Common name: pulsing xenia

Synonyms and Other Names: Xenia elongata

Identification: Unomia stolonifera is a soft bodied octocoral (8 tentacles) from the family Xeniidae. This species is characterized by the distinctive “pulsing” action of its fan-like eight-tentacled polyps (Bolick and Lee 2023).  Tentacles are yellow to pink in color due to the symbiotic zooxanthellae (photosynthetic algae that live in its tissues) (Benayahu et al. 2021). Its smooth unbranched stalks arise from a thin basal (base) membrane that spreads over the surface of the substrate (Gohar 1938). Unomia stolonifera can be differentiated from similar species of Xenia by the presence of ungrouped polyps growing down the stalk instead of being tightly grouped into the polypary (end of the stalk that usually bears the polyps) (Benayahu et al. 2021, see Figure 5D).

Size: Stalks up to 8 cm (Benayahu et al. 2021)

Native Range: Western Indo-Pacific and Indonesia, specifically Celebes Island (Sulawesi, Indonesia) (Bolick and Lee 2023, Ruiz-Allais et al. 2021).

Alaska	Hawaii	Puerto Rico & Virgin Islands	Guam Saipan

Hydrologic Unit Codes (HUCs) Explained
Interactive maps: Point Distribution Maps

Ecology: Unomia stolonifera is a pioneer species that grows rapidly, has high fecundity, and exhibits extensive vegetative reproduction (Ruiz-Allais et al. 2014). It thrives in well-lit conditions at water depths of 0-50 m (Ruiz-Allais et al. 2021). This species is not known to feed on any particulate matter and gets energy from photosynthesis (via zooxanthellae) and by absorbing dissolved organic compounds. Unomia stolonifera prefers stony substrate but is capable of colonizing soft substrates as well (Ruiz-Allais et al. 2014). It is somewhat ephemeral, and abundance decreases slightly with the rainy season (Ruiz-Allais et al. 2014). This species reproduces both sexually and asexually (via budding).

Means of Introduction: Unomia stolonifera was intentionally introduced illegally to northern Venezuela via commercial aquarists in the early 2000’s (Ruiz-Allais et al. 2014). Its spread has been aided by fishing activities (trawling, stationary nets, traps, etc.), boat ballast water, and larval and propagule dispersal (Ruiz-Allais et al. 2021). Fragments of U. stolonifera have also been observed floating with currents or attached to free-floating vegetation (Ruiz-Allais et al. 2021). The introduction to Pearl Harbor, Hawaii was most likely an aquarium release as this species is common in the trade (Bolick and Lee 2023).

Status: Established in Venezuela, Cuba, and Hawaii (Pearl Harbor).

Impact of Introduction: Unomia stolonifera has been shown to significantly reduce populations of native stony corals, hydrocorals, and other anthozoans (marine invertebrates) (Ruiz-Allais et al. 2021). In some invaded areas, percent cover of U. stolonifera reached 30-80%, massively outcompeting native corals (Ruiz-Allais et al. 2021). Colonies of U. stolonifera have been observed overgrowing beds of seagrass (specifically Thalassia testudinum), stony reefs, and soft substrates (Ruiz-Allais et al. 2021). The invasion of U. stolonifera has impacted the community structure of Venezuela’s reefsby causing harm to benthic organisms and fish and negatively impacting their habitat and food sources (Ruiz-Allais et al. 2021). It was noted by Ruiz-Allais et al. (2021) that, at sites highly colonized by U. stolonifera, fish stocks decreased significantly.  Their study also indicated a significant correlation between loss of species diversity and increase in cover of U. stolonifera.

Remarks: Unomia stolonifera does not appear to have any known predators in its introduced range (Ruiz-Allais et al. 2021).

References: (click for full references)

Benayahu Y., L.P. Ofwegen, J.P. Allais, C.S Mcfadden. 2021. Revisiting the type of Cespitularia stolonifera Gohar, 1938 leads to the description of a new genus and a species of the family Xeniidae (Octocorallia, Alcyonacea). Zootaxa. (2)4964.

Bolick, H., and K. Lee. 2023. Two new occurrence records for the Hawaiian Islands of invasive octocorals (Cnidaria: Anthozoa: Octocorallia: Malacalcyonacea) reported in Pearl Harbor: Unomia stolonifera (Gohar, 1938) and Capnella cf. spicata (May, 1899). Bishop Museum Occasional Papers 155: 181–184.

Ruiz-Allais, J. P., M.E. Amaro, C.S. McFadden, A. Halász, and Y. Benayahu. 2014. The first introduction of an alien soft coral of the family Xeniidae in the Caribbean, an invasion in eastern Venezuelan coral communities. Coral Reefs (33)287.

Ruiz-Allais, J., Y. Benayahu, and O. Lasso-Alcalá. 2021. The invasive octocoral Unomia stolonifera (Alcyonacea, Xeniidae) is dominating the benthos in the Southeastern Caribbean Sea. Memoria de la Fundación La Salle de Ciencias Naturales (79)63-80.

Sáez, J.E., R. Estrada-Estrada, J.P. Ruiz-Allais. 2023. The marine invasive species Unomia stolonifera (Gohar, 1938) (Octocorallia, Alcyonacea) in Cuba. Actions for its control and elimination. Revista de Investigaciones Marinas 43(1): 140-146.

Author: Reaver, K.M.

This information is preliminary or provisional and is subject to revision. It is being provided to meet the need for timely best science. The information has not received final approval by the U.S. Geological Survey (USGS) and is provided on the condition that neither the USGS nor the U.S. Government shall be held liable for any damages resulting from the authorized or unauthorized use of the information.