CHOOSING CORALS WISELY...

I think it is important to decide which types of cnidarians (e.g., anemones, corals, false corals) will be the focal point of your aquarium. We can divide them into the following taxonomic groups: soft corals, mushroom anemones, zoanthids, large-polyped stony corals and small-polyped stony corals. Of these groups, most people have the greatest success with soft corals, mushroom anemones and zoanthids, while the small-polyped stony corals are the most demanding. Large-polyped stony corals vary in their hardiness — we will discuss these in further detail later.

To ensure success it is best to keep either soft corals, zoanthids and mushroom anemones or stony corals, particularly if you want long-term success with small-polyped stony corals. The problem with keeping both hard and soft corals in the same tank arises from the competition that exists between them for growing space. Soft corals have evolved an arsenal of chemicals that they use to retard the growth or even destroy hard corals that grow around them. If you have ever been diving you may have seen large stands of soft corals, with relatively few hard coral species growing in close proximity. This is in part due to the effective chemical warfare that soft corals wage. A closed system that houses a forest of these animals will not be a good home for hard corals. We can keep these chemicals from soft corals in check, at least to some degree, by using activated carbon and protein skimming.

Mushroom anemones, especially the knobby varieties, can also interfere with your attempts to keep hard corals. They have potent nematocysts (stinging cells) that sting animals they are close to, and they also produce chemicals that irritate neighboring hard corals.

For the neophyte reefkeeper I would recommend keeping soft corals and mushroom anemones. These animals will grow and multiply if 1) your water quality is good, 2) you have adequate lighting and, at least in the case of soft corals, 3) there is ample current. You should also be aware that more fish can be kept in a soft coral aquarium than a hard coral tank because these invertebrates can withstand higher levels of dissolved organics and nitrogenous wastes.

The easiest soft corals to keep are colt corals (Cladiella spp.), finger leathers (Sinularia spp.) and tree corals (Lemnalia, Litophyton and Nephthea spp.). The only problem with these corals is that they often grow so well they take over the entire tank!

Leather corals (Sarcophyton spp.) are moderately easy, but can be temperamental at times. If the polyps refuse to extend, check the pH and make sure it is above 8.3 (J. Sprung, personal communication) or do a small water change (about 10 percent of the tank volume). Avoid the colorful soft corals of the Dendronephthya and Scleronephthya genera — they apparently have special dietary requirements and are difficult in the long term.

The star polyps (family Clavulariidae) are a wonderful introduction for the soft coral aquarium. They are beautiful to look at, especially when only the blue fluorescent lights are on, and are very prolific. They will grow from their original rock to other surfaces around them, including the aquarium glass.

The daisy polyps, which are also in the family Clavulariidae, are quite durable, while the members of the family Xeniidae, including Xenia spp. and Anthelia spp., can be more difficult to maintain. The members of the latter two genera are often confused with each other (most often Anthelia is sold as Xenia), and are known commonly as pulse, pom-pom or waving hand coral. The easiest way to tell them apart is that Xenia grows from a central stalk, while Anthelia polyps originate from an elongate or matte-like stolon.

Colonial anemones, or zoanthids, are durable and best kept with soft rather than hard corals. The yellow colonial polyps (Parazoanthus gracilis) are especially attractive, and are a durable aquarium species. They frequently reproduce in captivity asexually by a phenomenon known as budding. Several species in the genera Zoanthus and Palythoa are also hardy additions to the reef aquarium.

Mushroom anemones, or coralimorpharians, do well in low to high light and low to moderate water movement. Most rely principally on symbiotic algae (i.e., zooxanthellae) in their tissues to provide them with food, but some of the larger species, like the elephant ear anemone (Amplexidiscus fenestrafer), will feed on small fish by enveloping them in its polyps.

When mechanically stimulated, some mushroom anemones exude filaments from their mouths or from knobs on the polyps. These are loaded with stinging cells that ward off potential predators or other cnidarians competing with them for space. Beware, these can also cause welts on more delicate human skin. Mushroom anemones should be kept with soft corals and/or zoanthids.

As far as hard corals are concerned there are some hardier, large-polyped varieties, like open brain (Trachyphyllia geoffroyi), tooth (Lobophyllia spp.), bubble (Plerogyra sinuosa), fox (Nemenozophyllia turbida), plate or pagoda (Turbinaria peltata) and elegance coral (Catalaphyllia jardinei), that can be successfully housed with soft corals. However, bubble and elegance corals have a potent sting, and the former species can send out long sweeper tentacles, which it often does at night, to sting its neighbors. It is prudent to provide at least 10 inches of space between coral specimens so that they are not close enough to sting one another. Although these species are not immune to soft coral chemicals, they are not usually as adversely affected. All of these species are good candidates for the neophyte reefkeeper.

Other large-polyped hard corals that are easy to keep include disc corals (Fungia spp.), tongue corals (Polyphyllia spp. and Herpolitha limax), crater coral (Scolymia spp.), button coral (Cynarina spp.) and closed brain corals (e.g., Favia spp.). Beginners should stay away from long-tentacle plate coral (Heliofungia actiniformis), torch coral (Euphyllia glabrescens), hammer coral (Euphyllia ancora), frog spawn coral (Euphyllia divisa) and, especially, flowerpot corals (Alveopora and Goniopora spp.). The last species listed are hard to pass up because of their beauty, but most species within these two genera are difficult to keep for extended periods of time (a year or more). However, there are some species that appear to adapt to captive life more readily than most. When buying any large-polyped stony coral, make sure that the polyp has not been damaged, because this makes the specimen more vulnerable to parasitic and bacterial infections