Tauranga Harbour is a popular place to live, work and play. This
is causing our natural environment to come under increasing
pressure. Bay of Plenty Regional Council has identified key issues
that the harbour faces, and ways to manage them.
The Tauranga Harbour Integrated Management Strategy has
identified mangroves as one of these key issues.
For more information about Mangroves read the Tauranga Harbour
Facts about mangroves
There are 70 species of Mangrove found worldwide. In New
Zealand only one species is present, Avicennia marina subspecies
australasica or Manawa, which is native to New Zealand and has
inhabited New Zealand coastal environments for approximately 19
million years. The Manawa species is the most southerly growing
species in the world, found in estuaries as far south as Kawhia
Harbour on the west coast, and Ohiwa Harbour in the Bay of
Mangroves generally live in
shallow and low energy (calm) inter-tidal (dry at low tide) areas
of estuaries or harbours. They provide a buffer against
coastal erosion and storm surge and are a nursery ground for some
juvenile fish species like short finned eel and yellow eyed
mullet. They're also home to many native insects, birds,
shellfish, snails, crabs and algae. Mangroves can protect the
shoreline against large waves and storm surge and trap and
stabilise the sediment, resulting in more shoreline protection from
erosion. However, too many mangroves can create problems in
Changing the way we use land in the Tauranga harbour catchment has
caused more sediment and more nutrients to get into the harbour.
This includes activities like subdividing land and clearing land of
bush. The extra nutrients have caused more mangroves to grow to the
point where they've taken over large areas of the open tidal flats,
especially in the sub-estuaries ( i.e Te Puna, Waikareao and
Mangrove canopy cover (ha) over time within a number of
estuaries in Tauranga Harbour.
Waikareao Estuary in Tauranga Harbour with mangrove and
salt marsh habitats
When the mangroves spread, they increase sedimentation (sand
build-up), by changing currents and dampening wave energy.
The vertical root structure and low branches of the plant help it
to trap fine silty sediment.
Increased sedimentation and mangrove spread is a major concern
to communities living around harbours and estuaries who would like
to see open water and estuary habitats maintained in a healthy
condition. Mangroves are spreading in many of the harbours and
estuaries they inhabit, including parts of Tauranga
Harbour. Aerial photo comparisons (figure 4) over time
show the expansion of mangroves over 44 years.
The 1959 Aerial photo of the Tauranga Harbour showing a)
Welcome Bay and b) Matapihi sections of the estuary and the change
in mangrove abundance over time. Red areas show the mangrove
area in 2003 and yellow areas show mangrove distribution in
We have set up an Estuary Care programme which is similar to
Coast Care in the Bay of Plenty. Estuary care involves
our staff working with community groups that are concerned about
the increase in mangroves and silt. The programme has the
support of all Bay of Plenty coastal councils, the Department of
Conservation and other agencies. We provide the groups with
technical and other resources to form a functional community group
that links with other groups in that catchment. They address
environmental issues like biodiversity, riparian planting, animal
and plant pest control, as well as mangrove removal.
Removing mangroves requires a resource consent so our Land
Resources staff work with the groups to help them gain
consents to work in selected areas of their estuary, and to
comply with monitoring and consent conditions.
What you can do to stop further mangrove
There are some things you can do to help reduce the spread of
mangroves in Tauranga Harbour:
- Minimise sediment runoff when carrying out earthworks
- Plant out any riparian areas to trap sediment and reduce
- Join an Estuary Care group to help restore estuaries and their
catchments. Bay of Plenty Regional Council supports these group to
gain the necessary approvals. Otherwise ensure you have
the appropriate permission from Bay of Plenty Regional
Council - coastal areas are publicly owned and very sensitive
and it is important things are done right.
If you want to get involved in the community groups or would
like information on areas covered by Estuary Care programmes in
Tauranga Harbour, please contact Bay of Plenty Regional
Recently Bay of Plenty Regional Council commissioned an
independent review of the way it engages with community groups and
other agencies in the management of mangroves. Read
the review (1.1 MB, pdf) by Catalyst Consultants and the Chief
Executive's report on how the recommendations will be