The blastomussa coral (Blastomussa spp.) group produces as much confusion as it does popularity. The impressive polyps these large polyp stony (LPS) corals extend into the water disguise the underlying calcium skeleton. And they give it a similar appearance to mushroom, brain, and even candy cane corals. It isn’t until those polyps retract that you spot the unique structures underneath and realize you have a blastomussa. And the game of “Which coral is this?” It’s the tip of the iceberg when it comes to caring for blastos.
Table of Contents: Blastomussa Coral Care
Blastomussa corals fall on the list of “approved for beginners.” As you’ll find in the links below, they’re not overly demanding in their care. However, you won’t find first-time hobbyists lining up to purchase blastos. Enough quirks (including price!) cause people to pause and consider other LPS options first.
Blastos Quick Facts:
- Common Names: Blastomussa coral, Big polyp coral, Pineapple coral, Blastos, Posy coral, Open brain coral, Swollen brain coral, Wellsi’s brain coral, Big pipe, Moon coral
- Scientific Names: Blastomussa spp.
- Size: Individual polyps reach 1-5 inches (2.5-12.7cm) in diameter
- Minimum Tank Size: 30 Gallons (114L)
- Aggression Level: Peaceful
- Compatibility: Should not be placed with other corals; They don’t possess strong enough defenses
- Care or Experience Level: Easy-Moderate
- Feeding Recommended? For ideal growth
- Lighting: Low-Moderate
- Water Flow: Low
- Original Part of the World: Indo-Pacific
Description of the Blastomussa Coral
As with most LPS corals, the blastomussa coral starts with a skeleton of calcium carbonate. Unlike their cousins, though, blastos don’t form typical colonies. Instead of having corallites branch out of a central base, the corallites divide into individual tubes. Each disc is a genetic clone of the one beside it. They form dome-shaped clusters on the seafloor, and when the polyps retract, you can spot the separate structures. It’s what sets these corals apart.
At first glance, though, it’s easy to mistake them for other species. Blastomussa merletti have small polyps (1-2 inches/2.5-5cm) that remind some people of Duncans or zoas. Unlike zoanthids, underneath the beautiful, fleshy polyps, you find a stony skeleton, which distinguishes them from any of the soft corals, mushrooms or zoanthids. Blastomussa wellsi‘s polyps are also generally broader (4-5 inches/10.2-12.7cm) in size.
B. merletti and B. wellsi are the usual species kept in saltwater aquariums. That doesn’t mean you WON’T see one of the other four species show up in a fish store now and then, though. Although the newest member of the group – B. angulares – probably won’t make an appearance. Scientists only announced the discovery in February 2021. Since all corals create different shapes for their corallite skeletons, it went overlooked for – well, a long time.
The mouth on the oral disc usually comes in a different color from the tentacles. As the corallites cluster together, the contrast creates a “brain” pattern that gives blastos their common name of open brain coral. (Not to be confused with brain corals – though the similarity IS there) In the wild, you find them in shades of blue, brown, green, and red. But popularity – and the ease of fragging – has led to other purple, yellow, and pink options.
Creating the Ideal Blastos World
Blastos corals show up throughout reefs in the Indo-Pacific. You can spot them at popular dive spots around Fiji, the Great Barrier Reef, the Solomon Islands, and Tonga. (And, of course, that new addition to the genus calls the Indian Ocean home) Indonesia claims some of the most unique color variations.
The corals cluster along the upper slopes of a reef where the current’s at a low point. And they range reasonably deep into the water, going down to 130 feet (40m). They provide shelter for sessile mollusks, sponges, and other invertebrates. But you won’t see them in the company of too many other corals. And it ISN’T for the reason you think. (We’ll get to that in a second)
Blastos prefer to attach themselves to rock structures over sand. As such, you’ll want to have live rock handy. They do beautifully as centerpieces in reef tanks. And that dome shape looks perfect at the bottom of your tank. You just don’t want sand causing damage to the polyps. (Brown jelly disease is never fun)
Blastos Coral Tank Size
Blastomussa corals don’t swarm tanks the way other LPS corals tend to. The tubes of the corallites form up and out. As such, they don’t enact hostile takeovers of the aquarium. So regardless of the species you settle on, you can usually get away with a tank size of 30 gallons (114L).
That said, you need to allow room for your blasto within the tank. Placement of ANY coral is crucial. But blastos don’t have the fighting power of their cousins. If you crowd them into a tight space, you’ll end up with a lovely calcium skeleton in the middle of your aquarium. (At least until it dissolves) Make sure you give your coral colonies space to grow – without interference.
Water Parameters
As you’d expect from a beginner LPS coral, you don’t need to fret much on your water parameters. Blastomussa corals do well with standard saltwater aquarium conditions:
- Temperature: 76-81F (24.4-27.2C)
- Salinity: 1.023-1.025
- Alkalinity: 8-11dKH
- pH: 8.2-8.4
- Calcium: 400-450ppm
- Magnesium: 1200-1350ppm
Why do these parameters matter? Calcium and magnesium are critical for Blastomussa because they are the building blocks for the coral’s skeleton. Blastomussa, like other stony corals, deposits aragonite (a crystalline form of calcium carbonate) to grow and maintain its structure. Calcium is directly used in this process, while magnesium helps stabilize aragonite formation and prevents unwanted precipitation of calcium carbonate in the water column. If calcium is too low, the coral cannot deposit new skeleton, leading to stunted growth or even tissue recession. If magnesium is too high or too low, it can disrupt calcium uptake and skeletal formation.
Alkalinity is equally important, as it buffers pH and supports stable carbonate availability. Low alkalinity can cause pH swings and make it harder for the coral to build skeleton, while high alkalinity can stress the coral and lead to precipitation issues.
How do you know if something is off? Imbalances in these parameters often show up as visible symptoms: slow or halted growth, receding tissue, pale or faded coloration, or polyps that fail to extend fully. In severe cases, you might see tissue peeling away from the skeleton or a general loss of polyp “puffiness.”
To catch problems early, regularly test your calcium, magnesium, and alkalinity, and observe your coral’s behavior. If you notice changes in polyp extension, color, or growth, check your parameters before making adjustments. Avoid chasing exact numbers—instead, look for stable trends and respond to what your coral is telling you. Consistency is more important than hitting a specific target value.
Where to place Blastomussa coral?
The ideal placement for Blastos is on the sand bed or glass bottom of the tank in an area of moderate flow and lighting.
Out on the reef, blastos prefer a moderate range of sunlight. You don’t see them in shallow waters where they receive the full impact of the sun. And the same goes for your tank. You want a moderate or even subdued lighting scheme. This will encourage them to open the polyps and extend them fully. (You’ll also get the best color out of your little coral – hint, hint)
Why are Blastos sensitive to light and flow? Blastomussa are adapted to deeper reef zones where sunlight is filtered and water movement is gentle. Their large, fleshy polyps are designed to maximize light capture in lower-light environments, but they can be easily damaged by intense light (photoinhibition) or strong currents. Too much light can cause the polyps to retract, bleach, or swell abnormally as a stress response. Too little light, on the other hand, may result in faded colors and slow growth.
Water flow is equally important. Excessive flow can physically damage the delicate polyps, preventing them from feeding and causing them to remain retracted. Insufficient flow, however, can allow detritus to accumulate on the coral, increasing the risk of infections such as brown jelly disease. The goal is to provide enough movement to keep the coral clean and oxygenated, but not so much that the polyps are battered or unable to feed.
How to recognize placement problems:
- Polyps remain retracted or fail to open fully
- Bleaching or pale coloration
- Tissue swelling or “bubbling” appearance
- Accumulation of debris or signs of brown jelly disease
If you see these symptoms, try moving your Blasto to a shadier spot or an area with gentler flow. Observe the coral’s response for several days before making further changes. Placement is best adjusted based on coral behavior rather than rigid rules—let your Blasto’s appearance guide you. Just be careful not to move them around too much. Giving them enough time in an area that is good enough is better than moving them around too much.
You also want to place blastomussa corals in low water flow. While the polyps on the disc LOOK robust, they’re on the delicate side. If your blasto ends up in a strong current, they’ll retract to protect those tentacles. Then they won’t receive the nutrients they need. And you’ll have paid for an attractive, slowly-dissolving calcium structure.
Finally, you need to create a healthy perimeter around your blastos. They DO possess sweeper tentacles. And those tentacles contain the nematocysts (stinging cells) you expect from a coral. But when you rank blastomussa corals against other LPS species, they come out at the BOTTOM. They’re not strong enough to defend themselves. (It’s one of those “act tough” situations where you’re actually shaking in your boots)
Blastomussa corals need room to grow, feed, and look gorgeous – without intrusion by neighbors. So you want to place them far enough from your other corals that they’ll remain safe and sound.
Can Blasto corals touch?
Do not allow Blasto corals to touch other blastos or any other coral type. There are reports of them tolerating touching followed by sudden, unexplained problems.
Why is touching a problem? Even seemingly peaceful corals like Blastomussa can cause or suffer damage when their tissues come into contact. This can be due to allelopathy (chemical warfare), direct physical abrasion, or the transfer of pathogens. Sometimes, two blastos may appear to tolerate touching for a while, only to suddenly develop tissue recession, color changes, or necrosis at the contact point. These issues can escalate quickly and may not be reversible.
Prevention tips: Place each Blasto with enough space to allow for growth and movement from water flow. Regularly check for accidental contact as corals expand, and reposition frags or colonies as needed to maintain separation.
How fast do Blastomussa corals grow?
A thriving Blastomussa coral will add 1-4 polyps/heads every couple of months. Regularly feeding this coral will accelerate growth.
What influences growth? Growth rate depends on several factors: stable water parameters (especially calcium, magnesium, and alkalinity), adequate but not excessive lighting, gentle flow, regular feeding, and sufficient space. Competition with neighboring corals or poor water quality can slow or halt growth.
Signs of healthy growth: New polyp buds forming at the base, vibrant coloration, and regular polyp extension. If growth stalls, check your water parameters, review placement, and consider increasing feeding frequency. Slow or absent growth, faded color, or receding tissue may indicate a need for intervention.
Blastomussa Coral Feeding
Blastomussa corals contain zooxanthellae – symbiotic algae. Zooxanthellae account for most of the nutrition for blastos. And what they don’t receive from their algae friends, they capture with their polyps. As long as you have a healthy, cycled tank, you don’t need to do much to keep them happy and thriving. A refugium with pods will do the trick.
However, if you want to encourage growth, you CAN feed your blastos. They respond well to target feeding. You need to make sure you offer food to EVERY polyp, though. They’re NOT one colony that shares their nutrition. Each polyp is a separate organism. As for the foods blastos accept, you have your pick:
- DT’s Phytoplankton
- Marine Snow
- Phytoplex
Benefits and risks of feeding: Target feeding can accelerate growth and improve coloration, especially in lower-nutrient tanks. However, overfeeding can lead to nutrient spikes, increased algae growth, and declining water quality. Uneaten food may accumulate and rot, harming both the coral and other tank inhabitants.
How to know when to feed: Blastomussa polyps will extend and display feeding tentacles when receptive. If polyps remain tightly closed or food is consistently ignored, reduce feeding frequency. Signs of overfeeding include persistent uneaten food, cloudy water, or a rise in nuisance algae.
Practical feeding tips: Start with small amounts once or twice a week, adjusting based on coral response and tank nutrient levels. If your Blasto is growing well and displaying healthy polyp extension, additional feeding may not be necessary. Always monitor water quality and adjust your routine if you notice negative trends.
Blastomussa Coral Behavior and Tank Mates
Plenty of people consider blastos to be peaceful. After all, they don’t invade reef or aquarium space. The fact they CAN’T enact hostile takeovers doesn’t occur to anyone. Given a chance, blastos would happily clobber other corals. They can’t help it that their sweeper tentacles are the equivalent of a wet noodle.
Understanding aggression: In coral terms, aggression can be passive (chemical or physical defenses) or active (sweeper tentacles, overgrowth). Blastomussa’s sweeper tentacles are weak compared to more aggressive LPS corals, so they rarely harm neighbors. However, they are still capable of mild stinging and may stress more delicate species if placed too closely.
Tank mate consequences: Placing Blastomussa near more aggressive corals (like Euphyllia or Galaxea) can result in tissue recession or polyp loss, as Blastos cannot defend themselves effectively. Similarly, fish known to nip at polyps (such as butterflyfish or some angelfish) may damage or consume Blasto tissue. Watch for signs of stress: receding tissue, missing polyps, or sudden color changes.
Tank mate selection: Choose peaceful fish and invertebrates that do not nip at coral polyps. Observe new additions closely for the first few weeks. If you notice aggression or stress, be prepared to relocate either the coral or the offending tank mate promptly.
They’re not able to defend themselves from known polyp-nibblers, though. So you don’t want to place these corals in a tank with butterflyfish or angelfish. The broad polyps are too much of a temptation. You also want to watch any sponges or mollusks that make a home between the oral disks. Sure, it’s where those species usually reside in the wild. But you don’t want that low water flow to get restricted and cause the coral to lose a source of nutrients.
Blastomussa Coral Reproduction and Fragging
All blastomussa coral species are hermaphrodites. Corallites produce eggs and sperm they release simultaneously into the water column. The gametes combine and hatch into planula larvae. Planula resemble flattened, upside-down versions of blastos and reside in the plankton. When planula settle, they metamorphose into a polyp and begin secreting calcium carbonate to form a skeleton base.
Sexual reproduction happens all the time in the wild, but it’s not as common in aquariums. Instead, you see asexual reproduction. Blastos fragment. Starting from the central base of the coral, the corallites grow out into the dome shape. Over time, the connection to the base closes off (fragmenting).
Then you have an individual corallite with an identical genetic code to the parent.
Those solitary clones make fragging a cinch. All you need to do is look for the division between the branches. Then you can use a Dremel, scissors, or bone saw to cut the frag away. (Some people break it with their hands, but this can yield a damaged frag. It’s better to make a clean cut).
Fragging best practices and risks: When fragging Blastomussa, avoid cutting too close to the polyp, as this can cause tissue tearing and increase the risk of infection. Always use clean, sterilized tools to prevent introducing pathogens. After cutting, gently rinse the frag in tank water and consider an iodine dip to reduce infection risk. Place the frag in a low-flow, moderate-light area to minimize stress during recovery.
Monitor the frag for signs of healthy recovery: polyp extension, tissue healing, and no signs of necrosis or tissue loss. If you notice persistent retraction, discoloration, or tissue sloughing, check water quality and flow, and be prepared to intervene if necessary.
Set your blasto frag in a safe place (moderate light and low water flow), and it’ll grow in no time.
Pros and Cons
Once you get the knack of identifying blastomussa corals, you can’t resist picturing a few in your reef tank. And while they fall on the easy list for beginners, you still want to look at the pros and cons before you rush to the local fish store.
- Pros:
- Obtain most nutrition from zooxanthellae, with target feeding accelerating growth.
- Tolerant of standard water parameters, though sensitive to instability in calcium and magnesium.
- Easy to frag due to their individual skeleton bases, making propagation straightforward.
- Require low-moderate lighting and gentle flow, making them suitable for a range of tank setups.
- Peaceful and unlikely to harm neighbors, but require protection from more aggressive corals and polyp-nibbling fish.
- Cons:
- Often rare and expensive, especially for unusual color morphs.
- Slow to moderate growth rate compared to some other LPS corals.
- Vulnerable to damage from touching, aggressive tank mates, or unstable water chemistry.
For More Information
The shapes and colors of these gorgeous LPS come in set imaginations soaring. You don’t always get that kind of structure on the “easy” list of species. Of course, they’re not quite as bulletproof as other LPS corals out there. But if you’re excited about adding them to your reef tank, here are additional nuggets of info here for you to peruse.
Check out this video:
Want to know about some of the best blastos coral tank mates?
Maybe you’re interested in some of the corals that have a similar appearance. (Why not create a reef tank that keeps your visitors guessing?)
Conclusions
Everyone picks corals for a particular reason. Maybe you’re fascinated by blastomussa corals because they develop identical clones on one dome. Or it could be the strange “open brain” pattern they create. Perhaps it’s nothing more than the colors they come in.
Whatever the reason, as long as you create that perfect tank environment (and protect them from the mean kids on the playground), you’re sure to find yourself with a winning coral centerpiece.
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References
- Borneman, E. 2004. Aquarium Corals: Selection, Husbandry, and Natural History.
- Borneman, E. 2008. “Bevy of Blastomussa.” Reefkeeping Online.
- Calfo, A. 2007. Book of Coral Propagation.
- Sprung, J. 1999. Corals: A Quick Reference Guide.