Mānawa
Avicennia marina
Avicennia marina, commonly called Mānawa (grey mangrove), is Aotearoa New Zealand’s only native mangrove. It forms dense intertidal stands in sheltered harbours and estuaries of the northern North Island. Specialised aerial roots (pneumatophores) enable gas exchange in water-logged, saline muds; the species is highly tolerant of salt, wind and periodic inundation. See more in wetland plants.
Plant Description
Evergreen shrub to small tree, typically 2-10 m. Opposite, leathery leaves are grey-green above, paler beneath; salt is excreted through leaf glands. Trunks may develop prop-roots. Extensive horizontal roots produce numerous pencil-like pneumatophores that protrude from the mud surface. Small, yellowish flowers appear in summer; buoyant, pointed propagules (seedlings) are dispersed by tides and establish on soft mud.
Quick Facts
| Scientific Name | Avicennia marina |
|---|---|
| Common Names | Mānawa; grey mangrove |
| Family | Acanthaceae |
| Height | 2-10 m |
| Spread | 3-6 m (flattened crowns in exposed sites) |
| Water Needs | High (intertidal; brackish to saline) |
| Light | Full sun |
| Frost Tolerance | Low (frost-tender) |
| Salt Tolerance | Very high |
| Growth Rate | Moderate |
| Lifespan | Long-lived perennial |
Climate Best Suited to
In Aotearoa, mānawa occurs naturally in sheltered estuaries and harbours of the northern North Island (for example Northland, Auckland, Waikato and Bay of Plenty). It thrives in frost-free maritime climates with warm summers and mild winters.
Regional Suitability
| Whangārei | Ideal |
| Auckland | Ideal |
| Hamilton | Suitable |
| Rotorua | Suitable |
| Tauranga | Ideal |
| Gisborne | Ideal |
| New Plymouth | Ideal |
| Whanganui | Ideal |
| Palmerston North | Suitable |
| Napier | Ideal |
| Wellington | Ideal |
| Nelson | Ideal |
| Christchurch | Suitable |
| Dunedin | Suitable |
| Invercargill | Suitable |
| City | Climate Suitability |
|---|
Plant Habitat
Intertidal forest on sheltered muddy shores, tidal creeks and harbour margins; associates include saltmarsh rushes and herbs in upper and lower marsh zones.
Plant Conservation
Not Threatened nationally. Extent has expanded in some estuaries due to sediment and nutrient enrichment; management is regulated regionally. Forests protect shorelines and improve water quality by trapping sediments.
Growing Requirements
Soil & Water
- Prefers soft muds and silty sands in intertidal zones.
- Tolerates saline to brackish water and periodic inundation.
- Requires anaerobic-tolerant root zone; avoid fresh, free-draining uplands.
Light & Exposure
- Full sun; highly wind and salt-spray tolerant.
- Sheltered harbours and estuaries are ideal; avoid wave-beaten shores.
Maintenance
- Low maintenance once established; keep seedlings weed-free.
- Observe regional rules; mangroves are protected in many areas.
Planting Guide
For restoration sites, plant mānawa in full sun on sheltered, fine-sediment margins. Stagger plants 1-2 m apart and use tall pots to encourage strong taproots. In energetic sites, add brush matting or coir logs to reduce scouring and retain muds and silts around seedlings.
Ecological Value
Mānawa forests are powerhouse ecosystems that shelter juvenile fish (like flounder and mullet) and invertebrates, providing critical nursery grounds. They host estuarine birds for roosting and feeding, and play a vital role in trapping sediments and filtering nutrients from runoff, which protects open water quality. Their pneumatophore fields create complex 3D structure for epifauna and bacterial biofilms, further enhancing water clarity and shoreline stability over time.
Uses & Significance
Restoration & Erosion Control
Dense stands of mānawa are exceptionally effective at stabilising soft, muddy shorelines against tidal scour and storm surges. Their extensive root systems and pneumatophores dissipate wave energy and trap suspended sediments, gradually building up the foreshore elevation. This process not only improves water clarity but also creates new land that buffers coastal communities from erosion and sea-level rise.
Landscaping Uses
Use mānawa only where brackish inundation occurs naturally - bays, tidal creeks, and estuaries. Combine with oioi, raupō, and saltmarsh herbs to create resilient, low-maintenance coastal plantings that protect shorelines and provide wildlife habitat.
Seasonal Notes
Spring
Active growth; suitable time for planting propagules in restoration sites.
Summer
Flowering; maintain brackish moisture around nursery stock.
Autumn
Propagules ripen; collect and sow for best establishment.
Winter
Withstands storms and high tides; avoid frost exposure.
Pruning & Training
Pruning is seldom needed. Remove only dead or storm-damaged branches. Avoid cutting pneumatophore fields or root collar areas; these structures are essential for gas exchange in waterlogged, saline soils.
How to Grow Mānawa
From Propagules/Seed
- Collect ripe, buoyant propagules in late summer to autumn from beneath parent trees.
- Rinse in brackish water to remove debris. Sow half-embedded in a mix of estuarine mud and coarse sand.
- Keep trays constantly moist with slightly saline water (for example 5-15 ppt) and in full sun.
- Germination occurs readily; prick out once roots are established and plant into tall pots to encourage strong taproots.
From Cuttings
Semi-hardwood cuttings can be rooted under intermittent mist with bottom heat. Use a free-draining, saline-tolerant medium and irrigate with brackish water. While slower and less predictable than propagules, cuttings are useful for clonal plantings where uniform growth or site-specific performance is desired.
Site Selection and Care
Choose sheltered intertidal margins with fine sediments that remain wet or saturated. Avoid frost-prone sites. Plant in full sun and position seedlings at or just above the local high-tide level. Space 1-2 m apart in restoration to allow crowns to fill and pneumatophore fields to expand. Keep seedlings weed-free, replace losses after storms, and protect from trampling. In highly energetic sites, use brush matting or biodegradable coir logs to reduce scouring during establishment. Mānawa thrives in muds and silts with regular tidal wetting and tolerates a wide salinity range. Do not allow nursery stock to dry out; maintain constant moisture with slightly brackish water. Mulch with clean washed sand to suppress weeds and stabilise the surface. Weed control is essential in the first year to reduce competition from grasses and halophytes. Replace any plants lost to storm events promptly. Protect young trees from trampling. Pruning is rarely required; remove only damaged or dieback material. Over time, stands will trap sediment, raise the substrate, and expand seaward as conditions permit.
Pests & Diseases
Generally resilient; occasional scale insects and sooty mould. Biggest risks are frost, burial by sediment, or physical damage. Avoid fresh-waterlogging without tidal flushing.
Cultural Significance
Known to Māori as mānawa. Mangrove forests are valued for coastal protection, mahinga kai habitat, and as indicators of estuarine health; harvesting or removal is controlled in many rohe.
Bonus Tip
For plantings near public access, install temporary barriers to prevent trampling of fragile pneumatophore fields during establishment. These specialized aerial roots are essential for the plant's survival in waterlogged conditions and take time to develop properly.
Related Plants
More coastal and wetland species that pair well with mānawa for restoration and resilient seaside plantings, building layered habitat structure, filtering runoff, and improving shoreline stability in exposed bays and estuaries.
