Tuxedo Urchin
Mespilia globulus
The reef's neat little algae-grazing urchin — great on hair algae, and it decorates itself.
Difficulty: BeginnerCleanup crewReef-safe
The tuxedo urchin (Mespilia globulus) is the tidiest, most beginner-friendly urchin in the hobby — a small, striking blue-and-dark grazer that mows through film and hair algae, including the coralline and nuisance algae many snails ignore. It's reef-safe and easy, with one urchin-wide habit to plan for: it likes to "decorate" itself, carrying loose bits (and un-glued frags) around for cover.
Care at a glance
| Adult size | Small — around 2 in. |
|---|---|
| Minimum tank | 20+ gallons with plenty of rock to graze; captive-bred (ORA) specimens are widely available. |
| Temperature | 75–82°F (24–28°C). |
| pH | 8.1–8.4. |
| Specific gravity | 1.023–1.026 (reef-standard ≈35 ppt). |
| Other targets | Standard reef calcium and alkalinity keep the test and spines strong; like all inverts it has zero tolerance for copper. |
| Diet | Film algae, hair algae and coralline/nuisance algae grazed off rock and glass. Supplement with dried seaweed if algae runs low. |
| Temperament | Peaceful and reef-safe — a slow, methodical grazer. |
| Reef-safe | Yes — it eats algae, not coral tissue; the only issue is that it carries loose objects around. |
| Natural range | Indo-Pacific. |
The fish store gets these wrong
Common myths, kindly corrected — no shame for having believed them.
- "Urchins are hard and spiny-dangerous." The tuxedo is easy, small and short-spined — one of the most beginner-friendly grazers.
- "It'll only eat nuisance algae." It also grazes coralline — helpful, but in a clean tank feed it so it doesn't strip your rock.
Before you buy
- Glued-down frags — it carries loose objects around.
- A tank with real algae, or a plan to feed nori.
- A captive-bred (ORA) one if available; a cycled tank; drip-acclimate; never any copper.
Signs something's wrong
A struggling invert is usually telling you about water quality, acclimation, or (for shrimp and crabs) a fresh moult — here's what to watch for:
- Dropping spines or a bald patch — a water-quality problem (often salinity or copper); test and stabilise.
- Grazing coralline hard or looking thin — not enough algae; supplement with dried seaweed.
- Carrying frags around — normal "decorating"; glue corals down.
Never
- Never keep it with loose, un-glued frags.
- Never let it run out of algae without supplementing.
- Never dose copper, add to an un-cycled tank, or drop it straight in.
Common tuxedo urchin questions
Are tuxedo urchins reef-safe?
Yes — they graze algae (film, hair and coralline), not coral tissue. The one caveat is that, like all urchins, they pick up and carry loose objects for cover, so glue down your frags.
Do tuxedo urchins eat hair algae?
Yes — they're one of the better grazers for hair algae and film algae, and they'll work coralline too. In a clean tank, feed dried seaweed so they don't strip the rock bald.
Why is my urchin carrying shells and frags around?
That's normal "decorating" — urchins hold objects over themselves as camouflage. It's harmless except that it can move unsecured frags, so glue corals down.
Why is my tuxedo urchin dropping its spines?
Spine loss is a classic sign of a water-quality problem — most often a salinity swing or copper exposure. Test your parameters, make sure you acclimated it slowly, and never use copper with inverts.
How big do tuxedo urchins get?
Small — around 2 inches — which is why they're the reef-friendly urchin choice, unlike larger species that outgrow a tank.
Sources & further reading
This guide was written and fact-checked against these authorities. It's honest, general guidance — not a diagnosis, and not a substitute for an aquatic vet or your own test kit:
- AlgaeBarn — Tuxedo Urchins for Hair Algae Control — diet, hair-algae role, reef-safe
- Top Shelf Aquatics — Tuxedo Urchin — size, care, decorating behaviour
- Shrimp and Snail Breeder — Tuxedo Urchin Care — care, diet
Written and fact-checked by The Coralkin Team against marine-aquarist sources — if your tuxedo urchin is struggling, it's almost always water quality, acclimation or a moult — check those first and ask an experienced reefer. We never guess a care number.
🔬 Review status: team-written and fact-checked against cited sources · not yet reviewed by a marine vet. How we research & fact-check →