The Chain tunicate Botrylloides violaceus is a colony-forming ascidian native to the northwestern Pacific Ocean. Transported on ship hulls or attached to living marine organisms (e.g. the Japanese oyster), the species got introduced to Europe before 1998, where it continued to spread via attachment to recreational yachts. Established colonies of this sea squirt were first reported along our coast in 2004, in the port of Zeebrugge. The colonies are usually uniformly coloured but can be bicoloured. Red-coloured individuals appear to be most common in western Europe. Other colours often found in this continent include off-white, purple, bright yellow and orange coloured individuals. Furthermore, combinations of two of these colours also exist. The Chain tunicate is morphologically distinguishable from other Botrylloides species in western Europe based on its anatomy and larvae. Due to the rare occurrence of other Botrylloides species, observations of many colonies occurring close together most likely concern the species Botrylloides violaceus. |
