The sea urchin is a small, spiny animal that can be found in a variety of saltwater habitats. These creatures belong to the class Echinoidea in the phylum echinoderm which contains over 900 different species. Many people are familiar with the sea urchin but they may not realize that they are actually living creatures. Not only are sea urchins a unique and interesting creature, but they also make a great addition to the saltwater tank.
If you are looking for a unique invertebrate to add to your saltwater tank, take the time to learn a little bit about these intriguing creatures to see if it might be the right choice for you. Keep in mind that there are many different species of sea urchin, so even after you make the decision to add a sea urchin to your tank you will need to research the particular species to determine its tank requirements. In this article you will learn the basics about sea urchins and receive tips for caring for them in your own saltwater aquarium.
About Sea Urchins
Depending on the species, sea urchins range in size from 6 to 12 cm in diameter, though the largest recorded specimen measured 36 cm. These creatures are bilaterans which means that their bodies have bilateral symmetry, but most species develop fivefold symmetry as they mature. These species may develop five different parts of equal size that radiate from a central axis. Other sea urchins, like the sand dollar, are ovular in shape and have a distinct rear and front. The two halves of a sea urchin are typically divided into the lower half, called the oral surface, and the upper half, the aboral surface. The oral surface contains the mouth parts while the aboral surface contains the internal organs which are enclosed in a sac protected by fused plates of calcium carbonate. The most distinctive parts of the sea urchin are its spines which vary in length and are used to protect the sea urchin from predators. The length of these spines may range from 1 to 3 cm but some have spines as long as 10 to 30 cm.
Caring for Sea Urchins
The first thing you need to consider when adding a sea urchin to your saltwater tank is that you have enough space. You should plan to dedicate at least one gallon of tank space per inch of a sea urchin’s maximum size. These creatures may not take up a great deal of space and they do not move quickly, but they will contribute to the biological load of your tank. The ideal water temperature for a sea urchin may vary depending on the species but, for the most part, these creatures prefer a temperature around 80F. In addition to water temperature, the salinity of your tank is also important – you may want to research the specific needs of the species you choose but, in general, a salinity at or near that of sea water is preferable.
In addition to providing your sea urchins with the proper tank environment you also need to ensure that they have an adequate supply of food. In the wild, sea urchins feed on various types of algae including seaweed, kelp, laminaria and egregia. The preferred diet will depend on the species of sea urchin you select but you should be prepared to provide a variety of different types of algae to keep your sea urchin well-fed. Be careful not to overfeed your sea urchins, however, because any excess algae or vegetable matter in the tank could result in a build-up of harmful toxins like ammonia which could contribute to a decrease in water quality.
Other Things to Know
In addition to feeding your sea urchins you should also make sure to keep the tank clean. If you are adding a sea urchin to an existing saltwater tank you should already be performing routine water changes to keep the water quality in your tank high. As you perform your routine water changes, be careful not to disturb your sea urchins and be sure not to damage their spines when using an aquarium gravel vacuum. You should also keep in mind that sea urchins may not be compatible with all of the species of fish you have in your saltwater tank. Certain species of fish like triggerfish will prey on sea urchins and are thus not compatible. Starfish may also pose a danger to sea urchins.
Types of Sea Urchin
There are hundreds of different species of sea urchin out there, but not all of them are recommended for the pet trade. Below you will find a list of some of the best sea urchin species to keep in the saltwater tank:
Blue Tuxedo Urchin – The blue tuxedo urchin is a very peaceful species that only grows to about 3 inches in diameter. This species is easy to care for, though it does prefer warm waters between 72°F and 78°F and a pH range between 8.1 and 8.4. Blue tuxedo urchins are herbivorous and they may graze on the algae in your tank. This species does not tolerate high nitrate levels and it may require supplements of calcium, magnesium, iodine, and trace elements.
Black Longspine Urchin – This sea urchin is named for its black color and long spines – it generally grows to a diameter of about 10 inches. The black longspine urchin is native to the Caribbean and it is generally peaceful in the home aquarium. These urchins prefer water temperatures between 72°F and 78°F with water hardness between 8 and 12 dKH and pH between 8.1 and 8.4. There are also green, blue, and white color forms of the longspine urchin.
Pencil Urchin – The pencil urchin looks a little different from other urchins because its spines are much thicker. This species grows to a diameter around 5 inches and it comes in black, red, white, and tan. The pencil urchin is an omnivorous species, feeding on algae and small invertebrates. It prefers water temperatures between 72°F and 78°F with a pH between 8.1 and 8.4.
Shortspine Urchin – The shortspine urchin grows to a maximum diameter around 3 inches and it has hundreds of uniform reddish-orange colored spines. This species is peaceful by nature and reef compatible – it is also fairly easy to keep in the home aquarium as long as you provide plenty of live rock for grazing. The shortspine urchin cannot tolerate poor water quality or high nitrate levels.
By now you should have a basic understanding of what sea urchins are and what roles they can plan in the saltwater aquarium. Keeping sea urchins in the home aquarium is no easy task but, if you prepare your tank properly and if you are careful in selecting a species, you can be successful in keeping sea urchins as pets.