Invasion History

First Non-native North American Tidal Record: 1999
First Non-native West Coast Tidal Record:
First Non-native East/Gulf Coast Tidal Record: 1999

General Invasion History:

The origin of Didemnum perlucidum is unknown. It was first described in Guadeloupe in the Caribbean (Monniot 1983), but was subsequently found in Brazil, West Africa, the Gulf of Mexico, and the Indo-Pacific, including Hawaii, Guam, and the Pacific entrance to the Panama Canal (da Rocha and Kremer 2005). We consider this tunicate to be cryptogenic (status unknown) over much of its range, but there are several recent occurrences in harbors or on man-made structures where it is known to be introduced. These include the Gulf of Mexico, Florida, Guam, Hawaii, and the Pacific Coast of Panama (Godwin and Lambert 2000; Lambert 2002; Carman et al. 2010).

North American Invasion History:

Invasion History on the West Coast:

Invasion History on the East Coast:

In 1999, divers surveying an abandoned oil platform, converted to an artificial reef, off the coast of Texas found that it was incrusted with an unfamiliar colonial tunicate, which was identified by Gretchen Lambert as D. perlucidum (Culbertson and Harper 2001; Lambert 2002). Colonies of D. perlucidum were also tentatively identified on the SERC Invasions program fouling plates in Pensacola Bay (2002), Miami Harbor (2004), and the Indian River Lagoon (2005; 2010) (Ruiz et al. unpublished data). However, some of these colonies were young or in poor condition. D. perlucidum appears to be established in US waters, but its extent and abundance is unclear. 
 

Invasion History on the Gulf Coast:

In 1999, Didemnum perlucidum was found on an abandoned oil platform/artificial reef off the coast of Texas (Culbertson and Harper 2001; Lambert 2002) and was tentatively identified by the Smithsonian Environmental Research Center’s Marine Invasions Lab in Pensacola Bay (in 2002) (Ruiz et al. unpublished data).

Invasion History in Hawaii:

Populations of Didemnum perlucidum, confined to harbors and artificial structures, were reported in 1999 from Ke'ehi Lagoon and Kaneohe Bay, Hawaii (Godwin and Lambert 2000; Coles et al., 2002).

Invasion History Elsewhere in the World:

Didemnum perlucidum was described from the undersides of buoys in a marina in Guadeloupe, in the West Indies by Francoise Monniot (1983). It was found in Sao Sebastiao Channel, southern Brazil in 1994. It has been collected from Pecem and Mucuripe Harbors, Ceara state, northern Brazil, (2009, Lotufo and Oliveira Filho 2010), from Isla Margarita, Venezuela (2009, da Rocha et al. 2010), and Pelican Cay, Belize (1992, Goodbody 2000). In the eastern Atlantic, it was collected in 1990 on Madeline Island, off Dakar, Senegal (Monniot and Monniot 1994). 
 
In the Indo-Pacific, D. perlucidum has been collected in harbors in Zanzibar and Tanzania, Monniot and Monniot 1997), in the Maldives, in Indonesia and the Philippines (Monniot and Monniot 2001), and New Caledonia (Monniot and Monniot 1996). Among the Pacific islands, populations confined to harbors and artificial structures occur in Palau and Guam (Lambert 2002; Lambert 2003), Hawaii (1999, Ke'ehi Lagoon and Kaneohe Bay, Godwin and Lambert 2000; Coles et al., 2002a), and Papeete, Tahiti (Monniot et al. 1985). In the eastern Pacific, this tunicate was reported from natural rock wall communities (Witman and Smith 2003) and fouling plates (Lambert 2019) in the Galapagos Islands, and from Panama Bay, near the Pacific entrance to the Panama Canal (2008, Ruiz et al., unpublished data; Carman et al. 2010). A recent genetic study found a low level of genetic diversity, with only 3 mitochondrial COI haplotypes over the whole known range, and only 1 haplotype in Brazil and Australia. Notable new records in this survey were Veracruz, Mexico, in the Gulf of Mexico, Mazatlan, on the Mexican Pacific coast, and Kochi, Shikoku, Japan, where it was co-existing with D. vexillum (Dias et al. 2016).


Description

Didemnum perlucidumis a colonial tunicate. Colonial tunicates are communities of individuals, called zooids, which share a protective cellulose layer called a tunic. Didemnum perlucidum contains spicules; small crystalline structures embedded in the tunic. Colonies vary greatly in appearance and the number of spicules they contain. The largest colonies measure 8 cm but are only 1-3 mm thick, and are usually found encrusting rock, wood, ropes, or other structures (Monniot 1983). Colonies are marbled in appearance—white and gray, yellow, or brown—with the darker color due to fecal pellets visible in the cloacal canals, where the tunic has only sparse spicules. According to Monniot (1983), some colonies completely lack spicules, but the colonies observed by da Rocha and Monniot (1995) in Brazil, always had them. Spicules occasionally reach 40µm in size, but usually do not exceed 20–30 µm (Monniot 1983; da Rocha and Monniot 1995). The zooids are arranged in clumps, leading to meandering dark lines on the tunic surface which are areas lacking in spicules between the clumps of zooids. 
 
The zooids vary in appearance among colonies and the height of the colony is variable, but average around 1 mm (Monniot 1983; da Rocha and Monniot 1995). The oral siphon is short, large, and divided into six pointed lobes. The cloacal siphon varies in width, from 'modest' to exposing the whole branchial sac. There is an oval stomach followed by an annular post-stomach. The middle intestine is folded against the most posterior part of the abdomen. The single testis consists of a spherical body, surrounded by five to seven coils of the sperm duct. The ovary consists of one large oocyte and several smaller ones. The larvae are small (0.4-0.5 mm in diameter) in relation to the zooids, bearing three long adhesive papillae and four pairs of ampullae. The tail is long and forms a coil around the larva (Monniot 1983; da Rocha and Monniot 1995). 


Taxonomy

Taxonomic Tree

Kingdom:   Animalia
Phylum:   Chordata
Subphylum:   Tunicata
Class:   Ascidiacea
Order:   Aplousobranchia
Family:   Didemnidae
Genus:   Didemnum
Species:   perlucidum

Synonyms

Potentially Misidentified Species

Didemnum psammathodes
Probably native to Indo-Paciifc, broadly distributed. One disitnguishing feature is a gritty texture, due to embedded spicules.

Didemnum vexillum
Native to NW Pacific, widespread, mostly in col-water regions, but co-occurs with D. perlucidum in southern Japan.

Ecology

General:

Life History- A colonial tunicate consists of many zooids, bearing most or all of the organs of a solitary tunicate, but modified to varying degrees for colonial life. Colonial tunicates of the family Didemnidae have small zooids, completely embedded in an encrusting and thin tunic. Each zooid has an oral siphon and an atrial aperture which opens to a shared cloacal chamber. Water is pumped into the oral siphon, through finely meshed ciliated gills on the pharynx, where phytoplankton and detritus is filtered, and passed on mucus strings to the stomach and intestines. Excess waste is expelled in the outgoing atrial water (Van Name 1945; Barnes 1983).

Colonial tunicates reproduce both asexually by budding and sexually from fertilized eggs that develop into larvae. Buds can form from the body wall of the zooids. Colonies vary in size ranging from small clusters of zooids to huge spreading masses. The zooids are hermaphroditic, which means both eggs and sperm are released into the atrial chamber. Eggs may be self-fertilized or fertilized by sperm from nearby animals, but some species have a partial block to self-fertilization. Fertilized eggs are brooded within the tunic until they hatch into lecithotrophic (non-feeding, yolk-dependent) tadpole larvae. The larva has a muscular tail and a notochord, eyespots, and a set of adhesive papillae. The larvae are expelled upon hatching and swim briefly before settlement. Swimming periods are usually less than a day, but some larvae settle immediately after release or swim for longer periods if the water temperature is low. On settlement the tail is absorbed, the gill basket expands, and the tunicate begins to feed by filtering (Van Name 1945; Barnes 1983).

Didemnum perlucidum is known from tropical and subtropical climates in marine waters on rocks, coral reefs, shellfish culture operations, oil platforms, marinas, and docks (Culbertson and Harper, 2001; Lambert 2002; da Rocha et al. 2009; Sheehy et al. 2009). Large biomasses of colonial tunicates can filter large volumes of water, removing phytoplankton and other particles.

Food:

Phytoplankton; Detritus

Trophic Status:

Suspension Feeder

SusFed

Habitats

General HabitatCoarse Woody DebrisNone
General HabitatMarinas & DocksNone
General HabitatCoral reefNone
General HabitatRockyNone
General HabitatVessel HullNone
General HabitatGrass BedNone
Salinity RangePolyhaline18-30 PSU
Salinity RangeEuhaline30-40 PSU
Tidal RangeSubtidalNone
Tidal RangeLow IntertidalNone
Vertical HabitatEpibenthicNone

Life History


Tolerances and Life History Parameters

Broad Temperature RangeNoneWarm temperate-Tropical
Broad Salinity RangeNonePolyhaline-Euhaline

General Impacts

Economic Impacts

Shipping and Fisheries: Didemnum perlucidum is known to grow on boat hulls and on cultured mussels, such as Perna perna in Brazil. It overgrows mussels and could damage the bivalve industry; however, it was common but not dominant in mussel farms in southern Brazil (da Rocha et al. 2010).

Ecological Impacts

Competition: On artificial substrates such as oil platforms, Didemnum perlucidum settles on or overgrows a wide range of organisms. On an abandoned oil platform in the Gulf of Mexico it appeared to settle on and overgrow sponges, corals, bryozoans, hydroids, and mollusks (Culbertson and Harper 2001). In fouling plate experiments in Sao Sebastiao, Brazil, it grew rapidly on bare plates and was able to overgrow barnacles and bivalves in about 70% of the cases and algae, bryozoans, and other colonial tunicates in about 65% of cases (Dias et al. 2008). In similar experiments in Santa Catharina, Brazil the barnacle Megabalanus coccopoma and the solitary tunicate Styela plicata survived overgrowth (Kremer et al. 2010) and it did not influence taxonomic richness or inhibit colonization by any species and appeared to have only weak, sporadic effects. These weak effects may have been due to the low abundance of D. perlucidum at this site (Kremer and Rocha 2011). This tunicate is known to grow on natural substrates in Guadeloupe and Brazil, but colonies are rare and smaller than those that occur on artificial structures (Monniot and Monniot 1985; Kremer et al. 2010). In the Swan River estuary, Western Australia, D. perlucidum has been spreading from artificial structures to seagrass beds (Halophila ovalis), reducing growth and photosynthesis, and decreasing habitat for the nonindigenous snail Batillaria ovalis, and probably for native species, as well (Simpson et al. 2016).


Regional Impacts

CAR-INorthern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern FloridaEcological ImpactCompetition
On an abandoned oil platform in the Gulf of Mexico, Texas, Didemnum perlucidum appeared to settle on or overgrow 'sponges, corals, bryozoans, hydroids, and mollusks' (Culbertson and Harper 2001).
SA-IINoneEcological ImpactCompetition
In fouling plate experiments in São Sebastião, Brazil, Didemnum perlucidum grew most rapidly on bare plates, and when other organisms settled, it grew at a much slower rate, but overgrew solitary organisms (barnacles, bivalves) in about 70% of the cases. However, encounters with algae, bryozoans, or colonial ascidians resulted in stand-offs in about 65% of cases (Dias et al. 2008). In similar experiments in Santa Catarina state, overgrown species, such as the barnacle Megabalanus coccopoma and the solitary ascidian Styela plicata survived overgrowth (Kremer et al. 2010).  Didemnum perlucidum did not influence taxonomic richness or inhibit colonization by any species, and appeared to have only weak, sporadic effects (Kremer et al. 2010). These weak effects may have been due to low abundance at this site (Kremer and Rocha 2011). In a 3-species experimnent, D. perlucidum dominates over Botrylloides nigrer and Schizoporella errata when preators were excluded, during the summer (Oricchio and Dais 2020).
SA-IINoneEconomic ImpactFisheries
Didemnum perlucidum was common but not dominant in mussel farms in southern Brazil. It does overgrow mussels, so could 'be damaging to the bivalve industry' (da Rocha et al. 2010). In later studies, D. pelucidum was found to affect the growth of cultuered mussels, delying or preventing their growth to maretable size. Monthly cleaning of the mussels and the culture 'socks' improved the growth of the mussels, but increased labor costs, (Lins and Rocha 2020).
AUS-IVNoneEcological ImpactHabitat Change
Didemnum perlucidum has been overgrowing blades of the seagrass Halophila ovalis in the Swan River estuary, Western Australia, decreasing seagrass cover. Density of the nonindigenous snail Batillaria australis has decreased in areas of grass beds colonized by D. perlucidum (Simpson et al. 2016).
AUS-IVNoneEcological ImpactCompetition
Didemnum perlucidum has been overgrowing blades of the seagrass Halophila ovalis in the Swan River estuary, Western Australia, decreasing the plant's rate of photosynthesis and growth. The tunicate has been spreading outward from areas of human infrastucture, such as docks and buoys (Simpson et al. 2016).
SEP-HNoneEcological ImpactCompetition
Predator exclusion and natural (upwelling) eutrophication allowed D. cf. perlucidum to overgrow corals, polychaetes, and barnacles (Roth et al. 2017).
SEP-HNoneEcological ImpactHabitat Change
Rapid overgrowth of fouling communities by D. cf. perlucidum can potentially affecting the composition of the coral reef community (Roth et al. 2017).

Regional Distribution Map

Bioregion Region Name Year Invasion Status Population Status
SA-II None 1994 Def Estab
CAR-IV None 1980 Def Estab
CAR-I Northern Yucatan, Gulf of Mexico, Florida Straits, to Middle Eastern Florida 1999 Def Estab
WA-I None 1990 Crypto Estab
SP-XVI None 1984 Crypto Estab
EA-III None 0 Crypto Estab
SP-V None 1995 Crypto Estab
EAS-III None 1996 Crypto Estab
SP-XXI None 1999 Def Estab
AG-4 None 1994 Crypto Estab
AG-3 None 1994 Crypto Estab
SP-XII None 1998 Def Estab
G130 Pensacola Bay 2002 Def Estab
CAR-II None 1992 Def Estab
S200 Biscayne Bay 2004 Def Estab
S190 Indian River 2005 Def Estab
SEP-Z None 1999 Def Estab
SEP-H None 2008 Def Estab
CAR-III None 2009 Def Estab
SP-XIII None 2002 Def Estab
SA-IV None 2009 Def Estab
AUS-IV None 2011 Def Estab
SP-I None 2003 Crypto Estab
AUS-I None 2015 Def Estab
AUS-II None 2012 Def Estab
SA-III None 2011 Def Estab
AUS-V None 2015 Def Estab
NWP-3b None 2015 Def Unk
NEP-VIII None 2015 Def Estab
PAN_PAC Panama Pacific Coast 2008 Def Estab
PAN_CAR Panama Caribbean Coast 2008 Def Estab
CIO-I None 2017 Crypto Estab
CIO-II None 0 Crypto Estab

Occurrence Map

OCC_ID Author Year Date Locality Status Latitude Longitude
6828 Culbertson and Harper 2000 1999 1999-01-01 12 miles east of Stetson Bank Def 28.2500 -94.4667

References

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

Bridgwood, Samantha D.; Muñoz, Julieta; McDonald, Justin I. (2014) Catch me if you can! The story of a colonial ascidian’s takeover bid in Western Australia, BioInvasions Records 3: in press

Campbell, Marnie L] ; Hewitt, Chad L.[ Miles, Joel (2016) Marine pests in paradise: capacity building, awareness raising and preliminary introduced species port survey results in the Republic of Palau, Biological Invasions 7(4): 351-363

Carlton, J.T., Eldredge, L. (2001) <missing title>, Bernice P. Bishop Museum Press, Honolulu, Hawaii,. Pp. <missing location>

Carman, Mary, and 8 authors (2011) Ascidians at the Pacific and Atlantic entrances to the Panama Canal, Aquatic Invasions 6(4): 371-380

Coles, S. L.; DeFelice, R. C. : Eldredge, L. G. (2002a) Nonindigenous marine species in Kaneohe Bay, Oahu, Hawai`i, Bishop Museum Technical Report 24: 1-364

2001 Gulf of Mexico Fish and Fisheries. http://www.beak.com/info/features/abstracts/culbertsonharper.htm

da Rocha, Rosa Morales and 13 authors (2010) Inventory of ascidians (Tunicata, Ascidiacea) from the National Park La Restinga, Isla Margarita, Venezuela, Biota Neotropica 10: published online

da Rocha, Rosana M.; Kremer, Laura P.; Baptista, Mariah S.; Metri, Rafael (2009) Bivalve cultures provide habitat for exotic tunicates in southern Brazil., Aquatic Invasions 4(1): 195-205

da Rocha, Rosana M.; Kremer, Laura P. (2005) Introduced ascidians in Paranagua Bay, Parana, southern Brazil., Revista Brasileira da Zoologia 22(4): 1170-1184

da Rocha, Rosana Moreira; Monniot, François (1995) Taxonomic and ecological notes on some Didemnum species (Ascidiacea, Didemnidae) from São Sebastião Channel, south-eastern Brazil, Revista Brasiliera de Biologia 55(4, Part 1): 639-649

Dias, G. M.; Rocha, R. M.; Lotufo, T. M. C.; Kremer, L. P. (2013) Fifty years of ascidian biodiversity research in Sao Sebastiao, Brazil, Journal of the Marine Biological Association of the United Kingdom 93(1): 273-282

Dias, Gustavo Muniz; Delboni, Cynthia Grazielle Martins; Duarte, Luiz Francisco Lembo (2008) Effects of competition on sexual and clonal reproduction of a tunicate: the importance of competitor identity, Marine Ecology Progress Series 362: 149-156

Dias, P. Joana and 8 authors (2016) Investigating the cryptogenic status of the sea squirt Didemnum perlucidum (Tunicata, Ascidiacea) in Australia based on a molecular study of its global distribution, Aquaitc Invasions In press: <missing location>

Dias, P. Joana and 9 authors (2021) Multiple introductions and regional spread shape the distribution of the cryptic ascidian Didemnum perlucidum in Australia:: an important baseline for management under climate change, Aquatic Invasions 16: 297-313

Dias, P. Joana; Simpson,Tiffany; Hitchen, Yvette; Lukehurst, Sherralee; Snow, Michael; Kennington, W. Jason (2016) Isolation and characterization of 17 polymorphic microsatellite loci for the widespread ascidian Didemnum perlucidum (Tunicata, Ascidiacea), Management of Biological Invasions 7: in press

Godwin, L. S.; Lambert, G. (2000) New records of Ascidiacea (Urochordata) in the marine invertebrate fouling community of O'ahu, Hawaii., Bishop Museum, Occasional Papers 64: 59-61

Goodbody, Ivan (2000) Diversity and distribution of ascidians (Tunicata) in the Pelican Cays, Belize., Atoll Research Bulletin 480: 1-33

Granthom-Costa, Luciana Vieira; Werner Ferreira, Carlos Gustavo; Dias, Gustavo Muniz (2016) Biodiversity of ascidians in a heterogeneous bay from southeastern Brazil, Management of Biological Invasions 7: 5-12

Hulthuis, L. B. (1978) A collection of decapod crustaceans from Sumba , Lesser Sunda Islands, Indonesia, Zoologische Verhandelingen <missing volume>: <missing location>

Kremer, Laura P.; Rocha, Rosana M.; Roper, James J. (2010) An experimental test of colonization ability in the potentially invasive Didemnum perlucidum (Tunicata, Ascidiacea), Biological Invasions 12: 1581-1590

Kremer, Laura P.; Rocha. Rosana M. (2011) The role of Didemnum perlucidum F. Monniot, 1983 (Tunicata, Ascidiacea) in a marine fouling community, Aquatic Invasions 6: corrected proof

Lambert, Gretchen (2002) Nonindigenous ascidians in tropical waters., Pacific Science 56(3): 191-298

Lambert, Gretchen (2003) Marine biodiversity of Guam: the Ascidiacea., Micronesica 35-36: 584-593

Leonard, Kaeden; Hewitt , Chad L. Campbell, Marnie L.; Carmen Primo; Miller, Steven D. (2017) Epibiotic pressure contributes tobiofouling invader success, Scientific Reports <missing volume>(173): <missing location>

Monniot, C.; Monniot, F. (1985) [Littoral ascidians of Guadeloupe Island: IX. Characteristics of populations, ecology, relationships with the world fauna] (French), Tethys 11(3-4): 203-213

Monniot, C.; Monniot, F. (1997) Records of ascidians from Bahrain, Arabian Gulf with three new species., Journal of Natural History 31: 1623-1643

Monniot, Claude; Monniot, Francoise (1994) Additions to the inventory of Eastern tropical Atlantic Ascidians: arrival of cosmopolitan species., Bulletin of Marine Science 54(1): 71-93

Monniot, Claude; Monniot, Francoise; Laboutte, Pierre (1985) [Ascidians of the port of Papeete (French Polynesia); Relation to the environment and to intercontinental transport by navigation] (French), Bulletin du Museum National d'Histoire Naturelle. 4e Serie. Section A. Zoologie, Biologie et Ecologie Animales 7(3): 481-495

Monniot, Françoise (1983) [littoral ascidians of guadeloupe. i. didemnidae] (french), Bulletin du Museum National d'Histoire Naturelle. 4e Serie. Section A. Zoologie, Biologie et Ecologie Animales 5(1): 5-49

Monniot, Françoise, Monniot, Claude (1996) New collections of ascidians from the western Pacific and southeastern Asia, Micronesica 29(2): 133-279

Monniot, Francoise; Monniot, Claude (1997) Ascidians collected in Tanzania, Journal of East African Natural History 86: 1-35

Monniot, Francoise; Monniot, Claude (2001) Ascidians from the tropical western Pacific., Zoosystema 23(2): 201-383

Moura, Carlos J.; Collins, Allen G.; Santos, Ricardo S.; Lessios, Harilaos (2019) Predominant east to west colonizations across major oceanic barriers: Insights into the phylogeographic history of the hydroid superfamily Plumularioidea, suggested by a mitochondrial DNA barcoding marker, Ecology and Evolution 9: :13001–13016.

Muñoz, Julieta; Page, Mike; McDonald, Justin I. Bridgwood, Samantha D. (2015) Aspects of the growth and reproductive ecology of the introduced ascidian Didemnum perlucidum (Monniot, 1983) in Western Australia, Aquatic Invasions 10(3): 265-274

2010 New records of introduced ascidians at Ceara State harbors, Northern Brazil. International Invasive Sea Squirt Conference-III - Woods Hole April 26-28, 2010 http://www.whoi.edu/page.do?pid=33341&tid=282&cid=72284

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>

Sheehy, Daniel J.; Vik, Susan F. (2009) The role of constructed reefs in non-indigenous species introductions and range expansions, Ecological Engineering 36: 1-1

Simkanin, Christina; Fofonoff, Paul W.; Larson, Kriste; Lambert, Gretchen; Dijkstra, Jennifer A.; Ruiz, Gregory M. (2016) Spatial and temporal dynamics of ascidian invasions in the continental United States and Alaska, Marine Biology 163: Published online

Simpson, Tiffany Schenk; Wernberg, Thomas; McDonald, Justin I. (2016) Invasive ascidian Didemnum perlucidum (Monniot 1983) in an urban estuary, PLOS ONE 11(5): e0154201

Skinner, Luís F.; Barboza, Danielle F.; Rocha, Rosana M. (2016) Rapid Assessment Survey of introduced ascidians in a region with many marinas in the southwest Atlantic Ocean, Brazil, Management of Biological Invasions 7(1): 13-20

Smale, Dan A.; Childs, Samantha (2012) The occurrence of a widespread marine invader, Didemnum perlucidum (Tunicata, Ascidiacea) in Western Australia, Biological Invasions 14: published online

Smale, Dan A.; Wernberg, Thomas (2012) Short-term in situ warming influences early development of sessile assemblages, Marine Ecology Progress Series 453: 129-136

Soors, Jan; Faasse, Marco; Stevens, Maarten; Verbessem, Ingrid; De Regge, Nico;Van den Bergh, Ericia (2010) New crustacean invaders in the Schelde estuary (Belgium), Belgian Journal of Zoology 140: 3-10

Streit, Olivia T; Lambert, Gretchen; Erwin, Patrick M.; Lopez-Legentil, Susanna (2021) Diversity and abundance of native and non-native ascidians in Puerto Rican harbors and marinas, Marine Pollution Bulletin 167(112262): Published online

Van Name, Willard G. (1945) The North and South American ascidians, Bulletin of the American Museum of Natural History 84: 1-462

Witman, Jon D.; Smith, Franz (2003) Rapid community change at a tropical upwelling site in the Galapagos Marine Reserve, Biodiversity and Conservation 12: 25-45