Montipora-Eating Nudibranch (Phestilla subodiosus)
Last updated Jan 18, 2026
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Overview
Montipora-eating nudibranchs (Phestilla subodiosus) are one of those pests that can wipe out a Monti collection while you’re busy staring at your “good” corals thinking everything is fine. They’re small, excellent at hiding, and specialized coral predators—their whole deal is eating Montipora tissue.
Most hobbyists don’t notice the nudis first. They notice:
• Montipora edges looking “nibbled”
• Patchy tissue loss
• Receding margins
• A Monti that just slowly melts for no obvious parameter reason
If you keep Montipora—caps, encrusting, digitata—this is a pest you should assume can hitchhike in on frags. They’re annoying, but the pattern is predictable: they get introduced on new coral, they hide well, and they multiply if you don’t catch them early.
Quick Care Snapshot
Common Name: Montipora-Eating Nudibranch
Scientific Name: Phestilla subodiosus
Reef Safe: No (predator of Montipora)
Difficulty: Easy for them, hard for us
Target Host: Montipora spp.
Where They Hide: Undersides, edges, folds, shaded bases
Reproduction: Eggs laid on/near Montipora tissue (often spirals/ribbons)
Primary Signs: White bite patches, receding edges, tissue “scraped” look
Main Risk: Spreads through frag transfers and Monti plugs/rubble
Natural Background
Nudibranchs are sea slugs, and many species are highly specialized feeders. Phestilla subodiosus is one of the ones that has essentially evolved to treat Montipora as a food source.
In nature, predators and distance between coral colonies help keep outbreaks in check. In reef tanks, we concentrate coral, remove many natural predators, and move frags between systems—so the nudis get the perfect environment to do what they do.
Tank Requirements
Like other coral-eating pests, their “tank requirements” are simple:
If you have Montipora, your tank can support them.
They thrive when:
• New Montipora frags get added regularly
• Frags go straight into the display
• There’s no consistent underside inspection
• Montis are plated/encrusting with lots of protected folds
Where to look (the real spots)
• The underside of plating Montis (caps are prime real estate)
• Along the rim/edge where tissue meets skeleton
• Under frag plugs, around the glue line
• In shaded crevices near the base
Feeding
Montipora-eating nudibranchs feed on Montipora tissue. They don’t need “tank food” and they don’t get controlled by nutrient reduction. As long as there’s Montipora tissue available, they have a food source.
They often feed more actively at night or in shaded areas, which is why they’re so easy to miss.
Compatibility
With corals
• Montipora: Primary target. All common Montis are at risk.
• Other SPS/LPS/Soft: Usually not eaten, but can be used as “transport” if the nudis or eggs are on plugs, rubble, or shared surfaces.
With fish/inverts
Some tankmates may opportunistically pick at nudibranchs, but don’t rely on “something will eat them.” Even if adults get eaten, eggs can persist and restart the cycle.
Common Mistakes
1) Treating Montipora decline like a parameter problem
This is super common: alkalinity swings, lighting, flow—people chase numbers while the Monti is literally being grazed. If you see clean, pale bite patches, think pest early.
2) Only looking at the top surface
Most nudis and eggs are on the underside, edges, and shaded folds. If you don’t flip the frag or inspect the underside, you won’t see the real story.
3) Dipping once and calling it done
Dips can knock off adults, but eggs are the trap. If egg clusters remain, you’re just buying a short break.
4) Leaving “infected” Montis in place
If you confirm nudis, assume other Montis have been exposed. They move, and the tank becomes the habitat.
5) Missing egg masses
Egg clusters are often laid right on the coral or near the base, and they can be hard to see unless you’re specifically hunting for them.
Notes & Variations
What they look like (why they’re hard)
They often camouflage extremely well because:
• They’re small
• Their shape blends into Montipora texture
• Their coloration can match the coral or look “dusty”
Common symptom pattern
• Bite marks start at edges or underside
• Tissue loss looks “scraped” rather than “burnt”
• Colonies decline gradually unless the infestation is heavy
Eggs
Egg masses are often:
• Ribbon/spiral-like
• Placed on the underside or near the base
• Hard to see on textured coral
Final Thoughts
If Acropora has AEFW, Montipora has these nudibranchs. It’s the same lesson: coral collections get wrecked by pests when intake habits are sloppy, not because the hobbyist “failed” chemistry.
Montis are often the “easy SPS,” which makes this pest extra annoying. You’re doing everything right, and the Monti still fades—because something is eating it in the places you don’t casually look.
The win condition is:
• Inspect
• Catch early
• Treat the lifecycle, not just the visible adults
• Don’t assume the display is immune