Sea Urchins
Scientific Information:
Phylum: Echinodermata
Class: Echinoidea
Order: Multiple. See below
Common Names:
Pin Cushion, Tuxedo, Long Spine(v), Short Spine, Pencil(sn), Flower(vv), Fire(vv), Sand Dollar(sn)
v = venomous
vv = very venomous
sn = special needs
Origin:
Pin Cushion - Caribbean
Tuxedo - Indo-Pacific
Long Spine - Indo-Pacific
Short Spine - Indo-Pacific
Pencil - Indo-Pacific
Introduction:
This article is divided into four sections. General Information, Reef Safe Urchins, Special Needs Urchins, and Urchins to avoid. General Information contains general notes on husbandry while the other sections deal with specific species broken out by type of urchin and contains specific details on tank size, diet requirements, special needs, and the like.
General Information:
There are about eight different kinds of urchin, including the sand dollar, sold in the trade. Their habitats range from the Atlantic to the Indo-Pacific and Caribbean. Most urchins are reef safe with the notable exception of the Pencil Urchin which is carnivorous and will eat corals as well as fish and the very pretty but very venomous flower and fire urchins.
Urchins tend to be some of the more unusual and potentially entertaining additions to a cleanup crew and actually cut down substantially on the required number and diversity of said crew. In general one urchin can handle the job of several glass cleaning snails and several rock cleaning snails and hermits. They are no harder than other invertebrates, like crabs and hermits, to keep and do a good job relative to their size of keeping control of algae. While urchins tend to be nocturnal, many will come out during daylight hours.
The best Urchin for Nano tanks are the Tuxedo's as they remain relatively small while still providing entertainment and high cleaning to relative size value. Watching them work is interesting especially when they are on the glass and their mouth can be seen in operation. They will eat all kinds of algae including diatoms, green hair, etc and there is anecdotal evidence of them eating cyno as well.
There are three downsides to having an urchin in the tank. If the urchin selected is a Pinchushion or Tuxedo and there are small loose bits of rock, small bits of coral or frags, or hermits and snails in the tank the Urchin may take them for a free ride around the tank on its back. The reason for this is that this subspecies uses shells and loose strata as tactile and visual camouflage from their natural predators. Urchins are also very strong for their size and can inadvertently topple corals and/or rocks as they move about the tank. The caution used when putting a turbo snail into a tank would be the same for an urchin. Make sure the rocks and corals are stable and not easy to move. Finally, urchins eat all kinds of algae including coraline.
Predators:
Urchins are not recommended in a tank that contains any:
starfish
triggers
some types of larger wrasse
puffers
anglers
squirrel fish
snappers
sharks
rays
porkfish
parrot fish
harlequins
as urchins are a natural prey of these animals.
Diet:
Most Urchins are either herbivores or omnivores with the notable exception of the Pencil Urchin which is carnivorous. Urchins will eat all forms of micro-algae from all surfaces including rock work, glass, and substrate.
If algae is not prolific in the tank it is best to supplementally feed urchins with some form of sea weed such as Nori. A 2"x2" sheet about once every week or so should be sufficient.
Feeding can be handled in one of two ways. First, hang it on the glass or rock where they will find it. Second, hand feed them. If hand feeding the urchin will do something called an "urchin kiss" where their spines will gently grasp the tip of your finger as their sensory tentacles explore if you are worth eating. Press the sea weed gently on the spine or place it in the urchin's path and allow it to roll up on it.
Acclimation Process:
Gradual. If the delta between the salinity level they are used to and your tank is too high they can get salinity shock. An example acclimation method would be to place the urchin in a bucket or container with the water it came with, a heater, and a very small power head. Over a 30 to 40 minute period remove 4 oz of old water and replace it with 4 oz of water from your tank repeating every 7-10 minutes for about 30-40 minutes. (Note this assumes you have more than 12 oz of original water and that the original water is not fouled or contaminated. Drip method would be best if you do not have at least 12 oz of original water)
Things to watch out for:
If an urchin's spines fall off they are most likely dying and there isn't much that can be done to save them. While it is possible to attempt rehabilitation via a hospital tank coupled with offering allot of food like nori usually by the time the spines are falling off it is too late and humane euthanization such as via freezing is more appropriate. It is important to remove the urchin from the tank as soon as spine loss is observed as delay could cause the urchin to expire in a location difficult to access or see which would cause a spike in the tank.
As with all invertebrates copper based medications are fatal to urchins.
Urchins are also sensitive to rapid shifts in salinity and can get salinity shock which can be fatal.
Urchins do not tolerate high nitrates. If there are high nitrates in the tank an urchin will shed its spines.
Wound treatment from an urchin stick:
Spine sticks from urchins can be quite painful and in the case of flowerpot or fire urchins or with people who have allergies fatal. Prompt treatment is important to reduce pain and swelling as well as the risk of infection.
If stuck by a flame or flowerpot urchin, if you have a allergy, or feel unwell or concerned seek appropriate treatment immediately from a medical professional.
If stuck by an urchin spine remove the spines as quickly as possible. You will not get all of the spine and this will hurt but it is important to remove them quickly to minimize pain. Do not dig out the spine as this can do more damage and cause higher risk than leaving it in and allowing it to work its way out. Next soak the affected area with vinegar followed by a hot water soak at the highest temperature you can stand followed again by a vinegar soak. This should minimize the pain and swelling/stiffness associated with an urchin stick.
And specifically for (my favorite) the Tuxedo:
Common Name: Tuxedo (blue or black)
Scientific Name: Mespillia Globulus
Max size: 2 Inches
Tank size: 15 gallon+ (with feeding)
Food: All kinds of algae
Reef safe: Yes if well fed
Notes:
Will pick up debris/shells/rocks/etc as camouflage. If it isn't then it may be sick or dying
May need supplemental feeding with nori if in 30+ gallon tank and will need supplemental feeding if in smaller tank
