Rick Hennis

Photo courtesy of Rick Hennis

Just as the image of a clownfish nestled in a sea anemone evokes for many people the beauty and wonder of a coral reef, the image of a sea star is probably the single icon of the oceanic realm. No animals like these various kinds of star-shaped creatures are found on land or in freshwater environments; they are found only in marine environments. Seen only in photographs, at the sea shore, or by divers in oceanic environments, sea stars decidedly characterize their environment as one different from that of most human endeavors. Without a head, or even a front or back end, and with a structure based on fives, sea stars are decidedly alien animals. They are quite literally like nothing on the dry earth's surface. Probably because of their strange appearance, and oceanic symbolism, they are popular aquarium animals. Of course, it doesn't hurt that they are often brightly colored and quite beautiful.

In general, however, sea stars are not animals that do well in home aquaria. Because of their requirements for full oceanic salinity and delicate internal anatomy, they often do not seem to pass through the transition from nature to the home aquarium unscathed; more often than not they die within a few days of being added to the tank. If they do make a successful transition into the home aquarium, however, they may do well provided the aquarist can provide them with some appropriate food.

The sea stars in this slide presentation come from two substantially different groups of animals placed by scientists in the group called the Phylum Echinodermata. These are the sea stars proper (known as the Class Asteroidea) and the brittle or serpent stars (known as the Class Ophiuroidea). The true sea stars are characterized by more of a star shape, with the central body not generally discretely separated from the legs. They often have a fleshy appearance and they typically move by the action of several hundred to several thousand small tube feet projecting from the bottom of the animal. Although they are generally found with five rays, many sea star species have more than five rays, and some may have fewer. Brittle or serpent stars have a discrete central body and five rays that are snake like, often with long spines visible off of each side. While they have tube feet they move more by the action of the arms which pull or push them along.

True sea stars are more delicate than are the brittle stars, and relatively fewer species are successfully kept by aquarists. Success in keeping these animals must be measured in the number of years that they are kept. They don't die of old age, and may die of malnutrition slowly, so an aquarist can't count themselves as successful until they have kept the animal for more than a couple of years. The brightly colored Linckia stars, or their near relatives, characterized by long narrow finger-like arms and a small central disk, are probably the best bets for aquarium survival for moderately large true sea stars. They seem to feed on detritus and surface biofilms, and provided they are not too big for the aquarium, they may do well.

Brittle stars are, by and large, easier to keep than are their asteroid cousins. They seem to have more latitude in acceptable food, and that probably makes the difference. Many of them can be fed on just about any meaty food, and some are good scavengers. A few, such as the large green Ophiarachna incrassata, will find their own food if not kept well fed. This particular star, which may reach 18 inches from arm tip to arm tip, has been seen to eat several different kinds of aquarium fish, as well as capturing and eating live shrimp, and other brittle stars.

If chosen well, and acclimated carefully, sea stars may make a beautiful addition to a reef tank, but the aquarist need not maintain these large, often delicate, animals to have a sea star presence in their tanks. Even without actively choosing them, some smaller sea stars are commonly found in aquaria. Small brittle star species are very common in many aquaria where they live as scavengers or suspension feeders. Often overlooked, the populations in aquaria of these animals may be huge, literally thousands per tank. One or two small species of asteroid sea stars are also occasionally found in tanks in large numbers, adding to the diversity and interest in a well-established aquarium.

Text by Ronald L. Shimek, Ph. D.
Photos by Reef Central members.
Many thanks to John Love (Rock Anemone) for his assistance with this project.

from : http://reefkeeping.com/issues/2003-11/reefslides/index.php