Corals, Jellyfish, and Sea Anemones
Although they vary dramatically from one another in appearance, these animals are all members of the phylum Cnidaria and are thus closely related. Until recently, corals were considered by most as nearly impossible to keep and, indeed, they still present problems. Water quality is exceedingly important, as is the wavelength and intensity of lighting. Many coral species obtain a good deal of their food via the action of symbiotic algae, which live within them. Without proper lighting the algae perish, and no amount of additional food provided thereafter can keep the coral alive. Most corals feed upon plankton-sized food items, and although commercially prepared diets are now available, many are still difficult to maintain. One exception is the tooth coral. Now routinely available in the trade, this species eats large food items, such as pieces of shrimp, and is thus fairly easy to feed.
Until recently, collection of coral for commercial aquariums was a leading cause of coral reef destruction. Reef ecosystems are extremely delicate and very slow to recover from injury. Although collection is now outlawed in many areas, be sure that any coral you purchase is commercially cultured and not collected from reefs.
Jellyfish (see color insert for photo) are increasingly exhibited in public aquariums but are, as yet, too delicate for most home aquarists to maintain. Indeed, very few are offered for sale. One possible exception is the upside-down jellyfish (
Sea anemones are among the heartiest of the cnidarians, although even they will perish quickly if kept in suboptimal water quality. Most also require a fairly steady current of water flowing over them at all times. A very commonly available species is the Caribbean anemone (
All species of anemone, coral, and jellyfish possess stinging cells that are capable of causing painful rashes, and none should be handled with bare hands.