Zoanthid Coral Taxonomy and Aquarium Care

 Zoanthids are colonial cnidarian corals known for their dazzling colors and rapid growth. They belong to the order Zoantharia (also called Zoanthidea), within the subclass Hexacorallia (same group as stony corals and anemones)​. There are dozens of described zoanthid species – historically over 300 were named, though later taxonomic revisions reduced the number of distinct species to around 60 accepted species​. In general, zoanthids resemble small sea anemones, forming mats or colonies of individual polyps on reef surfaces​. They are extremely popular in reef aquariums for their hardy nature and stunning variety of color morphs​

Zoanthid Coral Taxonomy and Genera

In taxonomy, zoanthids are grouped into several families and genera based on their morphology. All zoanthids have a cylindrical polyp body with tentacles around the margin of the oral disc. Unlike stony corals, they have no hard skeleton, and many species (Palythoa, Protopaly) incorporate sand or sediment into their tissues for support

. The most commonly encountered zoanthid genera in the hobby include:

• Zoanthus – Typically small “button polyps” forming colorful encrusting mats. Zoanthus species (often called “zoas”) usually have smaller polyps and do not embed sand in their flesh​

  
  

  . Examples include Zoanthus sociatus and Zoanthus gigantus, known for neon colors.

• Palythoa – Generally larger polyps often containing sand in their base and oral disc (giving a rough texture)​

  
  

  . Palythoa (and the closely related Protopalythoa) include species like Palythoa grandis, which can reach 1–3 inches across and is infamous for strong toxins​

  
  

  . Hobbyists often refer to big polyps as “palys.” Because of this many Zoanthus gigantus are often mislabled as a Paly

  
  

• Parazoanthus – Colonial zoanthids often associated with other organisms. For instance, Parazoanthus gracilis (the common yellow polyps) grows long stems with bright yellow polyps. They usually lack zooxanthellae or have fewer, and some live commensally on sponges or gorgonians​

  
  

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• Isaurus – Unusual genus sometimes called “snake polyps.” They have elongated, tube-like polyps that retract into a leathery tube. Less common in the trade, they resemble braided stalks.

  
  

• Other genera: There are many other zoanthid genera (e.g. Epizoanthus, Acrozoanthus, Savalia, etc.), especially in deep-water or symbiotic niches​. Many of these are not found in the Hobby ecosystem.

  It’s worth noting that zoanthid taxonomy is complex and still evolving; many color “morphs” in the aquarium trade are simply variants of a few species, and distinguishing species can be difficult without genetic analysis​. Many color morphs have had additional names given to them (bam bam, seduction, scrambled eggs, fruit loops) to distinguish the unique color patterns from others. Those names will be discussed in a different post.

  
  
  
  

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Water Parameters for Zoanthids

Zoanthids thrive in stable, reef-like water conditions. They are tolerant of a range of parameters but do best within natural seawater levels​

• Temperature: ~72–78 °F (22–26 °C). Aim for a stable temperature around the mid-70s °F​

  . Like most corals, zoanthids prefer stability; avoid swings larger than 1–2°F​

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• Salinity: Specific gravity around 1.025–1.026 (35 ppt)​

  , matching natural seawater. Sudden changes in salinity can stress zoas, so top off evaporation and perform water changes carefully.

• pH: Keep pH between 8.0 and 8.4​

  . Adequate gas exchange and use of buffer (if needed) help maintain this range. Refugium with reverse light cycle can also stabilize this quite a bit

• Alkalinity: 8–10 dKH is a good target​

  . Zoanthids don’t build calcium carbonate skeletons, but a stable alkalinity within 7–11 dKH supports overall coral health​

• Calcium and Magnesium: Around 420 ppm Ca and 1300 ppm Mg (natural levels)​

  . While zoas themselves don’t uptake much calcium, these levels indicate good overall water quality for a reef tank.

• Nutrients (Nitrate & Phosphate): Avoid ultra-low nutrients. Zoanthids actually appreciate some dissolved nutrients. Aim for nitrates in the roughly 1–10 ppm range and phosphates around 0.01–0.05 ppm​

  
  

  They generally do not fare well in tanks with zero detectable nitrate – a small amount (e.g. 3–7 ppm nitrate) is ideal for color and growth​

  
  

  However, very high nutrients (nitrate >20–30 ppm or phosphate >0.1 ppm) can lead to algae issues and sluggish growth​. In general, zoanthids are forgiving and can handle “dirtier” water better than many hard corals, but it's best to keep nutrients moderate and stable.

Consistency is more important than chasing exact numbers. Regular water changes and monitoring will help keep parameters in range. Zoanthids can survive less-than-perfect conditions, but abrupt swings in temperature, salinity, or other parameters often cause them to close up or “melt” (disintegrate)​

Lighting Requirements

Zoanthids contain symbiotic algae (zooxanthellae) and thus require moderate to strong lighting for photosynthesis. In the wild, many zoanthids are found in shallow reefs under intense tropical sunlight, yet others inhabit dimmer areas – so they can adapt to a range of light levels. In aquariums, moderate light intensity is usually ideal, but they tolerate up to high light if acclimated properly​

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• Intensity: As a guideline, medium reef lighting (~100–200 PAR) often works well. For example, around 150 PAR is a “sweet spot” that many zoa colonies thrive in​

  Under higher light, their colors may become more vibrant, but excessive light can cause bleaching or the polyps to stay closed​

  If lighting is too low, zoanthids may stretch their stalks (“reach”) toward the light or turn brown due to increased zooxanthellae density​

• Type: Zoas grow well under a variety of lighting types – LED, T5 fluorescents, or metal halides have all been used successfully​. Many reef keepers use broad-spectrum LEDs which can be tuned for color. A blue-rich spectrum will make their fluorescence pop, but a balance of wavelengths supports health.

• Photoperiod: A standard reef tank photoperiod (8–10 hours of full light) is sufficient. They appreciate a regular day/night cycle.

• Acclimation: Always acclimate zoanthids to new lighting slowly​

  If you upgrade to stronger lights or move a colony higher in the tank, start with shorter photoperiods or lower intensity and gradually increase. Sudden jumps in light can stress zoas, leading to bleaching (loss of color) or refusal to open​

  
  

Many zoanthids will indicate their lighting comfort by their behavior: if a colony’s polyps remain open and color is good, the lighting is acceptable. Watch for warning signs like persistent gaping (overly open and thin) which could indicate insufficient light, or a pale/washed-out look indicating too much light. Adjust placement in the tank accordingly – higher up for light-loving varieties, or shaded lower spots for more light-sensitive varieties. Overall, zoanthids are not as light-demanding as some SPS corals, but good lighting will encourage them to spread and show their best colors.

Flow Requirements

Proper water flow is important to keep zoanthid corals healthy. They prefer a moderate, turbulent flow in most cases:

• Moderate Flow: In nature zoanthids often experience gentle surges. In a tank, moderate flow helps carry away waste and brings food and nutrients to the colony​

• Avoid Excessive Flow: If the flow is too strong or direct, zoanthid polyps may stay closed to protect themselves​. Constant strong blast can cause them to retract and eventually weaken. Signs of too much flow include the polyps remaining tightly shut or appearing pinched.

• Avoid Stagnant Spots: Too little flow can allow detritus to settle on the colony and lead to algae or bacterial growth around the polyps. Low flow may also deprive them of nutrition. In still water, zoas might accumulate slime or debris. You can solve this problem with a quick blast of a turkey baster.

• Variable Flow Best: Use wavemakers or alternating currents to create a varied flow. This ensures all sides of the colony get circulation. Aiming a powerhead indirectly (bounce off a wall or rock) usually creates a gentler random flow rather than pointing it straight at the zoas.

In practice, placing zoanthids in areas of the tank with low-to-moderate current works well. For example, they often do well on the lower half of the rockwork where flow is present but not as intense as near pumps. Observe the colony: if you see a thin film on them or debris collecting, increase flow slightly; if they remain closed and refuse to open for long periods, consider reducing flow or moving them to a calmer spot. Striking the right balance will keep them open and clean, enhancing their growth.

Feeding Habits and Supplementation

Zoanthids derive most of their nutrition from photosynthesis via their symbiotic algae, but they can also ingest food particles. In general, they do not require direct feeding – healthy zoas can get by on light and the nutrients available in the water​. However, supplemental feeding can boost growth and coloration if done carefully:

• Target Feeding: Many aquarists choose to occasionally feed zoanthids with fine particulate foods. They will accept micro-plankton, brine shrimp nauplii, rotifers, Reef-Roids, Benepets or other coral powders, etc.​

  Using a turkey baster or pipette to gently squirt food onto the polyps can elicit a feeding response – the polyps may close around the food. Not all zoas respond dramatically, but some larger palythoa will readily eat meaty bits. You can also broadcast the food into the water column and turn off return pumps and filtration for 5-10 mins

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• Feeding Frequency: Feed sparingly – perhaps once or twice a week at most. Overfeeding can foul water quality quickly, leading to algae and bacterial issues that harm the zoas​. Since they don’t need much, it’s better to under-feed than over-feed.

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• Nutrient Absorption: Even without direct feeding, zoanthids can absorb dissolved nutrients from fish food and waste in the water. They tend to thrive in tanks that aren’t too “nutrient poor.” A lightly dirty tank (with detectable nitrate/phosphate) essentially feeds zoanthids in part​

  
  

• Trace Elements: Regular water changes with a good salt mix usually replenish trace elements. One element often noted for zoanthids is iodine. Zoanthids are thought to utilize iodine, and in systems with many zoas, iodine can become depleted​. Some experienced keepers dose an iodine supplement to encourage growth (caution: overdose of iodine can be harmful, so test levels if dosing). Generally, if you observe slowed growth or dull color, checking iodine and other trace elements may be worthwhile. Otherwise, a balanced reef supplement regime (calcium, alkalinity, magnesium in line, plus minor elements via water changes) is sufficient.

  
  

• Amino Acids/Vitamins: There are reef additive products containing amino acids or vitamins that corals, including zoanthids, might benefit from. While not essential, some hobbyists report improved polyp extension and color when dosing these occasionally​. Use such supplements cautiously and observe for any positive or negative reactions.

  
  

Propagation Methods

One reason zoanthids are beloved in the hobby is that they are easy to propagate. They naturally reproduce asexually by budding new polyps and spreading over rocks​

• Natural Spreading: In a healthy tank, a zoanthid colony will grow and spread on its own. New polyps emerge from the mat (coenosarc) or stolons that connect existing polyps​. Over time, a small frag can cover a whole rock. You can encourage spreading by placing the colony on a flat frag tile or an isolated “island” rock with space around it.

  
  

• Fragging (Cutting): Zoanthids are commonly “fragged” (fragmented) to propagate them. Using a sharp scalpel, bone shears, diamond coated Dremel blade or band saw. You can cut a section of the mat or even individual polyps from the colony. Typically, hobbyists will remove a small cluster (e.g. 3-5 polyps) by slicing the connecting mat, Then glue that piece onto a new plug or rock. They attach easily to surfaces with reef-safe super glue gel. Within a few days to weeks, the frags heal and begin growing new polyps.

• Fragging Safety: Caution: Many zoanthids, especially Palythoa, produce palytoxin, one of the most potent natural toxins​. This can be harmful or even life-threatening to humans if ingested or if it enters cuts or aerosolizes. Always wear gloves (and eye protection) when cutting or handling zoanthids, and ideally perform cutting under water or in a well-ventilated area​. Do not squeeze or squish the polyps – this can squirt toxin-laden fluid​. Never attempt to boil rocks or coral to remove zoanthids; boiling can release palytoxin into the air and has caused serious poisonings​. By using basic precautions, propagation is safe and routine.

  
  

• Techniques: When cutting zoas, many hobbyists do it submerged in a container of tank water to minimize aerosol exposure and to rinse away slime. Gently detach the mat with a blade or peel a polyp off the rock. If the zoas are on a small rock, sometimes it’s easier to use bone cutters to chip the rock beneath the polyps, then glue (Thick Cyanoacrylate) that rubble piece to a plug – this avoids directly cutting the soft tissue. Dip the frag and mother in saltwater with coral dip like iodine (mix to the instruction of the dip) to reduce bacteria infection. After fragging, discard the wastewater and rinse tools. The new frags should be placed in low flow, moderate light to recover for a few days before returning to normal conditions.

  
  

• Healing and Growth: Zoanthid frags usually recover quickly. Within a week, you’ll often see the polyps reopening on their new mount. They can be surprisingly resilient to cutting. Regular feeding and stable water will help the frags grow out faster.

  
  

Overall, propagation of zoanthids is straightforward – cut, glue, and grow. Just remember to respect their toxin and practice safe handling. With time, you can grow a single polyp into a large colony and even create stunning “zoa gardens” by placing different color morphs next to each other.

Potential Pests and Diseases

Like all corals, zoanthids can suffer from pests and diseases. Being vigilant and taking preventive steps (like dipping new corals) is key to keeping zoa colonies healthy. Common pests and ailments affecting zoanthids include​

• Sea Spiders (Pycnogonids): Tiny spider-like marine arthropods sometimes prey on zoanthids. They are often called “zoanthid eating spiders.” These pests are thin, translucent, and crawl around the base of polyps, sucking out juices. Affected polyps may stay closed or slowly wither. Manual removal and dipping are the typical remedies as well.

• Zoanthid-eating nudibranchs are one of the most notorious pests. These are small (~1 cm) sea slugs that specialize in eating zoanthid polyps. They often have frilly appendages and take on the color of the zoanthids they consume, making them hard to spot among the colony​. They hide in between polyps and lay spiral clusters of eggs on the zoa mat​. Infested zoas will close up and begin to disappear as the nudibranchs eat them. Removal: The best defense is prevention – always dip new zoa frags in a coral dip (e.g. Coral RX or iodine solution) to kill nudibranchs and their eggs​. If they do appear, you can manually pick them off with tweezers and continue dipping weekly to eradicate any hatchlings​

• Sundial Snails (Heliacus spp.): Sundial snails are small, cone-shaped snails with a distinct black-and-white spiraled shell. They are zoanthid predators that feed on the polyps primarily at night. If you notice a sundial snail among your zoas, remove it immediately – even one can decimate a colony over time. Check for more, as they can multiply. Again, coral dips can help dislodge them, but manual removal is effective once spotted.

• Zoanthid Pox: Commonly called “zoa pox,” this is a disease that appears as tiny white or yellowish pimples or spots on the stalks and oral disc of zoanthid polyp. It is believed to be a bacterial infection (some sources say possibly viral) that can spread within a colony and to others in the tank​. Infected polyps often remain closed and may eventually die off if untreated. Treatment: Many hobbyists have success treating zoa pox by doing a series of baths in an antibiotic called Furan-2. Following a proper dip regimen (e.g. daily dips for a few days) can clear up the infection. Improving water quality and flow can also help prevent outbreaks.

• Fungal/Bacterial Infections (Necrosis): Sometimes a zoanthid colony may suffer a rapid tissue necrosis – polyps dissolve or “melt” one by one. This can be due to a bacterial infection or stress. If you see a brown or black sludge on a colony or a foul smell, it may be bacterial rot. Isolation and iodine dips may save the remaining polyps. Often called “zoa melt,” this condition is unfortunately somewhat mysterious, but maintaining stable parameters and prompt removal of diseased tissue can mitigate it.

• Irritators and Predators: In addition to dedicated pests, other creatures can bother zoanthids. Certain fish (angelfish, butterflyfish, some wrasses) will nip at zoa polyps​. Emerald crabs or hermit crabs may pick at food around them and inadvertently irritate the colony. Even bristle worms or amphipods usually harmless can irritate zoas if present in large numbers. If polyps refuse to open, it’s worth checking at night for pests or hungry critters.

• Algae Overgrowth: A more indirect threat is encroaching algae (hair algae, bryopsis, cyanobacteria) overgrowing a zoanthid colony. If nutrients are high, algae can smother the mat, causing polyps to starve or stay closed. Keep algae in check and consider manual removal (with care) of any that threaten to overrun the colony. Snails and other clean-up crew can help keep the area around zoas clean.

  
  

To prevent pests, always dip and inspect new zoanthid additions. Using a quarantine tank for new corals is wise if you want to be extra safe​. Periodically blowing detritus off the colony with a turkey baster can reveal any hidden pests and keep the colony clean. If issues arise, early intervention is key – a prompt freshwater dip or commercial coral dip can save a colony if pests are caught early. Zoanthids are hardy, but a severe pest infestation can overwhelm them, so diligence is important.

Troubleshooting Tips

If your zoanthids aren’t opening or don’t look right, run through a quick mental checklist – pests? water parameters stable? lighting/flow appropriate? any nearby corals bothering them? Is there detritus amongst the polyps? In many cases, the issue can be identified and corrected (for example, discovering nudibranchs and dipping the coral, or raising nutrients slightly in an ultra-low nutrient tank, or turkey basting closed polyps to clear debris and bacteria). Zoanthids are hardy and often recover once the underlying problem is fixed. By monitoring your tank closely and responding to changes, you’ll find that zoas are resilient and rewarding corals that can flourish for years, providing a kaleidoscope of color in your reef.