Acan Coral Care Guide: Complete Acanthastrea & Micromussa Care

If you're diving into the world of Large Polyp Stony (LPS) corals, you've probably encountered the term "acan coral" and noticed some confusion around what exactly these corals are. I've been keeping and studying these fascinating corals for years, and the taxonomic changes that occurred in 2016 still create confusion today. Let me clear things up and give you everything you need to know about successfully keeping these beautiful corals.

Acan corals, traditionally referring to the genus Acanthastrea, have undergone significant reclassification in recent years. What we used to call "Acan Lords" are now scientifically classified as Micromussa lordhowensis, while true Acanthastrea species like A. echinata remain in their original classification. This guide will cover both groups, as they share similar care requirements while having distinct characteristics that every reef keeper should understand.

Whether you're a beginner looking for your first LPS coral or an experienced reefer wanting to understand the latest scientific classifications, this comprehensive guide will provide you with the knowledge needed to successfully maintain these stunning corals in your reef aquarium.

Understanding the Taxonomic Reclassification: Acanthastrea vs. Micromussa

The coral hobby experienced a significant shift in 2016 when molecular studies by Huang and colleagues led to major taxonomic revisions. What most reef keepers called "Acan Lords" (previously Acanthastrea lordhowensis) were reclassified into the genus Micromussa. This wasn't just a simple name change – it reflected fundamental genetic differences discovered through advanced DNA sequencing techniques.

True Acanthastrea species, like Acanthastrea echinata (commonly called "Acan Echinata"), remain in the Lobophylliidae family and kept their original classification. These corals are characterized by their larger corallites, more pronounced septal teeth, and generally more aggressive feeding response. Understanding this distinction helps explain why different "acan" species sometimes behave differently in our reef tanks.

Micromussa species, including the popular M. lordhowensis and the smaller M. amakusensis, belong to the same family but exhibit different growth patterns and skeletal structures. These corals typically have smaller, more numerous polyps that form dense colonies with a more uniform appearance. The reclassification wasn't arbitrary – it was based on significant skeletal and genetic differences that scientists had overlooked for decades.

For practical reef keeping purposes, both genera share similar care requirements, which is why the hobby continues to group them under the informal "acan" umbrella. However, understanding the scientific distinction helps explain variations in growth rates, aggression levels, and feeding behaviors you might observe between different species.

Physical Characteristics and Species Identification

Identifying acan corals correctly starts with understanding their distinctive physical features. True Acanthastrea species display large, fleshy polyps that can extend significantly beyond their skeletal base. Each polyp typically measures 10-15mm in diameter, with A. echinata polyps sometimes reaching 20mm when fully expanded. The tissue is thick and often displays vibrant coloration with distinct oral discs that contrast with the surrounding tissue.

Micromussa lordhowensis, our former "Acan Lord," presents smaller polyps averaging 8-12mm in diameter. These polyps pack more densely together, creating that characteristic "brain coral" appearance that made them so popular in the hobby. The tissue tends to be slightly less fleshy than true Acanthastrea, but the color variations are equally stunning, ranging from deep reds and oranges to electric greens and rainbow combinations.

The smallest of the group, Micromussa amakusensis (formerly Acanthastrea bowerbanki), features polyps typically under 8mm in diameter. These create incredibly dense colonies with a almost carpet-like appearance when viewed from above. Their smaller size doesn't diminish their beauty – they often display some of the most intense coloration in the entire group.

Skeletal structure provides the most reliable identification method. Acanthastrea species have larger, more widely spaced corallites with prominent septa (the blade-like structures radiating from the center). Micromussa species show smaller, more closely packed corallites with less pronounced septal teeth. When examining your coral, look at the areas where tissue has receded or between polyps to observe these skeletal features.

Color morphs add another layer of complexity to identification. Both genera can display remarkable color variations including the coveted "rainbow" morphs with multiple colors in a single colony, solid color variants in deep reds or oranges, and two-toned specimens with contrasting oral discs. These color variations don't indicate different species but rather represent the natural diversity within each species, often influenced by collection location and depth.

Natural Habitat and Distribution

Understanding where acan corals naturally occur provides valuable insights for replicating optimal conditions in our aquariums. Both Acanthastrea and Micromussa species inhabit the Indo-Pacific region, with distributions spanning from the Red Sea to Australia's eastern coast. They typically colonize reef slopes and lagoons at depths ranging from 5 to 30 meters, though some specimens have been collected from depths exceeding 40 meters.

In their natural environment, these corals often settle in areas with moderate water movement and partial shading from branching corals above. This positioning protects them from intense midday sun while still providing adequate light for their zooxanthellae. The water clarity at these depths means they receive predominantly blue spectrum light, which explains their excellent response to LED lighting systems emphasizing blue wavelengths.

Acanthastrea echinata shows a preference for slightly turbid waters with higher nutrient levels, often found on reef slopes exposed to oceanic currents. These locations provide regular food sources in the form of zooplankton and organic particles. This natural feeding opportunity explains why these corals benefit significantly from supplemental feeding in captivity.

Micromussa lordhowensis, despite its name suggesting Lord Howe Island origins, actually has a broader distribution throughout the Western Pacific. These corals often inhabit protected reef areas with lower flow rates, growing on rock substrates or dead coral skeletons. They frequently form large colonies in areas where competition from faster-growing corals is limited.

Temperature ranges in their natural habitats typically fluctuate between 75-82°F (24-28°C), with seasonal variations that these corals have adapted to handle. This natural temperature tolerance makes them relatively hardy in well-maintained reef aquariums, though stability remains more important than hitting exact numbers.

Essential Water Parameters for Optimal Health

Maintaining stable water parameters is crucial for acan coral health and coloration. I've found these corals to be relatively forgiving compared to SPS species, but consistency remains key. Temperature should stay between 76-80°F (24.5-26.5°C), with daily fluctuations kept under 2°F. Sudden temperature changes stress these corals more than gradual seasonal adjustments.

Salinity should maintain at 1.024-1.026 specific gravity (34-35 ppt), matching natural seawater levels. These corals tolerate brief salinity fluctuations better than many SPS corals, but extended periods outside this range will cause tissue recession. I recommend checking salinity with a calibrated refractometer rather than hydrometers for accuracy.

Alkalinity levels between 8-11 dKH support steady growth without pushing these slow-growing corals too hard. Higher alkalinity can work, but I've observed better coloration and polyp extension at moderate levels around 8.5-9.5 dKH. Stability matters more than the exact number – daily swings exceeding 1 dKH will stress these corals.

Calcium should remain between 400-450 ppm, with magnesium at 1250-1350 ppm to maintain proper calcium and alkalinity balance. These corals don't consume calcium rapidly like SPS corals, but maintaining appropriate levels ensures steady skeletal growth. Test these parameters weekly and adjust dosing accordingly.

Nitrate and phosphate levels deserve special attention with acan corals. Unlike the ultra-low nutrient systems required for some SPS corals, acans thrive with detectable nutrients. Nitrates between 5-20 ppm and phosphates at 0.03-0.10 ppm promote vibrant coloration and robust tissue. Zero nutrients often lead to pale, slowly receding colonies.

pH should maintain between 8.0-8.4, with the natural daily fluctuation between night and day readings. These corals handle the lower end of this range well, making them suitable for systems without aggressive pH management. However, chronically low pH below 7.8 will impair calcification and growth.

Lighting Requirements: Finding the Sweet Spot

Lighting plays a crucial role in acan coral health, growth, and coloration. These corals thrive under moderate lighting conditions, typically requiring 50-150 PAR (Photosynthetically Active Radiation) for optimal results. I've successfully maintained colonies at PAR levels ranging from 30 to 200, but the sweet spot for most specimens falls between 75-125 PAR.

LED lighting systems work exceptionally well for acan corals, particularly those with adjustable spectrum control. These corals respond beautifully to heavy blue spectrum lighting (420-480nm) supplemented with some white and red wavelengths for optimal coloration. The popular blue-heavy settings that make corals fluoresce also provide the wavelengths these corals utilize most efficiently.

Acclimation to new lighting conditions requires patience. When introducing new acan corals, start them at the bottom of your tank or in shaded areas receiving 30-50 PAR. Over 3-4 weeks, gradually move them to their final position. Sudden exposure to high light causes tissue recession and bleaching that can take months to recover from, if at all.

Photoperiod should mimic natural conditions with 8-10 hours of peak lighting daily. I run a gradual ramp-up and ramp-down schedule over 12 hours total, with 8 hours at peak intensity. This approach reduces stress while providing adequate photosynthesis time. Some keepers report success with even shorter photoperiods of 6-7 hours at peak intensity.

Different color morphs may prefer slightly different lighting intensities. Rainbow and multi-colored specimens often display best coloration at moderate light levels (75-100 PAR), while solid red or orange morphs can handle slightly higher intensities (100-150 PAR) without color loss. Green variants typically prefer the lower end of the spectrum (50-75 PAR) to maintain their vibrant coloration.

Watch for signs of inappropriate lighting: tissue recession starting from the center indicates too much light, while stretching tissue and pale coloration suggest insufficient lighting. Polyps that remain retracted during peak lighting hours often signal excessive intensity. Adjust placement or lighting intensity based on these visual cues rather than strict PAR numbers.

Water Flow and Placement Strategies

Proper water flow significantly impacts acan coral health, feeding efficiency, and growth patterns. These corals prefer low to moderate flow that's enough to keep detritus from settling on their tissue but not so strong that polyps remain retracted. I've found that indirect, randomized flow patterns work best, avoiding direct powerhead streams that can damage delicate tissue.

Ideal flow creates gentle polyp movement without causing the tissue to ripple or fold over itself. You're looking for that sweet spot where polyps sway gently and feeding tentacles can extend without being blown flat. This typically translates to flow rates where you can see gentle movement but polyps maintain their expanded dome shape.

Placement within your aquarium should consider both flow and lighting requirements while accounting for aggressive feeding responses. Position acan corals on stable rockwork or the sandbed, ensuring they won't shift during maintenance or from flow changes. Leave 3-4 inches between different acan colonies and 4-6 inches from other LPS corals to prevent aggression issues.

Lower tank positions often work best for beginners, as these areas typically receive appropriate lighting and flow levels. As you gain experience with your specific specimens, you can experiment with positioning. Some advanced keepers successfully maintain acans in higher flow areas by gradually acclimating them over several months.

Consider creating dedicated acan gardens in lower flow zones of your tank. Grouping compatible specimens together not only looks stunning but simplifies feeding and reduces aggression concerns with other coral types. Just maintain adequate spacing between colonies to prevent warfare between even same-genus specimens.

Feeding Techniques and Nutritional Requirements

While acan corals host zooxanthellae for photosynthetic nutrition, supplemental feeding dramatically improves growth rates, coloration, and overall health. These corals are aggressive feeders with powerful feeding responses, readily accepting a variety of foods. I feed my colonies 2-3 times per week, though some aquarists report success with daily feeding of smaller amounts.

Ideal food sizes range from 0.5-5mm, with most acan species preferring particles around 1-2mm. Suitable foods include frozen mysis shrimp, brine shrimp, cyclops, and rotifers. High-quality prepared coral foods like Reef Roids, Coral Frenzy, and Benepets also work excellently. I've observed the best growth rates when rotating between different food types to provide varied nutrition.

Feeding technique matters as much as food selection. Turn off flow pumps to prevent food from being swept away, then use a turkey baster or feeding pipette to gently deposit food directly onto the coral's oral disc. Watch for feeding tentacles to emerge – this usually happens within 30 seconds to 2 minutes after food introduction. These tentacles are surprisingly effective at capturing and directing food to the mouth.

For broadcast feeding, dissolve prepared coral foods in tank water and pour the mixture into a low-flow area near your acan colonies. This method works well for feeding multiple colonies simultaneously but requires more food and can impact water quality if overdone. Monitor nutrient levels when broadcast feeding regularly.

Target feeding individual polyps yields the best results for growth and coloration. Using a syringe or pipette, place one or two pieces of food directly on each polyp's oral disc. The polyp will quickly close around the food and consume it over 20-30 minutes. This method minimizes waste and ensures each polyp receives nutrition.

Amino acid supplements can enhance coloration and tissue growth between regular feedings. Products like Red Sea's Reef Energy, Brightwell's Aminomega, or Polyplab's Reef Renu provide dissolved organic compounds that corals can absorb directly through their tissue. I dose amino acids 2-3 times per week, separate from particulate feeding.

Managing Coral Aggression and Compatibility

Acan corals pack a surprising punch when it comes to aggression. These seemingly peaceful corals possess powerful sweeper tentacles that can extend 3-6 inches at night, capable of damaging or killing neighboring corals. Understanding and managing this aggression is crucial for maintaining a harmonious reef tank setup.

True Acanthastrea species tend to be more aggressive than Micromussa species, with A. echinata capable of damaging corals several inches away. These sweeper tentacles contain powerful nematocysts that can cause significant tissue damage to other LPS and even some SPS corals. I've witnessed Acanthastrea completely eliminate neighboring Euphyllia colonies that were placed too close.

Micromussa species, while less aggressive than Acanthastrea, still require respect and proper spacing. They typically extend shorter sweeper tentacles (2-3 inches) and show less aggressive feeding responses. However, they'll still defend their territory vigorously if threatened or overcrowded.

Compatible tank mates include other LPS corals with similar aggression levels, provided adequate spacing is maintained. Hammer corals, torch corals, and brain corals can coexist with proper placement. Soft corals like leather corals and zoanthids generally keep their distance. SPS corals should be positioned well above acan colonies to avoid sweeper tentacle reach.

When planning your aquascape, position acan corals where their beauty can be appreciated but aggression won't cause problems. Islands of rock surrounded by sand create natural barriers. Elevating less aggressive corals above acans takes advantage of vertical space while maintaining safe distances.

If aggression issues arise, several interventions can help. Increasing flow around aggressive specimens can reduce sweeper tentacle extension. More frequent feeding often reduces aggressive behavior as well-fed corals expend less energy on warfare. As a last resort, fragging and relocating portions of overly aggressive colonies may be necessary.

Common Problems and Troubleshooting Solutions

Even experienced reef keepers encounter issues with acan corals occasionally. Recognizing problems early and responding appropriately can mean the difference between minor setbacks and colony loss. Here are the most common issues I've encountered and their solutions.

Tissue recession, where the coral's flesh pulls back from its skeleton, often results from poor water quality, excessive lighting, or aggression from neighboring corals. Check parameters immediately, particularly alkalinity stability and nutrient levels. Move the coral to lower light if recession starts from the center, or address flow if it begins at the edges where detritus accumulates.

Brown jelly disease, a bacterial infection causing rapid tissue necrosis, requires immediate intervention. Remove affected colonies to a quarantine tank and siphon away all diseased tissue. Treat with an iodine dip (follow product instructions carefully) and maintain pristine water quality. Some success has been reported with antibiotic treatments, though this should be a last resort in quarantine only.

Bleaching in acan corals typically indicates stress from temperature fluctuations, excessive light, or parameter swings. Unlike SPS bleaching, acans often recover if conditions improve quickly. Reduce lighting intensity, ensure stable temperatures, and maintain consistent parameters. Feed amino acids and small particle foods to support recovery.

Failure to extend polyps during daylight hours suggests environmental stress. Check for aggressive neighbors, excessive flow, poor water quality, or harassment from fish. Sometimes, colonies need several weeks to acclimate to new conditions before showing normal polyp extension. Patience and stability usually resolve this issue.

Slow or no growth despite good polyp extension often indicates insufficient feeding or inadequate nutrients. These corals grow slowly naturally, but noticeable growth should occur over 3-6 months. Increase feeding frequency, ensure detectable nitrate and phosphate levels, and verify alkalinity and calcium levels support calcification.

Color loss while maintaining good polyp extension typically points to lighting issues or nutrient imbalances. Too much light washes out colors, while insufficient light causes browning from excess zooxanthellae. Adjust positioning or lighting intensity gradually. Sometimes, increasing feeding and allowing slightly higher nutrients brings back vibrant coloration.

Propagation and Fragging Techniques

Fragging acan corals offers an excellent way to share these beautiful corals with fellow reefers or expand your collection throughout your tank. While these corals grow slowly compared to soft corals or some LPS species, successful propagation is straightforward with proper technique and patience.

Before fragging, ensure the donor colony is healthy and has been in your system for at least 3-4 months. Well-established colonies recover faster and have better survival rates for both the mother colony and frags. Feed heavily for a week before fragging to ensure the coral has adequate energy reserves for healing.

Essential tools include a sharp, clean bandsaw or Dremel with a diamond cutting disc, bone cutters for final adjustments, protective eyewear and gloves, a container with tank water for working, and super glue gel or epoxy for mounting frags. Sterilize all tools with alcohol or RO water between cuts to prevent disease transmission.

The fragging process starts with removing the colony from your display tank. Work quickly but carefully to minimize stress. For Micromussa species with tightly packed polyps, identify natural separation points between polyp groups. Cut through the skeleton between polyps, avoiding damage to the tissue. Each frag should have at least 2-3 polyps for best survival rates.

Acanthastrea species with larger, more separated polyps can be fragged into single-polyp pieces, though multi-polyp frags establish faster. Use a bandsaw or Dremel to cut through the skeleton, keeping cuts as far from living tissue as possible. The skeleton is surprisingly hard, so take your time and let the tool do the work.

After cutting, rinse frags in tank water to remove debris and inspect for tissue damage. Dip frags in an iodine solution (following product guidelines) to prevent infection. Mount frags on plugs or rubble rock using super glue gel or epoxy, ensuring good contact between skeleton and mounting surface.

Place new frags in a lower flow, moderate light area of your tank for recovery. Most frags begin showing polyp extension within 24-48 hours if healthy. Maintain stable parameters and offer small foods after a few days. Full tissue regrowth over cut areas typically takes 2-4 weeks.

Selecting Healthy Specimens: What to Look For

Choosing healthy acan corals sets the foundation for success in your reef tank. When evaluating potential purchases, whether online or at local fish stores, several key indicators separate thriving specimens from problematic ones.

First, examine tissue coverage and inflation. Healthy acans display full, puffy tissue that extends well beyond the skeleton. The tissue should look inflated and fleshy, not stretched thin or receding. Avoid specimens showing any exposed skeleton, particularly at the base or between polyps, as this indicates stress or tissue recession.

Coloration should appear vibrant and consistent across the colony. While some color variation is normal, especially in rainbow morphs, watch for bleached spots or unusually pale areas that might indicate lighting stress or disease. Deep, rich colors typically indicate a healthy, well-adjusted coral.

Polyp behavior provides excellent health indicators. In the store's display tank, polyps should show some extension even under retail lighting. While full extension might not occur in store conditions, completely retracted polyps suggest stress. If possible, observe the coral during feeding time – healthy specimens show immediate feeding responses.

Check for signs of pests or disease. Brown jelly infections, tissue necrosis, or unusual film on the tissue are immediate red flags. Look closely for flatworms, which appear as small, rust-colored ovals on the tissue. Acan-eating flatworms can quickly destroy entire colonies if introduced to your system.

When buying online, request multiple photos under different lighting conditions. White light photos reveal true tissue condition and coverage, while blue light shots showcase fluorescence. Ask about the coral's history – how long has it been in captivity, what conditions has it been kept under, and has it been fragged recently?

Consider starting with aquacultured specimens when possible. These corals are already adapted to aquarium conditions and typically prove hardier than wild-collected pieces. They also support sustainable reef keeping practices while often displaying unique color morphs not found in wild populations.

Integration with Reef Tank Ecosystems

Successfully integrating acan corals into your existing reef ecosystem requires understanding their role and relationships within the larger system. These corals contribute to the biological balance while competing for resources and space with other inhabitants.

In terms of coral compatibility, acans coexist well with many popular reef inhabitants when properly placed. They serve as excellent middle-ground corals, bridging the gap between aggressive species like hammer corals and peaceful ones like zoanthids. This positioning makes them valuable for creating transitions in mixed reef aquascapes.

Fish compatibility generally proves straightforward, as most reef-safe fish ignore acan corals. Tangs, wrasses, gobies, and cardinals make excellent tank mates. However, some species require caution. Angelfish, particularly dwarf angels, may nip at acan tissue. Butterflies should be avoided entirely. Some dottybacks and larger clownfish can irritate these corals through excessive hosting behavior.

Invertebrate interactions vary by species. Cleaner shrimp and peppermint shrimp typically leave acans alone, though they may steal food during feeding time. Hermit crabs and snails pose no threat and help maintain cleanliness around colonies. However, maintain caution with emerald crabs, which occasionally damage coral tissue when hungry.

These corals contribute to nutrient cycling by consuming dissolved organics and particulate matter, helping maintain water quality. Their feeding activities remove excess nutrients that might otherwise fuel algae growth. This makes them particularly valuable in systems with higher bioloads or heavy feeding regimens.

Consider the allelopathic effects – chemical warfare between corals. While less pronounced than with soft corals, acans do release compounds that can affect nearby corals. Activated carbon usage and regular water changes help minimize these effects. Protein skimming also removes these compounds along with other organic waste.

Frequently Asked Questions About Acan Coral Care

Conclusion: Mastering Acan Coral Care

Acan corals, whether true Acanthastrea or reclassified Micromussa species, offer reef keepers a perfect blend of beauty, personality, and manageable care requirements. These LPS corals bridge the gap between beginner-friendly soft corals and demanding SPS species, making them ideal for aquarists ready to advance their reef keeping skills.

Success with these corals comes from understanding their natural history and requirements rather than following rigid rules. Every reef system is unique, and these adaptable corals often thrive in conditions slightly outside the "ideal" ranges when stability is maintained. Pay attention to your specific specimens' responses and adjust care accordingly.

The taxonomic reclassification, while initially confusing, actually helps us better understand why different "acan" species behave differently in our tanks. This scientific accuracy, combined with practical experience from the reef keeping community, provides a solid foundation for success with these remarkable corals.

Whether you're drawn to the large, vibrant polyps of Acanthastrea echinata or the dense, colorful colonies of Micromussa lordhowensis, these corals reward patient aquarists with stunning displays and interesting feeding behaviors. Their moderate care requirements and compatibility with many reef inhabitants make them valuable additions to most reef aquariums.

As you embark on your journey with acan corals, remember that patience and consistency trump perfection. These slow-growing corals take time to establish and show their true colors, but the wait is worthwhile. With proper care, your acan colonies will become centerpiece corals that draw admiration from every visitor to your reef.

The reef keeping hobby continues evolving as our scientific understanding improves and collective experience grows. By staying informed about developments like taxonomic updates while maintaining proven husbandry practices, we can provide our acan corals with environments where they don't just survive but truly thrive. Your dedication to understanding these fascinating corals contributes to the broader knowledge base that helps all reef keepers succeed.