Setting Up a Reef Tank
Part 6

by Marty Ziegler
First published in Gravel Gossip, Diamond State Aquarium Society
Aquarticles

THE CORALS - Button Polyps

Another one of the easiest soft corals to keep in a reef tank are the zoanthids, or more commonly known as the button or mushroom polyps or polyp colonies. With around 300 species known, there are plenty to choose from. Zoanthids are very hardy and inexpensive, and another perfect coral for the beginning reef aquarist.

And now, for the scientific nomenclature, which I promise will be contained in this one paragraph. The zoanthids are from the Subclass Zoantharia and Order Zoanthidea. In the Suborder Brachycnemina and Family Zoanthidae, the genus Palythoa (polyps appear as a single mass with no body column or stalk) and Zoanthus (polyps grow from mats, body wall not sand encrusted) are most common, although there are others including the genus Isaurus (nocturnal, polyps not open during the day), Protopalythoa (containing the largest polyp species), and Sphenopus (solitary polyps, no clusters) available. The Suborder Macrocnemina contains the Family Epizoanthidae (polyps grow on sponges and hydroids) and the Family Parazoanthidae (contains the common yellow polyps). Zoanthids are small, round, anemone-like polyps that extend up from a base that is usually mat-like and attached to a rock. Some species will attach to sponges and even other corals. In the tank, they may attach to some of your accessories, such as a return tube, as they did in mine. The polyps have no skeleton and no basal disk. The skin is sort of rubbery and the base can include debris embedded, such as sand, making them fairly hard for a soft coral. They have a mouth in the center of an oral disk with 6 or groups of 6 tiny tentacles around the perimeter of the disk. The disks usually are less than 1 inch in diameter, but one species is at least 2 inches in diameter (Protopalythoa grandis). Colors range from brown, green, yellow, beige, blue, orange, pink, red, and two-tone of these shades. Generally, the polyps are in clusters, interconnected at the base, but are sometimes found as single polyps. They can extend upwards on a stalk several inches or be a mass of oral disks all interconnected without any stalk at all, depending on the genus. The button polyps contain photosynthetic zooxanthellae algae and need moderate lighting to survive. This can be accomplished with actinic and daylight fluorescents made for reef aquariums. The polyp rocks should be set in the upper levels of larger tanks, unless you go with higher intensity lighting, such as VHOs or metal halides. You can feed the polyps, although it is not necessary. They will eat live or frozen brine shrimp, or other small bits of fish, or invertebrate food solutions. I enjoy feeding them occasionally, watching them close up with their tentacles and disk, and folding up into a ball around the bit of food placed just above their mouth.

Reproduction in the tank is generally by budding or fragmentation. I have had several mushrooms fall off as a mini-cluster from the main polyp rock and later attach to a lower rock. Usually, I move these detached clusters to another location I prefer. I have also cut a cluster at the base with a sharp knife and propagated them to other parts of the tank. Once the cluster is attached, you will usually start to see budding occurring.

The button polyps like moderate current flow, although if they don't open up in a particular location, the water current may be too strong. Although they get most of their nutrition from the light, they will filter feed and need some current around them. This also helps remove their waste and prevent detritus and algae from settling on them. Iodine should be dosed periodically, along with calcium supplements for growth. Other then your normal water changes with a quality salt mix, you should not need anything else to successfully grow these corals in your tank.

The polyps are generally open during the light periods and close up during the night. Most do not retract into their mat-like base, but look like a group of stubs protruding out from the rock. Sometimes, if the water current is too strong, they will not open and will need to be moved. Most mushroom polyps have a weak sting from the tentacles, so you need to be careful where you place them. More likely, the polyps will get stung from other corals, especially hard corals, from being too close. They can be mixed with other species of polyps, to create an interesting look in your tank.

As with the mushroom anemones corallimorpharia in a previous article, there are plenty to choose from. The zoanthids, or button polyps, are very hardy, inexpensive, require only moderate lighting, do not require manual feeding, and grow and reproduce easily in a properly maintained reef aquarium.

Another easy to care for coral we will talk about next month will be the leather corals. Until then, happy reefkeeping!