Micromussa Corals: Taxonomy, Care Requirements, and Reclassification

Micromussa corals are a group of large-polyp stony (LPS) corals prized by reef aquarists for their vivid colors and fleshy polyps. Formerly known to many hobbyists as “Acans” (short for Acanthastrea), these corals have undergone taxonomic changes in recent years because of DNA sequencing. This comprehensive overview will cover their detailed taxonomy (including the reclassification of Acanthastrea to Micromussa), optimal aquarium care (water parameters, lighting, flow, feeding, and supplementation), propagation methods, and common health challenges.

Taxonomy and Recent Reclassification of Acanthastrea to Micromussa

Micromussa corals belong to the family Lobophylliidae, a family of Indo-Pacific LPS corals that was redefined in the late 2000s​. Until recently, the genus Micromussa was a minor group containing only a single notable species (Micromussa amakusensis). However, a major taxonomic revision in 2016 reshaped this genus​. Molecular (DNA-based) phylogenetic studies combined with detailed skeletal morphology comparisons revealed that several corals formerly classified as Acanthastrea were more closely related to Micromussa. As a result, those species were transferred into Micromussa. Genetic analysis showed this species is unrelated to the true Acanthastrea ( A. Enchinata ) group and fits within Micromussa​. Its corallites (skeletal cups) have the size, shape, and fine tooth-like septa typical of Micromussa, rather than the smoother septa of Acanthastrea​. Based on these findings, A. lordhowensis was reclassified as Micromussa lordhowensis in 2016​.

Key species in the genus Micromussa: After the reclassification, Micromussa now includes several species. The top two being the bulk of the corals of this type seen in the aquarium hobby.

• Micromussa lordhowensis – formerly Acanthastrea lordhowensis, the popular “Acan Lord” coral with large polyps​.

• Micromussa amakusensis – the original “Micro” coral, having smaller polyps (~8 mm corallites) and often encrusting growth. Sometimes nicknamed “Micro Lords” by hobbyists​

• Micromussa pacifica – a newly described species.

• Micromussa indiana – another recently described Indo-Pacific species​

• Micromussa multipunctata – formerly in Montastraea (an Atlantic genus), now recognized as a Micromussa​

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It’s worth noting that not all former “Acans” moved to Micromussa. For example, the large-polyped Acanthastrea bowerbanki and A. hillae were reclassified into a different genus (Homophyllia) after studies showed they form their own lineage​. Meanwhile, the genus Acanthastrea itself has been restricted mainly to a few species like A. echinata. In everyday aquarium practice, however, hobbyists still often refer to Micromussa corals as “Acans,” so understanding the naming history is helpful.

Water Parameters for Optimal Care

Like most reef-building corals, Micromussa thrive in stable, clean water conditions. They are generally hardy and can tolerate a range of parameters, but ideal water chemistry will promote better growth and coloration. Aim to maintain the following key parameters in a Micromussa aquarium:

• Temperature: ~75–78 °F (24–26 °C). They naturally live in warm reef waters (often around 82 °F in the wild), but they adapt well to typical reef tank temperatures in the mid to upper 70s​

• Salinity: ~1.025 specific gravity (35 ppt). Natural seawater salinity is ideal; keep within 1.023–1.026 for stability​

• pH: Maintain ~8.0–8.4 pH, with minimal daily fluctuation​. A steady pH (around 8.2) indicates good buffering (alkalinity) and gas exchange.

• Alkalinity (dKH): ~8–10 dKH. Moderate alkalinity supports calcification; Micromussa can tolerate 8–12 dKH​, but sudden changes should be avoided to prevent stress.

• Calcium and Magnesium: Calcium ~400–450 ppm and Magnesium ~1250–1350 ppm to support skeletal growth​. These levels ensure the coral has the ions needed to build its calcium carbonate skeleton.

• Nutrients (Nitrate & Phosphate): Moderate nutrients are beneficial. Aim for nitrates in the range of ~5–10 ppm and phosphates around 0.05–0.1 ppm​. Micromussa corals do not require ultra-low nutrient water; in fact, they often display better growth and coloration with some nutrients available. Extremely low nutrients can cause pale colors or starvation, whereas excessively high nutrients (e.g. >40 ppm nitrate) may lead to algae growth and brown coloration. The key is stability – avoid dramatic nutrient swings and maintain good filtration (protein skimming, refugium, etc.) to export excess after feeding.

In general, clean, stable water is the goal. Regular water changes or dosing of elements can help replenish trace elements (strontium, iodine, etc.) that Micromussa may use. They are fairly forgiving if parameters are slightly off, but will show best expansion and growth when conditions are kept consistently within the ranges above​.

Lighting Requirements

Micromussa corals prefer lower to moderate light levels in the aquarium. In the wild, they are often found in deeper or turbid reef environments (for example, M. lordhowensis is found down to ~30 m depth) where light is less intense​. In captivity, they thrive under gentle lighting and can suffer if exposed to very strong illumination without acclimation:

• Intensity: Low to medium. A PAR (photosynthetically active radiation) range of roughly 50–100 PAR is a good range, they can survive higher if gradually acclimated, but too much light can cause bleaching or color loss. Intense lighting is known to cause Micromussa colors to morph – often shifting toward dominant reds or oranges under extremely bright light​. For example, a multi-colored “rainbow” Micromussa may turn mostly red/orange if placed directly under high-intensity LEDs or metal halides. To preserve vibrant multi-colors, it’s often recommended to keep them in the shade or under predominantly blue-spectrum lighting​. A stronger blue/actinic spectrum helps prevent color morphing and maintains the neon greens, yellows, and blues in rainbow specimens​.

• Photoperiod: Standard reef tank photoperiods (8–12 hours of light) are fine. Provide a gradual ramp-up and ramp-down if using LEDs to simulate dawn and dusk, which helps avoid light shock.

• Placement relative to light: It’s usually best to place Micromussa corals near the bottom or mid-levels of the tank, rather than at the very top​. On sandbeds or lower rocks, they receive gentler light. If you have very powerful lighting, consider partial shade or an overhang. Always start new Micromussa frags in lower light and acclimate slowly to brighter conditions if you intend to move them. Watch for signs of stress: bleaching (too much light) or excessive stretching and dull colors (too little light). Micromussa will often expand fully under comfortable lighting; if they remain closed tightly, lighting (or another parameter) may be an issue.

  
  

Keep in mind that Micromussa contain symbiotic zooxanthellae algae in their tissues, which provide energy via photosynthesis. However, they are not as light-demanding as many small-polyp stony (SPS) corals. When in doubt, err on the side of slightly lower light, as Micromussa can be “light-sensitive.” Always monitor their coloration – faded or scorched-looking tissue indicates too much light, whereas browned-out colors might indicate both excessive light (zooxanthellae density increasing) or high nutrients. Proper balance of light and nutrients will yield the best coloration.

Flow Requirements and Placement in the Aquarium

Micromussa corals have large, fleshy polyps that do not tolerate strong, direct water flow. In their natural habitat, they are often found in sheltered reef areas with gentle currents. Providing the right flow in your tank is important for their health:

• Water Flow: Low to moderate, random flow is ideal. Avoid direct, laminar blasts of water at the coral. Strong flow can cause the fleshy polyps to retract or even tear the tissue​. A Micromussa should gently sway or have slight movement of its tentacles when extended, but it should not appear flattened or have its flesh whipping around. High flow can also prevent the coral from capturing food. For example, turbulent or direct powerhead flow may keep its feeding tentacles retracted, inhibiting its ability to eat​.

• Aim for enough flow to keep the coral clean (prevent debris from settling on it) but not so much that the polyps cannot fully inflate. Often, placing Micromussa in a low-flow corner or in the “shadow” of rocks (where flow is diffused) works well. If using wavemakers, set them to a gentle pulsing or reef crest mode rather than constant blast.

• Placement: Micromussa can be placed on sand beds or lower rockwork. Many aquarists keep them on the sand (often with the frag plug or coral mounted on a small tile/rock) to allow easy relocation and to ensure they are in lower light. They also do well on rock ledges in the lower half of the tank. Just be cautious that sand particles do not regularly settle on the colony – sand can irritate the tissue if a sand bed is very close and gets stirred up onto the coral. If placed on rocks, make sure the base is flat and secure; these corals do not like falling over or being jostled by crabs. Give them space from other corals (at least a few inches), because Micromussa are capable of aggression despite their slow movement. They have sweeper tentacles (and even mesenterial filaments) that can extend at night to sting nearby corals​.

Feeding Habits and Nutritional Needs

Micromussa corals are photosynthetic (housing zooxanthellae algae) but also strongly heterotrophic feeders. They benefit greatly from direct feeding, which can boost their growth and overall health. In the wild and in aquariums, Micromussa extend feeding tentacles (sweeper tentacles) primarily at night or when they detect food in the water, indicating they are ready to capture prey.

• Feeding Response: When food is present, Micromussa polyps become very plump and their tentacles elongate. Tentacle extension is a clear sign the coral wants to feed​. In a reef tank, this often happens after the lights dim or when you add fish food or plankton to the water. Many aquarists observe their Micromussa “smelling” the food and extending feeders at the slightest hint of meal time.

• What to Feed: These corals have relatively large mouths and can ingest surprisingly sizable prey for their size. They eagerly consume meaty foods. Suitable offerings include: mysis shrimp, brine shrimp, finely chopped krill or clam, zooplankton (e.g. calanus, pods), and prepared LPS pellets or coral foods. For instance, at Top Shelf Aquatics they report success using a mixture of PE Mysis, Fauna Marin LPS pellets, and Benepets (a powdered coral food)

• Feeding Frequency: Micromussa can be fed 2–3 times per week for optimal growth​. They do not need daily feeding, but regular target feeding accelerates growth, encourages new polyp buds, and maintains vibrant coloration. In my experience, consistent feeding is essential for their continued health, growth, and coloration​. Corals that are well-fed tend to keep their bright pigments and recover faster from stress. Be careful not to overfeed to the point that water quality suffers – always ensure proper filtration to remove the excess nutrients that heavy feeding introduces​. A good routine is spot-feeding a few polyps at a time and watching the coral ingest the food over a few minutes. After feeding, you may turn off pumps briefly to let them eat, then resume flow to carry away any leftovers.

• Nutritional Supplements: In addition to foods, Micromussa require balanced reef chemistry to supply the building blocks for their skeleton and tissue. Make sure your calcium, alkalinity, and magnesium are in range (as discussed in Water Parameters). Trace elements such as strontium, iodine, and iron can also be important, though these are usually replenished with regular water changes. If you run an ultra-low nutrient system, you might need to dose trace elements separately. Some reef keepers dose amino acid supplements, which can help coral tissue growth and coloration. While not strictly necessary, these can benefit LPS corals in nutrient-poor tanks by providing additional organic nutrients. Monitor your coral’s reaction – well-fed Micromussa will appear full, with fleshy, inflated polyps, and will display open mouths waiting for food. Pale or shrunken polyps could indicate hunger or lack of nutrients.

Remember that Micromussa corals have dual energy sources: photosynthesis and feeding. They can survive on light alone (thanks to their symbiotic algae), but feeding unlocks their full potential. A combination of good lighting (for baseline energy) and periodic feeding (for extra nutrition) will yield the best growth rates. Many aquarists find feeding these corals to be one of the most enjoyable aspects of their care – Micromussa often put on a dramatic display when catching food, showing off vibrant colors and swaying tentacles as they pull prey into their central mouths​.

Propagation Methods (Fragging and Reproduction)

Micromussa corals can be propagated in captivity through fragmentation (fragging) and, less commonly, through sexual reproduction (spawning).

• Fragging (Asexual Propagation): Micromussa, especially M. lordhowensis, are considered fragile-looking but actually quite durable when it comes to cutting. They grow as colonies of many individual polyps connected by a calcium carbonate skeleton. Frags can be made by cutting through this skeleton between polyps. The preferred method is to use a diamond band saw or Dremel with a diamond blade, as this provides a clean cut with minimal pressure on the coral​. It’s important to cut between polyp centers, along the skeletal ridges, to avoid damaging the fleshy polyp mouths​. With a steady hand, one can cut the colony into smaller sections, each containing one or several polyps. If a saw is not available, sturdy bone-cutting forceps can snap the skeleton, though this is less precise and may cause more collateral damage. Safety precautions are advised: wear gloves (both to protect yourself from coral mucus/bacteria and to keep the coral clean) and eye protection​. because cutting LPS corals can squirt water or tiny fragments. After cutting, mount the frag onto a plug or rock using reef-safe super glue or epoxy putty​. Finally, dip the fresh frags in an iodine-based coral dip to prevent infection​. An iodine solution (per bottle instructions) will help sterilize any cut edges and tissue, reducing the chance of bacterial invasion into the wound. Place the new frags in a quarantine or low-stress area of the tank with low flow for a day, then gradually increase flow. Good water flow is crucial during healing as it brings oxygen and removes slime/algae from the cut site​. Over the next days to weeks, the cut edges will heal and new tissue will grow over exposed skeleton. Micromussa frags, if healthy, usually heal well and start growing new mouths over the cut within a couple of weeks under proper conditions. Regular feeding can expedite recovery and growth of the frags. Each fragment will continue to bud new polyps as it grows out, eventually forming another colony.

• Sexual Reproduction (Spawning): In nature, Micromussa corals are known to reproduce sexually by spawning. Micromussa lordhowensis, for example, is a hermaphroditic broadcast spawner​. This means each colony produces both eggs and sperm and releases them into the water column during spawning events. The gametes unite to form larvae (planulae) that drift with the plankton. Remarkably, M. lordhowensis larvae have been observed to survive and remain free-swimming for up to 78 days before settling​. This long larval period allows them to disperse widely in the ocean. Upon finding a suitable substrate, the larvae metamorphose into a primary polyp and start a new colony. In home aquariums, sexual reproduction is rarely observed – it requires conditions that mimic natural spawning cues (temperature cycles, lunar cycles, etc.). There are few reports of successful coral spawning in captivity for large-polyp corals, and raising the larvae is challenging. However, as captive breeding techniques advance, it’s possible that aquarists may one day induce and raise Micromussa from spawn. For now, fragmentation is the main propagation method in the hobby.

By fragging responsibly, hobbyists can spread Micromussa corals without wild collection, contributing to sustainable reef-keeping. If you plan to cut your Micromussa, ensure the coral is healthy and expanded (not stressed) beforehand, have the right tools, and always dip afterward. Also be aware that cutting stony corals releases their slime and any toxins, so keep other corals downstream protected and run carbon in your filter after fragging to absorb any chemical cues or mucus. Given time and good care, a single polyp frag can grow into a stunning colony – patience is key, as Micromussa are not the fastest growers. Expect new buds to form at the edges of the colony over months. With ideal conditions, a healthy Micromussa might sprout several new polyps each month, but growth rates can vary. The good news is they generally won’t outgrow their space too quickly or become invasive​, so they are easy to manage in a reef tank.

Potential Pests, Diseases, and Common Health Issues

While Micromussa are relatively hardy, they can fall victim to certain pests and diseases in a reef aquarium. Early detection and intervention are important to keep your corals healthy. Below are some of the common issues and how to manage them:

• Brown Jelly Disease (BJD): This is a notorious affliction for many LPS corals, Micromussa included. Brown Jelly is essentially a bacterial/protozoan infection that causes the coral’s tissue to slough off as a brown, gelatinous mass. It often strikes after a coral has been stressed or damaged. Any LPS coral with zooxanthellae can develop “brown jelly” when severely stressed, and it’s basically the coral’s flesh rotting away in a mucus coating​. In Micromussa, you might see one or more heads suddenly turn to brown slime, often following an injury or parameter swing. Once brown jelly sets in, it can spread quickly and even infect nearby corals if the jelly drifts. Treatment: The best approach is to immediately remove the affected colony from the display tank to avoid spread​. Siphon or gently blow off the jelly (outside the tank) and perform an iodine or broad-spectrum coral dip. Often, you will have to frag off any remaining healthy heads and discard the infected parts​. Some hobbyists have experimented with antibiotics or even household cures (there are anecdotal reports of using diluted hydrogen peroxide dips). The key is that Brown Jelly usually indicates the coral was in a dire state (from some underlying cause like injury, aggression, or a big drop in water quality), so prevention is best: avoid injuring the coral, keep water quality high, and promptly blow off any debris that might cause tissue damage.

• “Pink Band” Disease: Another disease noted in Micromussa (especially “Acans”) is a pink band or pink rot that can appear on dead skeleton. Hobbyists have observed a pink cyanobacterial film that invades the coral’s base after tissue loss​. It’s thought to be a burrowing cyanobacteria that infects the skeleton and leaves a pink coloration once a head has died​. Unfortunately, like brown jelly, there is no surefire cure once it takes hold; it’s a sign the coral’s health had declined. The best practice is similar – remove and quarantine the affected pieces, and consider discarding severely infected parts to protect other Micromussa in the tank​. Maintaining excellent flow and low detritus accumulation can help prevent such bacterial or cyanobacterial infections from gaining a foothold.

• Pest Flatworms and Nudibranchs: Unlike some corals (like Acropora or Montipora) which have specific pest flatworms or nudibranchs, Micromussa are not known for a dedicated obligate pest species. However, generalist pest flatworms (e.g. red planaria) can sometimes irritate them by covering the tissue and blocking light. If you see small rust-colored flatworms on or around your Micromussa, consider doing a dip to knock them off.

• Vermetid Snails: Vermetid snails are a common reef tank pest – they are stationary tube snails that cast sticky mucus webs to catch food. These mucus nets can settle on corals and irritate them continually. Micromussa polyps may remain retracted if a vermetid snail’s web is constantly draping over them. If you notice thin mucus strings on your Micromussa, check for a spiral snail tube in the vicinity. Removal of vermetid snails (by breaking their tubes and sealing with glue or epoxy) is recommended, as their presence can lead to chronic inflammation of coral tissue. Some aquarists dose certain medications (like praziquantel or fenbendazole in a separate treatment tank) to eliminate vermetids, but manual removal is most common. A natural predator to vermatids often found in the hobby are Bumble Bee Snails

• Other Issues (Tissue Recession and Polyp Bail-Out): Sometimes a Micromussa will start to recede – the fleshy polyp shrinks and pulls back, exposing the white skeleton edges. This tissue recession can be caused by stress such as sudden temperature changes, alkalinity spikes, or aggression from a neighboring coral. If you notice recession, check all water parameters and look for any brown jelly onset. You might save the coral by cutting off affected heads and dipping the remaining colony in an antiseptic coral dip. Polyp bail-out (where the coral polyp detaches from the skeleton) is a very rare last-resort response to stress. The free-living polyp generally doesn’t survive long or reattach, so it’s indicative of severe distress.

Preventive measures: The best way to avoid pests and diseases is to quarantine and dip new coral additions. Many Micromussa issues come from introducing a new frag that harbors unseen pests or bacteria. Using a proper coral dip (iodine, peroxide at correct dilution, or commercial pest dip solutions) will eliminate most hitchhikers like flatworms and snails​. Inspect the coral for eggs (some pests lay tiny egg clusters that dips won’t kill) and scrape them off. Maintain good tank husbandry: stable water quality, moderate flow to prevent sediment buildup on corals, and avoid injuring the coral during maintenance. Running activated carbon can remove toxins (like allelopathic chemicals from nearby soft corals or the mucus from a distressed coral) which might otherwise weaken Micromussa. Lastly, keep an eye on tank inhabitants: certain fish can be “pests” too – angelfish, butterflyfish, and some wrasses are known to nip at fleshy LPS polyps. If your Micromussa is mysteriously retracting or losing flesh, observe at different times of day to see if a fish or shrimp is picking at it. Peppermint shrimp, for instance, sometimes irritate corals while stealing food from them.

By being vigilant and responding quickly to problems, you can usually save a Micromussa from most ailments. A healthy Micromussa will have full, puffy polyps, good coloration, and will extend tentacles at feeding time. A stressed or ill one will look deflated, may have discoloration or slime, and will not feed readily. Address issues as soon as noticed, and don’t hesitate to seek advice from experienced reef keepers if you encounter an unfamiliar problem.

In summary, keeping Micromussa corals successfully comes down to patience and attentiveness. They are not extremely demanding, but they respond best when you fine-tune their environment: gentle light, gentle flow, regular feeding, and a calm neighborhood in the tank. Both beginners and seasoned reefers enjoy Micromussa: beginners appreciate their hardiness and beautiful appearance at moderate cost, while advanced hobbyists often collect high-end color morphs (“Ultra” or “Holy Grail” Micromussa) and grow them out. As of 2016, we might have to get used to calling them Micromussa instead of Acanthastrea, but by any name they remain a colorful centerpiece LPS. With the guidelines above, aquarists can provide the proper care for Micromussa corals and enjoy their slow but steady growth and ever-changing kaleidoscope of colors in the reef tank.