MUDDY FEET - Auckland Regional Council

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3.1.1 Mangrove
The mangrove dominates situations with muddy substrates that are subject to tidal inundation,
particularly along streamsides and nearby mudflats. The dredged drainage channels that are
subject to tidal inundation are also colonised. Few other vascular plants occur amongst the
mangroves but in slightly better drained mangrove sites salt marsh ribbonwood may occur.
Aerial photographs also show that slightly raised, cleared areas amongst the mangrove may
be invaded by Spartina grass (Thomson 2000).
There are a number of management issues associated with mangroves throughout the Ramsar
Site, particularly along the Miranda – Kaiaua Coast. North of the Miranda Stream mangrove
zones are now established along the stream channels and coastal lagoons, with occasional
small patches in the coastal mud. Chapter 4 addresses mangroves in detail.
In summary, mangroves provide several valuable functions:-
• Consolidation of muddy foreshore areas, resulting in less erosion and protecting
coastal areas from wave and some storm damage. (Note: Powerful storms of rare
occurrence can erode the coast and wash away whole plants.)
• Because of the stability of the mangrove habitat and the number of stems and
pneumatophores for animals and plants to settle on, these areas provide protected
habitats for invertebrates and fish, particularly for spawning. A food chain develops,
the apex of which are predators such as fish and birds.
• The shade provided by the mangrove trees prevents the mud drying out – a factor
which can be important for the fauna, especially in prolonged periods of dry weather.
3.1.2 Recent Shellbanks
The large shell banks forming the spits into the sea and the eastern edge of the coastal Chenier
plain are comparatively “young”. Plants colonising this habitat are generally ruderal weeds
such as bur medick (Medicago nigra), pink bindweed (Calystegia sepium), viper’s bugloss
(Echium vulgare), oxtongue (Picris echioides) and ribwort (Plantago lanceolata). Plants
growing on these banks have to cope with exposure to desiccation from the wind and sun, and
a lack of soil in the surface layer. Though most of these plants have wind-blown seeds, it is
possible that some species may be dispersed by birds, as the shell spits and coastal meadows
are favourite roosting places of the waders, and nesting sites of at least three bird species. On
this western shore of the Firth these shell banks may abut salt marsh wetlands and grade into
more weathered older shellbanks that have been modified by shell extraction and grazing of
cattle.
Other plants recorded colonising these areas are herb Robert (Geranium robertianum), beet
(Beta vulgaris), stonecrop (Sedum acre), prickly sowthistle (Sonchus asper) and grasses such
as Lolium perenne, Bromus diandrus, B. hordeaceus and Parapholis incurva. Occasional
Scotch thistle (Cirsium arvense) with large taproots are found on these shellbanks.
3.1.3 Glasswort Salt Marsh
Salt marshes are generally located in the intertidal zone. They are flooded by the high tide
and are exposed at low tide. Mitsch & Gosselink (1993) defined two broad categories of salt
marshes as those formed from reworked marine sediments, and those formed by river
sediments in deltaic areas. The salt marshes along the Miranda-Kaiaua coastline are marine
dominated marshes. Salt marshes depend on a sufficient rate of sedimentation and avoidance
of areas of coastal erosion. In the Miranda area, coastal erosion is avoided due to the band of
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