The Salty Side: Saltwater Aquariums for Beginners

Why Your Tuxedo Urchin Could Be Losing It's Spines

Tuxedo urchins (Mespilia globulusare such a great addition to any saltwater aquarium.  They are not usually one of the first things that come to mind when thinking of a reef tank but they really add interest, do a great job of eating algae and are quite amusing waltzing around the tank dressed in camouflage.  

Help!  My tuxedo urchin is losing it’s spines

Unfortunately, if this invertebrate is already losing a large amount of spines then it’s prospects aren’t great.  If they are only losing a few spines however, they still have a chance of recovering and living to be a good 2 to 5 years old.  Read further for tips on how to help your urchin recover.

What causes an urchin to lose it's spines?

Stress due to environmental changes, acclimation shock, lack of food and high nitrate levels (above 10ppm) are some of the biggest causes for tuxedo urchins not surviving.  Once they start dropping spines, they are also prone to bacterial infections, from which it is hard to recover.

Like all invertebrates, tuxedo urchins need to be drip acclimated as inverts are very sensitive to changes in water parameters.  It has been said that longer acclimation times are needed but a lot of reefers have been successful in acclimating urchins for the same amount of time as other invertebrates.  BUT, they have ensured to match the salinity of the water and slowly allowing them to acclimate to the new aquarium’s temperature.  

Be careful of stirring up the sand in your tank as disturbing it could cause a poor water quality due to detritus etc. entering the water column.  Also, if doing water changes, make sure water is added slowly, over a few days, and not just dumped in.  This will ensure that the sand bed isn’t disturbed.  This also goes for bare bottomed tanks.  Detritus settles under rockwork and is easily released into the water column.

Tips on how to keep a Tuxedo urchin happy

Here are a few ideas on how to make your Tuxedo urchin happy:

  • Provide nori now and then, especially if there isn’t enough green hair algae for them to eat.

  • Provide stable water parameters.

  • Keep nitrate levels under 10ppm.

  • Be sure to match salinity when introducing any urchin to your tank.

  • Avoid stirring up the sand in your tank as this brings detritus to the surface and reduces water quality.  

  • In smaller saltwater aquariums, fluctuations are keenly felt by sensitive inverts so if doing a water change, make sure to do smaller amounts more often rather than the other way around.  

  • Do not buy predatory fish such as Triggers or Parrotfish as they eat urchins.

If you see them carrying bits of debris on their backs then chances are, they’re happy urchins.  That’s not to say they’re not happy if they’re aren’t carrying anything but just that they’re doing well.   

What do Tuxedo urchins eat?

Tuxedo urchins are great devourers of green hair and coralline algae.  Like all inverts though, if they have done such a good job and there is no algae left for them to eat, they will need dried seaweed (nori).  This can simply be attached to a rock with a rubber band near to the urchin or placed in a seaweed clip.  You can see my best seaweed clip article for more information on these.  My urchin will sit on it for an entire day just feeding on the nori.

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Can you touch it?

Yes, you can touch a Tuxedo urchin.  Their spines are very blunt so will not cause you any harm. 

Is a Tuxedo urchin reef safe?

Yes!  Tuxedo urchins are reef safe.  The only thing they might do is wear frag plugs, as well as rubble, bits of broken coral etc. as camouflage and take it for a walk around the tank. 

How long do they live?

When kept in an aquarium, the average life span of a Tuxedo urchin is around 2 – 5 years.  As with most sealife, they generally live longer when in their natural habitat.


Hopefully you now have a few ideas on what to look out for if you notice your Tuxedo urchin losing spines.  Remember, it doesn’t automatically mean it will die but it certainly isn’t happy.  Checking water parameters, nitrates in particular, would be the first thing I’d suggest testing for as this is often the cause of great stress to urchins. 

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