Biological Environment of the West Coast Coastal Marine Area: an outline of Marine and Coastal Ecosystems and Habitats
3.8 Marine Pests And Other Introduced Organisms
A notable feature of the West Coast is the virtual absence of adventive (introduced) marine species, except in the estuarine domain where some adventive fish and plants have established. The invasive cord grass Spartina was found at the Oparara Estuary but ongoing monitoring indicates that it has now been eradicated. Three possible introduced marine species have been recorded, but recent research suggests that they are all native to New Zealand:
- The small seaweed Polysiphonia sertularioides is a possible adventive (introduced) species, but has been recorded on the West Coast only at Scott’s Beach (Heaphy Track) and it is by no means a dominant component of the marine flora of that locality86;
- The red rock crab occurs on intertidal rocky shores and subtidal reefs throughout the region, but it is possible that this species is a ‘self introduced’ New Zealand native (perhaps arriving attached to drifting flotsam from other countries); and
- The blue mussel has been suggested as a possible adventive species,
but has been found from fossil records to be a New Zealand native87.
It is a notable and rare occurrence for such a large marine region of New Zealand to be free of introduced marine species. Furthermore, two environmental factors work in favour of reducing the likelihood of introduced species becoming introduced and established in the West Coast marine area. They are:
2. the relatively few human vectors (such as vessel traffic and marine farming) for introducing marine species to the West Coast
This all adds up to a high natural conservation value for the present West Coast marine environment.
However, there are a number of pest species that could be introduced to the West Coast by natural or human vectors. They include:
- the Japanese kelp Undaria (which is already established in numerous locations around New Zealand); and
- the North Pacific seastar Asterias amurensis (which is established in Tasmania and South Australia); and
- the clubbed tunicate sea squirt Styela clava.
Current modelling by NIWA suggests that there is a very low risk of species establishing naturally from Australian populations, due to the long required drift times of at least four to six months, and up to two years88. Because of the factors outlined above, the West Coast is in an almost unique situation – of being able to prevent or strongly limit the natural or human-assisted spread of exotic marine species into the region. This is relevant not just for the biosecurity of the West Coast marine and coastal area, but also for that of regions ‘downstream’ – such as Fiordland. This ‘upstream position’ means that should a marine species become established in the West Coast, the likelihood of it spreading to other parts of the country by natural coastal currents will probably be higher than for other regions.
85 e.g. see Partridge 2004
86 Neale & Nelson 1998
87 Gardner 2004
88 Stanton 1997