult to remove.
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To restate yet again, a refugium is a place provided to allow certain organisms to grow while freed of predation or herbivory. If one incorporates predators such as shrimp, fish, and corals into a refugium, the very reason for its existence is lost. Given the small size of most refugia, a handful of zoanthids and a couple shrimp will likely decimate any populations of small organisms that were originally supposed to breed and feed the main display tank. If one desires to keep an area for breeding or propagating organisms, it might be a tank that replicates a habitat and that may look like a refugium - but it is not a refugium. If one desires to have a display tank filtered by natural processes, it should be ideally (significantly) larger in scale than the display to be effective. Otherwise, any natural filtration is probably largely supplemental to what is already occurring in average reef aquaria, although I imagine with careful consideration it might become quite significant. The natural filtration of the display was already initially addressed with live rock and sand beds (Berlin, ATS, and Jaubert methods). Protein skimmers provide more than enough additional filtration in most other systems (Berlin method). A refugium design should incorporate food sources and habitats that are conducive to the growth and reproduction of organisms that would otherwise become food for the mouths present in a reef aquarium display. In all likelihood, these same elements will also provide additional benefits such as nutrient uptake and regeneration.
As a final point, many aquarists comment on the amount of small crustacean life in refugia - and there often is. However, many of these same crustaceans are benthic or demersal zooplankton, and are often associated with reef structure and cavities. Providing a fair amount of rubble in refugia is a good idea. In fact, I would suggest (and know personally for a fact) that most people would see far more crustaceans in a refugium filled with live rock rubble that is allowed to have turf algae grow on it than in the macroalgae and sand dominated refugia that are common today. The difficulty will be keeping enough turf algae growing as fast as the amphipods consume it.
Potential: slight to moderate. In most cases, a refugium of any sort provides some benefit, although it may be largely functionless for the desired purpose, depending on the species it contains. The only real risk may be with the inadvertent mass release and death of some macroalgae species during spawning events.
Distribution: moderate. The use of refugia is widespread but may be most common in the United States. Refugia, while common, are certainly not standard incorporations into most reef tanks yet.
This concludes the second part of my series on common myths in reef aquarium keeping. I had hoped to conclude the series with this installment, but there was a bit too much information in this installment to make the article length manageable. As a final offering, I suggest revisiting the first part of last month's article on the definitions of anecdote and the benefits of skeptical thinking. The reef aquarium hobby is filled with amazing insights, unreported observations, vast stores of knowledge (often unrequited), a few lies and untruths, and a whole lot of hearsay. It is everyone's responsibility to think and read and learn before doing and, worse, repeating things that may not be exactly as they are said or appear to be. Until next month, please visit my author's forum for questions or comments about this article.
from : http://reefkeeping.com/issues/2003-12/eb/index.php
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