Zoanthids, also called zoas and button polyps, are a type of colonial sea anemone. However, their care in aquariums is very similar to soft corals. In fact, zoanthids fall somewhere near the hardier end of the reef aquarium hobby, adapting to aquarium life better than more delicate corals. However, even an "easy" reef tank requires more care than a fish-only aquarium.
Picking Your Zoanthid
Picking the right zoanthid can greatly increase your chances of success -- and make your aquarium buck go further. To pick a healthy zoanthid, make sure the individual polyps are colorful and not washed-out. Keep in mind that some species and varieties of zoanthids have drabber colors than others, so make sure you know what's normal for your zoanthids. Regardless of their color palette, a healthy zonanthid will usually have its tentacles out and not retracted. Also, don't buy a large colony of zoanthids. You only need a small pebble of live rock with one or two polyps attached. They will breed and spread rapidly under good conditions, so buying a larger colony is something of a waste of money.
Zoanthids come from coral reefs, areas which tend to have pretty dramatic currents. However, unlike many reef organisms, they only need moderate current. This contrasts with many types of coral that need stronger water movement, as much as you can provide with water pumps. In your aquarium, it may take some trial and error to find the right current for your zoanthids. Excessive current will make a zoanthid retract its tentacles, so if you see this sign, you need to ease back on the current.
Let There Be Light
Experts recommend moderate lighting for zoanthids. Keep in mind however, that this is moderate lighting for corals. This still means more lighting than a fish-only aquarium. In the aquarium hobby, you can use the amount of lighting power per gallon, or watts per gallon, to measure lighting. For zoanthids, you need at least 4 to 5 watts per gallon of light. However, tall aquariums need more light, since light dissipates when traveling through water. Most reef tanks take advantage of powerful types of aquarium lighting like metal hallides, T5 fluorescents and LED arrays.
All zoanthids have photosynthetic algae in their cells, which provides them with energy from sunlight. However, many species also eat solid food, and extra food can encourage them to breed and spread. You can feed zoanthids either specialized prepared foods, available online or in high-end pet shops, or small organisms like rotifers or copepods. To culture rotifers or copepods, research the specific species you want to culture and purchase starter cultures online. To feed, mix the food with aquarium water in a separate dish, the spray it directly at the colony with a turkey baster. You can actually watch some species eating the food.
Handle With Care!
Never forget that some species of zoanthids are extremely toxic. Some carry a nerve-poison called palytoxin. There's some debate about the lethal dose for a human, but experts agree it's an amount measured in nanograms -- barely visible to the human eye. Since species-level identification is difficult for zoanthids, you may not know if you have a potentially dangerous species or not. Always wear gloves when handling zoanthids, and never kill unwanted zoanthids with boiling water since this produces toxic steam. Also, print out a fact sheet about palytoxin and keep it on hand in case you need emergency medical care; most physicians rarely see this poison and may not know what to do without a fact sheet.
- FishChannel.com: Choosing Coral
- Tropical Fish Hobbyist: Aquarium Science: Palytoxin and You: How to Avoid a Deadly Zoanthid Toxin
- Fishlore: Zoanthids -- Button Polys -- Zoas Corals
- FishChannel.com: Reefkeeper Trying to Rid Tank of Zoanthid Corals Winds Up in Hospital
- Tropical Fish Hobbyist: Aquarium Basics: Lighting