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| NAS - Nonindigenous Aquatic Species |
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Common Name: a white crust tunicate
Synonyms and Other Names: tunicate, colonial ascidian
Taxonomy: available through 
Identification:
Members of this genus are colonies of tough crusts densely infiltrated with microscopic calcareous spicules. Most comonly white, less often yellow to reddish. Sometimes encrusting and taking the form of bushy bryooans and other supports. D. candidum has spicules less than 0.02 mm (Gosner 1978).
Requires validation of species by an expert in tunicate systematics.
Size: Colonies 3-4 inches (75-100 mm); to 3/16 inches (5 mm) thick (Gosner 1978).
Native Range:
Tropical/subtropical colonial ascidian with wide distribution in the Atlantic and Pacific (Gretchen Lambert, personal communication). Didemnum perlucidum was described from Guadeloupe in the Caribbean by Monniot (1983) and is common on artificial surfaces in Brazil (da Rocha and Monniot 1995). It has been noted from Tobago and the Dominican Republic (Ivan Goodbody, personal communication) and in Puerto Rico on natural reefs (Jan Culbertson, personal communication). It is found in the Indo-West Pacific including Guam (Paulay et al. 2001) and in French Polynesia, Indonesia, New Caledonia, and Zanzibar (Monniot and Monniot 1996). Godwin and Lambert (2000) noted its occurrence in Hawaii.
Nonindigenous Occurrences: Didemnum perlucidum was not listed as being in the United States by Van Name (1945) or Plough (1978). This tunicate has been collected in the Gulf of Mexico off Texas (Culbertson and Harper 2000) and has been identified from Pensacola Bay, Florida (SERC, Nemesis Database); however, there is some question as to whether it is indigenous to the Gulf. Even if it is determined to be native to the Gulf, it may still be classified as invasive because of its aggressive nature and ability to rapidly colonize and overgrow artificial structures (Culbertson and Harper 2000). Collected from the island of Oahu, Hawaii (Coles 2002).
Means of Introduction:
Lambert (2002) found that the tunicate breeds year-round and releases large numbers of larvae daily, thus regional and local spread of this tunicate may occur through transport of larvae. Ascidian larvae have also been identified from ballast water (Lambert 2002). Adult ascidians may be transported by hull fouling and relocation of petroleum platforms. Lambert (2002) noted that Didemnum perlucidum sometimes hangs in long thick strands that easily break off and drift to other areas and that this may be an important method of spreading.
Status: Didemnum perlucidum found on shallow water, natural reefs do not appear to have the same aggressive nature as those colonizing artificial structures in deeper water (Jan Culbertson, personal communication). Although colonized oil platform structures are in close proximity to the Flower Garden Reef and Stetson Bank in Texas, the tunicate has not invaded the natural reef areas (Lambert 2002).
Impact of Introduction:
In areas where it is abundant, it overgrows other epibionts and smothers them. Lambert (2002) noted that in 14 months, Didemnum perlucidum, colonized and covered 100% of a sunken petroleum rig off Texas.
Remarks:
Life history characteristics of tunicates that facilitate wide distribution of species include, broad environmental tolerance, rapid growth rate, early sexual maturity, short life span, and high fecundity (Lambert 2002).
References
Culbertson, J. and D. Harper. 2000. Settlement of a colonial ascidian on an artificial reef in the Gulf of Mexico. In: Minerals Management Service, Gulf of Mexico Fish and Fisheries, Bringing Together New and Recent Research. New Orleans, Louisiana.
da Rocha, R.M. and F. Monniot. 1995. Taxonomic and ecological notes on some Didemnum species (Ascidiacea, Didemnidae) from Sao Sebastiao Channel, southeastern Brazil. Rev. Bras. Biol. 55:639-649.
Godwin, L.S. and G. Lambert 2000. New records of Ascidiacea (Urochordata) in the marine invertebrate fouling community of O'ahu, Hawaii. Bishop Mus. Occas. Pap. 64: 59-61.
Lambert, G. 2002. Nonindigenous ascidians in tropical waters. Pac. Sci. 56(3):291-298.
Monniot, F. 1983. Ascidies littorals de Guadeloupe I. Didemnidae. Bull. Mus. Natl. Hist. Nat. Ser. 4, 5:5-49.
Monniot, F. and C. Monniot. 1994. New collections of ascidians from the western Pacific and southeastern Asia. Micronesica 29:133-179.
Paulay, G., L. Kirkendale, G. Lambert, and J. Starmer. 2001. The marine invertebrate biodiversity of Apra Harbor: significant areas and introduced species, with focus on sponges, echinoderms, and ascidians. Naval Activities Guam, Cooperative Agreement N68711-97-LT-70001.
Plough, H.H. 1978. Sea squirts of the Atlantic continental shelf from Maine to Texas. John Hopkins University Press, Baltimore, Maryland.
SERC. Smithsonian Environmental Research Center, NEMESIS Database.
http://invasions.si.edu/nemesis/dodresults.jsp?bay=PB&species=
Van Name, W.G. 1945. The North and South American ascidians. Bull. Am. Mus. Nat. Hist. 84:1-476.
Author: Harriet Perry
Revision Date: 4/24/2006 Citation for this information:
Harriet Perry. 2008. Didemnum perlucidum. USGS Nonindigenous Aquatic Species Database, Gainesville, FL.
<http://nas.er.usgs.gov/queries/FactSheet.asp?speciesID=2389> Revision Date: 4/24/2006
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