Zoanthus
Zoanthus is a genus of colonial zoanthids: hexacorals with smooth, usually upright polyps, with no mineral encrustations in the body. 1 2 It lives in tropical and subtropical waters and hosts symbiotic algae. 2 Warning: palytoxin, a toxin that is dangerous to people too, has been detected in some species, and poisonings linked to aquarium zoanthids are documented. 8
At a glance
Data from the scientific sources listed at the bottom.
Depth in the wild
0–8 m
Size
up to 1.2 cm
maximum diameter of the living polyp in Z. sansibaricus, not of the colony
Conservation
IUCN Red List: not evaluated. The category refers to the genus as a whole: there is no single assessment. A search for the name Zoanthus in Species+ gives no results. 12 For Z. sansibaricus SeaLifeBase reports no CITES listing. 10
Where it lives
The genus has records in the tropical and subtropical zones of several oceans: the Caribbean and Brazil, South Africa and Tanzania, India and Thailand, Indonesia, Japan, Australia, Fiji, the Marshall Islands and French Polynesia. 11 Z. sansibaricus is an Indo-Pacific species. 10 In Ecuador, on the eastern Pacific coast, Z. cf. pulchellus and Z. cf. sociatus have been found. 3
How to recognise it
Tap a number on the photo: the key explains what to look for.
Life in the wild
Where it is found
The figures apply to a single species, Z. sansibaricus: 0-8 m depth and living polyps 3-12 mm across. 3 10 The descriptions collected in a 2018 study place it on rocks and reefs with strong currents and waves, while Z. sociatus and Z. pulchellus live on rocks in shallow water and in the intertidal zone. 3
Behaviour
In a 60-day experiment, a Caribbean Zoanthus in contact with a Porites coral clearly reduced its calcification, while suffering little or no effect itself. 7
Reproduction
In Z. sansibaricus from Sakurajima (Japan) the same colony contains male, female and asexual polyps; spawning takes place in mid-July, in sync with the moon. 5 At Okinawa, in Z. kuroshio, there are male, female, hermaphrodite and sterile colonies; the first release of the year took place one day after the new moon, 3.5-4 hours after sunset. 6 The authors point out that the reproductive biology of the genus remains poorly known. 6
In the aquarium
From the experience of the BallingMania community.
Zoanthus is a soft coral found in almost all tropical seas. It consists of a disc of varying size (from a few mm to a couple of centimetres depending on the species and the depth at which they can be found), a central mouth, a crown of tentacles and a stalk housing the rudimentary digestive system. They spread by encrusting the substrate, often rocky. If they find conditions favourable to their growth they can develop very large colonies, which need to be kept in check by fragging to avoid conflict with other corals.
They come in endless colours, so much so that in recent years they have become the object of real collections. Considered "easy" corals, the challenges of keeping them are often underestimated. They can be attacked by a particular species of nudibranch which, camouflaging itself among the polyps, leads to the slow but inexorable decline of the colony.
They need medium-high to strong light intensity depending on the depth at which they are found in the wild, oligotrophic water with detectable nitrate and phosphate, and good water movement to keep the colony clean; the colony forms a stunning, very dense carpet of polyps.
There is no need to feed them directly, since they use their zooxanthellae for their energy needs
Photo and description by Casina Lalli
What studies say about keeping it
Safety. Zoanthus and Palythoa are often sold without warnings about their toxicity; palytoxin has been detected in Z. sociatus, Z. solanderi and Z. pulchellus collected in the wild. 8 The most frequent route of exposure described is inhaling the vapours when boiling water is poured over the corals to get rid of them; cases through the skin and eyes are also documented. 8 In the reported cases the coral is often not identified with certainty; when it is, Z. gigantus and Zoanthus sp. also appear, but the toxin measurements in poisoning cases concern other genera. 8 Of 15 colonies bought from aquarium shops in the United States, the 4 highly toxic ones were Palythoa, while the 8 Zoanthus were non-toxic or only slightly toxic; the authors point out that a toxic Palythoa can arrive in the tank together with other corals or live rock. 9 For Palythoa, the 2016 review advises against working with bare hands and recommends sturdy gloves, goggles and a mask. 8
Did you know?
Sources
- Reimer J.D., Sinniger F. (2026). Zoanthus Lamarck, 1801. World List of Zoantharia, via WoRMS.
- Low M.E., Sinniger F., Reimer J.D. (2016). The order Zoantharia Rafinesque, 1815 (Cnidaria, Anthozoa: Hexacorallia): supraspecific classification and nomenclature. ZooKeys.
- Jaramillo K.B., Reverter M., Guillen P.O., McCormack G., Rodriguez J., Sinniger F., Thomas O.P. (2018). Assessing the Zoantharian Diversity of the Tropical Eastern Pacific through an Integrative Approach. Scientific Reports.
- Reimer J.D., Irei Y., Fujii T., Yang S.-Y. (2013). Molecular analyses of shallow-water zooxanthellate zoanthids (Cnidaria: Hexacorallia) from Taiwan and their Symbiodinium spp. Zoological Studies.
- Ono S., Reimer J.D., Tsukahara J. (2005). Reproduction of Zoanthus sansibaricus in the Infra-Littoral Zone at Taisho Lava Field, Sakurajima, Kagoshima, Japan. Zoological Science.
- Kawamura I., Jamodiong E.A., Reimer J.D. (2022). Sexual Reproduction in Zoanthus kuroshio and Isaurus tuberculatus (Cnidaria: Anthozoa: Zoanthidae) in Southern Japan. Zoological Science.
- Doucette V.E., Rodriguez Bravo L.M., Altieri A.H., Johnson M.D. (2022). Negative effects of a zoanthid competitor limit coral calcification more than ocean acidification. Royal Society Open Science.
- Pelin M., Brovedani V., Sosa S., Tubaro A. (2016). Palytoxin-Containing Aquarium Soft Corals as an Emerging Sanitary Problem. Marine Drugs.
- Deeds J.R., Handy S.M., White K.D., Reimer J.D. (2011). Palytoxin found in Palythoa sp. zoanthids (Anthozoa, Hexacorallia) sold in the home aquarium trade. PLoS ONE.
- Palomares M.L.D., Pauly D. (eds.) (2026). Zoanthus sansibaricus Carlgren, 1900. SeaLifeBase.
- GBIF Secretariat (2026). Zoanthus Lamarck, 1801: records by country. Global Biodiversity Information Facility.
- UNEP-WCMC (2026). Search for Zoanthus in the CITES lists. Species+.
Sources checked on 5 November 2026. Community texts and ratings are kept separate from the scientific data.
