Invasive Species — Didemnum Tunicate (Didemnum vexillum)

Didemnum vexillum can be moved between locations as biofouling on vessel hulls, as fouling on infested aquatic farm gear or infrastructure, or in ballast water as colony fragments. Transfers of shellfish stock or equipment may play a role in coastwise spread. Various sea squirts, including D. vexillum, along with barnacles, tubeworms, and bryozoans are commonly found growing on the hulls and niche areas of boats that have not received adequate cleaning and/or maintenance.

In some parts of the world, recreational boaters are considered the mostly likely vector for distributing invasive tunicates. As fouling organisms on vessel hulls and sea chests, commercial shipping is also recognized as a pathway to move species around. In some areas, floating infrastructure is moved between coastal locations, such material may include docks, mariculture superstructure, buoys, and other such floating structures. If boats and other floating material reside in an area infested by invasive species for any length of time, it is likely they will begin to harbor both invasive and native organisms. If floating structures and hulls are not cleaned before they are moved to a new site they can easily introduce communities of organisms to the new area.