A marine biosecurity group says an unwanted invasive organism has been found in Nelson waters.
Styela clava, also known as clubbed tunicate, was discovered during a routine marine biosecurity survey.
It has the potential to change the marine environment by displacing native organisms and may spoil mussel lines.
The Top of the South Marine Biosecurity Partnership confirmed the discovery of a single 3cm-long specimen at Dickson Basin in Port Nelson.
A further survey to determine the extent of the infestation is planned for early June, once dredging in the area is completed.