Invasion History

First Non-native North American Tidal Record: 1937
First Non-native West Coast Tidal Record: 1937
First Non-native East/Gulf Coast Tidal Record:

General Invasion History:

The Pale or Glass Anemone, Exaiptasia pallida was described in 1864 by Agassiz from Charleston, South Carolina, as Dysactis pallida. It had been described earlier from Naples, Italy by Rapp in 1829, as Actinia dipahana, but this description was largely overlooked. As this anemone became widespread around the world, it was described many times and thus has many synonyms. Populations and their symbiotic dinoflagellates in the tropical and subtropical West Atlantic have many geographically isolated clades, while many populations in more remote regions are genetically more similar (Thornhill et al. 2013; Glon et al. 2020). We are following Glon et al. (2020) in treating the species as native from North Carolina to the Caribbean and Brazil, but introduced in the Mediterranean, the Suez Canal, Japan, and Hawaii (as Aiptasia pulchella), California to Mexico (as Aiptasia californica) (Carlgren 1953), Pacific Panama, the Galapagos, St. Helena (as Aiptasia insignis), and South Africa (Grajales and Rodriguez 2014; Glon et al. 2020).

Exaiptasia pallida occurs in subtropical and tropical waters, usually at 0–5 m depth, in rocky habitats, mangrove roots, dead corals, marinas, etc. Its prolific asexual reproduction by fission, sexual reproduction of planktonic larvae, tolerance of variable temperatures and salinities, and the ability to obtain nutrition from symbiotic photosynthetic dinoflagellates, enable it to rapidly colonize shallow-water habitats. The most widespread vectors for its spread are hull fouling and larvae in ballast water (Thornhill et al. 2013; Glon et al. 2020). However, in the Bay of Biscay and Mediterranean France, it was associated with introduced Pacific oysters from Japan, as Aiptasia pulchella (Grizel and Heral 1991; Ardura and Planes 2015). It is also well-known as an aquarium pest, because of its asexual reproduction and photosynthetic symbionts (Glon et al. 2020). Aquarium releases are a possible vector for some recent invasions.

North American Invasion History:

Invasion History on the West Coast:

Exaiptasia pallida was collected in Mission Bay, San Diego, California in 1937, and later described as Aiptasia californica (Carlgren 1953; Grajales and Rodriguez 2014; USNM 5003, US National Museum of Natural History 2020). Specimens are known from Santa Barbara, California to Acapulco, Mexico, and Pacific Panama (Grajales and Rodriguez 2014; US National Museum of Natural History; 2020; GBIF 2020). Specimens were collected in the Gulf of California and Acapulco in the 1960s and 1950s (US National Museum of Natural History; 2020).

Invasion History in Hawaii:

Exaiptasia pallida (as Aiptasia pulchella), was collected in 1950 in Kaneohe Bay, and Pearl Harbor 1954 (US National Museum of Natural History; 2020; Glon et al. 2020).

Invasion History Elsewhere in the World:

The worldwide distribution of Exaiptasia pallida and its complex synonymy, as well as the wide distribution of its dinoflagellate symbionts, makes it challenging to define its native region. However, its more continuous distribution in the West Atlantic, and the occurrence of some unique clades and symbionts that are unique to Florida populations suggest greater generic diversity and support the tropical West Atlantic as the region of origin (Thornhill et al. 2013; Glon et al. 2020). Some of the invasions were very early, for example, its description in Naples, Italy in 1849 (as Dysactis diaphana). However, many of the early records (Agassiz in Verrill 1864; Coues and Yarrow 1878) were from the Western Atlantic (Coues and Yarrow 1878; Yale Peabody Museum of Natural History 2020; US. National Museum of Natural History 2020). The exception is its collection in Bermuda in 1878 (Yale Peabody Museum of Natural History 2020), where we consider it cryptogenic.

In the Eastern Pacific, as noted above, Exaiptasia pallida was introduced and established in California and Pacific Mexico but has disjunct populations in Panama (before 2014) and Hawaii (1950). In 2010, it was collected on rhodolith beds in the Cocos Islands, Costa Rica/Pacific Ocean (2010, Acuna et al. 2020). In 1995, in the Galapagos Islands, it was discovered forming extensive 'anemone meadows' (Okey et al. 2003; Carlton et al. 2019).

In the Northwest Pacific, it is known from Taiwan and Okinawa (Grajales and Rodriguez 2014). Probably, it is established elsewhere in Japan, such as Sendai Province, the source of the Pacific Oysters (Crassostrea gigas) introduced to France (Grizel and Heral 1991). In the Indo-Pacific, E. pallida was collected on Ralik Chain, Eniwetok Atoll, in the Marshall Islands Marshall Islands in 1955, (as Aiptasia pulchella), U.S. National Museum of Natural History 2020). In 2003, it was discovered in Jellyfish Lake, an important tourist attraction on Eil Malk island, Palau. It is known both from the Great Barrier Reef, near Townsville, Queensland (Tortorelli et al. 2020), and in the Gulf of St. Vincent, South Australia (GBIF 2020). In the Indian Ocean, it was collected in the Suez Canal in 1924 (GBIF 2020), near Mumbai (Bombay), India in 1950, and is established there (US National Museum of Natural History 2020; GBIF 2020). It is also established in East London, South Africa/Indian Ocean (1935, Swedish South African Expedition 1935, cited by Grajales and Rodriguez 2014).

The earliest known introduction of Exaiptasia pallida appears to be its description as Dysactis diaphana by Rapp in 1829) near Naples. It appears to be established in the Tyrrhenian Sea, from Naples to the tip of Sicily, but does not appear to be widespread on the Italian Coast. In the 1960s and 1970s, Pacific Oysters from Japan were introduced to the Bay of Biscay, France and to French Mediterranean lagoons. Though these anemones are often associated with oyster introductions, they did not become established in the Bay of Biscay (Grizel and Heral 1991; Goulletquer et al. 2002). They have become established in the Canet-Saint Nazaire lagoon, Mediterranean (Ardura,et al. 2015). In the subtropical-tropical Eastern Atlantic, E. pallida was collected in Madeira in 2008 (Canning-Clode et al. 2015), in the Canary Islands (Grajales and Rodriguez 2014), and Senegal in 2019 (GBIF 2020). In 1930, this anemone was collected on the mid-Atlantic island of St. Helena (Grajales and Rodriguez 2020).


Exaiptasia pallida (Agassiz in Verrill 1864), called the Pale Anemone or Glass Anemone, is native to subtropical and tropical waters of the Western Atlantic, but widely distributed around the world (Glon et al. 2020). An earlier description as Dysactis diaphana from Naples by Rapp (1829) was rarely used. Grajales and Rodriguez (2014) petitioned the International Committee on Zoological Nomenclature to validate the species name pallida, arguing that the frequency of use outweighed historical priority. This petition was overruled by the committee in 2017; however, the name pallida is treated as valid by the World Registry of Marine Species (WoRMS, Appletans et al. 2020). Currently, this petition is being appealed. This anemone has been widely studied and published under the name pallida, which was the name used in Glon et al. (2020), and in this account.

Anemones of the family Aiptaisidae have been widely studied, in part because of their symbiotic relationship with dinoflagellates. These anemones have a well-developed pedal disk, basal muscles, and longitudinal muscles. Exaiptasia pallida, the only species in the genus Exaiptasia (Grajales and Rodriguez 2014), has a regularly shaped pedal disc, with a column that is not divided into scapus and capitulum. It reproduces sexually through external fertilization and asexually by pedal laceration, a type of fission where a portion of its base is left behind as the anemone moves, and grows into a new anemone. They harbor symbiotic dinoflagellates of the genus Symbiodinium. The pedal disk is up to 10 mm wide and is wider than the column in living specimens. The column is smooth and up to 60 mm high in living specimens, when extended, and up to 30 mm in preserved specimens. The oral disk is up to 10 mm in diameter. There are up to 96 simple tentacles, which lack projections, taper towards the tips, and are all of uniform length (up to 20 mm). The column is grayish-brownish, with scattered spots and translucent toward the base. The oral disk and tentacles are grayish, the tentacles have occasional white transverse stripes. The mouth is white and the actinopharynx is yellowish (Carlgren 1952; Grajales and Rodriguez 2014).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Mollusca
Class:   Bivalvia
Subclass:   Heterodonta
Order:   Veneroida
Superfamily:   Tellinoidea
Family:   Tellinidae
Genus:   Exaiptasia
Species:   pallida


Actinia diaphana ( Rapp, 1829)
Aiptasia agassizii (Andres,, 1883)
Aiptasia californica (Carlgren, 1952)
Aiptasia inula (Duchassaing & Michelotti, 1864)
'Aiptasia leiodactyla (Pax, 1910)
Aiptasia mimosa (Duchassaing & Michelotti, 1864)
Aiptasia mnuta (Verrill, 1867)
Aiptasia pallida (Agassiz, in Verrill, 1864)
Aiptasia pulchella (Carlgren, 1943)
Aiptasia saxico (Andres, 1881)
Aiptasia tagetes (Duchassaing & Michelotti, 1864)
Aiptasiamorpha diaphana ((Rapp), 1829)
Aiptasiamorpha leiodactya ((Pax), 1910)
Bartholomea inlula (Duchassaing & Michelotti, 1864)
Bartholomea tagetes (Duchassaing & Michelotti, 1864)
Cribrina diaphana (( Rapp), 1864)
Disactis mimosa (Duchassaing & Michelotti, 1864)
Dysactis mimosa (Duchassaing & Michelotti, 1864)
Exaiptasia pallida (Grajalesand Rodriguez, 2014)
Exaiptasia diaphana (Rapp, None)
Paranthea pallida (Coues and Yarrow, 1878)

Potentially Misidentified Species



Exaiptasia pallida ranges from warm-temperate to tropical climates, tolerating temperatures up to 42 °C and salinities as high as 60 PSU (Gegner et al. 2017). Its tolerance to lower temperatures and salinities is not clear, but its occurrence in mangroves and shallow-water habitats probably implies tolerance of salinities below 30 PSU (Kaplan 1988; Glon et al. 2020). Exaiptasia pallida is known from a wide range of substrates, including rocks, mangrove roots, algal-coral beds on reef-flats, and marinas (Kaplan 1988; Okey et al. 2003; Acuna et al. 2020; Glon et al. 2020). Exaiptasia pallida is a predator, feeding on zooplankton and small mobile benthos with the nematocysts on its tentacles. However, it also benefits by photosynthesis by its dinoflagellate symbionts, or zooxanthellae. It can host a variety of dinoflagellates of the genera Symbiodinium, Durusdinium, and has become model organism for studying the relationship between corals and their symbionts (Thornhill et al. 2013; Gabay et al. 2018; Foo et al. 2020; Herrera et al. 2020). In Florida, E. pallida is eaten by a native nudibranch, Breghia coerulescens (Kaplan 1988). A number of species of fishes, and Hawksbill Turtles (Eretmochelys imbricata) feed on these anemones in the Galapagos (Okey et al. 2003).


Symbiotic production, zoopkankton


nudibranchs, fishes


other anemones

Trophic Status:

Primary Producer



General HabitatMarinas & DocksNone
General HabitatCoral reefNone
General HabitatMangrovesNone
General HabitatRockyNone
General HabitatGrass BedNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Salinity RangeHyperhaline40+ PSU
Tidal RangeLow IntertidalNone
Tidal RangeSubtidalNone

Life History

Exaiptasia pallida reproduces both asexually by pedal laceration and sexually, with external fertilization and planula larvae (Jennison 1983). In pedal laceration, as the anemone moves, a portion of its base is left behind and grows into a new anemone (Barnes 1983). This species is capable of rapidly colonizing aquaria and natural habitats (Okey et al. 2003; Glon et al. 2020).

Tolerances and Life History Parameters

Maximum Temperature (ºC)34

Gegner et al. 2017, highest temperature tested.

Maximum Salinity (‰)42Gegner et al. 2017, highest salinity tested
Maximum Width (mm)10Grajaleas and Rodriguez 2014
Maximum Height (mm)60Grajaleas and Rodriguez 2014
Broad Temperature RangeNoneWarm-temperate-tropical
Broad Salinity RangeNonePolyhaline-hyperhaline

General Impacts

Exaiptasia pallida is a remarkably widespread anemone, with many scattered populations around the world, mostly in subtropical and tropical habitats. It has an important role in research in the biology of coral reefs and bleaching, because it is easier to study symbiosis in a small anemone than in intact corals (e.g., Medrano et al. 2019). Exaiptasia pallida has also spread invasively in several coral-reef and algal communities of great tourist and biodiversity value.

Ecological and Economic Impacts

Competition, Habitat Change- Exaiptasia pallida has spread rapidly in at least two regions of great touristic and economic value. On reef flats around Fernandina Island in the Galapagos Islands, E. pallida replaced communities of algae and corals with 'anemone barrens', with lower biodiversity and visual appeal (Okey et al. 2003). Similar impacts on biodiversity and tourism were observed in Jellyfish Lake, Palau, a marine lagoon which attracts tourists for its dense populations of non-stinging jellyfish (Mastigias sp.). Dense cover of anemones were associated with decreased abundance of algae and invertebrates (Marino et al. 2008).

Regional Impacts

SP-XIIINoneEcological ImpactCompetition
'Currently, no quantitative data exist to describe the impact Aiptasia sp. is having on the ecosystem. However, it is clear from direct observation that Aiptasia sp. is a thriving competitor for space and can heavily alter benthic diversity (Figure 16.9). Mangrove root and shallow water communities that were once dominated (in terms of both space and numbers) by algae or diverse assemblages of invertebrates are now dominated by invasive anemones' (Marino et al. 2008). Patris et al. (2019) did not find strong associations between the abundance of E. pallida and native species, in spite of the growng abundnaceog thr anemone.
SP-XIIINoneEconomic ImpactAesthetic
Jellyfish Lake is one of Palau's major tourist attractions, where divers can swim among dense swarms of beautiful, non-stinging, migrating jellyfish (Mastigias sp.). Impacts of Aiptasia on this ecosystem are not known but could constitute a threat to this unique ecosystem. Small-scale attempts of eradication have been unsuccessful (Marino et al. 2008).
SEP-ZNoneEcological ImpactHabitat Change
Exaiptasia pallida was first noticed around Fernandina Island, and by 2001, had created extensive 'anemone barrens' of reduced biodiversity (Okey et al. 2003).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
NEP-VI Pt. Conception to Southern Baja California 1937 Def Estab
P022 _CDA_P022 (San Diego) 1937 Def Estab
NEP-VII None 1962 Def Estab
NEP-VIII None 1955 Def Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
CAR-VII Cape Hatteras to Mid-East Florida 1864 Native Estab
CAR-III None 1980 Native Estab
CAR-II None 0 Native Estab
SP-XXI None 1950 Def Estab
SP-XIII None 1955 Def Estab
SEP-Z None 1995 Def Estab
S190 Indian River 0 Native Estab
P050 San Pedro Bay 0 Def Estab
WA-V None 1935 Def Estab
SEP-H None 2014 Def Estab
NWP-2 None 0 Def Estab
WA-I None 2008 Def Estab
MED-III None 1829 Def Estab
NA-ET4 Bermuda 1878 Crypto Estab
SA-IV None 0 Native Estab
SA-II None 0 Native Estab
RS-2 None 0 Def Estab
WA-IV None 1930 Def Estab
P065 _CDA_P065 (Santa Barbara Channel) 0 Def Estab
P064 _CDA_P064 (Ventura) 0 Def Estab
P050 San Pedro Bay 0 Def Estab
AUS-XII None 0 Def Estab
AUS-VII None 0 Def Estab
CIO-I None 1958 Def Estab
RS-1 None 1924 Def Estab
MED-II None 1973 Def Estab
NEA-IV None 1973 Def Failed
CMAR1 Isla del Coco / Cocos Island 2010 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


Tortorelli, Giada; Belderok, Roy; Davy; Simon K. ; McFadden, Geoffrey.; Madeleine J. H. van Oppen (2020) Host Genotypic Effect on Algal Symbiosis Establishment in the Coral Model, the Anemone Exaiptasia diaphana, From the , Great Barrier Reef, Frontiers in Marine Science 6(833): Published online
doi: 10.3389/fmars.2019.00833

Acuña, Fabián H.; Cortés, Jorge; Garese, Agustín; González-Muñoz, Ricardo (2020) The sea anemone Exaiptasia diaphana (Actiniaria: Aiptasiidae) associated to rhodoliths at Isla del Coco National Park, Costa Rica, Revista de Biología Tropical 68(Suppl. 1): S283-S288

Acuña, Fabián H.; Garese, Agustín; Excoffon, Adriana C.; Cortés, Jorge (2013) New records of sea anemones (Cnidaria: Anthozoa) from Costa Rica, Revista de Biología Marina y Oceanografía 48(1): 177-184
DOI 10.4067/S0718-19572013000100015

Appeltans, W. et al. 2011-2015 World Registry of Marine Species. <missing URL>

Ardura, Alba; Zaiko, Anastasija; Martinez, Jose L.; Samulioviene, Aurelija; Semenova, Anna; Garcia-Vazquez, Eva (2015) eDNA and specific primers for early detection of invasive species- A case study on the bivalve Rangia cuneata, currently spreading in Europe, Marine Environmental Research 112: 48-55

Barnes, Robert D. (1983) Invertebrate Zoology, Saunders, Philadelphia. Pp. 883

Canning-Clode, João; Fofonoff, Paul; McCann, Linda; Carlton, James T.; Ruiz, Gregory (2013) Marine invasions on a subtropical island: fouling studies and new records in a recent marina on Madeira Island (Eastern Atlantic Ocean), Aquatic Invasions 8(3): 261-270

Carlgren, Oskar; Hedgpeth, Joel W. (1952) Actinaria, Zoantharia, and Ceriantharia from shallow water in the northwestern Gulf of Mexico., Publications of the Institute of Marine Science 2(2): 141-172

Carlton, James T.; Keith, Inti; Ruiz, Gregory M. (2019) Assessing marine bioinvasions in the Galápagos Islands: implications for conservation biology and marine protected areas, Aquatic Invasions 14(1): 1-20

Coues, Elliott; Yarrow, H.C. (1878) Notes on the natural history of Fort Macon, N.C. and vicinity (No. 5), Proceedings of the Academy of Natural Sciences of Philadelphia 30: 297-330

Foo, Shawna A.; Liddel, Lauren; Grossman, Arthur; Caldeira, Ken (2020) Photo-movement in the sea anemone Aiptasia influenced by light quality and symbiotic association, Coral Reefs 39: 47-54

Gabay, Yasmin; Weis, Virginia M.; Davy, Simon K (2018) Symbiont Identity Influences Patterns of Symbiosis Establishment, Host Growth, and Asexual Reproduction in a Model Cnidarian-Dinoflagellate Symbiosis, Biological Bulletin 234: 1-10

Gegner, Hagen M. ; Ziegler, Maren; Rädecker, Nils ; Buitrago-López, Carol; Aranda, Manuel; Voolstra. Christian R. (2017) High salinity conveys thermotolerance in the coral model Aiptasia, Biology 6: Published online

Gimenez, Lucas H.; Brante, Antonio (2021) Do non-native sea anemones (Cnidaria: Actiniaria) share a common invasion pattern? – A systematic review, Aquatic Invasions 16: 365-390

Gimenez, Lucas H.; Rivera, Reinaldo J.; Brante, Antonio (2022) One step ahead of sea anemone invasions with ecological niche modeling: potential distributions and niche dynamics of three successful invasive species, Marine Ecologicy Progress Series 690: 83–95

Glon, Heather; Daly, Marymega; Carlton, . James, T.; Flenniken, Megan M.; Currimjee, Zara (2020) Mediators of invasions in the sea: life history strategies; and dispersal vectors facilitating global sea anemone introductions, Biological Invasions 22: pages3195–3222

Goulletquer, Philippe; Bachelet, Guy; Sauriau, Pierre; Noel, Pierre (2002) Invasive aquatic species of Europe: Distribution, impacts, and management, Kluwer Academic Publishers, Dordrecht. Pp. 276-290

GRAJALES, ALEJANDRO; RODRÍGUEZ, ESTEFANÍA (2014) Morphological revision of the genus Aiptasia and the family Aiptasiidae (Cnidaria, Actiniaria, Metridioidea), Zootaxa 3826(1): <missing location>

Grizel, H; Héral, M (1991) Introduction into France of the Japanese oyster Crassostrea gigas)., Journal Conseil Internationale d' Exploration de la Mer 47(3): 399-403

Herrera, Marcela; Klein, Shannon G.;Schmidt-Roach, Sebastian; Campana, Sara; Cziesielski Maha J.; Chen, Jit Ern; Duarte Carlos M.; Aranda, Manuel (2020) Unfamiliar partnerships limit cnidarian holobiont acclimation to warming, Global Change Biology 26(26): 5539–5553

Kaplan, Eugene H. (1988) A Field Gude to Southeastern and Caribbean Seashores, In: (Eds.) . , Boston. Pp. <missing location>

Marino, Sebastan and 14 authors (2008) The State of Coral Reef Ecosystems of the United States and Pacific Freely Associated States: 2008, NOAA/NCCOS Center for Coastal Monitoring and Assessment’s Biogeography Team, Silver Spring MD. Pp. 488-507

Medrano, Emmanuel Merselis, Daniel G. Bellantuono, Anthony J. Rodriguez-Lanetty, Mauricio (2019) Proteomic basis of symbiosis: a heterologous partner fails to duplicate homologous colonization in a novel cnidarian– Symbiodiniaceae mutualism, Frontiers in Microbiology 10: Published online

Okey, Thomas. A. ; Shepherd, Scoresby. A.; Martínez, Priscilla C. (2003) A new record of anemone barrens in the Galápagos, Noticias de Galapagos 62: 17-20

Patris, Sharon; Martin, Laura E; Bell, Lori J.; Dawson. Michael N. (2019) Expansion of an introduced sea anemone population, and its associations with native species in a tropical marine lake (Jellyfish Lake, Palau), Frontiers in Biogeography 11(1): Published online

Quintanilla, Elena; Thomas Wilke; Ramırez-Portilla, Catalina; Sarmiento, Adriana; Sanchez, Juan A.2017 (2017) Taking a detour: invasion of an octocoral into the Tropical Eastern Pacific, Biological Invasions <missing volume>(17): 2583–2597
DOI 10.1007/s10530-017-1469-2

Ruiz, Gregory M.; Geller, Jonathan (2018) Spatial and temporal analysis of marine invasions in California, Part II: Humboldt Bay, Marina del Re, Port Hueneme, and San Francisco Bay, Smithsonian Environmental Research Center & Moss Landing Laboratories, Edgewater MD, Moss Landing CA. Pp. <missing location>

Thornhill, D. J.; Howells, E. J.; Wham. D. C.; Steury, T. D.; Santos, S. R. (2013) Population genetics of reef coral endosymbionts (Symbiodinium, Dinophyceae), Molecular Ecology 28: 2640-2659
doi: 10.1111/mec.14055

U.S. National Museum of Natural History 2002-2021 Invertebrate Zoology Collections Database.

Yale Peabody Museum of Natural History 2008-2016 YPM Invertebrate Zoology - Online Catalog. <missing URL>

Zanolla, Marianela; Carmona, Raquel; Kawai, Hiroshi; Stengel, Dagmar B.; Altamirano, María (2019) Role of thermal photosynthetic plasticity in the dispersal and settlement of two global green tide formers: Ulva pertusa and U. ohnoi, Marine Biology 166(123): Published online