Mangroves
Map ID Number: Examples include 6, 9
Location: Mangroves occur in many estuaries and shallowwater coastal areas north of 38ºS. (This corresponds with Raglan/Whaingaro on the west coast of the North Island and Ohiwa on the east coast.) There is some evidence from analysis of pollen samples that mangroves have occurred further south in the past (e.g. Mildenhall 1994).
Approximate area: Unknown – there is some historical information available (e.g. Crisp et al. 1990) and more recently, mangrove extent has been mapped at a number of individual locations by different agencies/organisations.
Description of habitat type:
The mangrove (Avicennia marina subsp. australasica) 11 is a broadleaf evergreen tree that flourishes in estuarine and sheltered coastal areas. The trees grow between midtide and high spring tide levels on sheltered accretive shores with low energy wave action. They have a number of physiological adaptations that aid survival in these areas.
Biological attributes:
Mangroves are highly productive in terms of litter production (e.g. May 1999). They are thought to contribute substantially to the organic material available to estuarine/ coastal food chains. Mangroves provide habitat structure for high and mid-intertidal areas, but there is little information on the biodiversity value of mangrove habitat in New Zealand. Mangroves also contribute to prevention of shore erosion and act as sediment and contaminant retainers.
In many New Zealand localities mangroves are reported to be increasing in spatial extent, which is a unique phenomenon globally. This expansion is generally considered to be a consequence of catchment activities. In some areas the expansion of mangroves is considered by some to be having undesirable consequences, conflicting with other estuarine resources and values, both natural and human.
Criteria applied:
Trophic/functional diversity; conservation status/threat classification both nationally and globally; extremities of range and adaptation to environment; special conditions and specialised organisms; habitat complexity/diversity.
Status and management:
The 1994 New Zealand Coastal Policy Statement identifies the protection of areas of significant indigenous vegetation as a national priority for the preservation of natural character of the coastal environment. Some areas of mangroves currently receive some level of protection (e.g. mangroves in the southern Firth of Thames Ramsar site). With the increase in the spatial extent of mangroves in a number of estuaries there has been an increased demand for active management of mangrove areas.
State of information:
There is some historical information on mangroves. Currently there is a demand for increased information related to the biodiversity of mangrove forests and the changes in estuarine biodiversity associated with the increase in extent of mangroves in New Zealand.
References and further reading:
Crisp et al. (1990), May (1999), Mildenhall (1994). The Mangrove Steering Group has compiled a bibliography of New Zealand mangrove publications.