Coral Culture in Suspension

So many lovely corals... and so many power tools to choose from! Ahem... pardon me. I was just daydreaming about coral propagation. Yes, "Coral Propagation:" a rather noble term for what has until recently been the delightfully brutal sport of fragmenting divisions of coral by breaking, cutting, sawing, snapping, dropping, and kicking (but never punting them... er, well... OK. Just once. But that was because it was dropped in stride during a brisk walk to a prop bath). Many aquarists have lost their natural fear of imposed propagation techniques with coral over the last decade. Nowadays, successful coral propagation is not so much a matter of how but rather which way best to conduct it. Furthermore, as more informed aquarists maintain systems of advanced years, we are beginning to see exciting events of reproduction via planulae and medusae among maturing captive reef invertebrates. Indeed, success to date with such reproduction has been mostly limited to asexual events (like many Neptheid, Pocillopora, Millepora and Tubastrea spawns), but each step along the path toward a self-sustaining trade is obviously necessary to lay a foundation for future advancements.

As such, asexual fragmentation has been a fine vehicle for propagating coral to help satisfy the many aquarists seeking to study and enjoy their own private piece of the ocean. Some corals have matured to the point where spawns of asexually produced planulae are lending aquarists some experience with more voluminous production strategies of reef animals. And all experiences with coral propagation will hopefully contribute to great knowledge in attempts to encourage and harness the significant product of sexual reproduction with reef invertebrates in captivity. This is indeed our future if we are to realize a self-sustaining hobby for reef keeping. Beyond the threat of having our privileges to keep reef animals "legislated away," we should be naturally inclined as empathetic and passionate admirers of the coral realm to want to guide our charges in good husbandry to grow and reproduce optimally.

And so, what we have in our wonderful cottage industry of coral farming aquarists is a tremendous resource for coral study and culture in display aquariums, basement culturing systems, backyard greenhouses and beyond. From the many different perspectives and positions of aquarists abroad, participants in coral culture have begun to explore the possibilities of improving husbandry and farming techniques to not only succeed in producing free-living divisions of coral, but to do it with great speed and efficiency. One of the most intriguing and effective methods of culturing coral is by suspension. Coral farmers have discovered that some corals respond superbly to culture in this manner and have demonstrated better growth than when grounded upon a substrate. If grown out and delivered whole, consumers get a product that may be oriented in any desired position. Any tissue that is forcibly stifled by settlement onto a substrate is really in the optimal position/environment to encrust/attach. Otherwise, the process of suspension culture may simply be a fast track to producing greater mass for a secondary technique imposed by the farmer. The strategy is not so unnatural as it might appear at first. Experienced aquarists and industry professionals have often noticed that at least several species of coral are imported naturally without solid base. That is to say, some corals have been collected in full circumference with healthy tissue, and without any apparent or conspicuous orientation. Most notably, Psammocora (Cat's Paw) and Siderastrea (Star/Starlet) species appear regularly in fully encrusted, spherical shapes as if they had been growing on a reef like scleractinian "tumbleweeds". Such animals are called coralliths as our good friend in the industry, Eric Borneman, has so kindly schooled me on (with a teaser that his adviser has a fascinating collection of such specimens including some surprising species!). Even as artifacts of a process in captivity (the growth in suspension) that may not be continued by the final consumer, the bottom line is that some species grow faster by this method of coral farming that serves a very useful purpose, if only as a prelude to secondary techniques like additional fragmentation.

In suspension, corals are to be tethered from monofilament string (fishing line cleaned of oil, if any; or better yet, polyester sewing thread) for the purpose of maximizing water flow and light around the colony during growout. Evenly spaced, transverse PVC or plastic rods (square extruded rod works nicely) will support the colonies on strings and can be dated or otherwise catalogued for livestock management (see simple illustration at bottom of the page). Coral farmers can have a great time experimenting with various staggered levels and lengths of string for corals held in suspension to exploit the water column in a manner physically unattainable with coral fixed to rock (just envision all of the wasted space in a traditionally rockscaped reef if you are propagating coral aggressively... perhaps better than half of the tank in front of the forward slope!). Corals grown in suspension are liberated from the influence of shelter and shadow from the rockscape, as well as from competitors. This unique method of propagation/display gives the vulnerable divisions further protection from many benthic pests and predators (worms, crabs, encroaching nuisance algae, etc.). It also affords the utmost control over coral colonies from interspecific aggression while pushing the envelope of maximum stocking potential in a given display/vessel. Coral growout in suspension contributes significantly to efficient quality control in commercial and private applications. Admittedly, this strategy of culture for coral growout is not ideal for heavily rockscaped, mixed garden-reef displays (although it will work with limitations). By "mixed garden-reef", I mean the common assembly of scleractinians, zooanthids, corallimorphs, octocorals, hamsters and smurfs (heehee...) all mixed together in random fashion in traditional "reef tanks". Suspension culture is better suited for an aquarist deliberately trying to culture coral with a focus on results. The setup for such endeavors will likely be a reflection of the intent. Indeed, any aquarist even contemplating the thought of coral suspension is most likely less concerned about aesthetics than with coral growth/mass.

Ideally, the growout vessel for suspended coral will be free of any impediment between divisions and have a white/reflective substrate. The exclusion of any live rock or similar obstruction between the suspended fragments and the "seafloor" enhances the quality of light reaching divisions from all sides, and a white sand bottom will act as a reflector. Some coral farmers have gone so far as to culture suspended coral in highly reflective, white plastic vessels with very interesting results. There are many options, as one might imagine, for dedicated vessels like a "rockless" in-line refugium or raceway without benthic cnidarians. In this manner, unobstructed water flow is more easily achieved and less expensive to produce. Personally, I like to have a suspension vessel downstream (in-line) from a fishless plankton-generating refugium, such as rubble troughs for larger zooplankton, seagrass refugia for phytoplankton and epiphytic material, etcetera. The growout tank could literally be a plastic storage box like those used under beds and lit simply by standard output fluorescents in a shop light (target species permitting) if the water is shallow (less than 18" deep). For many corals, a cheap, daylight-colored lamp (6500K, or very close to it) from the hardware store will be adequate in such shallow water. This will not work for all corals, of course... but many. Coral behavior and polyp cycles are also quite interesting to observe with surge and wave devices in systems without the impediment of a rockscape. Very efficient indeed. Overall aggression will hopefully be tempered or controlled by efficient nutrient export processes and chemical filtration. Ultimately, a coral propagator will enjoy lower mortality, higher success and growth rates, and a most artistic display of mariculture with suspended corals. In essence, coral culture in suspension can be conducted with great economy and may be an effective strategy of coral propagation where profitability is a consideration. This technique has been demonstrated to be especially effective with Pocilloporids (Pocillopora, Seriatopora and Stylophora), Agariciids (Pavona), Galaxea, Psammocora and Hydnophora, to be specific. Most Acroporids (Acropora and Montipora) fare equally well grown this way, although some species and morphologies are less forgiving (such as tabling forms that we may want to fix securely and coax into an expected natural form).

There certainly is no single best way to tether and manipulate suspended corals. It is all so wonderfully experimental at this point. And each farmer will decide to employ techniques that best suit their goals, time and patience. For many, a simple slipknot works best around the fragment. Others prefer to pat a fragment dry, and put a dab of super glue at the end of the line. Still others will take the time to drill a small hole in a stony frag and thread a line through it and tie it off. In my greenhouse, I simply got in the habit of making a slipknot and tied the noose around the center of the frag. If you will be producing more than a few divisions, you need not feel bad in using the fastest procedure for the sake of reduced handling time. There should be no concern for the aesthetic orientation of the fragment initially. It will indeed grow appropriately to exploit the available life supporting parameters.

Coral cultured in suspension may also benefit from the application of more aggressive feeding in dedicated prop tanks without competition or impediment from live rock and other animals. Continuous rotifer drips, an in-line phytoplankton reactor, and other techniques can be used with greater confidence of efficacy in a simple vessel housing only the targeted, grow-out specimens of coral. A greater feeding efficiency logically contributes to the overall success of corals cultured in suspension.

When all is said and done, from an aesthetic point of view, fixed corals will grow in a more "attractive"/natural morphology if secured to a rigid substrate from the beginning. But then again, coral suspension is really not about aesthetics, but rather it is a means to an end. It is about growing corals faster and larger. Indeed, if one is successful in exploiting proper husbandry, the end result is perhaps an awkward sphere that requires a secondary or imposed action (fragmentation, gluing, epoxy, strap/tie, etc.). Nonetheless, the suspension farmer's goal is realized: faster/greater mass of product.

I must admit that in the presentations on coral propagation that I have given to aquarium societies, many aquarists have singled this aspect of coral culture out as one of the most interesting. So if coral suspension interests you, too, then show us how crazy you can get! And please don't forget to document and report your experiences. Documenting and reporting success is critical from all participants in the trade of ornamental aquarium livestock. Aquarists often feel that they have little to contribute without a scientific background. But let's remember that we are all truly pioneers in this very young science of reef aquariology. Truth be told, no information is bad information regarding reef invertebrate husbandry when there is still so much to be discovered and cataloged. The recording of careful notes, pictures and observations can be extremely useful to other aquarists, and even science at large. From any level of participation (hobbyist, professional aquarist, or scientist), reporting events of success and failure is a wonderful way for coral reef enthusiasts from all walks of life to contribute to the expanding body of knowledge that will help to preserve our beloved wild reef environments.

This pioneer spirit of free exchange of knowledge was a great motivation to me for writing the Book of Coral Propagation, V.1. It is my sincere hope that through my work I might help to inspire aquarists to develop the industry of coral propagation beyond its aquaristic roots.