NEMESIS Bioregion Distribution:

Native  Introduced  Cryptogenic  Failed

First Non-native North American Marine/Estuarine Record: 1899
First Non-native West Coast Marine/Estuarine Record: 1899
First Non-native East/Gulf Coast Marine/Estuarine Record: 1975

General Invasion History:

Diplosoma listerianum was first described from the English Channel by Milne-Edwards in 1841. Initially, this species was described, under different names, from many different places around the world, such as Australia (D. rayneri Macdonald 1859) Brazil (D. macdonaldi Herdman 1886), and Japan (D. mitsukurii Oka 1892). These and many other names were synonymized by Kott (1990; 2001). This tunicate now has a cosmopolitan distribution and represents a species complex (Perez-Portela et al. 2013). In most of these regions, D. listerianum was already established when researchers began surveying tunicates and, as a result, many populations have not been recognized as true introductions. One cryptic species (clade A) occurred in most of the sites sampled worldwide, while three other clades had more local distributions (Perez-Portela et al. 2013). We consider this species complex to be cryptogenic (of unknown origin) through most of its range. However, it appears to be a definite introduction in several locations, including the Northeast Pacific (California to British Columbia), the Northeast Atlantic (north of Cape Hatteras, North Carolina), Hawaii, New Zealand, and South Africa. In European waters, near the site of first description, range expansions have been noted in the North Sea (UK, Vance et al. 2008) and in the Netherlands (1st Record 1977, Gittenberger et al. 2007).

North American Invasion History:

Invasion History on the West Coast:

Diplosoma listerianum was collected in San Diego Bay, California in 1917. It was described by Ritter and Forsyth as D. pizoni from a single colony (Van Name 1945). Five additional colonies collected in 1899 were also identified as D. pizoni by Ritter (Eldredge 1966). Diplosoma listerianum apparently expanded its range northward, reaching Monterey Bay, CA by 1939 (Van Name 1945; Eldredge 1966). In 1948, D. listerianum was found in San Francisco Bay, CA (Eldredge 1966). In 1960, it was collected on Vancouver Island, British Columbia and by 1966 it was common in Puget Sound, Washington (Lambert 1966). Populations in Bodega Bay, CA and Washington State (Snug Harbor, San Juan Islands) belonged to the cosmopolitan clone A (Perez-Portela et al. 2013). 

Since D. listerianum was treated as a native species, we have not been able to find first dates of record for many West coast water bodies. By 1980, it was considered common from San Diego, CA to British Columbia, Canada (Abbott and Newberry 1980). In Southern California, Lambert and Lambert (1998) described it as occurring in 'all harbors, at all times of year' and subsequent surveys have confirmed this (Fairey et al. 2001; deRivera et al. 2006; Ruiz et al. unpublished data). Further north, it occurs in Humboldt Bay, CA (Fairey et al. 2003; Ruiz et al. unpublished data) and Coos Bay, OR (in 1988, Hewitt 1993; Ruiz et al. unpublished data). It is widespread throughout Puget Sound (Ruiz et al. unpublished data) and has been collected as far north as Bamfield, Vancouver Island, BC (Mackie and Singla 1987).

Invasion History on the East Coast:

Diplosoma listerianum was first collected in 1880 in the Atlantic Ocean off South Carolina, and subsequently found from Cape Fear, NC to Biscayne Bay, FL (U.S. National Museum of Natural History 2002; Van Name 1921; Ruiz et al. unpublished data). We consider it cryptogenic in these southern US waters. The first reported occurrence of D. listerianum north of Cape Hatteras, NC was in Long Island Sound, CT in the 1970s (R. Whitlatch to James T. Carlton, personal communication, 2002). In 1981, it was found at the east end of the Cape Cod Canal, in the Gulf of Maine (R. Whittaker to James T. Carlton, personal communication, 1984). In 1997, it was found in Great Bay, near Portsmouth, New Hampshire (Blezard 1999). In 1998, it was found in Narragansett Bay, Rhode Island and Vineyard Sound, Massachusetts (Whitlatch and Osman 2000). In 1999, it was found near Cape Neddick, Maine (ME) (Harris and Tyrell 2001), and in 2003 it was found in Casco Bay, ME (MIT Sea Grant 2003). It was found in the Gulf of St. Lawrence, in the Magdalene Islands, Quebec in 2008 and in Lunenburg Harbour, Nova Scotia in 2012; however establishment in both locations is uncertain (Willis et al. 2011; Moore et al. 2014).  There are no published records of this tunicate south of Long Island Sound, CT. However, in 2001 and 2002, specimens were found on fouling plates in lower Chesapeake Bay near Cape Charles, VA. Since there were concerns about identifications, specimens were confirmed as D. listerianum by Gretchen Lambert. Colonies in Cape Charles, Virginia (VA) appeared to be abundant (Ruiz et al. unpublished data).

Invasion History on the Gulf Coast:

Diplosoma listerianum was first found at Cedar Key, FL in 1885 (U.S. National Museum of Natural History 2002; Van Name 1921). It has been collected from Cape Sable, FL to Laguna Madre, Texas (U.S. National Museum of Natural History 2002; Van Name 1921, Lambert et al. 2005; Ruiz et al. unpublished data). We regard it as cryptogenic in the Atlantic Ocean south of Cape Hatteras, NC.

Invasion History in Hawaii:

Diplosoma listerianum was first reported in 1900 from Pearl Harbor, Oahu, Hawaii (Carlton and Eldredge, 2009) and subsequently reported from Pearl Harbor in 1976 (Coles et al. 1999).

Invasion History elsewhere in the World:

Diplosoma listerianum has been reported worldwide from tropical to cold-temperate regions. Among locations where it is considered a recent invader are Guam (in 1998, Lambert 2002), the Galapagos Islands (1999, Wittman and Smith 2003; Lambert 2019), New Zealand (in 1946, Cranfield et al. 1998), and South Africa (1st Record 1949, now found from Saldanha Bay to Durban, Monniot et al. 2001; Mead et al. 2011b). Genetic studies may result in changes to cryptogenic/introduced status of D. listerianum populations. A recent study suggests that one cryptic species (clade A) is widely distributed in the world's oceans, and has been anthropogenically distributed along shipping routes, but does not indicate a region of origin (Perez-Portela et al. 2013).