Around the Harbour
Many unwanted plants and animals live in or around the land
surrounding the Tauranga Harbour. Pest animals around the harbour
that eat native plants and birdlife or eat food that native animals
- mustelids (ferrets, stoats and weasels),
- mice; and
- Argentine ants.
Tauranga Harbour hosts a substantial population of resident
black swans (Cygnus atraus) which are becoming pests and
destabilising sea grass (Zostera) which they appear to graze. In
1994, Environment Bay of Plenty estimated that black swans had
removed 25-35% of seagrass at the southern end of the Otumoetai
foreshore. Seagrass beds are important in increasing species
diversity and abundance, and the biomass of benthic
Pest plant species in and around the Tauranga Harbour include:
Spartina, salt-water paspalum, morning glory, ice plant, gorse,
pampas, woolly nightshade and wild ginger. These weeds can
smother and replace native plants or increase coastal sedimentation
around the harbour.
Vessels from all over the world enter Tauranga Harbour every
week bringing in imports such as oil and fertiliser, and taking out
exports such as kiwifruit and logs. Unfortunately these and
other vessels can also bring in marine pests - either hitching a
ride as fouling on ships' hulls, or in ballast water discharged
into our coastal waters.
There have been two recent marine pest identifications in
Tauranga Harbour - the Asian date mussel (Musculista senhousia) and
the Asian kelp (Undaria pinnatifida).
For more information about Biosecurity and Tauranga Harbour read
The Asian date mussel is small (up to 3cm) and brown to green in
colour. It lives in shallow and calm areas of the
harbour. Young date mussels seep out tiny threads which
attach to sand grains and join with those from neighbouring mussels
to form a thick, hard mat. These mats can prevent other
shellfish species and sea grass from growing. These mats survive
for one or two years before they die or move to somewhere else.
Undaria or Asian kelp, grows on rocky surfaces, shell beds and
artificial structures like wharves, marine farming equipment and
boat hulls. It grows very fast, forming forests of up to 2 m
in height. Undaria can prevent native marine species from
growing and may cause problems to the aquaculture industry as it
grows on equipment and smothers produce. Undaria has
spread to most major New Zealand ports and many harbours. It
was first recorded in Tauranga Harbour in November 2005 and has
been found on shell banks inside the harbour entrance and on
man-made structures at the southern end of the port wharves.
Other threats and future threats
In the future the sea squirt, Styela clava, which is well
established in Auckland's Hauraki Gulf, may be a threat to the
harbour. This sea squirt is a club-shaped marine animal,
usually brown with a fuzzy coating to its tough leathery
skin. It can grow to about 16 cm long and anchors itself to
hard surfaces, particularly man-made structures and aquaculture
equipment. It is a pest species that can affect marine
Another type of sea squirt, Didemnum vexillum, is established in
Tauranga Harbour. There is uncertainty as to whether this
invasive organism is native to New Zealand or introduced. So
far this species is only established in Marlborough, Whangamata and
Tauranga. Didemnum vexillum has a leathery or spongy texture
and often looks like wax dripping over a structure. It is
similar to other sea squirt species but can be identified because
of its yellow mustard like colour and leaf-like veins. It has
similar impacts to Styela clava, smothering man-made structures and
What are we doing?
We have pest animal and plant control and surveillance
programmes in place.
Bay of Plenty Regional Council works with the Department of
Conservation and other land owners to ensure that pests such as
spartina are controlled.
The Bay of Plenty Polytechnic has been working with Bay of
Plenty Regional, taking surveys of Asian date mussel in Tauranga
harbour. A 2006/07 survey of the southern half of the harbour
detected four live Asian date mussel beds. The on-going
environmental effect of Asian date mussels within Tauranga harbour
will be further monitored.
Bay of Plenty Regional Council also works with MAF Biosecurity New
Zealand to advance marine biosecurity awareness in the
What can you do?
Keep a look out for the species on this fact sheet and anything
else in the Tauranga Harbour area that seems out of the
ordinary. Report any suspicious finds to: MAF Biosecurity New
Zealand freephone 0800 80 99 66
Boat owners - regularly clean and anti-foul your vessel's hull
to minimise the chance of transporting pests, including those
featured in this fact sheet, around the coast and
particularly to high value marine areas such as Tuhua - Mayor
Island. Clean boats are unlikely to spread marine pests.
Need more information?
For more information on unwanted species in and around our
harbour check out the pest watchlist on the Biosecurity New Zealand
Other useful websites include: