Zoanthus sociatus
A colonial zoanthid forming green mats in tropical shallow reefs.
Zoanthus sociatus, called the green sea mat or button polyp, is a zoanthid that lives in shallow reef zones across tropical waters from the Caribbean to southeastern Brazil. It forms extensive, patchy mats of green to turquoise polyps and is currently under study for its potential to treat human lymphatic parasites. As a cnidarian, it has nematocysts. Its polyp form places it among the anthozoans, and because its tentacles appear in multiples of six, it belongs to the subclass Hexacorallia. It lacks a calcium carbonate skeleton, which puts it in the order Zoanthidea. The polyps, connected by stolons, usually have 30 short tentacles and stay extended day and night, feeding mainly on detritus rather than zooplankton. They are often found on reef flats with high light and intermittent strong currents. This species lives in the lower intertidal and upper subtidal zones of protected Caribbean reefs. It is a sessile, colonial organism that grows in the reef understory and on disturbed substrate. It can tolerate desiccation and lower salinity levels, and it tends to dominate other zoanthids in its habitat. Reproduction is mostly asexual, though sexual reproduction can occur. Asexual methods include extratentacular budding (a new polyp forming from an old one) and fission (a fragment breaking off). Fragment size is limited by higher mortality in smaller fragments. Colonies are generally genetically identical. Even when a colony reproduces sexually, many polyps remain infertile, highlighting the greater role of asexual growth. Colonies do not become reproductive until they reach a certain size. Fertilization is external, and most polyps are hermaphroditic, though some are male or protogynous (starting female then becoming male). In Panama, reproduction is seasonal and synchronized with extremely low tides. Nearly half of the polyp’s energy comes from symbiotic zooxanthellae; the rest must come from feeding. Zoanthids use nematocysts on their mesenterial filaments to capture prey. Z. sociatus eats anything of suitable size, from Artemia cysts to dissolved organic matter. Though less efficient as heterotrophs, they generate more energy through photosynthesis because they lack a calcified skeleton, allowing more light to reach their chloroplasts. Digestion uses both extracellular and intracellular methods.
Quick Facts
- Taxon
- Zoanthus sociatus
Facts from the source article.
Lore & Background
Zoanthus sociatus forms elaborate piecemeal mats of normally green to turquoise polyps. Polyps are stolon-connected and normally have 30 short tentacles. They are often found on reef flats exposed to high light intensity and intermittently strong currents, and can survive desiccation and lower levels of salinity. It grows in the reef understory and on disturbed substrate, and appears to dominate other zoanthids. Polyps are extended continuously day and night and feed predominantly on detritus, not zooplankton. They obtain nearly half of their required energy from symbiotic zooxanthellae. Zoanthids have nematocysts on their mesenterial filaments used for prey capture, and they digest prey using both extracellular and intracellular methods. Reproduction is mainly asexual, through extratentacular budding and fission, though sexual reproduction may occur. Colonies are generally genetically the same. They use external fertilization, are mostly hermaphroditic (some male or protogynous), and synchronize gamete release with extremely low tides in Panama. Colonies do not become reproductive until they reach a certain size.
Reader's Guide
Zoanthus sociatus is a sessile, colonial cnidarian in the order Zoanthidea, lacking a calcium carbonate skeleton. Its nematocysts place it within Cnidaria, and its polyp morphology with tentacles in multiples of six places it in subclass Hexacorallia. The species forms mats of stolon-connected polyps, each with 30 short tentacles, and is found in the lower intertidal and upper subtidal zones of protected Caribbean reefs, often on reef flats with high light and strong currents. It can tolerate desiccation and reduced salinity, and dominates other zoanthids in its habitat. Ecologically, Z. sociatus obtains nearly half its energy from symbiotic zooxanthellae; the rest comes from feeding on detritus, Artemia cysts, and dissolved organic matter. Its lack of a calcified skeleton allows more light to reach chloroplasts, making it more efficient photosynthetically than calcified corals. It uses nematocysts on mesenterial filaments for prey capture and digests prey both extracellularly and intracellularly. In the aquarium trade, the species is notable for its continuous day-and-night polyp extension and its ability to thrive under high light. It reproduces mainly asexually via budding and fission, with colonies remaining genetically uniform. Sexual reproduction occurs seasonally in Panama, synchronized with extremely low tides, but a large proportion of polyps remain infertile, underscoring the importance of asexual growth.
Did You Know?
- Zoanthus sociatus is currently being studied for its use against human lymphatic parasites.
- Polyps have 30 short tentacles and are extended continuously day and night.
- Reproduction synchronizes with extremely low tides in Panama.
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