Invasion History

First Non-native North American Tidal Record: 1898
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1898

General Invasion History:

Chthamalus fragilis is native to the Eastern Coast of North America and was first described from Charleston, South Carolina by Darwin (1854). By 1893, it had been collected in Clearwater, Florida, in the Gulf of Mexico (US National Museum of Natural History 2008), and from Ocean City, New Jersey, sometime before 1916 (Pilsbry 1916). The northern limit of its native range is unknown, but was probably somewhere between Cape Hatteras and Long Island Sound. It appears to be introduced in Connecticut, Rhode Island and Massachusetts. Gosner (1978) describes C. fragilis as ‘abundant’ north to Delaware Bay, but ‘only found locally north to Cape Cod’.

Records of C. fragilis from the Caribbean Islands are based on confusion with the more recently described Chthamalus proteus (Dando and Southward 1980). Chthamalus fragilis also occurs in the Cape Verde Islands, off Africa. O'Riordan et al. (2010) attributed this occurrence to plate tectonic events, noting fossil and recent faunal similarities of this region with the Western Atlantic. However, it is considered to be a ship fouling introduction to the Eastern Atlantic, perhaps in the era of the slave trade (J.T. Carlton, personal communication, 2013)

North American Invasion History:

Invasion History on the East Coast:

Although Chthamalus fragilis is conspicuous, and is restricted to the upper intertidal in the northern part of its range, it was not observed in an 1870s survey of the Woods Hole-Martha's Vineyard region. It was collected in 1898-1899 in Woods Hole by M. A. Bigelow (Sumner et al., 1913; Carlton et al. 2011) for a series of experiments on barnacle larvae. F. B. Sumner (1909) reported the occurrence of C. fragilis growing conspicuously at Woods Hole Massachusetts, and subsequently observed it at Vineyard Haven and New Bedford, growing on piers and rocks. At many Woods Hole locations, this barnacle now forms a conspicuous gray band above the whitish zone of Semibalanus balanoides (Fofonoff, personal observations). Sumner (1909) considered that this species would be difficult to overlook, and was probably a recent invader in southern New England. Sumner et al. (1913) wrote: ‘It is hard to believe that this species has been habitually confused with Balanus balanoides by the long succession of field naturalists who have exploited the shores of New England for over a century.’ This barnacle also occurs in Long Island Sound (Weiss et al. 1995; Connecticut Sea Grant 2005) and Narragansett Bay, Rhode Island (Lang 1980; MIT Sea Grant 2003), and is probably introduced to these areas as well, but dates of first record have not been found. Wethey (2002) found that C. fragilis was abundant at the warmer western end of the Cape Cod Canal (Buzzards Bay), but very rare at Sagamore Bridge in the cooler end of Cape Cod Bay at the end of the canal, only 8 km away. Experimental transplants suggest that rarity of this barnacle, and its absence in Cape Cod Bay, were due to lower air temperatures, allowing S. balanoides to settle in the upper intertidal, and thereby exclude C. fragilis. Transplanted C. fragilis in Nahant, Massachusetts (Gulf of Maine) survived well when competition was excluded. Chthamalus fragilis is, however, common along much of the north shore of Cape Cod, in the southern margin of Cape Cod Bay (J.T. Carlton, personal communication, 2013). Genetic studies support a range expansion, probably anthropogenic, of C. fragilis from source populations in the Chesapeake Bay region northward to New England (Govindarajan et al. 2015).


Chthamalus fragilis is a small barnacle (up to 9 mm in size). Its orifice is large, toothed, and sub-hexagonal. The surface is brownish-colored, with distinct sutures, and the plates never fused together. The side plates overlap over the end plates. The scutum is long with a somewhat sinuous tergal margin. The adductor muscle insertion is comparatively shallow, fairly narrow, and 'open' at the rostral end. The tergum is wide with a noticeable spur. The lateral margin is usually deeply indented, and the scutal margin is only slightly sinuous (Darwin 1854; Gosner 1978; Dando and Southward 1980).


Taxonomic Tree

Kingdom:   Animalia
Phylum:   Arthropoda
Subphylum:   Crustacea
Class:   Maxillopoda
Subclass:   Thecostraca
Infraclass:   Cirripedia
Superorder:   Thoracica
Order:   Sessilia
Suborder:   Balanomorpha
Superfamily:   Chthamaloidea
Family:   Chthamalidae
Genus:   Chthamalus
Species:   fragilis


Chthamalus stellatus var. fragilis (Darwin, 1854)

Potentially Misidentified Species

Chthamalus angustitergum
Florida and Caribbean (Dando and Southward 1983)

Chthamalus bisinuatus
Brazil (Dando and Southward 1983)

Chthamalus proteus
Florida and Caribbean, Brazil (Dando and Southward 1983)



Chthamalus fragilis, like many other barnacles, is hermaphroditic, but is capable of cross-fertilization. The fertilized eggs are brooded in the mantle cavity, sometimes for several months, and are released as nauplius larvae with three pairs of appendages (Barnes 1983). The nauplii feed in the plankton and go through five successive molts, spending approximately one to three weeks in the water column before molting into a non-feeding cypris stage, covered with a pair of chitinous shells (Lang 1979; Lang 1980). Cyprids swim, investigating suitable surfaces, and then settle, secreting a shell and molting into the first juvenile barnacle stages. Juvenile and adult barnacles are filter feeders, sweeping the water with their long bristled appendages to gather phytoplankton, zooplankton, and detritus (Barnes 1983).

In its native range from New Jersey to Texas, Chthamalus fragilis occurs on a wide range of habitats, including marsh grasses. But in its introduced range in southern New England, it is limited to the upper rocky intertidal (Dando and Southward 1980). The northern range limit of Chthamalus fragilis appears to be set by temperature and competition with Semibalanus balanoides (Rock Barnacle). High summer temperatures on exposed rocks south of Cape Cod (up to 40?C) are lethal to S. balanoides, but tolerated by C. fragilis, allowing C. fragilis to dominate the upper edge of the barnacle zone. In transplant experiments conducted in Nahant, Massachusetts, north of Cape Cod, C. fragilis survived winter weather for as long as eight years, if S. balanoides settlement was prevented, but was otherwise outcompeted at all tide levels by S. balanoides (Wethey 2002).




Semibalanus balanoides

Trophic Status:

Suspension Feeder



General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatRockyNone
General HabitatOyster ReefNone
General HabitatVessel HullNone
Salinity RangeMesohaline5-18 PSU
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeMid IntertidalNone
Tidal RangeHigh IntertidalNone
Vertical HabitatEpibenthicNone

Life History

Tolerances and Life History Parameters

Minimum Salinity (‰)20Dando and Southward 1980
Maximum Width (mm)9Gosner 1978
Broad Temperature RangeNoneCold temperate-Warm temperate
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Impacts of Chthamalus fragilis have not been reported from its introduced range. 

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
CAR-VII Cape Hatteras to Mid-East Florida 1854 Native Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 0 Native Estab
NA-ET3 Cape Cod to Cape Hatteras 1898 Def Estab
M020 Narragansett Bay 1977 Def Estab
M010 Buzzards Bay 1898 Def Estab
M040 Long Island Sound 1995 Def Estab
M080 New Jersey Inland Bays 1916 Native Estab
M090 Delaware Bay 0 Native Estab
M130 Chesapeake Bay 1916 Native Estab
N195 _CDA_N195 (Cape Cod) 1909 Def Estab
NA-ET2 Bay of Fundy to Cape Cod 1963 Def Estab
N180 Cape Cod Bay 1963 Def Estab
WA-VI None 0 Def Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude


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

Carlton, James T. (2002) Invasive aquatic species of Europe: Distribution, impacts and management., Kluwer Academic Publishers., Dordrecht, Boston, London. Pp. <missing location>

Carlton, James T.; Newman, William A.; Pitombo, Fábio Bettini (2011) In the wrong place- Alien marine crustaceans: Distribution, biology, impacts, Springer, Dordrecht. Pp. 159-213

Celis, Antonio; Rodríguez-Almaráz, Gabino; Álvarez, Fernando (2007) [The shallow-water thoracican barnacles (Crustacea) of Tamaulipas, Mexico], Revista Mexicana de Biodiversidad 78: 325-337

Connecticut Sea Grant 2005 Invasive species of Long Island Sound.. <missing URL>

Dando, P. R.; Southward, A.J. (1980) A new species of Chthamalus (Crustacea: Cirripedia) characterized by enzyme electrophoresis and shell morphology: with a revision of other species of Chthamalus from the Western shores of the Atlantic Ocean., Journal of the Marine Biological Association 60: 787-831

Darwin, Charles (1854) A Monograph on the Sub-class Cirripedia: With Figures of All the Species: The Balanidæ (or Sessile Cirripedes); the Verrucidæ, Etc, The Ray Society, London. Pp. <missing location>

Fowler, Henry (1911) The Crustacea of New Jersey, Annual Report of the New Jersey State Museum, part 2 <missing volume>: 29-610

Gosner, Kenneth L. (1978) A field guide to the Atlantic seashore., In: (Eds.) . , Boston. Pp. <missing location>

Govindarajan, Annette F.; Buksa, Filip; Bockrath, Katherine; Wares, John P. Pineda, Jesus (2015) Phylogeographic structure and northward range expansion in the barnacle Chthamalus fragilis, PeerJ 3: e926

Kennedy, C., Pappal, A. L.; Bastidas, C.; ; Carlton, J. T.; David, A. A.; Dijkstra, J.A.; Duffey, S; Gibson, J.; Grady, S. P.; Green-Gavrielidis, (2020) Report on the 2018 Rapid Assessment Survey of Introduced, Cryptogenic, and Native Marine Species at New England Marinas: Massachusetts to Maine, <missing publisher>, Boston MA. Pp. <missing location>

Lang, W. H. (1980) Cirripedia: balanomorph nauplii of the NW Atlantic shores, Fiches D’Identification du Zooplancton 163: 1-6

Lang, William H. (1979) Larval development of shallow water barnacles of the Carolinas (Cirripedia: Thoracica) with keys to naupliar stages., NOAA Technical Report NMFS Circular 421: 1-39

Lang, William H.; Ackenhusen-Johns, Anne (1981) Seasonal species composition of barnacle larvae (Cirripedia: Thoracica) in Rhode Island waters, 1977–1978, Journal of Plankton Research 3-4: 567-575

MacIntyre, Chris; Adrienne Pappal; Pederson, Judy; Smith, Jan P. (2011) Marine Invaders in the Northeast Rapid Assessment Survey of non-native and native marine species of floating dock communities, Massachusetts Coastal Zone Management, Boston MA. Pp. <missing location>

Massachusetts Office of Coastal Zone Management (2013) Rapid assessment survey of marine species at New England floating docks and rocky shores, Massachusetts Office of Coastal Zone Management, Boston MA. Pp. <missing location>

MIT Sea Grant 2003-2008 Introduced and cryptogenic species of the North Atlantic. <missing URL>

O'Riordan, Ruth M.; Power, Anne Marie; Myers, Alan A. (2010) Factors, at different scales, affecting the distribution of species of the genus Chthamalus Ranzani (Cirripedia, Balanomorpha, Chthamaloidea), Journal of Experimental Marine Biology and Ecology 392: 46-64

Pilsbry, Henry A. (1916) The sessile barnacles contained in the collections of the U.S. National Museum, including a monograph of the American species., United States National Museum Bulletin 93: 1-366

Singletary, Robert 2006 Checklist of the marine flora and fauna at Seaside Park, Bridgeport, Connecticut. <missing URL>

Sumner, F. B. (1909) On the occurrence of the littoral barnacle Chthamalus stellatus (Poli) at Woods Hole, Massachusetts., Science 30(768): 373-374

Sumner, Francis B., Osburn, Raymond C., Davis, Bradley M. (1913a) A biological survey of the waters of Woods Hole and vicinity. Part I. Section I. Physical and Zoological. Section II. Botanical, Bulletin of the Bureau of Fisheries 31: 1-544

Sumner, Francis B.; Osburn, Raymond C.; Cole, Leon J.; Davis, Bradley M. (1913b) A biological survey of the waters of Woods Hole and vicinity Part II. Section III. A catalogue of the marine fauna Part II. Section IV. A catalogue of the marine flora, Bulletin of the Bureau of Fisheries 31: 539-860

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

Wass, Melvin L. (1972) A checklist of the biota of lower Chesapeake Bay, Special Scientific Report, Virginia Institute of Marine Science 65: 1-290

Weiss, Howard M.; Bennett, Don; Dawley, Ellen; Jokinen, Eileen; Klemens, Michael W.; O'Donnell, Jane; Pondick, Jeffrey S.; Rubega, Margaret (1995) Marine animals of southern New England and New York., Bulletin of the State Geological and Natural History Survey of Connecticut 115: 1-19.16

Wethey, David S. (2002) Biogeography, competition, and microclimate: the barnacle Chthamalus fragilis in New England., Integrative and Comparative Biology 42: 872-880