Invasion pathways

Pathways are human activities that, intentionally or unintentionally, may move a harmful organism from one place to another. 2645  The Biosecurity Act 1993 defines a “pathway” as “movement that is of goods or craft out of, into, or through a particular place in New Zealand or a particular kind of place in New Zealand, and has the potential to spread harmful organisms”. 2646

There are many marine pathways, but the most pressing issue facing marine biosecurity is increasing international shipping, and the consequential transfer of non-indigenous species from one country to another.

The Whangamatā sea squirt (Didemnum vexillum) is a marine pest that was first seen in Whangamatā in 2001. It has quickly established itself in the Marlborough Sounds, Port Nelson, Golden Bay, Whangamatā and Tauranga. It is a leathery or spongy, light mustard-coloured sea squirt. It can look like wax dripping over a structure such as a rope or mussel line and can quickly smother sea life. The Whangamatā sea squirt can be spread over long distances by infected vessel hulls and marine equipment and as fragments in ballast water. 2648


Biofouling risk occurs when marine organisms attach themselves to the hulls of vessels overseas and are then transported into New Zealand waters on the vessel. This is the most common cause of marine pest invasions. Large structures which are towed into New Zealand waters, such as drilling rigs, can also create biofouling risks. Biofouling of vessels and structures (both international and domestic), moving around the country, is also responsible for the spread of pests around New Zealand once they arrive here. 

In November 2013 a boat infested with the unwanted marine sea squirt Styela clava, (discussed below in a case study) was found berthed in Tauranga Harbour. It was the second boat with the sea squirt attached to its hull that had been found in Tauranga Harbour. One of the boats was moored in Pilot Bay and the other was berthed at Bridge Marina. Both boats had come from Auckland, where the sea squirt is established, without prior cleaning of their hulls. 2651

The Asian seaweed Undaria pinnatifida has established in many parts of New Zealand over the last 20 years. However, much of Fiordland has remained free from this invasive marine pest. Undaria is an highly invasive seaweed that rapidly overruns native species, altering marine ecosystems. In April 2010 a single mature Undaria plant was found on a line mooring a barge to the shoreline in the remote Sunday Cove in Breaksea Sound. 2652  Fiordland is a high value area and the presence of Undaria in Fiordland is considered a threat to this globally unique marine environment. As a result of the discovery, and following consultation with stakeholders and tangata whenua, a response involving the MPI, the Department of Conservation (DOC) and Environment Southland (lead–agency) was initiated to eliminate Undaria from Fiordland. Joint agency decision-making is undertaken at both the strategic and operational level, with an equal three-way split of operational costs.

Ballast water

Another major pathway for the introduction of marine pests is the movement and discharge of ballast water. This is seawater that has been pumped aboard a ship to provide stability and manoeuvrability. If this seawater is discharged in a different port from which it came, it can disperse the eggs and larvae of exotic marine organisms, which are able to establish in the new marine environment after discharge.

Other sources of risk

The rapid growth of the aquaculture industry, some of which involves the movement of juvenile animals (spat and smolt) and equipment around the coast, can play a role in the domestic spread of non-indigenous species once they have arrived in New Zealand. The aquaculture industry has codes of practice and industry standards in place to reduce this risk, as discussed in Chapter 10: Aquaculture.

Another source of risk is the aquarium trade. Although there are industry standards designed to avoid the release of exotic organisms, there is still considerable risk associated with the spread of marine species, if captive fish or algae are released into the wild. Import Health Standards and risk analysis have been developed to address and mitigate these risks (discussed further below).

Last updated at 1:42PM on February 6, 2018