Editing Tunicate (section)

==Invasive species==
Over the past few decades, tunicates (notably of the genera ''[[Didemnum]]'' and ''[[Pleurogona|Styela]]'') have been [[invasive species|invading]] coastal waters in many countries. The carpet tunicate (''[[Didemnum vexillum]]'') has taken over a {{convert|6.5|mi2|abbr=on}} area of the seabed on the [[Georges Bank]] off the northeast coast of North America, covering stones, molluscs, and other stationary objects in a dense mat.<ref name="sh.nefsc.noaa.gov">{{cite web |url=http://sh.nefsc.noaa.gov/tunicate.htm |title=Have You Seen This Tunicate? |publisher=NOAA Fisheries Service |date=2004-11-19 |access-date=2011-12-07 |archive-url=https://web.archive.org/web/20090109034514/http://sh.nefsc.noaa.gov/tunicate.htm |archive-date=9 January 2009 |url-status=dead }}</ref> ''D. vexillum'', ''[[Styela clava]]'' and ''[[Ciona savignyi]]'' have appeared and are thriving in [[Puget Sound]] and [[Hood Canal]] in the [[Pacific Northwest]].<ref name="dornfeld">{{cite web |url=http://www.pnwscuba.com/invasives/ |title=Invasive Tunicates of Washington State |author=Dornfeld, Ann |date=2008-05-01 |publisher=NPR |access-date=2013-04-06 |archive-url=https://web.archive.org/web/20140714124309/http://www.pnwscuba.com/invasives/ |archive-date=14 July 2014 |url-status=dead}}</ref>

Invasive tunicates usually arrive as [[Fouling community|fouling organisms]] on the hulls of ships, but may also be introduced as larvae in [[ballast water]]. Another possible means of introduction is on the shells of molluscs brought in for marine cultivation.<ref name="dornfeld"/> Current research indicates many tunicates previously thought to be indigenous to Europe and the Americas are, in fact, invaders. Some of these invasions may have occurred centuries or even millennia ago. In some areas, tunicates are proving to be a major threat to [[aquaculture]] operations.<ref>{{cite web |url=https://woodshole.er.usgs.gov/project-pages/stellwagen/didemnum/ |title=Marine Nuisance Species |publisher=Woods Hole Science Center |access-date=2011-12-07}}</ref>
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