A Propensity to Interfere and the "Geology" of Coral Reef Aquariums

Over the years, I have moderated or participated in many coral and aquarium related web sites, message boards, and mailing lists. One of the reasons I do so is that it allows me to keep a "pulse" on the aquarium hobby; getting an overall feel for the status of both the relative pervasiveness of information and techniques throughout the hobby, as well as knowing, perhaps in advance, when certain trends are beginning to emerge.

When I began moderating the AOL reef aquarium message boards many years ago, certain facets of aquarium and coral husbandry were obvious and trends came and went over the years. Some stayed, some are long forgotten or, for newcomers, were never known: the widespread use of wet/dry filters, the use of novel additives (Molybdenum, Vitamin C, Liquid Gold, Boron supplements, Coral Vital, sugar, various "X-products", yeast, Lugol's solution, etc.), plenums, sulfur lights, blacklights, and so forth.

An advertisement for a "miracle product" 1992. Freshwater and Marine Aquarium 15 (4): 174.

This first article for Reef Central's exciting new online magazine is the beginning of my plan for addressing some of the more prominent themes that emerge from The Coral Forum. I would like to take some of the more common "threads" and look at them in some depth; essentially offering not only more information about some of those things that seem to be causing either questions or troubles for many aquarists, but perhaps efficiently addressing some far reaching areas of misunderstanding. As usual, I will be drawing my information from my experiences in the field and with aquariums, as well as from scientific literature and, where possible and useful, aquarium observations and anecdote.

Part One:
The Coral Reef Aquarium: Operating Room, Emergency Room, or Both?

One thing that has certainly not changed over the years is our seemingly irrepressible need to intervene into the normal function of an aquarium. It has been known for quite some time that it is usually better to keep one's hands out of the tank, yet this does not seem possible for most. The topic for this issue was overwhelmingly obvious to me, and had caused me several hours of private consternation. One phrase typed many times in The Coral Forum over the past several months keeps coming back to haunt my thoughts:

"Should I Cut It Out?"

Why is it that aquarists seem to be budding surgeons? Is it perhaps that we are so attached to our corals that we tend to anthropomorphize, pretending as if they were patients of ours, requiring constant medical supervision? Is it the fear of the unknown pathogen? It is a concept that has so firmly entrenched itself in the minds of aquarists around the world that it is frightening. Coral bleaching, coral disease, coral predators. What is it? Is it harmful? Will it kill my coral? Will it spread?

DO I NEED TO CUT IT OUT??!!

I don't want to poke fun at those genuinely concerned and empathetic aquarists who are so caringly worried for their animals. In fact, it's great that you all have such a strong attachment that you would be willing to brave the waters of unknown pathogens, predators and diseases with your bare hands to rescue this poor suffering cnidarian!

So, is the aquarium an operating room? Yes, occasionally. There are indeed times when the natural regenerative function of these colonial animals can be put to great advantage. Excision can be done, effectively and with minimal risk, in many cases. But when are those cases? Soon, I will attempt to answer that question.

Is the aquarium an emergency room where corals appear mortally wounded with sometimes-slipshod procedures performed in order to stabilize a condition that requires long-term treatment? Is it a place where corals are admitted when it's a false alarm, like the patient who ate too many jalepenos and thought that pain in his abdomen was an abdominal aortic aneurysm when all he needed was a Maalox? The answer is a resounding yes.

The question that begs to be answered is "What's wrong and just how serious is it?" The question is rarely, "Do I need to cut it out?"

Part Two:
Some Facts About Colonial Animals

A colonial animal is one where groups of related organisms live together, sometimes interconnected and even indistinguishable from one another. We have discussed aspects of this subject in other threads in The Coral Forum. In the case of colonial organisms like many of the stony corals, groups of polyps live in various degrees of connection with others, sharing the same skeleton, but each polyp residing in its own skeletal element called a corallite. In some, like the genus Acropora, the polyps are highly interconnected and share tissue elements, such as gastrodermal canals and nerve net elements. Even in genera of corals with somewhat less connection, the tissue is often unified across the skeletal surface (corallum) and this tissue is termed to coenosteum. There are stony corals with even less connection that are still considered colonial. For example, Caulastrea spp. and some Euphyllia spp., often reside within the same major skeletal elements, but each polyp is separate from all the others, having divided from a parent by fission and then continuing off in its own direction, calcifying more of its own corallite separately from its parents, until it too divides. Soft corals, corallimorphs and zoanthids are similar; some have polyps inextricably fused in a mass of tissue called the mesoglea. Others are almost totally separate, perhaps connected by a thin sheet or mat, or not at all.

This Euphyllia parancora is an example of a coral with separate polyps that still forms colonies. The individual polyps become disconnected from each other over time, although the newly dividing polyp in the foreground is still connected to each half. Here, one can also see the dead parts of the skeleton, and dead polyps. These fragments form the base of a low relief reef comprised entirely of broken corals and are the substrate for fields of Goniopora spp. and Nemenzophyllia turbida. Eventually, the amounts of bioerosion, already clearly visible in the upper right, will become sand. Right now, it is home for sponges, tunicates, and other encrusting and boring life.

So what does this mean? Well, in the case of the highly interconnected types, what affects one polyp may well affect numerous polyps. This spans the range from nutrition to local necrosis. With the individual polyps, if a polyp dies, unless the other polyps are subjected to the same effector, it dies alone. In a highly interconnected colony, it's more difficult to separate the influence and prevent it from affecting other polyps. However, such colonies have other aspects that have given them an evolutionary edge. In living in large accumulations of numerous individuals, a colony is often able to tolerate some degree of mortality or damage without the loss affecting the entire colony. In fact, a coral reef is such a highly competitive environment, this type of advantage is almost mandatory to ensure the continued reproductive presence of such important components of the ecosystem. As such, coral colonies are extremely long lived and show limited senescence and yet are almost always enduring alternating periods of growth and set-back. The term used to describe this is partial mortality.

Two species of coral, a Porites sp. and an Oxypora sp., battle it out on the reef. The dead zone between them is covered with cyanobacteria, itself an important component of coral reefs. This dead space can be settled by a new variety of life, or the dominant coral can continue to grow. The Porites sp., a competitive subordinate, has the advanatge in that it tolerates partial moratality with ease and is extremely long lived.

The Geology and Growth of Corals, Coral Reefs, and Coral Reef Aquariums

Corals grow by precipitating calcium carbonate underneath their lower polyp surface using cells of the calicoblastic epithelium. This is the same tissue layer that forms the upper surface of the coral that is visible, but the cells are slightly different and attached to the skeleton itself. Over a continuous time frame that can span centuries, huge formations of calcium carbonate are formed that, along with the biomineralizations of crustose red algae (coralline algae), foraminiferans, mollusks, bryozoans, and other calcifying reef biota, comprise coral reefs. The carbonate skeletons of these animals, long dead, provide for the complexity of surfaces and small niche habitats that allow for the huge biodiversity of life on a coral reef. Animals and plants live around these structures, within the cracks and crevices used as both home and shelter, and even within the pore structure of the carbonate itself. Boring organisms make their home inside the solid skeletons, and many such eroding organisms are ultimately responsible for the production of dissolved calcium carbonate in seawater that, in turn, feeds more calcification. Furthermore, old skeletons are ground up by mechanical, chemical and biological processes to form the sands that support their own integral communities; from decomposition areas to plain benthic habitats for an abundance of lifeforms. As coral reefs grow, they gain surface complexity and area, and are thus able to support even more life.

This Leptoria sp, is a colonial group of polyps so integrated that the skeleton formed by the polyps is even incapable of distinguishing the fused polyps that lie side-by-side within the sinuous meanders.

Corals that die only lose the thin veneer of tissue that created the massive carbonate skeletons beneath them. This surface then becomes an important settlement area for new plants, animals, and even coral planulae that will continue forming the outward growing margins of the reef. An entirely dead coral colony merely becomes habitat and substrate for further growth. Most of the time, barring massive mortality from bleaching, disease, competition, predation, storm, etc., any mature coral colony on a reef will have a very high likelihood of having suffered at least some partial mortality over its potentially extremely long history since settling as a tiny planula. In some cases, the partial mortality may have occurred because part of the colony was growing under suboptimal conditions. Perhaps some branches of a colony had grown too close to a strong competitor, or had grown under a shaded ledge and could not receive adequate light. In this case, the partial mortality might even be considered adaptive as the colony can expend energy in growing outwards in more favorable areas.

In fact, ideal coral reef growth is considered to be accomplished under what is termed the "periodic disturbance hypothesis." That is, coral reefs maintain their highest diversity and health when periodically subjected to disturbances that cause partial mortality. This prevents any of the fiercely competitive plants and animals from achieving spatial and ecological dominance. It"clears the brush," so to speak, much as forest fires renew forests over the long term, and allows for the introduction, settlement, and growth of new genetic and ecological diversity that ultimately benefits the reef as a whole.

This solitary polyped coral, Scolymia sp., cannot tolerate partial mortality. It can, however, tolerate injury even to the extent that skeleton is exposed.

In aquariums, we have a vested interest in the life behind the glass. Hopefully, it is more than just a financial interest, although this may be a strong motivator, as well. We try very hard to separate each individual "specimen," protecting it from the ravages of competition. We place it carefully as a tiny juvenile colony to maximize its health, and then, as our efforts succeed and the coral grows, we decide to play doctor and landscaper, trying to maintain a miniature dollhouse of corals.

What's Wrong With This Picture?

Almost too much to consider. Can you imagine what would happen to a coral reef if everytime a death occurred, it was removed? Given the description of coral reef growth above, it would obviously not be a great benefit to the net growth or health of a reef. So why do we feel it is good for our tanks?

Some might feel that is because of aesthetics. I would argue that good money is paid for high quality live rock, and that is exactly what is being removed every time a dead coral is removed from the aquarium - a future piece of high quality aquacultured live rock. Additionally lost is net growth of a reef aquarium, countless unseen plants and animals residing within the skeleton, areas of potential microbial processes such as denitrification, and spatial complexity that ultimately makes a tank look like a reef and not a pile of rocks with coral placed on them. When one considers it carefully, aesthetics are lost over time, the continuous change that characterizes a coral reef is lost, and the tank remains more or less unchanging and stagnant from this compulsive behavior. If coral dies in the aquarium, the only thing that really happens is there is now an exposed surface for new settlement.

Like live rock, the first colonizers will probably be filamentous algae. This is normally thought of as a "bad thing to have" in aquariums. But, if the reef aquarium is generally healthy, this is a temporary succession that will provide some new food for herbivores. They will graze it, grow, and reproduce. Over time, other things will replace the algae. Each of these successions will be important for some community in the tank, perhaps even for the development of some species that was latently existing in some dark crevice of the aquarium, unseen, without an area for settlement, like a beautiful sponge or colony of fanworms.

This Acropora sp. is dependent on fragmentation for its ecological dominace of areas produced by such asexual spread. The thin delicate branches house many polyps, well interconnected, and yet the colony is quite tolerant of breakage as a whole.

What else is wrong with the notion of "cutting it out?" Corals live on the edge, delicately balanced in most cases on a bare minimal energy budget from light and limited food availability. In aquariums, it is probably even more of an issue because of the limitations of a closed water volume and the amount of food availability. As corals reach a certain size or age, if the energy is available, they may reach reproductive maturity and spawn. It is, to this day, an exciting and applaudable event to have coral spawn in the tank. If, however, a coral is subjected to constant pruning, the energy needed to provide injury repair and reallocation of energy to growth may compromise the coral and it may never reproduce. In fact, with enough pruning, its growth may be significantly slowed, as well.

Furthermore, pruning corals results in tissue injury that compromises its integrity and can allow for the invasion of potentially deleterious microorganisms, perhaps even the dreaded "mystery pathogen." It is generally found that pruning and fragmentation is well tolerated in a healthy coral reef and coral reef aquarium, but the fact remains that it does pose some risk to both parent colony and produced fragment. Constant pruning also entails the constant introduction of hands into the aquarium, and thus increases risks of tank mishaps and the introduction of contaminants, toxins, and non-native microbial flora. Such non-native flora has a long history of producing problems in coral reefs, and the implications within a closed system are even more likely to be problematic.

Cut It Out!

Is there ever a time for the scissors and knives to be taken from their holders and used? Of course. Necrotic areas that may compromise the integrity of the entire colony should be excised. Intentional propagation, if it is the aquarist's goal, requires some amount of cutting or breaking. If a known disease is present and spreading, excision is often a good treatment method. However, a dead branch or corallite is not a reason for excision. Competition is rarely if ever a reason for removal of parts of a coral. Certainly, a coral that has already died does not need to be removed - unless of course the aquarist is someone like me who is dying to know the identification of what species was present in the once living coral!

I finally removed this dead Trachyphyllia from one of my aquariums because I needed to look at its skeleton for comparison to another skeletal morph. The enrusting polychaete tubes are only part of the abundant life that would have eventually turned this coral skeleton into a small version of a coral reef or piece of live rock.

In summary, I would urge aquarists to begin to think of their tanks as they aspire them to be; living fragments of a coral reef that are subject to all the ups and downs, the cycles, the growth and decline; the life and the death of coral reefs. It's probably in the best interest of your tank, and you can keep those scissors and knives from rusting, too.

Keep reading, keep posting, keep learning, and keep sharing.

Until then, I will see you all in The Coral Forum.