Didemnum vexillum

<h2 id="description">Description</h2>
A colony of Didemnum vexillum consists of a number of sac-shaped <a href="/facts/Zooid/c3cJ1zeT">zooids</a> connected by a common tunic. Each zooid is about 1 mm (0.04 in) long and has a buccal siphon through which water is drawn into the interior. The water then passes into a shared cavity from which it is pumped out through an atrial siphon. The surface of the colony is smooth, leathery, and often veined in appearance; the buccal siphons appear as numerous fine pores, and the atrial siphons as a smaller number of larger holes. The colony is firmly attached to a hard surface from which it can be difficult to detach.<a class="footnote-ref" id="fnref:8" href="#fn:8">8</a>
D. vexillum has different forms in different locations. It can form a thin or thick encrusting mat, or form large or small lobes. The colour can be orange, pink, tan, creamy yellow or greyish-white and the tunic is sparsely strengthened by stellate spicules with nine to eleven rays.<a class="footnote-ref" id="fnref:9" href="#fn:9">9</a> Where there is little water movement, the colonies may dangle in ropey masses from hard <a href="/facts/Substrate_(biology)/EBDd458H">substrates</a>, such as cables, docks, and the hulls of vessels. These stringy formations have led to it being colloquially referred to as "sea cheese" in Canada. In places with stronger currents, they cover the surface of rocks, boulders, pebbles, gravel, and oysterbeds in a thin, encrusting layer.<a class="footnote-ref" id="fnref:10" href="#fn:10">10</a>

<h2 id="distribution">Distribution</h2>

Didemnum vexillum appears to be native to Japan, where it was recorded in <a href="/facts/Mutsu_Bay/NN2qzRkv">Mutsu Bay</a> in 1926. It is still common there and, as well as growing on rock surfaces and seagrasses (<a href="/facts/Zostera/FfPuepP1">Zostera</a>), it grows as a <a href="/facts/Biofouling/LmkrjvN2">fouling organism</a> on cultured <a href="/facts/Bivalvia/IQDxHVc8">bivalves</a>, net cages, pilings and other man-made structures.<a class="footnote-ref" id="fnref:11" href="#fn:11">11</a> Its depth range is from the intertidal zone down to a depth of about 80 m (262 ft).<a class="footnote-ref" id="fnref:12" href="#fn:12">12</a>
The <a href="/facts/Portuguese_oyster/NDbbrz7M">Portuguese oyster</a> (Crassostrea angulata) cultivated off the Atlantic coast of France and Portugal was largely killed by an <a href="/facts/Iridoviridae/WjHjUowb">iridoviral disease</a> in 1969. To replace the stock, large quantities of <a href="/facts/Pacific_oyster/nKas1EBU">Pacific oyster</a> (Crassostrea gigas) <a href="/facts/Spawn_(biology)/nYF12vfX">spat</a> were imported from Japan. Some efforts were made to kill any fouling organisms that might be associated with the spat by immersing it for two periods, each of one hour, in fresh water. However, in the early 1970s, there were reports of a brown Didemnum <a href="/facts/Ascidiacea/Vkqqavut">ascidian</a> on oyster beds in the region. Around the same time, oyster spat from Japan was introduced into the Pacific coastal regions of Canada and the US and soon afterwards an ascidian was observed there, and later identified as D. vexillum.<a class="footnote-ref" id="fnref:13" href="#fn:13">13</a> By 2014, this tunicate was present in the eastern Atlantic, North Sea and Mediterranean Sea in the Netherlands, the United Kingdom, Ireland, France and Italy. On the east coast of North America its range extended from New Jersey, New York, Connecticut, Rhode Island, Massachusetts and New Hampshire, to Maine. In the eastern Pacific its range extends from Alaska to California. It is also present in New Zealand, where it was first observed in 2001, its only known encroachment into the Southern Hemisphere.<a class="footnote-ref" id="fnref:14" href="#fn:14">14</a> The Massachusetts Institute of Technology (MIT) built an autonomous underwater vehicle, named "Odyssey IV" that was used to monitor the spread of Didemnum at George's Bank.<a class="footnote-ref" id="fnref:15" href="#fn:15">15</a>
Because this ascidian broods its embryos and the larvae are free-swimming for only a brief time, natural dispersal of D. vexillum is limited in extent. Dispersal to new habitats in far flung parts of the world is likely to be through its accidental conveyance on the hulls of boats or other floating structures, or its introduction to aquaculture installations, perhaps with commercial oyster spat, seed mussels or aquaculture equipment.<a class="footnote-ref" id="fnref:16" href="#fn:16">16</a>

<h2 id="biology">Biology</h2>
Like other colonial ascidians, Didemnum vexillum is a <a href="/facts/Filter_feeder/hmVLwWB5">suspension feeder</a>. Water is drawn in through the buccal siphon of each zooid, the <a href="/facts/Plankton/WGo3LU9T">plankton</a> and fine particles of <a href="/facts/Detritus/8IjhrXA6">detritus</a> are filtered out, and the water and waste products leave through a common atrial siphon.<a class="footnote-ref" id="fnref:17" href="#fn:17">17</a>
Each individual <a href="/facts/Zooid/c3cJ1zeT">zooid</a> is a <a href="/facts/Hermaphrodite/C4aYIk4n">hermaphrodite</a>. Sperm is liberated into the sea and may get drawn into another zooid with the water current, fertilisation taking place internally. The <a href="/facts/Embryo/9QHnLVLN">embryos</a> have yolks from which they derive nourishment while they are brooded inside the colonial tunic. When they hatch, after about two weeks, the <a href="/facts/Larva/GKo2FIew">larvae</a> have a short free-living stage lasting up to a few hours, before undergoing <a href="/facts/Metamorphosis/nKDTSjsK">metamorphosis</a> into a zooid ready to found a new colony. The new colony grows by <a href="/facts/Asexual_reproduction/HpovW0VS">asexual reproduction</a>, with new zooids <a href="/facts/Budding/TEB3zXxB">budding</a> off existing ones. A fragment of a colony may become detached (perhaps by "dripping" off a floating structure), adhere to a new <a href="/facts/Substrate_(biology)/EBDd458H">substrate</a> and found a new colony.<a class="footnote-ref" id="fnref:18" href="#fn:18">18</a> Such colonies can grow rapidly, with a six- to eleven-fold increase in colony size having been observed over a fifteen-day period.<a class="footnote-ref" id="fnref:19" href="#fn:19">19</a>

<h2 id="invasive-impact">Invasive impact</h2>
Didemnum vexillum is capable of forming large colonies which can overgrow rocks and gravel, smother <a href="/facts/Benthos/DeHzh0sN">benthic</a> organisms and change the marine balance of the seafloor community. In some places in the Netherlands it covers 95% of the seabed and there is a marked decrease in populations of the <a href="/facts/Sea_urchin/RQrB6XTH">sea urchin</a> <a href="/facts/Psammechinus_miliaris/ShQUhPUN">Psammechinus miliaris</a> and the <a href="/facts/Brittle_star/PUSmanNu">brittle star</a> <a href="/facts/Ophiothrix_fragilis/hxpfqIJu">Ophiothrix fragilis</a>. On the <a href="/facts/Georges_Bank/Q2BzFDgD">Georges Bank</a>, Massachusetts, the seabed community is also changed, with some invertebrates decreasing but others, such as two species of <a href="/facts/Polychaete/Uo2YIINM">polychaete worm</a>, increasing in abundance. Here, D. vexillum restricts the potential settling sites for larvae of the <a href="/facts/Argopecten_irradians/kKlPMhv7">bay scallop</a> (Argopecten irradians) and the <a href="/facts/Placopecten_magellanicus/SldBUHdy">sea scallop</a> (Placopecten magellenaicus).<a class="footnote-ref" id="fnref:20" href="#fn:20">20</a> It exudes a toxic substance which discourages <a href="/facts/Predation/JEGdrX3f">predators</a> and prevents the larvae of other species from settling on it.<a class="footnote-ref" id="fnref:21" href="#fn:21">21</a> In New Zealand it overgrows <a href="/facts/Mussel/SNdrkjfl">mussels</a> and aquaculture equipment, but has not had quite such a devastating effect on the <a href="/facts/Ecology/YE8upuJU">ecology</a> as anticipated.<a class="footnote-ref" id="fnref:22" href="#fn:22">22</a>

<h2 id="genome-assembly">Genome assembly</h2>
In 2016 the draft genome of Didemnum vexillum reported the non-coding RNA annotation complement.<a class="footnote-ref" id="fnref:23" href="#fn:23">23</a> To this end a combination of several computational approaches, including blast searches with a wide range of parameters, and secondary structured-centred survey with infernal. The resulting candidate set was curated extensively to produce a high-quality ncRNA annotation of the first draft of the D. vexillum genome. It comprises 57 miRNA families, 4 families of ribosomal RNAs, 22 isoacceptor classes of tRNAs (of which more than 72% of loci are pseudogenes), 13 snRNAs, 12 snoRNAs, and 1 other RNA family. Additionally, 21 families of mitochondrial tRNAs and 2 of mitochondrial ribosomal RNAs and 1 long non-coding RNA.
A new version of D. vexillum genome is online available.<a class="footnote-ref" id="fnref:24" href="#fn:24">24</a> This new version combines PacBio technology and the Illumina raw data used to assembly the first draft genome version published in BMC genomics.<a class="footnote-ref" id="fnref:25" href="#fn:25">25</a>

<h2 id="external-links">External links</h2>
<ul><li><a href="https://www.invasivespeciesinfo.gov/aquatic/invertebrates/colonial-sea-squirt">Species Profile – Sea Squirt (Didemnum vexillum)</a>, National Invasive Species Information Center, <a href="/facts/United_States_National_Agricultural_Library/hohXT8HC">United States National Agricultural Library</a>. Lists general information and resources for Sea Squirt.</li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1">Alaska Center for Conservation Science. "Guide to some tunicates of Alaska". Field Guides for Kachemak Bay. <a href="https://accs.uaa.alaska.edu/kbnerr/field-guides/" target="_blank">https://accs.uaa.alaska.edu/kbnerr/field-guides/</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></li>
<li id="fn:2">"Didemnum vexillum Kott, 2002". NBN Atlas. <a href="https://species.nbnatlas.org/species/NHMSYS0020545709/" target="_blank">https://species.nbnatlas.org/species/NHMSYS0020545709/</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></li>
<li id="fn:3">"Invasive Tunicates". Fisheries and Oceans Canada. <a href="https://www.dfo-mpo.gc.ca/species-especes/profiles-profils/invasivetunicates-tuniciersenvahissants-eng.html" target="_blank">https://www.dfo-mpo.gc.ca/species-especes/profiles-profils/invasivetunicates-tuniciersenvahissants-eng.html</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></li>
<li id="fn:4">"The carpet sea squirt (Didemnum vexillum)". The Marine Life Information Network. <a href="https://www.marlin.ac.uk/species/detail/2231" target="_blank">https://www.marlin.ac.uk/species/detail/2231</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></li>
<li id="fn:5">"Invasive Species — Didemnum Tunicate (Didemnum vexillum)". Alaska Department of Fish and Game. Retrieved 2015-01-22. <a href="http://www.adfg.alaska.gov/index.cfm?adfg=invasiveprofiles.didemnum_characteristics" target="_blank">http://www.adfg.alaska.gov/index.cfm?adfg=invasiveprofiles.didemnum_characteristics</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></li>
<li id="fn:6">Leeuw, T; Boss, ES; Slade, WH (2011). Pollock NW (ed.). Spectral Reflectance as a Method to Identify the Invasive Tunicate Didemnum vexillum. Proceedings of the American Academy of Underwater Sciences 30th Symposium. Diving for Science 2011. Dauphin Island, AL: AAUS. Archived from the original on April 15, 2013. Retrieved 2013-03-18. <a href="https://archive.today/20130415180550/http://archive.rubicon-foundation.org/10176" target="_blank">https://archive.today/20130415180550/http://archive.rubicon-foundation.org/10176</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></li>
<li id="fn:7">GB Non-native species secretariat (2011-04-07). "Carpet sea squirt, Didemnum vexillum". Retrieved 2015-01-21. <a href="http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209" target="_blank">http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></li>
<li id="fn:8">"Invasive Species — Didemnum Tunicate (Didemnum vexillum)". Alaska Department of Fish and Game. Retrieved 2015-01-22. <a href="http://www.adfg.alaska.gov/index.cfm?adfg=invasiveprofiles.didemnum_characteristics" target="_blank">http://www.adfg.alaska.gov/index.cfm?adfg=invasiveprofiles.didemnum_characteristics</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></li>
<li id="fn:9">Lambert, Gretchen (2009). "Adventures of a sea squirt sleuth: unraveling the identity of Didemnum vexillum, a global ascidian invader" (PDF). Aquatic Invasions. 4 (1): 5–28. doi:10.3391/ai.2009.4.1.2. <a href="http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf" target="_blank">http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></li>
<li id="fn:10">Andrea Toran (2014-11-14). "Species Didemnum vexillum colonial tunicate; ascidian; sea squirt". Marine nuisance species. USGS. Retrieved 2015-01-21. <a href="https://woodshole.er.usgs.gov/project-pages/stellwagen/didemnum/" target="_blank">https://woodshole.er.usgs.gov/project-pages/stellwagen/didemnum/</a> <a href="#fnref:10" class="footnote-back-ref">↩</a></li>
<li id="fn:11">Lambert, Gretchen (2009). "Adventures of a sea squirt sleuth: unraveling the identity of Didemnum vexillum, a global ascidian invader" (PDF). Aquatic Invasions. 4 (1): 5–28. doi:10.3391/ai.2009.4.1.2. <a href="http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf" target="_blank">http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf</a> <a href="#fnref:11" class="footnote-back-ref">↩</a></li>
<li id="fn:12">GB Non-native species secretariat (2011-04-07). "Carpet sea squirt, Didemnum vexillum". Retrieved 2015-01-21. <a href="http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209" target="_blank">http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209</a> <a href="#fnref:12" class="footnote-back-ref">↩</a></li>
<li id="fn:13">Lambert, Gretchen (2009). "Adventures of a sea squirt sleuth: unraveling the identity of Didemnum vexillum, a global ascidian invader" (PDF). Aquatic Invasions. 4 (1): 5–28. doi:10.3391/ai.2009.4.1.2. <a href="http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf" target="_blank">http://pdfs.semanticscholar.org/4cda/641aae05b9df11570d6d71c12bb8c4b85410.pdf</a> <a href="#fnref:13" class="footnote-back-ref">↩</a></li>
<li id="fn:14">Andrea Toran (2014-11-14). "Species Didemnum vexillum colonial tunicate; ascidian; sea squirt". Marine nuisance species. USGS. Retrieved 2015-01-21. <a href="https://woodshole.er.usgs.gov/project-pages/stellwagen/didemnum/" target="_blank">https://woodshole.er.usgs.gov/project-pages/stellwagen/didemnum/</a> <a href="#fnref:14" class="footnote-back-ref">↩</a></li>
<li id="fn:15">"MIT's new underwater robot can hover in place". MIT News | Massachusetts Institute of Technology. 2008-09-25. Retrieved 2023-10-10. <a href="https://news.mit.edu/2008/mits-new-underwater-robot-can-hover-place" target="_blank">https://news.mit.edu/2008/mits-new-underwater-robot-can-hover-place</a> <a href="#fnref:15" class="footnote-back-ref">↩</a></li>
<li id="fn:16">Bishop, John (2012-01-06). "GB non-natives factsheet editor". Archived from the original on 2015-01-23. Retrieved 2015-01-23. <a href="https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273" target="_blank">https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273</a> <a href="#fnref:16" class="footnote-back-ref">↩</a></li>
<li id="fn:17">Ruppert, Edward E.; Fox, Richard, S.; Barnes, Robert D. (2004). Invertebrate Zoology, 7th edition. Cengage Learning. p. 945. ISBN 81-315-0104-3.{{cite book}}: CS1 maint: multiple names: authors list (link) <a href="81-315-0104-3" target="_blank">81-315-0104-3</a> <a href="#fnref:17" class="footnote-back-ref">↩</a></li>
<li id="fn:18">GB Non-native species secretariat (2011-04-07). "Carpet sea squirt, Didemnum vexillum". Retrieved 2015-01-21. <a href="http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209" target="_blank">http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209</a> <a href="#fnref:18" class="footnote-back-ref">↩</a></li>
<li id="fn:19">GB Non-native species secretariat (2011-04-07). "Carpet sea squirt, Didemnum vexillum". Retrieved 2015-01-21. <a href="http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209" target="_blank">http://www.nonnativespecies.org/factsheet/factsheet.cfm?speciesId=1209</a> <a href="#fnref:19" class="footnote-back-ref">↩</a></li>
<li id="fn:20">Bishop, John (2012-01-06). "GB non-natives factsheet editor". Archived from the original on 2015-01-23. Retrieved 2015-01-23. <a href="https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273" target="_blank">https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273</a> <a href="#fnref:20" class="footnote-back-ref">↩</a></li>
<li id="fn:21">"Didemnum vexillum (Colonial sea squirt)". Conservation. Washington Department of Fish and Wildlife. Retrieved 2015-01-23. <a href="http://wdfw.wa.gov/ais/didemnum_vexillum/" target="_blank">http://wdfw.wa.gov/ais/didemnum_vexillum/</a> <a href="#fnref:21" class="footnote-back-ref">↩</a></li>
<li id="fn:22">Bishop, John (2012-01-06). "GB non-natives factsheet editor". Archived from the original on 2015-01-23. Retrieved 2015-01-23. <a href="https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273" target="_blank">https://web.archive.org/web/20150123214654/http://www.brc.ac.uk/gbnn_admin/index.php?q=node%2F273</a> <a href="#fnref:22" class="footnote-back-ref">↩</a></li>
<li id="fn:23">Velandia-Huerto, Cristian A. (30 August 2016). "Automated detection of ncRNAs in the draft genome sequence of a colonial tunicate: the carpet sea squirt Didemnum vexillum". BMC Genomics. doi:10.1186/s12864-016-2934-5. PMC 5006418. <a href="https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-2934-5" target="_blank">https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-2934-5</a> <a href="#fnref:23" class="footnote-back-ref">↩</a></li>
<li id="fn:24">Velandia, Cristian. "Didemnum vexillum genome". Didemnum vexillum genome. Retrieved 2 December 2021. <a href="http://tunicatadvexillum.bioinf.uni-leipzig.de/Home.html" target="_blank">http://tunicatadvexillum.bioinf.uni-leipzig.de/Home.html</a> <a href="#fnref:24" class="footnote-back-ref">↩</a></li>
<li id="fn:25">Velandia-Huerto, Cristian A. (30 August 2016). "Automated detection of ncRNAs in the draft genome sequence of a colonial tunicate: the carpet sea squirt Didemnum vexillum". BMC Genomics. doi:10.1186/s12864-016-2934-5. PMC 5006418. <a href="https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-2934-5" target="_blank">https://bmcgenomics.biomedcentral.com/articles/10.1186/s12864-016-2934-5</a> <a href="#fnref:25" class="footnote-back-ref">↩</a></li>
</ol>

Didemnum vexillum open-in-new

Didemnum vexillum