It has been the topic of significant debate as of late whether tropical scleractinia and associated flora/fauna of coral reefs can be maintained at an ethical standard of  "living" in captivity; regardless of whether the artificial habitat is recreated and maintained by a formally educated professional aquarist for public display, or by an amateur aquarist as a private/home display. Typically, the reef aquaria of an amateur aquarist will average in volume from approximately 55 gallons into the 200-400 gallon range.

  Obviously, such a scenario brings instant ambiguities to the forefront of attention. Filtration and light levels that corals and reef flora/fauna receive in the wild cannot be exactingly duplicated in captivity. However, by looking at the general biology, ecology, chemistry and geography of coral reefs, aquarists can develop (and have developed) a fair idea of how to adequately reproduce a scenario in which an appreciable number of coral reef-dwelling species can both survive and thrive.

            Wild, high-energy coral reefs are typically low in dissolved inorganic nutrients (mainly nitrogen), as they are jealously coveted and guarded by the flora and fauna (both aerobes and anaerobes) of the reef (Fossa, 1996; Hatcher, 1985; Delbeek, 1994). Yet, many conventional reef aquarium methodologies use fundamentally aerobic means of nitrogen utilization (bacteria on reef "live rock", etc.), leading to disproportionately high rates of nitrification (Paletta, 2000). The end result is a high level of nitrates. in the system; subsequently, aquarists rely inefficiently on the scores of photosynthetic organism species present to pull the nitrates through their catabolic metabolism (corals also assist in this process indirectly, as many scleractinia have symbiotic dinoflagellates, zooxanthellae, residing in their tissue; these zooxanthellae use both the ammonia from the coral host"s waste, as well as ambient nitrogen, to photosynthesize in order to feed themselves and their host) (Bythell, 1990; Gladfetter, 1989; Meyer, 1985; McGuire, 1997; Tentori, 1997). However, nitrates are usually still recognizably present in substantial concentrations in the system. Many "extra" sub-methodologies, such as using a macroalgae "refugium", deep sand beds (which are often incorrectly set up in the high energy area, i.e., display section, of the system), grass flat beds, and mangroves in systems, are all trying to utilize these nutrients. How could you implement elements of nutrient utilization and still have a system who's water quality resonates that of wild, high-energy coral reefs?           

Professor Jean Jaubert, originally of the University of Nice, in France, found the answer in something far less technological than the protein skimmers and endless square feet of plastic and electrical equipment found on Berlin or Dutch systems. The answer he found was sediment.  Prof. Jaubert also determined through closed system experimentation that the key to unlocking the potential to the sediment was diffusion. His discovery began to materialize in the late 70's, and reached an apex in the 90's with an American patent (which was obtained subsequent to his European patents of the same system), # 4,995,980 (Delbeek, 1994).

Initially, let's look at the sediment regime of high-energy tropical coral reefs. Most of the sediments found there are chlorozoan, composed of broken down mollusk shells, corals, high-density calcareous algae, echinoderms, and recently broken pieces of large calcareous green algae (called choloralgal sediments, but their size immediately subsequent to being broken off the reef and becoming "sediments" is more reminiscent of chlorozoan sediments). For the most part, these sediments are composed of an orthorhombic calcium carbonate polymorph called aragonite. Aragonite is unique; when, for example, its components are precipitated by saturation when in their ionic form (this type of aragonite, after precipitation, is called oolitic aragonite), it can only form a solid at a pH of approximately 8.1. This fluke is due to the presence of magnesium in the water column, which interferes with precipitation at lower pH's. Therefore, when the pH of a solution in which aragonite is presence falls below 8.1-8.0, dissolution occurs, releasing the components of  the aragonite into the solution (i.e. calcium ions, carbonate ions, magnesium ions, strontium ions, and potassium ions). The released carbonate buffers the pH of the water and the calcium and other "hermatypic" ions become available for scleractinian skeletogenesis. (Tomascik, 1985) 

The sediment substrate of coral reefs is notoriously coarse due to the powerful wave dynamics found there. This vertically cyclonic energy effectively strains substrate, removing particles of sediment with a mass small enough to be resuspended into the water column, leaving currents and tides to remove the resuspended particles from the reef topography. This giant, natural decanter generally leaves no sediment around the shallow reef topography smaller than 2 millimeters. (Delbeek, 1994; Fossa, 1996; Tomascik, 1985, 2nd ).   

Moving on to a correct setup and utilization of the system, an understanding of nitrogen utilizing bacteria is required. As many aquarists are familiar with the nitrogen cycle in aquaria, and that upper layers of sediment are excellent for aerobic nitrogen breakdown/utilization, they also realize that for nitrate to be effectively utilized by the bacteria (and converted to nitrogen gas), a substantial surface area of space that is low in oxygen (generally below 2 mg/L) needs to be present (in an aerobic environment, if present, these bacteria needn't spend energy deriving oxygen for cell respiration from nitrate, so instead they simply utilize dissolved oxygen, and mineralize nutrients as a source of "food"). Well, deeper sediments provide an ideal area for nitrate breakdown and utilization by bacteria. Thus, the Jaubert system, or the Microcean, to use Prof. Jaubert's name, consists of a 4'-6' deep layer of sediment having mass resonant of that found on high energy reefs (i.e., variable sizes, with little to none smaller than 2 millimeters, Carib-Sea's Geo Marine Crushed Coral generally makes the ideal substrate, along with some large grains mixed in), which rests on top of an elevated diffusing plate (usually plastic lighting louvre/eggcrate covered with fiberglass screen to prevent sediment from falling through). The sandbed/diffusion plate rests 1'-2' above the bottom of the container/aquarium, supported by small sections of one or two inch PVC pipe.  

It is important to keep the sides (below the sand line) and underneath of aquarium covered to prevent any light from entering the sandbed/plenum system itself beyond what comes through the exposed topside. Keeping all light (other than what naturally diffuses down through the top in a natural gradient) from the sandbed and "plenum" space system prevents extra growth of oxygen producing autotrophs in the space meant for low-oxygen, nitrate utilizing bacteria. This assists in maintaining the oxygen concentrations in the plenum space at around an optimal 1-1.5 mg/L, whereas the bulk water should measure about 8 mg/L (E. Mueller, personal conversation). Some oxygen should be present in the plenum/lower sandbed, as just mentioned, in order to prevent hydrogen sulfide buildup, etc.. This small allowance of oxygen is provided through bioturbation by absolutely pivotal sanded infauna. These infauna also allow diffusion of nitrogen gas back up through the sandbed to escape the system. 

Once established, bacterial metabolism produces organic acids and bacterial respiration forms carbonic acid in the local water. These processes/substances lower the pH of the sandbed and allow dissolution of the aforementioned and described aragonitic chlorozoan substrate, with diffusion assistance from the plenum space below. The ions liberated by these actions are diffused in the display/bulk water via the same bioturbation that allows nitrogen to escape. These ions and their functions in terms of scleractinian corals and maintenance of reef-quality water, described earlier, replace the familiar dosing of "kalkwasser" or use of a carbon dioxide calcium reactor. In fact, using kalkwasser or a reactor can cause ionic supersaturation, compacting the sandbed beyond what is manageable by the infauna, and leading to the eventual metabolic death of the system. Of course, this process does require that some sand be replaced, usually annually, and, depending on system size and demand, usually amounts in the tens of grams yearly (E. Mueller, personal conversation). The trick to gauging the amount of ions liberated and the demand for their maintenance of water quality lies in initially monitoring the carbon/nitrogen/food input of your system, and testing for the ions and their rates of depletion. Also, sandbed area has to be large enough to be able to completely utilize nitrogenous nutrients in order to maintain oligotrophic (nutrient poor) conditions.  It should also go without saying that high energies above the sandbed and light resonant of levels found on natural reefs are integral (of course, "resonant" referring to "as close as possible by a hobbyist/aquarist").           

With many other systems used today, "filtration" modifications can make for interesting and progressive adaptations of a system. However, with the Microcean System, any such alterations from original theory and practice seems to work against the system itself. The protein skimmer is an excellent example of this, as it removes carbon necessary to feed the bacteria in the system as well as disallows a  budgeted  release of hermatypic ions. Thus, it is important not to stray from the original concept. And, just to toss this in here, as it seems to be a recently occuring rumor that Prof. Jaubert's original experimental system, in which the system of this article's subject was developed, used natural seawater on daily exchange. This is incorrect. As a mattor of fact, the original system had gone six years without a single water change (Delbeek, 1994). The only water introduced to the system was topoff by freshwater (a required maintenance practice for any aquarium), and the occasional replacement of the little bit of seawater lost through cleaning or other maintenance. Using a "plenum" has apparently become one of the more maligned aspects of hobbyist reef aquaria, probably due to the amount of misinformation being published about the system via hobby magazines, etc.. Regardless, the Jaubert system is ecologically sound in principle, and its low technology and ecology minded approach has made it preferred by a number of research institutions. 

Works Cited/Bibliography: 

Bythell, John C. (1990) Nutrient uptake in the reef-building coral Acropora palmata at natural environmental concentrations. Publ. Marine Ecology Progress Series, Vol. 68.                                   

Delbeek, J. C.; Sprung, J. (1994) The Reef Aquarium: A Comprehensive Guide to the Identification and Care of Tropical Marine Invertebrates (Volume 1 & 2). Two Little Fishies. 

Fossa, S.; Nilsen, A. J. (1996) The Modern Coral Reef Aquarium (Volume 1 & 2). Birgitt Schmettkamp Verlag. 

Gladfelter, E.; Michel, G.; Sanfelici, A. (1989) Metabolic gradients along a branch of the reef coral Acropora palmata. Publ. Bulletin of Marine Science, Vol. 44, No. 3. 

Hatcher, A.I. (1985) The relationship between coral reef structure and nitrogen dynamics. Proc 5th Int. Coral Reef Congress, Tahiti. 

McGuire, M.P.; Szmant, A.M. (1997) The course of physiological responses to NH4 enrichment by a coral-zooxanthellae symbiosis. Proc 8th Coral Reef Sym 2. 

Meyer, J. L.; Schultz, E. T. (1985) Migrating haemulid as a source of nutrients and organic matter on coral reefs. American Society if Limnology and Oceanography, Inc. 

Meyer, J. L.; Schultz, E. T. (1985) Tissue condition and growth rate of corals associated with schooling fish. American Society if Limnology and Oceanography, Inc. 

Paletta, Mike (2000) The Berlin system. Post. http://www.ffexpress.com/.

 Szmant, A.M. (1997) Nutrient affects on coral reefs: a hypothesis on the importance of topographic and trophic complexity to reef nutrient dynamics. Proc 8th Coral Reef Sym 2. 

Tentori, E.; Coll, J. C.; Fleury, B. (1997) ENCORE: effects of elevated nutrients on the C:N:P ratios of Sarcophyton sp. (Alcyonacea) Proc 8th Coral Reef Sym 1. 

Tomascik, T.; Sander, F. (1985) Effects of eutrophication on reef-building corals I. Growth rate of reef-building coral Montastrea annularis. Marine Biology. Springer-Verlag. 

Tomascik, T.; Sander, F. (1985) Effects of eutrophication on reef-building corals II. Structure of scleractinian coral communities on fringing reefs, Barbados, West Indies. Marine Biology. Springer-Verlag.