First Non-native North American Marine/Estuarine Record: 1898
First Non-native East/Gulf Coast Marine/Estuarine Record: 1898
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)
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).