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Scientists carry out Biosecurity NZ survey

12 October 2005

Scientists carry out Biosecurity NZ survey for clubbed tunicate

Scientists from the National Institute of Water & Atmospheric Research (NIWA) are diving in Waitemata Harbour to establish precisely how far an invasive sea squirt, known as the clubbed tunicate (or Styela clava), has spread.

The aim is to determine and map the distribution and density of it in the port and marine facilities and structures within the Viaduct Harbour and Freemans Bay. The work is being conducted for Biosecurity New Zealand so that they can assess the feasibility of various management options.

The survey team from NIWA will use a range of techniques including shore-based and snorkel and scuba searches for the sea squirt. These will allow the team to sample a variety of habitats quickly over a large area.

NIWA will also be identifying ‘vectors’ such as boats, barges, fuel and supply jetties, which have the potential to spread the sea squirt.

The work will focus first on the Viaduct Harbour, where the sea squirt was initially found, and neighbouring Freemans Bay. Further surveys will search the wider Waitemata Harbour.

About the clubbed tunicate

The clubbed tunicate is a fast-growing organism, which filters suspended plankton and organic materials from the water. It can grow up to 160 millimetres long and reach densities of up to 500–1500 individuals per square metre.

It is thought to be native to the coastal waters of Japan, Korea, Northern China, and Siberia, and is known to have spread to parts of northwestern Europe, USA, and Australia. While it mostly occurs in shallow water, the clubbed tunicate can live in water as deep as 25 metres.

It competes for space and food with native and aquaculture species. It can also be a nuisance by fouling marine farming lines, vessel hulls, and other structures.

It is also known as the Asian sea squirt, leathery sea squirt, or Pacific rough sea squirt.


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