Green Sea Mat, Zoanthus sociatus
Green Sea Mat, Zoanthus sociatus. Underwater photographs taken in coastal waters off Akumal, Quintana Roo, April 2016. Photographs and identifications courtesy of Juan Rojo, Akumal.
Phylogeny: The Green Sea Mat, Zoanthus sociatus (Ellis & Solander, 1786) is a zoanthid in the Zoanthidae Famiily of Zoanthids. The Zoanthus Genus is one of three genera in the Zoanthidae Family, and there are twenty-two species in the Zoanthus Genus. They are also known as the Button Polyp.
Morphology: The Green Sea Mat is a sissle, colonial. The individuals range in size from 3.0 cm (1.2 inches) to 5.0 cm (2.0 inches) and the colonies are generally 10 cm (3.9 inches) x 10 cm (3.0 inches). The stolon-connected polyps have 30 short tentacles and their polyps are extended continuously day and night. They have the ability to survive desiccation and lower salinity levels. They also have the ability to regenerate lost portions when disturbed. The body of the polyp is deep red to orange in color and the tentacles are orange to yellow. The tentacles are located on the margin of the disk, giving the polyp a flower-like appearance.
Habitat and Distribution: The Green Sea Mat grows in a colonial, green mat, on the reefs understory on top of the substate. It is found in the lower intertidal zone on protected reefs in water temperatures between 20oC (73.4oF) and 28oC (82.4oF) at depths up to 2.3 m (7 feet). The lack a calcareous skeleton and form elaborate piecemeal mats with green to turquoise polyps that are connected via stolons. They are found on shallow water reef flats that are exposed to large amounts of sunlight and intermittently strong currents. The Green Sea Mat is found in all Mexican waters of the Atlantic Ocean including the Gulf of Mexico and the Caribbean east of the Yucatan Peninsula.
Diet: The Green Sea Mat has a symbiotic relationship with the Inoflagellate Zooxantghellae, Symbiodinium pilosum, from which obtains about 50% of its fixed carbon required for respiration. The balance of their energy comes from collection of passing zooplankton and detritus with their tentacles which possess nematocysts.
Predators: The Green Sea Mat is known to be preyed upon by coralivorous gastropods and sea urchins. They lack the chemical compounds used for defense found in some zoanthids. They have become strongly attached to the sediment and able to survive strong currents with their only ability to avoid predation is growth in shallow areas where the gastropods and sea urchins cannot survive. In such environments they are the dominate zoanthid having to strong compete for space.
Reproduction: Reproduction in the Green Sea Mat is primarily asexual, however they have the ability to reproduce sexually. Asexual reproduction involves budding whereby a new poly is created from an old polyp followed by fusion. They are broadcasters with external fertilization and are mostly hermaphroditic with a small percentage being male or protogynous. The zygote develops into a planktonic planula larva. Metamorphosis begins with early morphogenesis of tentacles, septa and pharynx before larval settlement on the aboral end. Each colony is genetically the same.
Ecosystem Interaction: The Green Sea Mat does not have any documented commensal or parasitic relationships.
Human Interaction: The Green Sea Mat is used extensively by the aquarium trade being aesthetically pleasing, easy to maintain and can be propagated in captivity. There are on-going studies evaluating the use of the Green Sea Mat against human lymphatic parasites and a source of osteoporotic drugs to prevent bone density decrease. From a conservation perspective the Green Sea Mat has not been formally evaluated, however they are fairly common with a wide distribution and should be considered to be of Least Concern. They posess a toxin that is toxic to humans.
Synonyms: Actiniav sociata, Zoanthus flos-marinus. Zoanthus nobilis, Zoanthus poriticola and Zoanthus proteus.