Australian droplet tunicate

[Image: Crispin Middleton, NIWA]

The Australian droplet tunicate, (Eudistoma elongatum (Herdman, 1886)).

Status in New Zealand

Present in some areas of New Zealand

Legal Status in New Zealand

Under management

Description

The Australian droplet tunicate is an ascidian native to Australia, which forms large colonies that attach to hard substrates. It is generally found in muddy bottomed tidal habitats and on man-made structures such as wharf piles and aquaculture equipment. It is generally submerged just below the waterline, but can often be seen at low tide. The size of the Australian droplet tunicate in New Zealand is influenced by seawater temperatures, with it decreasing in size over the winter months, but rapidly re-growing to its full size once summer arrives.

Why is it a problem?

The Australian droplet tunicate forms dense colonies, smothering beaches, rocks and tide-pools. It displaces native species and grows on boats, aquaculture equipment and other marine structures. It was first reported in New Zealand in early 2005, but was not originally regarded as a pest, given its low density and the fact it appeared to die off in winter. In the summer of 2007-2008 it became more prolific in a number of locations in Northland and has continued to reappear over the summer months.

A swim over the Australian dropletÂ tunicate in Whangarei Harbour. [Video: Shaun Lee]

What do they look like?

Key Features

The Australian droplet tunicate looks like clusters of white or cream coloured tubes or "sausages". Each tube or "sausage" is actually a cylinder or tunic, containing numerous small individuals. The long cylindrical heads are generally 5-30 cm long and in some instances can reach 1.5 metres and 5-20 mm in diameter. The white tunics contain many small individual organisms and can sometimes appear orange flecked due to the presence of bright orange larvae.