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 need include:
- 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 (bottom-feeding) communities.
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 our Tauranga Harbour Factsheets.
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 farms.
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 mussel lines.
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 region.
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 website:
Other useful websites include:
- MAF undertook a survey of non-indigenous species in the harbour in 2004. Read the report 2005 Port of Tauranga Biosecurity Report (2.4 MB, pdf)