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Future Trends and Possibilities in Sustainable Coral Farming

By Eric Borneman. Presented February 6th 2000 on #reefs IRC.

I want to thank Roger Griffis for taking the time earlier to make the US Coral Reef Task Force available to aquarists in the other forum and in their action plans. The issues are complex, enormous, and often seem insurmountable. Although there is much controversy among aquarists over the potential action concerning trade in coral reef species, the ultimate goal of this organization and the efforts of scientists involved are to try and effectively and sustainable manage, preserve and protect these increasingly threatened ecosystems. If successful, the efforts will only serve to ensure the long-term sustainability of harvest for marine ornamentals. I also feel, personally, that the current situation (whatever the scope of future management) will only serve to push us towards the development of non-destructive alternatives. This is something I have hoped for since I purchased my very first wild coral reef animal, knowing all-too-well the watery paradise it left to arrive in my all-too-often-questionably-capable care.

When I was most recently asked to present a topic to this group, I knew it would be happening at the dawn of a new millennium. On December 31, I started out very early for the Texas/Mexico border in my car and paused some halfway there to stand outside along a barren highway and watch a most spectacular sunrise - the last of this thousand-year period. I was struck by a vision of change that I hoped would usher in the new epoch that very next day. I thought about how wonderful it would be if we, as a rapidly emerging global society, could pool our collective knowledge and inventiveness, to stave off the rapid degeneration of our world, especially with the coral reefs that I am so very familiar.

Although we are only beginning the infant stages of coral propagation and farming, I am very honored to live in the time when private aquarists began growing and reproducing corals. The concept is still very foreign to the world at large, even science. Unfortunately, the vast majority of corals, especially the important hermatypic scleractinia, are still being collected from coral reefs. Many of these reefs are from areas that are among the most threatened in terms of their long-term survival. Equally disturbing is the fact that not only are most of these animals easily reproduced asexually, but that the numbers being collected are increasing to fuel what is becoming an exponential increase in reef aquaria (however more successful they have become, in general).

It may seem a bit premature to begin discussing techniques and possibilities for "coral farming" when we have so many looming and pressing obstacles to overcome with the status quo. Nonetheless, I think that if we, as aquarists, have been at the forefront of coral husbandry to this point, presenting some of the future possibilities may be similarly productive. So, I will conclude this introduction with a clipped quote (which I have used before); one I hope will inspire some of you to begin work with the provocative concepts to follow:

" What I advocate is this - a sensible, pragmatic, and non-destructive approach towards existence. We need to re-evaluate our practices. It doesn't make sense to derive power from nuclear, coal, and petroleum when we have solar, hydro, and wind power. It doesn't make sense to maintain destructive systems just because people earn their living from them. Basically we should stop doing those things that are destructive to the environment, other creatures, and ourselves, and figure out new ways of existing...that's it."

What follows are but a few possibilities.

(I will be happy to provide the references herein (and then some!) to any interested parties)

Electrolytic Mineral Accretion

This technique was first developed by W. Hilbertz in 1977 and has been extensively developed by him (1981, 1992, 1996), as well as by T. Goreau (1995, 1996), H. Schumacher (1997, 1999), P. van Treeck (1997), and others. It works like a galvanic cell, where electrochemical deposition of the abundant calcium and magnesium ions in seawater is accreted onto a substrate. A "DC" current between 1 and 24 volts [optimally around 9 volts (Schumacher, personal communication)] is applied to a metal mesh and calcium carbonate is deposited at the cathode with chlorine and oxygen evolving around the anode. Higher currents precipitate minerals faster, although brucite is favored over aragonite and the resultant material is more fragile (van Treeck 1997). Higher temperatures and water currents, not surprisingly to aquarists, increase accretion rates, with a lowered pH around the cathode being responsible for the increase. To date, this technology is being applied in reef transplantation efforts and in the formation of artificial reefs. Its use in aquaculture is only beginning. A French group has reported growth in Acropora of 50cm/year, although the skeletons are somewhat brittle (Goreau, personal communication)

There are several possibilities and advantages for coral farming. The first is that corals simply calcify faster in the presence of the current. Coral fragments collected from parent colonies could be put into conventional mariculture areas and grown faster. The second is that the rapid cementing of coral fragments to an accreted calcium carbonate matrix allows for stability and increased survival of fragments. Much of the energy resources of a fragmented coral are put into forming new attachments. In field studies, normal growth rates only commence in fragmented corals after several months to a year. The quick establishment of a firm anchorage can allow coral fragments to allot their energy toward apical and marginal growth, the production of mature gonads, and more quickly reestablish normal metabolic and biochemical processes.

Several obstacles must be overcome for private aquarists to utilize these techniques. The first is accurately measuring the voltage across a grid. The current must be measured in the air and not in the water. Second, the choice of conductive materials must prove non-toxic in a closed system. A sheet of lead or steel in an aquarium would likely prove toxic or problematic to organisms present. However, carbon and titanium, along with other lightly sheathed or nontoxic, non-corroding conductive materials could be employed. This method holds much promise for aquarist experimentation and investigation.

Larval Fusion

In some animal phyla, larvae of both kin and genetically unrelated same-species can, in some cases, fuse and form chimeras. These animals have a mixture of genetically different cells. Natural chimeras are known to exist in sponges (especially the Desmospongiae), with fused larvae growing larger and faster than unfused larvae (Maldonado 1998).

Chimeras are also known to exist in corals. Genetic larval fusion can be used to create hybrid corals. This technique has been used in horticulture for years, and is even done by elementary school students with the cacti. By fusing the planulae of a fast growing coral to that of a slow growing coral, or other combinations, growth can be increased by magnitudes. R. Richmond (1999) claims that they can match cultivation rates and be able to provide all needed corals for the aquarium trade within five years with techniques already being used in reef replenishment efforts.

The methods and materials needed to begin work at this level for the aquarist may be currently out of reach. However, those involved with commercial mariculture should be able to implement them fairly easily - if not now, in the near future. They may become more available given the advancement and possibilities of some of the procedures to follow.

Oriented Translocation

Related to larval fusion in some ways, oriented translocation takes advantage of an unusual competitive behavior in certain corals. It is not known whether this behavior is common or atypical, but the possibilities are intriguing. Rinkevich (1983) described oriented translocation in colonies of Stylophora pistillata . Ordinarily, purple morphs are competitively dominant over yellow morphs. However, the reasons for their dominance are notable.

When fragments of corals touch each other, there are a number of outcomes, sometimes involving the mortality of the submissive colony for various competitive reasons well known to aquarists. Sometimes, and especially in same-species corals, fusion of the branches occurs. Rarely is there tissue fusion, but instead a thin line of demarcation exists where their skeletons fuse. In Stylophora , something unusual happens in cases where purple morphs and yellow morphs fuse. The purple morph gains control over the yellow morph's metabolism and uses the products of the yellow morphs' photosynthesis for its own growth. Thus, there is a donor coral and a recipient coral in such grafts.

Pocillopora, Montipora, Acropora, Porites, Montastraea , and Scolymia are all genera well known to have dominant color morphs of the same species. There are many others, and it is possible such hierarchies of color and other traits, especially when genetically determined, exist universally. Pocillopora damicornis , for example, has a dominant pink morph over its faster growing brown morph. There is a distinct possibility that hardy, common, or fast growing donors could be used to enhance or aid the growth and development of more fragile, rare, desirable or slow growing corals through similar grafting and the resultant oriented translocation.

Experimentation by aquarists is already possible using corals' innate abilities. However, it is important to remember that grafting corals is not without hazard. First, the "donor" coral may exhibit delayed mortality without retreat growth or supplemental energy procurement. Also, these competitive animals may just as likely cause one or the other's mortality through their self/non-self recognition and aggressive behaviors. However, immunity studies with corals show that same species corals rarely have acute responses to each other. Barring other factors, the more divergent the genetic makeup, the more likely that acute reactions will occur. To me, the use of this technique could be valuable to enhance the propagation of desirable color morphs or those with greater durability in captivity.


Grafting is also being used in other ways that may not involve oriented translocation, and can be seen as intermediate between larval fusion and oriented translocation. L Raymundo (1999) used cultured Pocillopora damicornis to rehabilitate a reef in the Philippines. Along with other researchers, she has found that fused pairs and fused groups of corals show significant differences in growth rates. Also, she found that there were not significant differences in mortality. Stocking same species corals in high densities results in faster growth. Similarly, juvenile corals and apical/marginal sections of corals grow faster. The fusion of several juvenile coral colonies and/or fast growing sections of corals result in colonies with faster growth rates. These techniques are easily available to coral propagationists and can be utilized immediately.

Positive Interactions

The interactions of corals with each other and with other organisms on a coral reef are astonishingly complex and variant. Because of the competition for space, most interactions are engaged at the expense of one or more of the competing organisms. However, coral reefs are also well known for their commensal and symbiotic relationships. For example, there is a well-known study that showed increased growth rates in corals when the schooling fish that inhabit their branches were present. The waste material from the fish provides an important nutrient source to the coral colony.

There are many such positive associations to be exploited. Symbiotic crabs that inhabit branching corals are frequently called "crustacean guards." They enhance the growth and survival of their host coral by protecting and defending their host from predators, providing waste material as food, consuming excess mucus and mucus-associated microorganisms, and increase respiration and metabolism through their movement and "combing" actions. Similarly, there are other crustacean symbionts, such as pontoniine shrimp.

Some algae are also reported to enhance the growth of corals if they are not encroaching. Their production of oxygen and "leakage" of certain amino acids and other materials provides an energy source for nearby corals. Sponges, while often boring or toxic, can also provide a similar role for corals. For example, certain zoanthids grow on or associated with sponges. They were once thought to be parasitic (hence the names Parazoanthus and Epizoanthus ), but are now known to be commensal. The sponge or zoanthid often gains the warning coloration of its partner, or the toxicity. The zoanthids also gain from the increased availability of gases and nutrients by congregating near the sponges' incurrent canals.

As we have seen, not all coral interactions are harmful, either. There are a number of studies that show certain corals to grow faster when in the presence of certain others. This type of work in various associations and hierarchies is far from established, but the observations of aquarists could be important. For example, Porites, Acropora, Goniastrea , and Seriatopora have all been shown to have certain species, when grown together, that result in enhanced growth and net positive interactions. The possibilities are almost unlimited and careful observations and experimentation can already be utilized by aquarists in propagation efforts.

Zooxanthellae Inoculation

Corals are known to harbor various symbiotic dinoflagellates, collectively known as zooxanthellae. The various types inhabit corals based on fitness and some degree of species-specificity. This research is ongoing, but the implications are profound. The means by which these symbionts are ingested and incorporated by corals is not entirely known, but probably involves some sort of chemical signaling and immune recognition events. For example, Xenia and Pachyclavularia regularly overproduce zooxanthellae within their tissues for digestion. Yet, they do not digest those to be incorporated as symbionts. As it happens, certain zooxanthellae are more adapted to certain conditions and/or certain corals. If the mechanism of recognition can be ascertained, zooxanthellae most adapted to the conditions of culture can be utilized to maximize survivability and growth.

Spawn and Spat Collection, Recruitment and Settlement

Using techniques currently available and in use, the massive spawns of broadcasting corals can be collected and induced to settle on substrate forming new colonies. The surface slicks of corals spawns, while biologically wasteful, are important in ensuring long-range dispersal, genetic mixing, and hybridization in corals. However, it also results in billions of gametes being lost to currents, grazers, and the lack of appropriate settlement sites. Small samples of such slicks could contain the material for the production of thousands or millions of corals. Spawn easily forms viable planulae and can be induced into settling. The work of A. Morse (1992-1999) and others have determined that the settlement cues for planulae are chemical in nature. The morphogens are lactosamine sulfates isolated from the cell wall of their producers: the coralline algae. There are hierarchies of preference in various corals and various algae, but thus far all other factors to induce metamorphosis and settlement seem secondary - if present at all. While the collection or production of sexual spawns is not yet realized in captivity, the use of these techniques can be simple and invaluable to those involved in mariculture near coral reefs. The viability of some species' planulae is extraordinarily long-lived, and collection of spawn and spat from these species could easily be shipped to private and remote facilities for development. Viable but short-lived larvae could also be shipped using fast shipping or preservation/storage techniques such as those utilized in cell culture. Spawn collection apparatus are available and described, even to the point of isolating certain species by chemical cues using differentiating columns.

Induced Injury

While perhaps striking a chord of sympathy for the affronted coral, injury can be a means to produce asexual coral colonies. Injury by burial induces the formation of anthocauli and the production of juvenile asexual colonies in many fungiids. Injury to certain soft corals, gorgonians, and some scleractinia induces the formations of buds and branchlet dropping. Injury to the mouth (hypostome) of corallimorphs and actinians (anemones) induces fission and the production of asexual daughter colonies. Obviously, fragmentation is another method of injury resulting in the formation of new colonies. The limits and types of asexual reproduction that can be brought about by injury are yet to be established, but could provide for many new colonies, perhaps without even the loss of the parent colony.

Maximizing Needs

This is an obvious area, but one which is rarely met. Corals derive energy for growth and reproduction from heterotrophy (feeding) and the photosynthetic products of their autotrophic zooxanthellae. Not all corals eat the same food, and not all corals need the same light irradiance. Many coral species are known to grow faster in intermediate light than full sunlight. Similarly, the gorgonians feed heavily on detritus, some neptheids feed mostly on phytoplankton, and most scleractinia feed heavily on zooplankton. Abundance of ammonia and nitrate can be maximized to provide for growth, while limiting overproduction of zooxanthellae. Substrate preferences, rugosities, carbonate availability, pH, and temperature are all controllable variables that can have profound effects on the growth rate of corals, often species-specifically. The diligent tracking of such parameters by aquarists for various species could have profound implications for the culture and farming of corals.

Giving Back to the Reef

I would be remiss without noting another characteristic of corals that has been established and is now becoming recognized by the scientific community (Mueller 1999). Corals grown in captivity show an increased tolerance to many stressful environmental factors. Perhaps the most notable of these is a tolerance of higher nutrients. The reasons for this adaptation are not known, but we, as aquarists, are clearly in a position to help. One of the most significant reasons for the worldwide degradation of coral reefs is the eutrophication (nutrient enrichment) of oligotrophic (nutrient poor) waters. If corals we grow in aquaria and are collected from the wild (especially if provided using the non-destructive means outlined here) are then fragmented, perhaps we can begin giving back these more tolerant daughter colonies to the reef. I am particularly hopeful that efforts to save Acropora cervicornis and Acropora palmata in the Caribbean can be accomplished with our help. There are issues to be addressed, such as endemicism, species validation, and the care to not introduce pathogens or species back to non-native waters. However, what a perfect scenario! A time where there would be no net loss to coral reefs or to aquarists, a net gain for both, and invaluable opportunity for advancement, study, and understanding.

To finish with a very familiar quotation…

"I have a dream!" Dr. Martin Luther King

Thank you, everyone, for having me.

Eric B.


Borneman, Eric. 2000. Aquarium Corals. Microcosm, Ltd. Shelburne, VT. (In

Freney, R.., and Kelly, M.S. 1997: Reviving reefs. Audubon March-April: 23

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mineral accretion structures in Jamaica. Abstracts, European Meeting of
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Goreau, T.J.; Hilbertz, W. 1996. Reef restoration using sea-water
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Symposium, Panamἢr />
Hilbertz, W. 1992: Solar-generated building material from seawater as a
sink for carbon. Ambio 21(2): 126-129

Hilbertz, W. 1981. The electrodeposition of minerals in sea water for the
construction and maintenance of artificial reefs. Florida Sea Grant
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Hilbertz, W., Fletcher, D., and Krausse, C. 1977. Mineral accretion
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Hilbertz, W.,Goreau, T.J. 1996. Method of enhancing the growth of aquatic
organisms, and structures created therby. United States Patent

Maldonado, Manuel. 1998. Do chimeric sponges have improved chances of
survival? Marine Ecology Progress Series 164: 301-306.

Morse, A. N. The use of a novel chemo-inductive substrate to determine
species- specific factors that influence successful recruitment of corals.
Proceedings: International Conference on Scientific Aspects of Coral Reef
Assessment, Monitoring, and Restoration April14-16, 1999 Fort Lauderdale,
FL: 141

Morse, A,N.C. 1992. Unique patterns of substratum selection by distinct
populations of Agaricia humilis contribute to opportunistic distribution
within the Caribbean. Proc 7th Int Coral Reef Sym 1: 501-2.

Morse, D.E. and A.N.C. Morse. 1992. Sulfated polysaccharide induces
settlement of metamorphosis of Agaricia humilis larvae on specific crustose
red algae. Proc 7th Int Coral Reef Sym 1: 502.

Morse, Daniel E., and Aileen N.C. Morse. 1991. Enzymatic characterization of
the morphogen recognized by AgarIcia humilis (Scleractinian coral)
larvae. Biol Bull 181: 104-22.

Mueller, E., and L. C. Becker. 1999. The culture, transplantation, and
storage of Montastraea faveolata, Acropora cervicornis, and A. palmata: what
we have learned so far. Proceedings, International Conference on
Scientific Aspects of Coral Reef Assessment, Monitoring, and Restoration
April 14-126, 1999, Ft. Lauderdale, Florida: 53.

Pearce,F. 1996. Scrapyard reef a home to coral. New Scientist 2047

Raymundo, L. J., and A. P. Maypa. 1999. Using cultured coral to rehabilitate
a degraded reef in the central Philippines. Proceedings, International
Conference on Scientific Aspects of Coral Reef Assessment, Monitoring,
and Restoration April 14-126, 1999, Ft. Lauderdale, Florida: 160.

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restoration, environmental assessment, monitoring and the aquarium trade.
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Assessment, Monitoring, and Restoration April 14-126, 1999, Ft.
Lauderdale, Florida: 161-2.

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van Treeck, P., Schuhmacher, H. 1997. Initial survival of coral nubbins
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ss Series 150: 287-292

Prof. H. Schuhmacher:

Now it is time for the questions...

Could you provide more details on Electrolytic Mineral Accretion, or provide URL's to further reading? Also could stray voltage play into growth rates? I've always experienced high stray voltage, around 5 volts, having never had a problem, I've let it go, as it never bothered anything, could this be contributing to high growth rates I experience in some species?

Yes, I will provide references; they will be at the end of the talk when it is published to the library. Stray's possible, but I couldn't say for sure.

What method of settlement induction would be best? Merely providing coralline-encrusted substrate(s)?

Yes. Mesophylum (a species of coralline) is the most used substrate. Different corals prefer different corallines. The types of corallines and corals are just now beginning to be uncovered. So yes, providing coralline rock would be enough.

Has LPS like Scolymia or Heliofungia been captive bred yet?

I'm not aware of Scolymia, but heliofungia can be fragmented, however, it does not form anthocauli like Fungia.

Who, then, are these researchers working on corallines and settlement?

Alina Morse and her Husband have pioneered and are at the forefront, other researchers have accepted the coralline markers and work with them regularly.

Why not make a grid coated with a given coralline alga, place into the ocean and retrieve later?

Absolutely. Larvae metamorphose after certain periods of time the trick is giving them enough time and knowing their location so that the plates could be placed properly. In many square kilometers of reef there is a lot of leeway not so with plates. You'd probably get something though…

I noticed that you stated that certain species of corals grow faster when put together . Can you give more detail or further references?

Yes, it will be at the end of the article, but one example: is Seriatopora hystrix and Porites rus. You would want to grow both of those corals together to maximize their growth, rather than putting corals together that are competitive and sap each-others energy reserves.

What species have been grafted and where can we find more info?

Pocillopora damicornis, Acropora sp.. I think Montastraea (a Caribbean coral) references to follow (I'll summarize the references).

I've noted that we're mainly discussing propagation techniques used for what 10% of the consumer *really* wants. In my experience in an LFS, I found that the coral that truly get the customer riled are flambeomeandroid (per TRA 1) species such as euphyllia, catlaphyllia, and plerogyra. I would note that some of euphyllia produces phaceloid variants, but...Is there any research on implementing their successful propagation in captivity. I've been working with the slice and dice, but man.. I've killed some stuff. And, even still, catalaphylia specimens that are successful are becoming more and more rare Just to keep, not to prop any thoughts?

LOL. That’s probably going to be unfortunate, as they will probably be looked at carefully with coming regulations. But, there is the possibility that larval fusion would be a good candidate.

The global demand for bananas spurred creation of more banana farms. Why haven't market forces turned coral collectors into coral farmers? Are there non-market forces preventing this?

I would say that the status quo is comfortable and requires less capital outlay to change over but that is my guess. I think USCRTF will eventually provide these answers. (US Coral Reef Task Force).

If added voltage to water to helps corals grow better, what affect does this have on the fish?

This is not something you would do in an aquarium; this is something you would do in a propagation tank FOR corals or other calcifying organisms NOT fish! The current is between the coral and the water, NOT the aquarium water and ground (a powerhead cord). And remember a 9v current across a meter square grid is not a lot of electricity. "DC"

You had talked about a place in Guam a year or so ago that had high hopes of propagating a # of species, did anything come of this?

To my knowledge they are still working on their facility. That was Nolan Hendricks and he is around some of the newsgroups. The question would be better asked of him.

Any idea on what the electric current would do to say coralline algae and echinoderms?


Where do we find more info on USCRTF?

Roger Griffis and should be a good source of information. They will be holding a public meeting in Washington DC to discuss their action plan on March 2nd. Everyone is welcome to provide input, it will be a public meeting.

Would a Rio pump work as an electrode?

I'll draw a diagram of how an aquarist could set such a system up, and put it in the library, along with my talk.

OK everyone that is it for the questions this evening. Thank you very much for a very thought provoking and interesting talk. Great stuff. Thanks a bunch Eric!

Eric's Images:

Electrolytic Grid

Grid in action

© 1999

Created by liquid
Last modified 2006-11-26 13:55