Let’s Talk Coral! – Euphyllia paraancora, Branching Bicolor Hammer

​by Anthony Soussou

​The Bicolor Hammer is one of the aquarium industry’s most frequently-traded LPS corals, and one of several species belonging to the popular genus Euphyllia. This group’s classification is slightly contested, but it is commonly associated with the hammer (or “anchor”) corals, torches, and frogspawns. Each of these can be found in a variety of shapes and colors with brightly-tipped tentacles of differing lengths. When both advanced and rookie hobbyists alike learn that Euphyllia are also relatively simple to keep, it becomes clear why these wonderful corals are so desired in the home aquarium. Here, we will not only discuss the fundamental aspects of Euphyllia paraancora, the Branching Bicolor Hammer, but I will also include the most valuable details of my hands-on experience with this species over several years. By educating the average aquarist regarding strategies of successful growth and propagation of this species in captivity, I hope to contribute to the reversal of its increasingly-threatened state in the wild.
 
Hardcore Corals
Found throughout the hotspots of marine diversity that make up the Indo-Pacific region, Euphyllia paraancora and its relatives are beautiful and hardy corals that make wonderful additions to our home reef aquariums. Many of the reasons why members of this genus are able to thrive in captivity have been attributed to different aspects of their physiology. Like the majority of other corals, Euphyllids house within their tissues different colonies of symbiotic algae (known as zooxanthellae), which naturally photosynthesize and thereby provide energy to their hosts. However, unlike many other corals, our hammers, torches, and frogspawns of the genus Euphyllia can readily adapt to various wavelengths and intensities of light and still grow optimally. In fact, the entire genus is characteristically-tolerant of many adverse or fluctuating conditions, including high and low water temperature, elevated phosphate and nitrate levels, turbulent or still flow, and even surface level versus bottom-sitting aquarium position.
 
Not usually trifled with, E. paraancora is also reasonably capable of defending itself from predators. The texture of its tentacles as well as the slime produced by its soft tissues are both generally unappealing to most marine animals. As far as the tentacles themselves go, the stinging cells found in these Cnidarians seem to be nothing more than uncomfortable to the touch of most fish, let alone dangerous to humans. In fact, many corals of the genus Euphyllia serve as less-abrasive hosts to clownfish and other damsels than do their naturally-compatible anemones. In captivity, hammers have been observed allowing multiple fish to reside amongst their branches. Although they may retract their tentacles in mild discomfort at first, these corals will adapt to the presence of fish in due time and satisfy their guests’ natural inclination to seek shelter. Perhaps the employment of an aggressive fish is simply another strategy for the coral’s own self defense.
 
In general, as long as these animals are healthy upon arrival and are allowed to slowly adapt to the parameters offered by a given aquarium, the chances that they survive are far and beyond those of the average coral. However, this is not to say that Euphyllids do not deserve great care. They may be able to survive less-than-ideal circumstances, but their hardy nature is no match for the reckless power with which humans sweep through a coral reef. Over-collection of these corals is now their main threat in the wild, but the captive population may very well provide the key to their recovery. Like with any animal, aquarists are responsible for providing the best possible conditions under which their pets can happily thrive, enrich themselves, and possibly even reproduce. In order to accomplish this goal, we must learn in greater detail the fundamental aspects of genus Euphyllia.

​Branching Bones
Euphyllids in general belong to the common-tongued category of “LPS” or long-polyped stony corals, which is to say that the soft tissue making up their tentacles and mouths grows out of a constantly-expanding carbonate skeleton. Within the genus, one will find that the structure of this skeleton constitutes the main difference between two distinct species that seem otherwise identical. For example, Euphyllia paraancora is the branching (or phaceloid skeleton) counterpart of Euphyllia ancora, which grows a continuous (or meandroid) skeleton. While both of these species absorb calcium and other minerals directly from the surrounding water in order to facilitate the development of their “bones”, the branching configuration of E. paraancora, E. paradivisa, and E. paraglabrescens gives them a slight edge in captivity over their cousins that build continuous skeletons. This is because phaceloid skeletons tend to break less-dangerously than meandroids, and will more likely be able to sustain significant trauma without suffering from degenerative tissue loss. In other words, those corals that are broken upon collection or distribution are more likely to avoid damage to their organs if their skeletons are branched, because they will usually break only at the joints of the branches. Conversely, meandroids generally break or must be cut at locations where their tentacles and other soft tissue are growing, which is much more difficult for the coral to heal from. This trait also makes branching Euphyllids like E. paraancora much easier to intentionally propagate in captivity via fragmentation (or fragging) of the separate branches, which we will discuss in much greater detail later on.

​Species Specific
Like many beginning aquarists, Euphyllia paraancora was one of the first species of coral that I ever personally attempted to house in a reef aquarium. Aside from their aforementioned hardiness, novice reef-keepers adore branching hammers for their vibrant (often referred to as “toxic”) green color, the pleasant movement of their tentacles through the water, their knack for becoming accustomed to any position in a tank, and their reasonable availability and price within the hobby. One frag of paraancora, consisting of an inch-long branch stem and a single mouth surrounded by 5-15 tentacles, can often be purchased for $5-$10 in a local fish store or at an open frag swap. After introduction to its new home, the coral’s tissue will begin to grow and spur the formation of new branches, which further increase the fledgling colony’s capacity for photosynthesis and skeletal expansion. In a matter of months, aquarists can find themselves counting several new branches on their coral. This growth can become even more rapid once the colony reaches twenty heads or more, as the cluster is then able to absorb significantly higher amounts of both light and bone-forming calcium from the water.
 
As the colony grows, the tips of its tentacles can begin to display some interesting morphological differences. E. paraancora is known as the bicolor hammer not only because the green (or sometimes yellow) tips are differently-colored than the stalks of its tentacles, but also because some branches tend to lack the bright pigment altogether. This sometimes results in adjacent branches looking completely different from one another (hence “bicolor). Having raised mostly the neon green variety myself, I can offer no strong hypothesis explaining why certain branches will spawn tentacles that are all-brown in color. In fact, I have observed some individual tentacles displaying tips that are half neon green and half brown, appearing as though green paint had been spilled on some of the tentacle’s end, but not all of it. These variations in pigmentation could be a result of differing amounts of light, proximity to other off-colored branches, perhaps even the dwindling diversity of genetic material as branches continue to bud, or a combination of some, all, or none of these. Whatever the reason and regardless of color, growing new branches is something that Euphyllia paraancora certainly knows how to do.
 
                                                                                        
Manifest Destiny
Like its Euphyllid relatives, E. paraancora will often reach a growth capacity determined by the amount of rockwork surrounding it, a lack of necessary nutrients in the water, or a limitation on the amount of available light. At this point, the coral must decide on the single best direction in which to continue growing. This ensures that it will only expend energy and resources on creating new branches with the highest probabilities of survival. In order to solve this dilemma, many corals of the genus Euphyllia have evolved the ability to extend “sweepers” far and beyond the reach of their other tentacles. These sweeper tentacles scout out the space surrounding the current colony, helping it to gather information about which new areas would be the most hospitable and conducive to further growth. However, these sweepers also reveal the true aggressive nature of genus Euphyllia. Should the tips of any Euphyllid tentacle come into contact with the mucus coating of an unrelated coral, the aggressor will begin to extrude digestive enzymes that effectively consume and destroy the tissue of its weaker neighbor. Countless grieving hobbyists can attest to the dangers of placing their most prized chalice too close to a torch or hammer. Even the different varieties of frogspawn, known for their shorter and stubbier tentacles, have been known to overtake all but the most resistant corals. However, as if they are able to communicate with neighboring relatives, Euphyllid tentacles have not been known to cause damage to nearby Euphyllia. I theorize that, similar to the slime coating of an anemonefish that prevents its host’s stinging cells from firing, Euphyllia recognize the consistency or the makeup of a fellow coral’s mucus layer and refrain from causing it any damage.
 
Hungry Hammers
Although the hostile takeovers exemplified above are not undertaken by E. paraancora for the primary purpose of feeding, the branching hammer and its congeners are known to occasionally consume solid foods. Euphyllids are equipped with tentacles that can be used to capture both small prey and detritus, as well as mouths that serve as two-way digestive tracts as the corals consume bits of protein. Like other captive coral, these animals can be “trained” to respond to the stimulus of a paused powerhead in order to accept frozen preparations. In these instances, E. paraancora can be observed widening its mouth and stretching out its tentacles in anticipation of solid fare. However, it is worth noting that Euphyllids in general do not require sustenance other than photosynthetic light in order to survive. In the wild, much of the solid food that corals consume comes in the form of fish waste and other floating particulate matter, which should be at least moderately available in a stocked reef aquarium. As an additional supplement, feeding of enriched or basic food such as mysid shrimp once per week applied directly to the mouth should be more than enough of a meal for the average Euphyllid. Otherwise, it is possible that feeding these corals too frequently is just as likely to result in undesirable increases in nitrate and phosphate levels as it is to directly contribute to the growth of E. paraancora. It may be worth conducting a structured experiment in order to determine the effectiveness of feeding on coral growth in the future, but suffice it to say that proper lighting is a far more vital component to Euphyllids.
 
Background
My home aquarium is a 150 gallon mixed reef that has been running smoothly in the wall for about ten years. At the start of that period, my original colony of E. paraancora consisted of about 10 heads, which quickly grew into nearly 40. It was after my first adventure into separating that mother colony into two pieces that I began to explore different methods of bicolor hammer propagation and growth. Through very informal experimentation and oftentimes shot-in-the-dark forms of trial and error, I began testing different placements, forms of cutting, and even moving corals from place to place in the aquarium based on the observed progress that a growing cluster would make. First, allow me to detail the conditions under which these corals were allowed to grow, more or less, over the many years.
​
Temperature: Through the use of a chiller, the display tank is constantly maintained at 77 degrees Fahrenheit with no more than 2 degrees of variance on either side at any given time.
Lighting: Since day one, the aquarium has sported a custom 40” array of blue and white LED lights. I can’t accurately determine wattage, however it is important to note that white light is always kept at minimum strength and only run for eight hours, while blue light is dialed up to 75% of the maximum output and runs for twelve hours each day. One side of the tank receives 1 hour of direct sunlight daily.
Flow: Also constant throughout the tank’s life has been the inclusion of two 1,320 GPH power-heads, each placed opposite the other so as to create a dispersal of flow throughout the entire aquarium. The least turbulent areas are therefore the very bottom, the far-reaching corners, and rockwork tunnels.
Feeding: Over the course of my aquarium’s existence, I have only hand-fed my Euphyllia a handful of times. It is safe to assume that all of the observation I am about to detail has occurred without feeding.
Water: Target parameters have always been 1.025 specific gravity, 8.0 pH, 10 dKH Alkalinity, 500 ppm Calcium, 1,400 ppm Magnesium, no more than 10 ppm Nitrate, and no more than 0.1 ppm Phosphate.
 
Obviously, a new sump, hardware malfunctions, and other inconsistencies have occurred over the many years, but E. paraancora are resilient enough that death has never come by way of poor water quality. Similarly, these parameters and the equipment creating them are by no means a recommendation for every aquarium. This is simply an account of my personal experience that may help to explain reasons why E. paraancora has been able to reproduce successfully. Alterations may result in either better or worse results, and can hopefully be shared in the comments and further discussed here.
 
Growth Tips
The general rules of thumb are that bicolor hammers prefer mid to low-level placement in the aquarium, moderate to low light, and moderate flow. The caveat to this guideline is that E. paraancora will survive under a variety of conditions, and deviating from this set of rules can sometimes elicit responses from your coral that will assist in its propagation. When a new colony of bicolor hammer is introduced to the aquarium, it is best to adhere to the recommended conditions as closely as possible so that a baseline of well-being can be established. This will allow for the pet owner to evaluate the health of the new arrival under optimal conditions by monitoring indicators such as the level of tentacle extension, completion of skeletal coverage by healthy soft tissue, condition of the mouth and tentacles, and overall appearance and color.  
 
As the coral begins to adjust to the aquarium, it will inflate and deflate in coordination with the intensity of the light and time of day. If it does so regularly and without issue, it should be allowed to enjoy its position for at least a couple of weeks before being moved or disturbed in any way. Hopefully it has been glued down to a rock, set securely in the sand-bed, or stuck in a crevice where it can grow safely. From here, the general objective is to advance the coral closer to the light over time to allow for faster growth. This must be done slowly and carefully, however, so that there is reasonable time to adapt and so that the branches are not physically damaged by frequent contact with hands and tools. Not long after introduction, E. paraancora will generally display full tissue volume and eager growth in captivity.
 
Proper Parenting
Once E. paraancora is growing steadily in the aquarium, the real question is how to know when a colony is ready to be fragged. Although separating a single branch can sometimes begin the growth of a new colony, it should only be done if that branch was doing well enough within the collective to survive on its own. My opinion has been that a threshold must be met before a solitary branch can survive, and that this threshold is the point that must be reached before fragging is recommended. Unfortunately, there is no definitive indicator of this “fragging point”, and aside from careful observation of the coral’s tissue, tentacle expansion, and vibrancy of color, the hammer itself will do little to notify the aquarist. For this reason, I rarely condone the splicing of a single head, and opt instead to isolate a frag with no less than two or three healthy branches. The size of a branch to be fragged is also paramount in its survivability, so we must therefore understand how these corals come to form new branches.
 
The bicolor hammer maintains its soft tissue at the end of each branch, which is made up of several septa, or the connecting points from which the tissue grows out of the skeleton. Tissue and mucus that is extending far beyond the septa and down along the sides of the branch is indicative of a healthy and growing coral (this goes for most soft corals in general, not just members of the genus Euphyllia). It is from this point, where the healthy tissue extends over the side of the branch, that an entirely new head has the potential to bud. The coral has the ability to sense light contacting its body in these areas, and responds by condensing its tissue into clumps in order to gather more of that light for photosynthesis. Once the lump becomes thick enough, bright specks of green color become visible and will eventually extend to form the tentacles of the new head. From here, the tissue nearest the base of the bud starts to solidify, initiating the skeletal growth of a new branch. These buds begin formation at a microscopic level, and should never be removed until they are at the very least an inch or two in length with a substantial skeletal base to grow from.
 
Fast Frags
Through its budding process, E. paraancora can multiply from a single head into a colony of countless branches, if given enough space, resources, and time. Whether the objective is to share, trade, sell, or relocate the separated branches, fragging these corals could not be easier. Thanks to the phaceloid configuration of their skeleton, all it takes to separate one or two branches is a swift cut or an even break between the target frag and the colony. I believe that the amount of calcium available in the water contributes to the strength of the coral’s skeleton, and in turn, the strength of its branches. In other words, an aquarium with low calcium levels will result in weaker branches that may be more easily fragged, but this may also grow less healthy coral.
 
However, even the strongest bicolor hammer is no match for a plier or cable-cutter of the right size. Thinner branches can even be separated carefully by hand (with a bit of strength) if they have grown in a less-stable direction away from the rest of the colony. In fact, I have sometimes completed an entire fragging process without ever removing my hands or the coral from the aquarium. Unlike frags of most other corals, separated branches of bicolor hammer don’t even need to be iodized, dipped, or sterilized in order to prevent infection (unless the soft tissue is damaged in the process) because the only contact point should be the base of the joined bone. The only required post-break care should be intensive observation of the new frag after its placement back into the aquarium. Preferably, each frag can be replaced as closely as possible to the original site of its growth so as to maximize its potential for recovery. By maintaining the conditions under which the bud originally grew, it will be more likely to continue healthy development on its own.
 
Be sure to take great care with any instance of touching your coral with bare hands. Pressure on the coral’s soft tissue that is too violent can result in necrosis that can quickly spread to the rest of the irritated polyp. Even exposing some of the septa beneath the tissue can lead to the slow death of an entire head. The septa can easily become surfaces that allow for the growth of opportunistic algae. Once this occurs, the algae will overtake the septum, and it becomes nearly impossible for the hammer to replace its soft tissue over the affected area. Also be wary of fragging by hand, as the branches themselves can break into sharp points that will easily cut unprotected fingers. Safety of both the coral and the hobbyist should be of the utmost concern during the fragging of any species.
 
Advanced Acceleration
An interesting method that I have developed for eliciting the growth of new buds on an existing hammer colony involves the selective limitation of available light and flow. I noticed that hammers tend to grow in the direction of strongest light, but also that they prefer to grow away from direct flow. By placing a healthy cluster so that half of the coral is shaded, and by also orienting the shaded half towards the direction of heavy flow, it can be coaxed into growing new buds near the top where the light is strongest and flow is more relaxed. I have used this technique to round out a colony that became misshapen, as well as to further develop buds that I have noticed sprouting on my hammers. A colony that receives the same amount of light all around will generally sprout new buds along the bottom branches in order to grow wider and expand laterally, as this will allow for greater surface area to contact light from above.
 
Colonies of E. paraancora that have been significantly advanced towards the surface in order to receive more light will often display shorter tentacle extension, brighter color, and more closely-grouped branches. They will become used to photosynthesizing much more quickly than they can absorb minerals necessary for bone growth, so the hobbyist will notice slower addition of new branches, a smaller average size of branches that do develop, and a larger number of tentacles on each existing branch. If these corals are placed at lower positions in the aquarium, their tentacles will reach great distances in an attempt to collect the same amount of light to which they have become accustomed. Doing this requires a significant expansion of soft tissue, which can usually lead to a higher likelihood of new buds growing from existing branches. The same logic applies to a cluster that has been shaded for an extended period of time. These corals are generally growing their bones more quickly than they are photosynthesizing, so that extra calcium is used to create more branches that will eventually provide the colony with the means of absorbing more light.
 
Big Picture
By taking advantage of this information regarding the needs and tendencies of E. paraancora, any hobbyist can gain a slight edge in the healthy propagation of its branches. The mechanisms by which these corals “make decisions” can be easily manipulated once understood, and can then be controlled in order to spur significant growth. It is my hope that these techniques and others will become more readily-available within our hobby so that the propagation of corals in captivity will aide in the supply of the most popular species for aquariums. As ornamental corals become more-frequently aquacultured, our dependence on the collection of wild colonies will diminish in response, which will hopefully result in mankind seldom interfering with life on a natural reef.
 
Our readers that believe in this goal are encouraged to experiment, record observations, and share their findings as well. Through the joint effort of many aquarists sharing information, this field of study has always been able to grow, and milestones that had previously been considered impossible have been reached and surpassed. Please like, share, and subscribe in order to discuss your impressions with us as well as to contribute in whatever way possible to the mission of protecting our hobby’s threatened species. We hope you enjoy all of our articles and posts. Thanks, as always, for taking the time to read.