Today we will be talking about yet another fascinating saltwater coral- the zoanthids, also known as “Button polyps”, “Zoas” or “Zoos” and “Colonial anemones”.
Zoanthids are erroneously regarded as soft corals, however, this is not really true because of different morphology.
Zoanthids are a group of marine animals comprising of over 15 known genera, zoas are extremely popular in the reef aquarium hobby because of their attractive color bursts, ease of care, and wide availability.
There are many varieties of zoanthids suitable for reef tanks, and they are mostly known by informal and sometimes fictional nomenclature. Fire and ice, Fruit loop zoas, Blue hornet zoas, Orange bam bam, Utter chaos, Sunny D’s, and Night Fury zoas are good examples, and they are available at relatively low prices.
This article provides an insight into the captive care of zoanthids, including a detailed care guide on how to grow these amazing creatures. Now, let’s get right into it.
Quick Notes about Zoanthids Corals
||Button polyps, Zoas, Zoos, and Colonial anemones|
|Scientific Name||Zoanthus sp.|
|Tank size (minimum)||10 gallons (~40 liters)|
|Keeping||Easy to moderate|
|Optimal Temperature||24 – 27°C (~75°F – 80°F)|
|Optimal Salinity||SG = 1.023 – 1.025|
|Optimal PH||8.1 – 8.4|
|Optimal KH||8 – 12|
|Nitrate||Less than 10 ppm|
|Color Form||Red, purple, grey, blue, green, brown, pink, orange, etc.|
Zoanthidea or Zoanthiniaria are an order of cnidarians commonly found in The Great Barrier reef, The Mediterranean Sea, and in a variety of marine environments all over the world.
Zoanthids can be characterized by the ability to incorporate grains of sand and other similar materials into their body wall.
They possess a cylindrical body and an oral disc surrounded by numerous simple tentacles, colonial anemones propagate sexually and asexually, and the progeny remain tightly or loosely connected to each other by a tissue- coenenchyme that may form stolons.
Zoanthids can be scientifically classified as follows:
Sub order: Brachycnemina & Macrocnemina.
1. Brachycnemina: This sub-order contains three families of zoas popular in the aquarium trade:
Neozoanthidae (Genus: Neozanthus),
Sphenopidae (Genus: Palythoa, Protopalythoa, and Sphenopus) and lastly,
Zoanthidae (Genus: Acrozoanthus, Isaurus, and Zoanthus).
2. Macrocnemina: This sub-order contains two families:
Epizoanthidae (Genus: Epizoanthus, Paleozoanthus, Thoracactis), and
Parazoanthidae (Genus: Antipathozoanthus, Isozoanthus, Parazoanthus, Savalia).
Details of some of these genera can be found in the description section below.
Description of Zoanthids
Species from this genus commonly possess pale yellow or brown pigments, vibrant green and orange colonies have also been found in some regions. They mostly inhabit reef flats or the top of reefs, where they may form colonies over several meters across.
Palythoa has toxins and should be distanced from stony corals in the aquarium, it will thrive best under high lighting while fed meals like copepods, artemia salina, or daphnia.
This is a rarely seen genus characterized by the formation of small colonies of cryptic polyps that have a resemblance to Epizoanthus.
Neozanthus spp. have sand grains trapped in their tissues, they require moderate to high lighting for proper growth, and should be fed with copepods or brine shrimp nauplii.
Known to have the largest polyps of all the zoanthids in the aquarium hobby. Species from this genus possess slimy thick tissue alongside some sand grains trapped in the lower portions of the columns of each polyp.
They occur on reef slopes, sandy reef flats, and hard bottoms in shallow or deep water. Most species are brownish, sometimes with green oral discs, while others have stripes or mottled oral discs.
Protopalythoa possesses toxic mucus that has the ability of destroying scleractinian coral tissue, therefore, they should not be in close contact with stony corals. They feed on meaty meals e.g. shrimp, worm, mollusk flesh, as well as fish eggs, flakes, and pellet foods.
Acrozoanthus polyps are large, brown in color, and possess very long stringy tentacles. These polyps are docile and easily adaptable to new environments. They prefer strong illumination and will feed on copepods, and thawed meaty foods.
This genus contains three valid species Isaurus tuberculatus, Isaurus cliftoni, Isaurus maculatus, they are regarded as Snake polyps.
They possess elongate columns with bumps, and the columns are typically oriented so that the ends face downward. Isaurus should be fed copepods, daphnia, and brine shrimp nauplii.
Species form this genus are the most colorful, they possess contrasting shades of green and brown mostly, but sometimes red, orange, pink, blue, yellow, lavender, grey, and are usually two-toned. They form colonies of densely crowded polyps attached in a common tissue at the base, while some varieties form branched stolon-like creeping bases that firmly adhere to the substrate surface.
Zoanthus spp. grow in the intertidal zone being exposed at low tides to the baking sun, cold fronts, or rain showers. In aquariums, they need moderate to strong illumination to thrive, and they will feed on blackworms, shrimp, and flake foods.
Epizoanthus are epizootic, this implies that they live on other animals. Just like Parazoanthus, Epizoanthus live in close association with sponges and hydroids (offering them protection), they may also grow on gorgonian skeletons, and even freely in some cases.
They do not possess zooxanthellae like other zoanthids, hence the need for regular feeding.
Behavior of Zoanthids
Zoanthid corals may be peaceful and docile most of the time, however, they will join in the competition for space like other sessile colonial invertebrates. They do this by expelling toxins and rapidly spreading out outgrowths from their mat-like coenenchyme.
Species from the genera Palythoa and Protopalythoa and Zoanthus are known to be toxic, they possess a lethal substance- palytoxin, and tends to inflict injury to most stony and soft corals.
As observed by enthusiasts, species from the genera- Zoanthus, Protopalythoa, and Palythoa can all be grown next to each other without any fear of harm being done.
Now, this is something that fascinates me; all zoanthids have a specialized mechanism for feeding. This is made possible by the presence of symbiotic & photosynthetic algae in their cells. This algae is known as zooxanthellae. Through this medium, they can trap energy from the light which supports their various life activities.
In addition, zoanthids prey on certain microorganisms. They can feed on the phytoplankton and zooplankton suspended in the water column using their tentacles that open to trap these organisms.
Asides that, you can equally feed zoanthids with specialized prepared diets obtainable from pet stores, for example:
- frozen mysis,
- brine shrimp,
- polyp booster (link check the price on Amazon),
- coral frenzy (link to Amazon)
- reef roids (link to Amazon) amongst others.
If you are going to feed solid meals to the zoanthids, then you have to practice target feeding. This practice entails using an equipment e.g. turkey baster to squirt food particles (mixed with a bit of tank water) directly on the polyps, preferably in the center.
When you do this, the polyps will respond by folding inward, thereby opening their mouths to ingest the food for digestion.
Manual feeding is not really a necessity because zoanthids can make do with the energy provided by the symbiotic zooxanthellae that live within their tissue, as well as actively capturing small prey within the reef tank. However, I would still recommend it.
The good thing about manual feeding the polyps is that you will be rewarded with rapid growth spurts.
Tank Requirements and Water Parameters
In the captive care of corals, higher chances of success are attainable if water parameters remain stable. This is one duty to enforce if you are keen on their survival.
Here is the recommended tank size for housing zoas, and standard water parameters to be maintained:
The minimum recommended tank size for housing zoanthids is 10 gallons. Larger tanks should be utilized if you plan on keeping zoas with other corals, in order to ensure that they are well spaced out, thereby avoiding competition.
Water type, Temperature, Hardness, and pH:
Temperature: The ideal temperature range is between 75 – 80 degrees Fahrenheit (24 – 27C).
pH: pH values should be between the range of 8.0 – 8.4.
Hardness: Ideal water hardness values between 8-12 dKH should be maintained.
Salinity: Zoanthids will thrive best under optimal specific gravity – 1.025.
Phosphates: It would be best to keep them below 0.03 ppm.
Nitrates: Nitrates value should be around 5ppm.
Note: Some people might not know that but any filter feeders need a food source in the water. Therefore, keeping the nitrate levels at 5ppm will not hurt your reef tank, but will help any filter feeders to grow. Your tank will benefit from it and you will see extra colors in the zoa corals.
Just check the phosphates from time to time, as long as their level is low, the chance of unwelcome algae growth is minimal.
Zoas need moderate to high lighting in order to maximize the zooxanthellae’s potentials through photosynthesis to provide energy. In addition, they need strong lighting for their colors to pop.
Zoanthids only require moderate currents, although some reefkeepers argue that they need stronger water currents since they come from natural coral reefs with high currents.
Regardless of your decision, bear in mind that excessive water currents will make the zoanthids retract its tentacles. In light of this, go easy on the water flow and adjust accordingly, do not place zoas close to the powerheads.
Care and Maintenance of Zoanthids in Aquariums
Generally, caring for Zoanthids is very easy, it is one of the few corals that can thrive successfully in most reef tanks.
Nonetheless, due to the fact that there are so many species of zoas, they still have some different preferences (mostly regarding lighting, water flow, and placements). In addition, even within the same species Zoanthid corals will react differently to a different environment.
For example, Chaos Zoanthids will get slightly bigger under low light and smaller at high light. At the same time, under low light, they lose some of their colorations. Hornet colas will be better at moderate to high lighting, etc.
However, if you want to make Zoanthid corals happy and healthy – start dosing Iodine at least once a week and you will see the difference. Iodine is an extremely important element for zoas, it boosts their growth and improves the colorations.
Do not overdose. Use the instructions on the bottle based on your tank size.
Placement of Zoanthids in Aquariums
Placing zoas in the reef tank can be a bit tasking. Normally, they should be placed in a medium – high flow area in order to guarantee higher chances of the polyps opening up fully.
When they are placed in areas with very high / excessive flow, the polyps are likely to have a hard time opening up, and this has a negative impact on their growth and development.
Subsequently, the polyps should not be placed in shaded or overexposed areas. They enjoy lighting a lot but you should not overdo it. The placement of these animals can be subjected to a continuous trial and error exercise until you find the perfect spot for them to settle.
Fragging and Propagation Zoanthids
You may be wondering how do zoanthids reproduce. Well, in the wild, these polyps reproduce by sexual reproduction, the union of gametes to produce free-swimming larva or planula that matures with time, zoanthids may have separate sexes while some are hermaphrodites.
Another way of reproduction is by asexual budding whereby the Zoanthid divides to form young polyps, which will hold tightly or loosely to the main parent.
Fragging. You can as well propagate a zoa by cutting it together with the live rock it is attached to. For this exercise, you can utilize a dremel, precision knife, scalpel, stony coral cutter or inland band saw.
Once the polyp has been split, you can glue it to a frag plug or disc with a cyanoacrylate gel or super glue gel before putting it back into the tank.
Very Important: As a safety precaution, always wear gloves while handling zoanthids, and eye goggles when it is time to cut them to prevent palytoxin from squirting into your eyes. Make sure to rinse your hands thoroughly with soap and water immediately after handling them.
Warning: DO NOT EVER put zoanthids into boiling water. All these toxins in the water will be in the air and it will affect your whole house! This is very dangerous!
Things that you might need depending on your method:
Problems Associated with Zoanthids
There’s quite a number of diseases and pests that militate against the good health of zoanthids, these include:
Zoa pox manifests by forming small yellowish / white marks / dots on the outside stalks of zoanthids. Eventually, the affected polyps will gradually close up, and get covered with the pox. If left untreated, the sick polyps will decline and die.
This infection can be cured using Furan-2, following these steps:
- Empty 1 packet of Furan-2 into a cup of fresh saltwater (with the same salinity as your tank water).
- Stir thoroughly until it is completely dissolved. Keep stirring a few minutes more.
- Put affected zoas in the mix.
- Soak the polyps for at least 15 minutes, but not more than 30 minutes.
- Repeat treatment once daily for 3 consecutive days with 24 hours between each treatment.
- Rinse the zoas with aquarium water in a separate container to get rid of zoa pox and Furan-2 residue.
- Place the zoas back into the tank, preferably in areas with strong flow.
- Allow the zoas to rest for 4-7 days, use this period to assess its healing.
- If the zoa pox still persists, then you should perform another series of treatments (dipping time should be reduced to 10 minutes).
Note: Some aquarists dip infected Zoanthid corals into freshwater for 10 – 15 minutes. Although Zoanthids are pretty hardy I still do not recommend this method.
Note #2: Some guides will tell you that it is better to use a fresh saltwater mix to ensure anything that may be causing the ailment in the first place isn’t included in treatment. The problem, though, is that if you try to use fresh saltwater mix, you will see that it is almost impossible to match all the parameters of fresh saltwater to the tank water that your zoa’s were currently in.
That is why I still recommend using tank water for that. The treatment itself is going to shock them. So, we do not need to make it even worse by putting them in different parameter water from what they are used to.
Note #3: Do not confuse sand irritation and Zoa pox.
Once again, nobody really knows that is the cause of this white mold. However, the most popular theory says that it might be due to a lack of water motion. The tank can also manifest it after an accidental injury of the corals.
Possible treatments include: Lugol’s solution, hydrogen peroxide, Maracyn 1, and Furan 2.
Lugol’s solution: 300 ml (~0.01 gallon) of tank water for 3 – 5 drops of Lugol’s solution for 3min.
Hydrogen peroxide: slowly start adding hydrogen peroxide until you see bubbles forming around the base of the zoas. Let the bubble for about 5 minutes. Take a small paint brush and gently use it to rub between the polyps. The next step is to dip them into a weak solution of Lugols or Furan 2. Repeat it for a week.
Do not use any of these treatments in the tank. It is only for dipping.
Coral bleaching can be simply explained as a phenomenon whereby zooxanthellae are expelled from the coral. This results in the loss of the natural color of the polyps, and a transition to a translucent (white) color.
Bleaching is caused by an increase in lighting/ ultraviolet radiation, extreme temperatures / salinities, extreme changes to the salinity, and excessive water flow. It can equally occur as a coral’s natural reaction to an underlying infection.
Dark brown/black stems:
This is often a sign of severe bacterial infection which can cause your zoas to die.
- use a soft toothbrush and gently scrub the brown and black dying tissue away,
- dip in iodine diluted saltwater, or/ and use Furan-2 treatment.
These hitchhikers include zoa-eating nudibranchs, sundial snails, and sea spiders. They are likely to feed on zoanthids, and may have been introduced to the tank by zoanthids or other new tank inhabitants.
They can be eliminated by handpicking them from the polyps (using a pair of tweezers). Asides the procedure of removing nudibranchs with a pair of tweezers, they can also be eliminated by quarantining the zoanthids using CoralRX.
- Add 20 ml of CoralRX to 1 gallon of aquarium saltwater.
- Mix thoroughly.
- Submerge the zoas into the dip.
- Gently shake the zoas in the dip.
- Using a turkey baster or pipette, blast the corals with the dip for 5-10 minutes (ensure it gets between the polyps and the underside of the coral).
- Ensure the coral stays submersed in the dip for at least 5 minutes, and not more than 10 minutes.
- Rinse the coral with aquarium saltwater, and place it into the tank.
Warning: Chemicals can kill zoa-eating hitchhikers but not the eggs. Therefore, we have to repeat the treatment once they hatch. Also, if nothing helps, use the freshwater method as the last resort.
If you dip them in freshwater do it outside and wear a mask.
Buying Zoanthids Corals
As you already know; buying a healthy zoanthid will significantly increase your chances of success. Healthy zoas can be identified by the presence of colorful polyps (not washed-out), this factor may be hampered by the fact that not all varieties possess punchy colors, some have dull colors.
Ensure that the tentacles of the individual polyps are out, and not retracted. This is an indication of good health and activeness.
Buying a large colony of zoanthids is a waste of money because a small frag or colony with few polyps attached will grow and multiply rapidly under the right conditions.
Zoanthids are relatively cheap, they can be purchased in local fish stores, and online from reputable vendors, you can also check out worldwidecorals.com, they sure have a variety of colorful zoas in stock for your tank.
Quarantine Zoanthids Corals
Never forget to quarantine any corals before introducing them to the tanks. Even if it is from a reputable source – play safe. Use a magnifying glass and be patient, it will save you a lot of time and nerves!
As I have already said, Zoanthids Corals can have parasites and unwelcome hitchhikers. DO NOT add them to your main reef tank right after you bought it.
Introducing zoanthids to your reef tank is one of the best decisions you will ever make.
Most reef hobbyists have a soft spot for these fantastic corals because of their unique structure, a large variety of brilliant color patterns, and combination morphs which contribute greatly to the aesthetic value of reef tanks.
We would like you to get one for your tank, you will totally love it.