Articles

Chemical Supplements

By Ronald L. Shimek, Ph. D.

The Small Print

One of the sad, but undeniable, facts about all advice – on any subject – is that the person giving the advice has an agenda; a specific reason for giving the advice.  This is even true when the advice is given in a supposedly neutral setting such as an educational institution.  What is even sadder is that most authors are unwilling or unable to explicitly state their agenda.  Such “authorities,” and the reef aquarium literature is rife with such people, want the reader to assume that they are giving advice “out of the goodness of their heart.” However, their final line of advice is often, “please buy my product…”

So, what is my agenda?  Personally, I sell no tangible product, only advice.  Within the context of this small series of articles, I am being paid to write them.  I have known Dennis Tagrin for over 10 years and have used his products for much of that time.  Unlike the products of many other manufacturers, his products are what he says they are. 

My agenda is twofold:  First, I want to give the best advice I can.  That enhances my reputation, but more importantly, it keeps reef organisms alive.  Reefs, worldwide, are in perilous condition, so anything we can do to keep the animals alive is important.  Second, I see absolutely no reason to spend more or do more than is necessary to keep the animals in good health.  If we can purchase a few good high quality products that do the job, no other products need to be purchased.

The Bottom Line

I am not a chemist.  I am marine ecologist; specifically, I am a marine invertebrate biologist specializing in predator-prey interactions.  However, I have several years of chemistry courses under my belt and one of the major subdisciplines of my doctoral training was cellular physiology; or cellular biochemistry.  So, I can “speaka da language” of chemists.  Additionally, the reader will find that ALL of my statements and suggestions are fully referenced, both in some reef aquarium articles, but more importantly in the peer-reviewed scientific literature.  The necessary references are given at the end of each of my essays.  Should the reader have any questions, I urge them to take a look at the science that the advice is based upon.  It really isn’t that hard to understand.

The Milieu

Trite statement number one:  Reef organisms live in water.  Sea water.  This is an interesting fluid, it is the root of all life, and yet if an aquarist were to drink it exclusively they would die, in agony, within a few days.  So, herein, is the first of our problems.  The water surrounding reef organisms is not the water that comes out of a tap, nor is it the water a human can drink.  It is something else.  Frankly, it is everything else.  There is some argument in paleontological circles as to how and when the Earth first got its oceans, but as the first fossils appear to be found in sedimentary rocks deposited some 3.8 billion years ago, there has been an ocean on this world of ours since at least that time (Ward, 2000, 2006, 2007; Knoll, 2003). 

All water is corrosive; it has been called “the universal solvent.”  The peculiar chemical properties of water allow it to dissolve anything meaning the term, “insoluble” is a lie.  With regard to water, provided there is enough water and enough time, some small amounts of every substance will dissolve in it.  More than that, given that all rivers have been flowing to the sea since the first raindrop fell, the sea is the repository of everything that has had the chance to dissolve.  This means sea water is, indeed, water.  However, as I have indicated, it is also everything else.  In today’s sea water, are all of the dissolved materials washed into the sea since there has been a sea to wash them into.  If we exclude items of exclusively man-made origin, those delightful materials as PCBs, PAHs, and other organic materials, we are left with a soup of all the elements and several specific compounds.

The sea has not had a consistent nor a stable array of materials contained within it.  In fact, one of the surprising results of the vast amount of paleontological research of the last generation has been a realization of the vast amount of change that has occurred in the oceans (Hallam and Wignall, 1997; Ward, 2000, 2006, 2007; Knoll, 2003).  Not only have the oceans not been stable over time in their composition, they do not have a consistent composition completely through them right now

(Pilson, 1998).  The composition of sea water in the oceans’ depths, below about 4000m (13,200 feet) or roughly the bottom half of the oceans, is so decidedly different than what is found in the shallower regions that we might actually consider these as two separate bodies of water.

Even in the shallower regions, there is a rather surprising amount of change in some oceanic components from place to place, and from time to time at the same place.  Within the shallow
waters, however, the major dissolved constituents of sea water are relatively constant.  These
constituents are indicated in Table 1, taken mostly from Pilson, 1998.  It is worth noting  
that the information from Pilson, 1998, is no longer wholly accurate.  The relative amount of the bicarbonate ion, HCO3-, has been changing significantly over the last couple of decades due to changes in the atmospheric concentration of carbon dioxide (Kleypas, et al, 1999; Orr, et al., 2005). 

Most manufacturers – but, rather interestingly, NOT all – of artificial salt water mixes tend to try to emulate the natural mixture (Atkinson and Bingman, 1999).  There is good reason to duplicate natural sea water if one wants to keep salt water dwelling organisms alive.  All organisms alive today have an equivalent length of evolutionary history, 3.8 billion years, in this salt water medium, and while the medium has changed drastically in that time (Hallam and Wignall, 1997; Knoll, 2003; Ward, 2006), it has remained more-or-less constant in shallow waters, at least, for the last 35 million years.  That means organisms have adapted to this particular mixture.  Salt water animals such as crustaceans or fishes have impermeable and water-proof skins or integuments and cannot absorb materials out of the sea water surrounding them, however, many other animals, such as the cnidarians (corals, sea anemones and their kin) and echinoderms (sea stars, sea urchins and their kin) are able to this, to some extent, under laboratory conditions, anyway (Whithers, 1992; Ruppert, et al. 2003).  IT IS WORTH STATING THAT JUST BECAUSE THE ORGANISMS CAN DO THIS UNDER SOME LABORATORY CONDITIONS, DOES NOT NECESSARILY IMPLY THAT THEY ACTUALLY DO IT AT ALL UNDER NORMAL AND NATURAL CONDITIONS (Prosser, 1991; Withers, 1992; Ruppert, et al. 2003).

One of the enduring dogmas of reef aquarium lore is that after a time the “sea water” of one’s tanks must be supplemented to maintain a proper balance of the dissolved chemicals.  This dogma has some aspects of truth to it.  It also has some major aspects of mythology to it.  It is important that reef aquarists know the difference between truth and mythology.  Not only will that save them money, it will also save their organisms from some rather unpleasant consequences.

 

The question being of course, what ARE the materials are consumed in normal healthy metabolism?

The answer to this is – surprisingly – relatively straight-forward.  The only materials that need to be supplemented are those that utilized in the construction of the organisms’ skeletons.  In an aquarium, these are calcium, possibly both magnesium and silica, and the constituents that contribute to alkalinity.  Nothing else.  Strontium is also consumed, but as I will point out, it is mildly toxic and is consumed as part of a detoxification process.  Once it is removed from solution, it need not be added.   Trace metals are not absorbed by animals; animals get all the trace elements they need from their foods, and in most cases these have to be metabolically dealt with as the poisons they are.  Trace metals ARE utilized by some (not all) algae, and if the aquarist wishes to promote the growth of some algae, such as hair algae, by all means they should add trace elements, but be aware that such materials are very toxic to animals.  One point to be made here is that animals and algae are VERY different kinds of LIFE (Lecointre and Le Guyader, 2006).  While they do have similarities, they do NOT have the same overall biochemistry; while many so-called “algae” require these chemicals, animals definitely do not.    

Mineral Supplements

Calcium And Alkalinity

In general aquarists supplement a variety of various mineral substances, however, the number of these that are beneficial is really pretty limited (Holmes-Farley, 2007).  Only two additives are absolutely necessary to supplement in all cases.  These are additives to maintain the level of calcium and the level of alkalinity.  The reason for this need is relatively straight forward:

The formation of a calcium carbonate skeleton, by any of the animals (primarily these are corals, mollusks, echinoderms, and crustaceans; fishes have a skeleton made of calcium phosphate) that have such may be demonstrated by a simple and basic chemical formula:   

Ca= + CO=3 ↔ CaCO3

As should be evident, this reaction consumes both calcium ions (Ca=) and carbon dioxide (as carbonate) ions (CO=3).  In brief, both the calcium and the carbonate ions are taken from the water surrounding the organisms, in the aquarium these ions are primarily present as dissolved calcium and the constituents of the alkalinity reactions.  What actually occurs in the secretion of mineral calcium carbonate, in those very tiny interstices between the various epidermal cells and the mineral crystal is not actually known for any animal; however the shorthand for the final result is the equation above (Prosser, 1991; Withers, 1992; Ruppert, et al. 2003).

In many marine animals, the mineral skeleton also contains some magnesium carbonate and some odd mixtures of magnesium/calcium carbonates.  It is relatively unclear how much of this is actually due to the active utilization of magnesium versus the passive utilization of a material (magnesium) that is similar chemically to calcium.  However, in cases where the skeletal formation in a reef aquarium is relatively rapid or intense, it is probably a good idea supplement magnesium as well as calcium.

Figure 1. The mineral part of this coral skeleton is primarily comprised of CaCO3, with minor amounts of Strontianite (a form of SrCO3)) and Mg CO3 The raw materials for this come from the dissolved materials in the water but have to pass through at least two coral epithelia before they are deposited into the skeleton.

Silica

The question of what to do about silicates is another puzzle.  It is very difficult to get a handle on just how much silica is dissolved in sea water, but the general consensus is that it present at all times, often in very high concentrations, mostly as dissolved clays (Pilson, 1998).  In fact, there is significant amount of evidence that the buffering capacity of silicates is much greater than that of the normally thought of buffer, the alkalinity system, and as a result silicates may control and buffer, in the long run, the oceanic pH.  Howsoever, the wide variety of various silicate species is so great and the chemistry to measure them so difficult that it is essentially impossible to easily get a good picture of the silicate concentrations at any given time or place in the oceans.
Relatively few animal groups can easily metabolize silicates, but premier among them are sponges.  A few snails, and some crustaceans, also deposit silica on occasion.  Because of this, some aquarists find it useful to supplement silicates.  Silica additions, however, are probably not necessary for the vast majority of animals, and if the aquarium is well fed with foods of marine origin, enough silica probably enters the system in this way to make silica additions superfluous. 

Figure 2.  SiO2 is the constituent of these hexactinellid sponge spicules.  Hexactinellids are a peculiar type of sponge whose supportive skeleton is made wholly of fused silica. 

Iron

Iron is a limiting nutrient element in the oceans for phytoplankton.  This means that there is a demand for iron that remains unutilized in oceans.  Because of this phytoplankton, which need dissolved iron, are often found in lower concentrations than they would be if iron were present in “sufficient” concentrations.  Some aquarists, wanting to encourage algal growth may routinely dose or add iron solutions to their system (Holmes-Farley, 2002).  Fortunately, if done in decided moderation, excess iron is probably not harmful to most animals.

The Strange Case of Strontium

Strontium is an element that has a lot of affinities to both calcium and magnesium.  In fact these three elements, magnesium, calcium, and strontium constitute a triplet, three sequential elements in column IIA, the alkali earth metals of the periodic table.  The whole column is, in order, beryllium, magnesium, calcium, strontium, barium and radon.  All of these elements form ions with a +2 valence, and all of them are somewhat “similar” chemically.  Similar – but not identical… and therein lies the rub.  Apparently while magnesium and calcium are beneficial for animals, the other elements of that group are not.

Figure 3.  The "Periodic table (from Wikipedia, The Free Encyclopedia. 9 Jan 2007, 22:44 UTC. Wikimedia Foundation, Inc. 11 Jan 2007).  The alkali earth metals, such as magnesium, calcium and strontium, are on the left in the orange column.

Nonetheless, there is a prevailing myth in the aquarium literature that one should add strontium to aquarium water to replace the strontium that is used up.  And used up it is.  So, it might seem reasonable that it should be added.  Might seem – but, not if one looks at the scientific literature written over the last twenty or so years.  The tale of strontium and corals constitutes one of the more fascinating stories in coral biochemistry. 

The story starts about sixty years ago, shortly after the first American hydrogen bomb tests, which were done on Pacific atolls in the early 1950s.  The thermonuclear reactions of such explosions transmuted some of the calcium in the vaporized atoll limestone into an isotope of strontium, strontium90.  Strontium90 soon became important because, like all other strontium isotopes it behaves similar to calcium and in that regard it soon became apparent it was being deposited in human bones.  It is also highly radioactive and quite dangerous.  As a result of these two facts, the human usage and the radioactivity, a widespread program of testing for strontium in the natural world was initiated.  One of the more interesting facts that came from this was the information that strontium, of all isotopes, was deposited in small amounts in coral skeletons.  The second fact of interest was that this deposition of strontium in coral skeletons was related to temperature, so there was a minor, but widespread, survey of corals and fossil corals to measure the amount of strontium.  In this way, it became possible for paleontologists to estimate the temperature of ancient seas.  If the strontium was being deposited the same way in ancient times as it was being deposited today, and if there was a temperature relationship, then one could assume what happened then was similar to what was happening now and make a guess as to the ancient seas’ temperatures.

Well, the tale wasn’t as simple as it first appeared.  It was presumed that strontium being just slightly larger than calcium was being used in chemical reactions, “by happenstance” or mistake, at about the relative proportional abundance of strontium to calcium.  That was the state of the art in the early 1980s.  In the late 1970s, a student working at a site in the Great Barrier Reef did an experiment where he incubated corals with an excess of strontium in solution.  By golly, he got good, and extra, coral growth in the skeleton.  And he published this in 1980 (Swart, 1980).  The conclusion was that extra strontium in solution boosted coral growth.  A few years later this was noticed by some coral reef aquarists and they incorporated that information into some publications (Delbeek, and Sprung, 1994). 

Unfortunately, what those reef aquarium authors didn’t do was read the next article that the initial researcher wrote (Swart, 1981).  Here he explained that his first conclusion was an error.  What had happened was that in the region where he did his research, the sea water concentration of calcium was only about 310 ppm, and any material similar to calcium  - including – Golly, Gee, Surprise, Calcium itself, added to the sea water would increase the growth of corals.  So the data saying that strontium was causing extra growth in corals was in error.  What was happening was that anything like calcium (including calcium, magnesium and strontium) added to the sea water of that area would increase coral growth, up to a maximum level of about 525 ppm, after which the increase in growth ceased.  Of course our stalwart aquarium authors (Delbeek, and Sprung. 1994) never bothered to get the message…

But, as they say, “That ain’t all…”

Other researchers, more interested in how strontium was added to the coral skeleton, found some very neat things.  They found that strontium is incorporated into the coral skeleton differently than is calcium.  It doesn’t simply replace calcium in the aragonite crystal lattice (Chalker, 1981; Ip, and Krishnaveni. 1991).  This means that there is a special biochemical process or pathway in corals to ensure that strontium is put into the coral skeleton. 

The question any scientist – and aquarist – interesting in strontium should ask themselves is, “Why is strontium deposited differently than is calcium?”  The answer to that question was found by two other researchers (Wright and Marshall, 1991).  These scientists found that strontium inhibits or “poisons” calcium ion transport across coral epithelial tissues.  This very important and bears repeating:

 “Strontium “poisons” calcium ion transport across coral epithelial tissues.”

Why is this important?  The answer is that calcium is very important to corals.  One might think that it is most important in that it goes to form the skeleton, but that is probably a secondary issue.  What is more important is that calcium is used and found in high concentration in the nematocysts that corals use to catch their food.  Additionally, calcium is important in the relaxation and resetting of the coral animal’s muscles.  Once the muscle contracts, unless there is an excess of calcium ion in the coral’s epithelium, that muscle cannot relax and reset itself to contract again and the animal can’t move. 

The final piece to this puzzle of strontium is that strontium is deposited in coral skeletons as a specialized mineral called Strontianite (Greegor, et al. 1997).

The whole strontium story with regard to corals is that strontium is a weak poison, inhibiting the transfer of calcium into the coral’s tissues and thus affecting all of the biology of the coral.  Because of this, natural selection has favored a process to remove strontium from its tissues.  The way in which the coral does this is by specifically depositing strontium as a special mineral in small clusters in its skeleton.  Once the strontium is precipitated as a mineral it is out of solution and no longer a threat to the coral’s metabolism.  Ideally, for a coral, its sea water would not have an excess of strontium, but it would strontium-free. 

Consequently, it is to the advantage of a reef aquarist to NEVER add any material containing strontium to their system.  

And, of course, most stalwart aquarium authors never bother to get the message…

Iodine

Like strontium, iodine is another element where a decidedly “odd” aquarium mythology has developed in the last couple of decades.  Iodine is a chemical that is found in a number of marine organisms.  Most of these, are algae, and in fact most are brown algae (phaeophytes) such as kelp that are never found in aquaria.  Vertebrates also require iodine to produce thyroid hormone.  Primitive chordates such as tunicates as require iodine, in their case for the production of the mucus they use to capture the plankton they feed up.  That mucus, by-the-way, is 9-hydroxythryonine – or human thyroid hormone, indicating a close and similar evolutionary relationship between politicians and sea squirts, those rather amorphous blobs that sit on the bottom of the ocean and feed on dissolved waste; I guess, that fits… 

Some other animals do appear to accumulate iodine, probably as a defensive chemical, as iodine containing compounds are often unpalatable or toxic.  Because iodine is present in many algae that are used in the manufacture of marine aquarium foods, the amount of iodine in most marine aquarium foods is very high, and as a result in most tanks the concentration is probably excessive, well above natural levels (Shimek, 2002).

Figure 4.  Phaeophytes, such as this huge kelp, Macrocystis integrifolia, which reaches lengths of more 30 m, sequester iodine containing compounds, primarily as anti-predator defensive chemicals (Boney, 1966).

Iodine, per se, will never be found in marine aquaria or marine systems as it is rapidly oxidized to iodate.  Additionally, iodine is capable of forming numerous organo-iodine compounds of varying toxicity.  This creates a significant problem for aquarists; it is essentially impossible to ascertain the amount of iodine found in a marine aquarium.  Given the toxicity of many of the various iodine containing materials, I do not recommend supplementing iodine to any marine tank.  And no, Xenia doesn’t need iodine. 

Trace Elements

The measurement of trace elements in marine waters is exceptionally difficult.  As Pilson, 1998, states (with my emphasis, in red, added),

“We may conclude that data on the concentrations of trace substances in seawater should be taken with a grain of salt (so to speak) unless there is very good reason to believe them.  Perhaps no trace element data may be considered entirely trustworthy until the methods and data have been duplicated in more than one laboratory. ...  The real concentrations are so vanishingly small that the quantities present are easily swamped by contamination.  An undertaking to make such measurements involves much planning and attention to detail, and is not to be entered into lightly.  The difficulty involved means that only a limited number of laboratories will be in a position to make such measurements routinely.” 

Suffice it to say, no aquarist will ever be able to reliably test any trace metal concentration in their tank.  It is also likely, that no manufacturer of salts or additives will be able to reliably test their own materials for these elements.

Additionally, all of the trace elements are toxic to animal life at levels that barely exceed their natural levels.  As with iodine, they tend to be concentrated as they pass up the food chain, so in the manufacture of foods using marine animals and plants, they are often rather highly concentrated.  Really the problem in aquaria is not supplementing trace materials but removing them.  They are toxic to most animals in very low amounts, yet interesting they are required by many of the algae.  This is one of the pieces of evidence used to indicate the evolutionary “distance” between animals and algae.  While many of us tend to think that “life is life is life;” the differences between some life forms are often extreme, and the biochemical differences between these algae and animals show this very well.  What these algal organisms require for nutrients will kill many animals (See for example: Carey, 1981; Heyward, 1988; .Goh and Chou, 1992; Sadovy, and Severin. 1992; Rumbold and Snedaker. 1997; Reichelt-Brushett and Harrison. 1999; Breitberg, et al., 1999; Alutoin, et al., 2001; Negri and Heyward, 2001; Velasquez, et al., 2002; Morel and Price. 2003; Hintz, et al., 2004). 

Conclusion

This is the first of a couple of short articles discussing animal nutrition and chemical requirements.  If the reader has any questions or comments, I urge that person to contact me at my forum and we will discuss them.

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