How Do Zoanthids Reproduce?

The sex life of a coral is complicated. 

The biggest complication is that corals cannot move. Instead of being a free-moving organism, they are stuck down in one location, so they have to wait for the right conditions to produce offspring. 

Another complication is gender. Many corals are hermaphrodites, which complicates Zoanthid reproduction even more. Not to mention the conditions must be just right for them to get in the mood to reproduce in the first place.

However, whether you are a Zoanthid diehard that wants to create an amazing zoa garden, or are a beginner who wants to know more about how your Zoanthid Coral can reproduce, you’ve come to the right place. 

Knowing how Zoanthids reproduce is something you should take notes on, plus this extra coral knowledge will really impress your friends, family, and fellow reefers!

Zoanthid Reproduction Explained!

Corals reproduce both sexually and asexually, however, as Zoanthids are not “true corals” there is often confusion if they can reproduce the same way. 

Zoanthids come from the order Cnidaria, however, they belong to the same kingdom as stony corals (LPS and SPS) and softies, live in colonies like other corals, and dominate reefs and aquariums worldwide. 

Zoanthid Corals can reproduce both sexually and asexually, however, asexual reproduction is more common among corals. 

Zoanthid Asexual Reproduction 

All Zoanthid Corals (except Sphenopus) can form colonies and propagate via budding. If your Zoanthid reproduces asexually, new polyps are formed as buds and break away from the parent polyps (main colony), this is one way new Zoanthid colonies can form. 

The budding process does not happen overnight and unfortunately, you have no control over when it will happen. When the parent polyp in your Zoanthid colony reaches a particular size, it will divide (bud off). This process will continue to happen in your aquarium throughout your Zoanthid’s life if the conditions are right

When your Zoanthid Coral asexually reproduces, it is pretty impressive. Because they are colonial species, it is thought they do not have independent male or female polyps. This is likely why they can produce offspring from internal fertilization and brooding. When Zoanthids reproduce asexually, the offspring released will be a fully competent larva that can create a new colony elsewhere in your aquarium. 

Zoanthid Sexual Reproduction

You are probably more aware of sexual reproduction as this is how we are made, however, corals perform sexual reproduction quite differently from humans. 

Biologically speaking, “reproducing sexually” means producing gametes (eggs and sperm) that can be fertilized. Your Zoanthid polyps will either produce sperm or eggs, which are then released into your aquarium at the same time, performing external fertilization. This is why coral sexual reproduction is also known as spawning.  

During the external fertilization process, your Zoanthid is likely to perform broadcast spawning. This is when your coral will release many eggs and sperm into the aquarium water, so their offspring can be well-distributed. In the wild, corals need to broadcast spawn, so they can cover a broad geographical area in the ocean. 

So, once your Zoanthid has released the eggs and sperm into the aquarium water the gametes join to form planula, free-floating planktonic larvae. As there are many potential hazards on their reproduction journey, your Zoanthid will produce large numbers of planula to ensure they have been successful. These hazards include predators such as fish you may have in your aquarium, or strong flow that will carry them away or send them flying towards the filter. This part of the reproduction process has the highest possible mortality for your Zoanthid Coral. 

The next stage is phototaxis, this is where the planula makes its way towards the light. The planular then sink and settle, where they will form into more beautiful corals to brighten up your aquarium. 

So, what evidence is there?

A study, over two years (1974-1976), looked at two colonies of Zoanthids (Zoanthus sociatus and Z. solanderi) to determine their reproductive behavior and conditions. After a 2-year study, they found that both species were broadcast spawners with external fertilization. 

Are Zoanthid Corals Male Or Female?

Zoanthid Corals are a colony of one living organism that is connected, therefore they do not need to have two different genders to reproduce. 

Interestingly, in the same study mentioned above, marine scientists found that both the Zoanthid species could not be separated into independent male, female or hermaphroditic colonies

Will Mass Spawning Happen In My Aquarium?

Coral mass spawning (broadcast spawning) is a natural phenomenon that happens every year when different species of coral (like your Zoanthid coral) synchronize the release of eggs and sperm into the ocean at the same time, following a full moon. 

The timing of the broadcast spawning event is vital, as corals cannot move around to find a sexual partner. Coral colonies can be separated very far away from a suitable mate, so the release of their eggs and sperm must be precise and broadly timed for their coral colony to reproduce successfully. 

So, if mass spawning can happen in the ocean, could you see it in your reef aquarium? Well, yes you can, and it is rather exciting if it does happen!

Your Zoanthid(s) can be part of a mass spawning event. As your aquarium does not follow the cycle of the moon, an event like this can only be triggered by something else such as fluctuations in your salinity and temperature, which is why your Zoanthid will not become sexually reproductive until something like this triggers them.

If it does happen, do not panic. This is a natural phenomenon and pretty special to see. Your aquarium will appear cloudy for a while until the planula settles. During this time your fish may be shy until the water is clearer which can be helped with water changes and using a skimmer. 

Watch this reefer’s Zoas reproduce sexually

A Complex Sex Life

A coral’s sex life is complicated! Some corals can only reproduce sexually, some asexually, and others can do both. Zoanthid Corals can reproduce, both asexually via budding, and sexually by releasing gametes and mass spawning. 

  • Roy Lee

    I have an unhealthy obsession with reef keeping and maintaining successful tanks. If you haven't noticed from the website, I love everything related to saltwater tanks like coral, fish, and everything else in between.

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