MUDDY FEET - Auckland Regional Council

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• Approaches to Franklin District Council regarding the preservation of roadside
colonies from verge maintenance activities. [Note: Waitakere City Council has
introduced measures to protect its endemic roadside Hebe bishopiana.]
• Conservation measures and possible covenants on Thompson’s Bush.
• Further propagation of this species. Work is currently underway at Unitec.
3.6 Exotic invaders – Adventive plant species
3.6.1 Spartina
The estuarine grasses of the genus Spartina are vigorous invaders of coastal mangrove and
salt marsh, estuarine areas and mudflats, rapidly colonising suitable bare ground. They are
tolerant of immersion in saltwater.
Three taxonomic entities are possible, Spartina anglica, S. alterniflora and S. x townsendii.
Of these, only S. anglica has been identified from the Firth of Thames, though this area is
within the known range of S. alterniflora, (Partridge 1987). The Auckland and Waikato
Regional Councils have the responsibility for control of Spartina and other weeds in the
Ramsar Site (in accordance with lines of jurisdiction).
Spartina anglica can form dense stands. This grass has vigorously growing rhizomes and
roots that form a dense mat near the surface of the mud or sand. Anchor roots penetrating a
metre or more down into the mud secure the plants, which can grow to more than a metre
high. This species spreads both by seed and by pieces of the rhizome breaking off the parent.
Distribution.
Spartina anglica, a native of Britain, was deliberately introduced to New Zealand in the
1920s to stabilise mudflats and provide food for stock. It is now found in coastal regions
throughout much of New Zealand (Partridge 1987). Within the Firth of Thames it is found in
most of the mudflat areas and estuaries of the Coromandel Peninsula and along the Miranda-
Kaiaua Coast. Nineteen sites were identified in the mangrove zone from the Waihou to the
Waitakaruru River during a 2000 aerial survey (P. Thomson, personal communication 2000).
Some of the Spartina patches covered areas of nearly one hectare. Much of the Spartina was
sprayed and eliminated by late 2004, but there were still numerous small patches of it
remaining in difficult to access areas (S. Clark, personal communication 2004).
Significance.
Spartina prefers deep, soft fertile mud with a sandy loam texture, (Environment Waikato
1998). The dense mats of Spartina bind the mudflat and help to trap sediment. The vigorous
growth habit, which can outgrow most of the native reeds and other plants on the mudflat
edge, result in colonies extending over these flats. The plants trap silt, thereby altering the
conditions for shellfish, particularly the cockle, Austrovenus stutchburyi. Some cockle beds
have been wiped out by Spartina invasions (Department of Conservation 1998).
Considerable areas may be colonized. Simpson (1995) reports on one such invasion in
Victoria, Australia: “In the 1980s the mudflats off Nolans Bluff, situated on the landward side
of the Inlet, were a prime habitat for migratory waders, significant both in numbers and
diversity of species reported. Today, completely colonized by Spartina, the area has been
deserted by waders, to the extent that Nolans Bluff is no longer included as a count
location…”
EcoQuest Education Foundation EQRS/1 12/04