The Ultimate Refugium: In Defense of the Reef Aquarium

Reef with large stands of Acropora, Heron Island, Great Barrier Reef. Image © Gary Bell/OceanwideImages.com

With coral reefs starting to slow in growth and even dissolve, the last refuge of corals may be the marine aquarium

by RONALD L. SHIMEK, PH. D.

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Once again, we are hearing calls to list corals as Endangered Species and to somehow restrict, ban or completely terminate their importation. Should this come to pass, we can expect to hear calls for all the remaining corals and then all coral reef organisms to come under the same protection. Not to be flippant, but such suggestions seem to arise at regular intervals from one or another council of well-meaning but, generally, poorly-informed people.
On the face of it, a ban stopping the importation of coral reef animals would seem to be a no-brainer. If reefs are threatened, and they are, the harvesting and importation of reef animals for an aquarium hobby, of all the ridiculous things, would seem to be an obvious first step in protecting reefs. Every animal that stays on a reef is one additional animal to maintain that reef, right?

Well... No! The situation is much more complicated than that.
Granted, the coral reef aquarium hobby is the driving force for the collection and importation of, quite literally, millions of animals annually. Additionally, a large number of those animals perish, many, unfortunately, through the actions of poorly informed hobbyists. However, there are a few important reasons for opposing the knee-jerk approach that suggests a wholesale ban is warranted.

Probably the most obvious of these counter arguments is an economic one; that being that the collection of reef animals supports a large number of native people in predominantly poorly- or under-developed nations. Many of these collectors and mariculturists were previously fishermen who indiscriminately harvested reef animals for their own consumption and sale to generate a cash income. If the collection and culture of reef creatures were banned, these fishermen would likely take up their traditional trade. Reef fishing of any sort can be terribly destructive, and in this sense at least, the ecological difference between regulated collection and indiscriminate fishing is clear. Regulations are in place in most countries that allow reef creature collection with the intent of managing the resource, although the management and regulation are often poorly funded. Nonetheless, regulated and intelligent collection could be, and should be, a way to preserve the economic well-being of the collectors, and the overall well-being of the reef.

Not to belabor the advantages of well-regulated collection, but a century ago, throughout the American west, over-hunting and habitat destruction had virtually eliminated all of the large native mammals. Successful management, including well-regulated collection (hunting) has now brought the populations of deer, elk, and other mammals back. In many cases and areas, the populations of these animals are at all-time highs, while much of the clear-cut forest and many other habitats throughout the region have been brought back.

Schooling Lyretail Anthis, Pseudanthias squamipinnis, males purple and females orange, on Great Barrier Reef, Queensland. Image © Gary Bell/OceanwideImages.com

The reasons to regulate rather than ban collection are logical and valid, but there is another far more important reason for allowing the continued importation of reef creatures: that being the training of aquarists and the maintenance of a large pool (pardon the pun) of people who care deeply about coral reef animals and know how to take care of them.
In the last couple of decades, long strides have been made in aquarists’ abilities to maintain reef animals, and although the total variety of animals that are presently maintained is relatively small, in many of those cases, the organisms are maintained very well, indeed. Growth rates of some corals and other animals can equal or, in a few cases, exceed what occurs in nature, particularly in the systems of knowledgeable aquarists who know enough to disregard some of the persistent and idiotic hobbyist myths.

Certainly, aquarists don’t know it all. With the exception of a few fish species, there is the persistent failure of hobbyists to successfully breed many animals. Additionally, the total number of species maintained in the hobby is relatively low, especially considering the vast biodiversity of the world’s reefs. Nonetheless, the vitally important basic knowledge base is present, along with a great deal of appropriate equipment all developed to support healthy marine life in a captive, reef-like environment.
So, why should this be important to anybody but the hobbyists?

The answer lies in one largely ignored but terribly important subset of the great environmental disaster of our time resulting from the increase in the concentration atmospheric carbon dioxide. In the not too distant future, probably about 20 to 30 years from now, many reef animals, including most corals, are going to start to perish on a large scale.
 
This will have nothing specifically to do with the temperature increases of global warming, although those increases won’t help. On the contrary, the first reefs to go will be those that are in cooler water: the southern-most Great Barrier Reef, the northern-most Hawaiian reefs, and the Caribbean region (provided other things haven’t taken out that poor region’s particularly trashed reefs before then). These first reefs, and eventually, by the end of the century, all of the world’s reefs are going to suffer the effects of what has been called “oceanic acidification.” This disaster is demonstrably waiting for us, and as long as the atmospheric carbon dioxide concentration continues to rise there is nothing whatsoever we can do about it.

This article documents the processes wherein the increase in atmospheric carbon dioxide will change the calcification chemistry of the seas, resulting in the inability of corals to secrete their aragonitic skeletons.

The Case of the Burning Wall of Carbon
Imagine an unspoiled rural landscape but with a black, sooty, charcoal wall a mile (1.6 km) thick and one and a third miles (2.1 km) high running through it, say from Los Angeles to New York (or Lisbon to Moscow or roughly Tasmania to Darwin, Australia). Now picture some inventive Industrial Age pioneer happening by around the year 1750 and somehow setting this monstrous mass ablaze, to burn with accelerating ferocity from that day to present.

Consider that up until that day a couple of hundred years ago and for the last 35 million years, the Earth’s atmospheric composition hadn’t varied terribly much. Oh, there were small changes due a series of volcanic eruptions here, or an ice age or three, there, and there was the always present minor year-to-year variability, but the overall atmospheric composition when some of mankind’s early progenitors were discovering just what it might be like use their feet to scurry around on the forest floor rather than to peel bananas, was pretty much what would have be present when the first Pilgrim fell on his behind after sliding on the algae at Plymouth Rock beach.  
 
With the full advent of the Industrial Revolution, the dynamic chemical equilibrium that had characterized the world’s atmosphere and oceans for so long began to change. For better or worse, the industrialization of the world was driven by fires fueled by oxidizing the carbon sequestered in trees, peat, and fossil fuels such as coal, natural gas, and oil. Although it started small, the amount of humanly-generated oxidized carbon, primarily carbon dioxide, added to the atmosphere has become impressive by any standards. According to some pretty reliable references, the cumulative amount of carbon added to the Earth’s atmosphere by man’s activities in the period between 1751 and 2006 was about 332 billion tons. That number is huge, large enough to be meaningless except as a “BIG” number used as a gross indicator of an amount. “BIG” numbers such as this are incomprehensible; most people cannot really understand them emotionally, or scientifically.

To try to give that huge mass of carbon some perspective; if converted to a block of standard, run-of-the-mill charcoal, it would form a cube that would be a bit over 15 miles (24 km) on a side containing about 3,400 cubic miles of charcoal—enough to form our imaginary long, black, burning, smoking wall. Now that’s just carbon. When fired up and converted to carbon dioxide, man’s contribution to the atmosphere weighs in at about 1.217 trillion tons, another “BIG” number. That’s a lot of smoke up the chimney, but to be relevant to those of us who keep marine aquariums and have a passionate interest in coral reefs, it also gives a base to estimate just how much CO2 has made its way into earth’s oceans.

The atmosphere rests on the solid and liquid parts of the planet beneath it, and although the exchange is not visible, the atmosphere contributes significant amounts of its constituent vapors with both, and receives gases, such as water vapor, in return. The atmospheric conduit of gas exchange has moved a significant amount of carbon dioxide from smokestacks into the atmosphere, and thence into the upper layers of the ocean. Depending upon the particulars of what is being measured, it has been estimated that from about 42% to about 48% of the carbon dioxide generated by man’s activities has been transferred to the ocean—an amount equivalent to a walloping half trillion tons, give or take a few really, really, deep breaths. To put a bit of scale on that particular meaningless amount, and given about 2.2 grams of carbon dioxide is in a standard can of soda, the amount of extra CO2 that mankind has recently dissolved in the oceans is enough to put the fizz in more than 200 quadrillion cans of soda pop. “BIG” Burp….

Coming to Terms with Oceanic Changes
But, actually, so what? Carbon dioxide is a natural atmospheric component, and even with what humankind has pushed up the chimney, it is still present in the atmosphere in really tiny amounts. The concentration of atmospheric carbon dioxide is miniscule; as is anything measured in “parts per million.” And any changes in that itty bitty concentration are smaller still. On top of that, nobody even knows what to call this phenomenon; if it really were important, it would have a catchy name. But no; this “thing” has been called, variously, “the loss of the aragonitic ocean,” or “the reduction in oceanic alkalinity,” or the ever popular, “ocean acidification.”

Without a good label, this predicament, no matter how real, seems, well… kind of geeky and trivial. What the hell does “the loss of the aragonitic oceans” mean, anyway? And “the reduction in oceanic alkalinity” isn’t going to get anybody jumping up and hollering about it. “Ocean acidification” is verging on being okay; the phrase conveys a feeling of something vaguely ominous, but carries no weight in Peoria, Fargo, Ulan Bator, Beijing, or Nairobi. To make people aware of this issue, perhaps all we need is a set of better buzzwords; perhaps a better understanding of the problem would help in that regard.

As CO2 Goes Up, Coral Calcification Goes Down
On the first glance, it might seem that an increase in atmospheric carbon dioxide would be positive benefit to coral reefs by increasing calcification. After all, if there is more carbon dioxide in the atmosphere, that should mean that more carbon dioxide would dissolve into the ocean and that, in turn, should result in more carbonate ions. And, as calcification is the fusion of calcium and carbonate ions, anything that would boost either calcium or carbonate ions should promote and accelerate calcification, provided there is enough of both ions to go around. In fact, that sort of boosting is just what aquarists do when they add calcium ions to their systems in the form of kalkwasser, or through a calcium reactor.
When a carbon dioxide molecule dissolves in sea water, it immediately complexes with water and other ions enters into a series of several reactions, depending upon the various physical conditions and concentrations of all of the other ions present. If all of the various other carbon bearing compounds are present in equilibrium amounts, the overall series of reactions culminates in the production of a coral skeleton (Figure 1, Table 1, Reaction 6).

All of the reactions involving carbonate, bicarbonate and carbonic acid are easily reversible, as indicated by the double-headed arrows. Under changing conditions, especially temperature, salinity and the concentration of the various constituents, the various carbon-containing species, carbonic acid, bicarbonate ion, and carbonate ion, will change rapidly from one to another proceeding until they reach equilibrium concentrations. This occurs readily in a small container; in the oceans, it almost never actually occurs.

What can happen to a carbon dioxide molecule during the series of reactions from when it dissolves the ocean until it precipitates as calcium carbonate is shown by reactions 2 through 5 in Table 1. This is the overall series of reactions that occurs on a global scale, given enough time for the water masses to mix and bring all of the appropriate constituents in contact with one another. When the atmospheric carbon dioxide concentration remained more-or-less the same, a situation that held until mankind started pouring carbon dioxide into the atmosphere, about 250 years ago, the whole mixing process took several thousand years to complete, as a minimum. The ocean takes so long to mix, in fact, that a true equilibrium condition with regard to carbonate probably has not occurred since at least the extinction of the dinosaurs, 65 million years ago. However, as both the atmospheric carbon dioxide concentration, and ocean circulation patterns remained roughly the same for a very long period, a dynamic, but stable dis-equilibrium condition was the norm until recently. The overall surface area of the oceans is so huge that carbon dioxide is added to the system far faster than reactions can utilize it. The net result of both of these processes was that shallow oceanic waters were highly supersatured in carbonate ions, in other words, they contained far more carbonate ion than could be normally found in a solution.

The calcium ion concentration in the oceans is slightly supersaturated, however, the peculiarities of carbonate chemistry prevent spontaneous calcium carbonate precipitation in most areas. This also helps keep the shallow water carbonate ion concentration level highly supersaturated; much beyond the equilibrium level predicted by laboratory chemistry. As with the atmospheric carbon dioxide concentration, prior to mankind’s alterations, that supersaturation concentration was also more-or-less constant stable. On a global level it varied between about 3 times saturation in the cool boreal waters, to about 5 times saturation in warmer tropical waters, and appears to have remained at those values for a very long time, at least 35 million years.

Figure A. Steadily declining average monthly values of Ωaragonite in the Greater Caribbean Region. The values are greatest in the August-September period, and lowest in February-March due to the combination of temperature and biological factors.

Enter Homo
The Disappearing Carbonate Ion
Unfortunately, adding at lot of extra carbon dioxide to this system does something that seems very unexpected and counter-intuitive. When a carbon dioxide gas molecule first dissolves in sea water, it often combines with a water molecule and a carbonate ion to create two bicarbonate ions (Table 1, Reaction 1). CO2 + CO=3 + H2O = 2HCO-3. This formula shows that the net result of each additional carbon dioxide molecule under these conditions is the net loss of one carbonate ion, reducing the total amount of carbonate in solution.

Table 1.
Some Of The Reactions Resulting From Carbon Dioxide Dissolving In Water.

1. CO2 + CO=3 + H2O = 2HCO-3     Carbon Dioxide Combines With Carbonate Ion And Water To Form Two Bicarbonate Ions, Lowering The Concentration Of Carbonate Ion.

2. CO2 + H2O = H2CO3
    Carbon Dioxide Dissolves In Water To Form Carbonic Acid

3. H2CO3 = HCO-3 + H+
    Carbonic Acid Forms Bicarbonate Ion and Hydrogen Ion

4. HCO-3 = CO=3 + H+
    Bicarbonate Ion Forms Carbonate Ion and Hydrogen Ion.

5. Ca++ + CO=3 = CaCO3     Calcium ion and Carbonate Ion Form Calcium Carbonate
Combined Reactions Following Carbon From Carbon Dioxide In The Atmosphere To Calcium Carbonate In A Coral Skeleton.

6. CO2 + H2O ↔ H2CO3↔ H+ + HCO-3 ↔ H++ CO=3 + Ca++ → CaCO3

On top of the reduction in the carbonate ion concentrations, the carbon dioxide addition also reduces the pH, forcing the ocean to become slightly more acidic. The ocean is by no means in danger of becoming an acid solution; instead, the shallower parts of it are just in the process of becoming slightly more acidic than they are now. As the atmospheric concentration of carbon dioxide approaches 1,000 ppm (it is now about 390 ppm, and rising between 3 ppm and 4 ppm per year) the pH will be drop to 7.8, down from the pH of around 8.2 in pre-Industrial times. The rate of addition of carbon dioxide to the atmosphere is increasing and rather rapidly so; the 1,000 ppm value has been projected to occur about 2100.

Nonetheless, the really important result of CO2 addition to ocean waters is the reduction in the concentration of carbonate ions, as that reduction causes some dramatic changes in the precipitation of calcium carbonate. Calcification, the process of combining a calcium ion with a carbonate ion to produce solid calcium carbonate, is a simple reaction (Table 1, Reaction 5) that should be a relatively straight-forward process. Provided that the concentrations of the two ions are high enough, solid calcium carbonate should spontaneously precipitate out of sea water. In a beaker in a lab, this type of calcium carbonate precipitation will occur in a salt water (but, interestingly, not normally in a seawater) solution. It also occurs, spontaneously, in the fresh water of an aquarist’s kalkwasser vat.
Normally, however, inorganic calcification just will not occur in the oceans at normal saturation concentrations. Why this is so is unknown, although many factors have been proposed as explanations, from interference by other ions, particularly magnesium, to interference by organic materials.

Figure B. The same data that are in Figure A, graphically modified.

Calcification
Calcification is one of the most important chemical processes occurring in the oceans, and yet, on both the very fine, and the very large, scales it is incompletely understood. Calcium ion is added to the oceans by fresh water run off. Given that the oceanic calcium concentration has remained approximately the same for millions of years, calcium must be precipitating out of solution somewhere, at approximately the same rate that it is entering the system. That precipitation, mostly as calcium carbonate, occurs as sediments in the deep sea, and as limestone rock and sediments in shallow-water coral reef areas. Virtually all of the precipitation is biologically mediated by an array of important organisms (Table 2).

Table 2. Sources Of Biological Calcification

Group                  Mineral                World-Wide Amount
Foraminifera         Calcite                            ++++
Coccolithophora    Calcite                              +++
Clams                  Calcite/Aragonite                 +
Benthic Snails       Calcite/Aragonite                 +
Planktonic Snails
(Pteropods)          Aragonite                          +++
Corals                  Aragonite                        ++++
Coral Reef Algae   Calcite/Aragonite             ++++

The different minerals secreted by the different groups are an indication of different calcification processes specific to each group. So, quite obviously, oceanic calcium carbonate precipitation is occurring; however, much investigation has shown that for spontaneous inorganic calcification to occur requires a very much higher level of carbonate ion than one would normally think is either possible or necessary. Biologically-mediated calcification can occur under lower carbonate ion supersaturation levels than inorganic calcification, but those carbonate levels are still very much higher than theory predicts that they should be. A general rule may be formed: for any kind of oceanic calcification to occur, calcium ions must be saturated, and the carbonic level must be highly saturated.

Consequently, the reduction in carbonate ion caused by the increasing atmospheric carbon dioxide concentration will have the overall effect of reducing calcium carbonate formation, everywhere in the seas.
There is one other exceedingly important consequence of the reduction in amount of carbonate ions. The amount of excess carbonate ions present when calcium carbonate solidifies directly determines the mineral form the precipitate takes. Solid calcium carbonate can take the form of either one of two common minerals, aragonite and calcite, as well as a couple of other less common forms. These minerals all have the same chemical formula, CaCO3, but they differ in crystal structures which changes their solubility and other properties. A critically important point, at least biologically, is that the crystal shapes and structural properties of the two minerals are quite different and are not interchangeable. Organisms that secrete aragonite cannot secrete calcite in its place, and vice versa.

Figure C. Projected future values of Ωaragonite presuming the continued addition of atmospheric CO2 at the current rate. The projection was graphically created by extending the values shown in Figure B. The arrow indicates 2010. The projected Ωaragonite level drops below 3 in the early 2030s. By about 2050, the value remains wholly below 3 where scleractinian skeletons will not form, and previously formed skeletons exposed to sea water will dissolve.

Coral Calcification
Although intensively studied, many details of coral calcification remain unknown; however, some processes involved with the formation of a coral’s skeleton have become much clearer in the last decade. Very importantly, it has been found that stony coral calcification occurs in exceptionally small volumes created between the coral epidermis (“skin” tissue) and the underlying, previously secreted, skeleton. The reason for this appears to be that only in such a small “calcification volume” can the polyp successfully expend enough energy to control and change the necessary chemical conditions allowing the precipitation of calcium carbonate.

How the volume is created is not known, but it has been suggested that the coral epidermis somehow lifts off the underlying skeleton briefly letting in a very tiny amount of sea water while creating the volume. It has been recently shown that, in at least some corals, the calcium ions used in constructing a coral’s skeleton do not pass through the animal’s tissues, as previously thought, but enter into the calcification volume dissolved in sea water from outside the animal. Corals absorb quite a lot of calcium, but apparently that calcium is used elsewhere in the coral’s cells, while the calcium for the skeleton comes from the surrounding water.

There are quite a number of necessary prerequisite chemical reactions that must happen prior to calcification. Among the most important, an organic matrix that apparently provides the “trigger” sites for the crystal formation must be secreted. Subsequently, the epidermis secretes carbonate ion (CO=3) into the water filling the volume. This causes both the carbonate concentration in the volume and the pH to increase. The carbonate ion concentration may exceed supersaturation by a factor of nine to eleven times, compared to about three or four normally found in the surrounding water. With such high carbonate ion concentrations, calcium carbonate readily precipitates, forming crystals at specific sites on the organic matrix. Additionally, the excessive amounts of carbonate ion present in the small volume cause the precipitate to form as the mineral aragonite. The final crystalline form and shape of this aragonite varies depending upon a number of things, including whether or not it is secreted during the day or the night. However, the net result is the creation of the specific skeletal ultrastructure for the particular coral species.

Carbon Dioxide Increases
and Coral Calcification
What does that burning mass of carbon we started with and the rise in atmospheric carbon dioxide do to coral calcification? Recall this reaction: CO2 + CO=3 + H2O = 2HCO-3. The net result of each addition of a carbon dioxide molecule under these conditions is the net loss of one carbonate ion, as it is converted into a bicarbonate ion. Obviously, if this happens enough, it will reduce the carbonate saturation level. Mankind’s addition of carbon dioxide to the atmosphere is currently forcing a drastically dropping concentration of the carbonate ion, wherever it is being measured, and of course, concurrently the pH rises.
These two changes drastically and dramatically alter the process of coral calcification. As mentioned, the coral polyp actively uses energy, sugars from its symbiont or from food, to pump carbonate ions into the calcification volume boosting the carbonate level and forcing the production of aragonite. As the carbonate ion concentration decreases in the surrounding ocean, the polyp needs to pump much more carbonate into the calcification volume. As a result, pumping becomes energetically much more costly.

Experimental evidence indicates that once the oceanic carbonate ion supersaturation level drops below about three, corals cannot pump enough carbonate into the calcification volume and the formation of aragonitic crystals fails. Furthermore, at these lowered supersaturation levels, previously secreted aragonite crystals become less stable and start to dissolve, a process further facilitated by the dropping pH. Consequently, the coral is hit by a classical “double whammy;” not only does secretion of new skeleton become very much harder— to the point of cessation—but any already secreted skeletal material that becomes exposed to seawater starts to dissolve.

Dissolving Corals???
Is this really happening? The answer is unequivocally and unambiguously, yes. The process is in its early stages, but there are clear indications what will happen. The drop in carbonate supersaturation level, measured relative to aragonite formation, is happening in all the oceans, including the Caribbean (Figures A, B, C). If the drop in aragonitic saturation continues at the present rate, the greater Caribbean basin waters will be dissolving exposed coral skeletons, as well as the exoskeletons of some other organisms by 2030, at least during part of the year. By 2050, it will be occurring during all the year, provided additions of carbon dioxide to the atmosphere happen as usual.  

Upcoming or Downgoing Events?
Because of thermodynamic factors, both of these problems will be more apparent in cooler waters first, but as the atmospheric carbon dioxide concentration continues to rise the effects will progress toward the equator. Cooler shallow water coral reefs, such as the Southern Great Barrier Reef have already begun to show degradation that may be attributed to these factors. If atmospheric carbon dioxide concentrations continue to increase at the present rates, large areas will be suffering significant damage in no more than 20 years, and by the middle of this century reefs in near equatorial regions will be… dissolving…
Initially, and without much supporting evidence, the discovery and announcement of the drop in carbonate supersaturation levels was met with a fair degree of rather vocal anguish by those few scientists who had realized what was occurring. This occurred in the mid-to-late 1990s, and literature of that period is filled with dire but ambiguous warnings, including being able to watch reefs dissolving in a fizzing cloud of bubbles. A scenario resulting in a change in the calcification chemistry of the world oceans had seemed so unlikely that nobody had done any experiments to see what would happen to organisms under those conditions.

Experimental Evidence
Subsequently, experiments were, and continue to be, undertaken to assess how various organisms would fare under the new conditions. Possibly unfortunately, there has been no central clearing house of experimental designs, and different sorts of organisms have been deemed important to test by each set of experimenters, so there is no unified approach. In some cases, the data are clearly comparable, in others, well… not much… (See Table 3, PDF Download).

Table 3. Results of Experimental Studies Of Oceanic Acidification (From Downey, et al. 2009, And Other Sources). N = The Number Of Different Experimental Species/Strains.

 Download PDF

These experiments have, to date, been primarily of two types. In the first type, the test organisms are placed in experimental aquaria and the pH and carbonate levels of the system are altered, primarily by increasing the level of bicarbonate ion, essentially by adding soda water. In the second type, the test apparatus is basically the same, but it is enclosed in a chamber that allows the atmospheric carbon dioxide concentration to altered and maintained at a given level. The second experimental type is clearly more realistic. The first is clearly easier, and much cheaper. So in this situation, as the experimental carnival barker might say, “You pays your money and you takes what results you get.” In both experimental types, the test organisms are maintained under otherwise normal conditions, the ambient lighting is not changed, and the organisms are given the appropriate nutrients, in the case of algae, or food, in the case of animals. Of course the pH changes, and depending upon the experiment, the temperature may also be changed. The organisms were monitored over the experimental periods and changes noted. The experimental periods varied a lot, from a few days to more than a year.
The experiments have given some very interesting results; given in detail in some of the references in the references sidebar. Experiments of growing some colder water stony corals with aragonitic skeletons, such as Oculina patagonica, in conditions that would be expected in a couple of decades are truly interesting. Under these experimental conditions, the animals were able to persist, provided they were fed. However, they ceased to be corals; they totally lost their supportive skeleton, and appeared much more like colonial sea anemones. In some specimens, the individual polyps wandered off on their own, and acted indistinguishable from anemones. As long as they can catch food, these animals seem to be able to stay alive. Other corals, ones more characteristic of tropical regions, such as the acroporids, don’t appear to fare as well. They also collapse into a lump of small polyps, but long term survival is problematic, as their ability to get food was compromised.

How the changes in calcification and pH will affect the organisms at the base of the food chains, microscopic algae, is open to debate. One major group of mostly colder water phytoplankton is the coccolithophorids. These are exceptionally small algal cells, smaller than small Nannochloropsis, but they are covered in calcareous plates. The increase in bicarbonate ions may accelerate their photosynthesis, but the drop in the aragonitic saturation level will cause them to decalcify. Experimental results trying to culture them in the upcoming conditions were mixed; some species survived, others died (Table 3). Being the base of the vitally important boreal and cold temperate oceanic food webs, if they are removed, it is quite possible those food webs could collapse. Big problems, as well, are anticipated with regard to the small swimming snails, pteropods, that constitute a major portion of the cold temperate zooplankton. What shells they can secrete will dissolve off their backs, and they, quite literally, will drop out of the picture – all the way to the ocean bottom where they will perish.
 
Calcite?
The astute reader will notice that this discussion about calcareous dissolution has focused on aragonite, and the question may be asked, “What about those organisms with skeletons of calcite?”(Table 2). The situation for animals with calcitic skeletons may be very much better. Such animals include gorgonians and some other soft corals, as well as many other animals. Indeed, some of these creatures may fare better than they do now. Recently published tests have indicated that the cold-water lobsters will grow larger and faster than at present. These animals presumably use calcite as their calcareous skeletal material, and have no problem secreting it.

The major problem that is apparent from the experimental tests is that there are simply too few of them to be able to discern any patterns for either the problems, or the benefits that will occur. Logic and knowledge predict that coral reefs are in for a bad time, perhaps a terminally bad time, but more data might show some evidence for hope.

Everybody Is Equal, But
Some Are More Equal Than Others
There is a potential interesting variable in all of this, which might become evident with more testing. All scleractinians today possess an aragonitic skeleton, but it is just possible that some lineages of them may have the genetic capability for secreting a calcitic skeleton. There is one good report of a calcitic calcareous scleractinian from the Cretaceous Era, the last dinosaur period. During this time, the atmospheric carbon dioxide concentration was much higher than today, and the oceans were much warmer. Scleractinian corals were present, but not reef-forming through most of the 80-million-year era, presumably because their skeletons were aragonitic and dissolved shortly after the animal died. It had been thought that most of the fossil corals were rapidly buried in sediments and thus preserved before they could disappear. However, the one recent report of a calcitic skeleton means that at least one species with calcitic skeletons existed. Where there was one, there are likely to be others. If such species passed through the extinction period of 65.5 million years ago, and persisted, it is possible they adapted to the different seas by producing aragonitic skeletons, but just maybe the genetics for the cellular basis of the calcitic pathway is still present in their genome, just turned off. If the environmental changes to a warmer, more acidic, lower carbonate ion ocean are “just right” they might trigger the modern descendents of those ancient animals to produce their old skeletons again.
Or not…

Chevron Butterflyfish (Chaetodon trifascialis) amongst Acropora corals. Great Barrier Reef, Queensland, Australia. Image © Gary Bell/OceanwideImages.com


An Aquarist’s Gambit
I think that unless one is an irrepressible fool or a Pollyanna, possibly the same thing in this case, it is apparent coral reefs as we have grown to know them are in for a very hard time and quite possibly doomed. The increasing rate of atmospheric carbon dioxide accumulation is unlikely to be moderated before reefs are seriously impacted. Unless unforeseen events drastically change the world over the next few years, it is likely that the shallow water oceans will have changed enough chemically that the aragonitic skeletons of reef animals will not be able to persist.
It appears to me that the only option for survival of reef creatures is a miniature coral reef in a box. Aquarists, both hobbyists and professionals will be able to keep reef animals alive in their tanks when those animals would die under the natural wild conditions of the future, because all aquarists can presently maintain their systems’ parameters at levels that don’t let a coral skeleton fizz away.

Without any hyperbole at all, it is quite possible that reef aquarist tanks (public and private) will be the only places in the world where a large number of coral reef animals will be surviving—nay, thriving!—in 50 years. For aquarists to become the actual saviors of reef animals is truly not out of the question; however, it will take a significant increase in the capability of aquarists to propagate the animals. Slicing and dicing will have to give way to propagation by selective breeding, and long-term care will have to become the norm rather than the exception. It is a trite statement, but if our hobby is going to survive, the animals will have to survive. It will be necessary to build up a much larger reserve of animals in hobbyist, commercial and professional aquarist tanks, as well as networks for communication, mutual aid, and the interchange of specimens. None of these requirements are beyond the present capabilities of aquarists. With a bit of foresight and dedication, when the natural reefs are altered beyond recognition or even destroyed, aquarists should be able to maintain thriving populations of many organisms that would be otherwise slated for extinction. While not the same casual hobby that exists today, dedicated aquarists not only would have the opportunity to maintain beautiful aquaria, but the hobby would become a significantly beneficial asset to the biosphere. Of course, hobbyists must beat the learning curve to get the point where a larger array of animals can be kept in better shape is presently possible.

Such changes are not only possible, but likely. All-in-all, the necessary changes will take some degree of effort, but they will also take a ready supply of organisms as the hobby, as whole, trains itself to do better. Getting back to the first paragraphs of this article, I am afraid that if there is a ban on the importation of coral reef animals… phizzz…

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REFERENCES

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