Nature and conservation
IntroductionMotu Manawa-Pollen Island Marine Reserve includes intertidal mudflats, tidal channels, mangrove swamp, saltmarsh and shellbanks.
The Motu Manawa-Pollen Island Marine Reserve protects approximately 500 ha of the inner reaches of Auckland's Waitemata Harbour. It includes the intertidal mudflats, tidal channels, mangrove swamp, saltmarsh, and shellbanks surrounding Motumānawa/Pollen Island and Traherne Island.
The intertidal flats to the west of the island are probably the best example of mangrove and saltmarsh habitat in the Waitemata Harbour and are rich feeding grounds for white faced herons, pukeko, spotless crake and the endangered banded rail. These wetlands are equally important for several non-waders, including kingfisher and fernbird.
The shy fernbird or matata (Bowdleria punctata) is found in the marine reserve area. It is a weak flier and the few surviving populations in the Auckland area are confined to isolated scrubby salt marshes because the continuous fringe of shoreline scrub and coastal forest no longer exists. The bird, eggs and young are vulnerable to predation by rats, cats and dogs as they nest close to the ground.
The outer flats are regularly visited by red-billed gulls, black-backed gulls and their mottled brown juveniles, and by two terns. The smaller white-fronted tern is usually in small flocks and has a black beak and cap separated by a narrow white forehead band. The larger caspian tern is less common. It has a full black cap and a large bright red bill and is usually only seen in pairs.
Some birds, such as godwits, knots and sandpipers, are international migrants that breed in the north Asian wetlands during the northern spring and summer. They avoid the frozen winter by flying south. Most return to the northern hemisphere in March but a few, too young to breed, remain here over winter.
The South Island pied oystercatcher and the wrybill are national migrants. They breed on the shingle beds of South Island braided rivers in spring and fly to northern harbours and estuaries for the late summer, autumn and early winter, making the return journey south in July or August.
Motumānawa / Pollen Island shore profile
A fringe of mature mangrove trees gives wave protection to the island's outer shore, which is being alternately eroded or built up by washed up sand and shells. Further out, cockles are the dominant shellfish of the extensive mudflats, which are patrolled by wading birds. At high tide the flats are the feeding ground of flounder and grey mullet.
The peaty remnants of an ancient rush marsh, thought to be over 170,000 years old, are exposed at the front of the island and help resist erosion. On top of this bank, drifts of shells, mostly cockles, have steadily built up and though some mounds are unstable and mobile, most older parts are now stabilised by a maritime scrub, home to rare fernbirds.
At the back of the island, mature upright mangroves are girdled by clumps of shore needle grass and joined and maritime rush, bordered by salt tolerant flowering herbs like shore primrose which stabilise the sandy soil. Gradually, this vegetation gives way to a salt marsh dominated by glasswort and pockmarked with the burrows of thousands of mud crabs.
Near the motorway is a fringe of large, mature mangroves and beyond, a broad expanse of old stunted mangrove trees growing with a prostrate form in the saturated muddy ground. The sloppy surface is criss-crossed by trails of thousands of amphibious mud snails. The area is home to snapping shrimps and mud crabs, and a feeding ground for white faced herons.
The marine reserve was created in 1995 as a representative example of inner harbour ecosystems. Benthos and sediments of the marine reserve were evaluated during May 2002. A survey was conducted on the non-vegetated intertidal and shallow subtidal areas of the reserve using a small hand-hauled dredge to collect samples of sediment and benthos.
Results illustrate that the marine reserve has two main benthic associations.
- To the south of the embankment, the enclosed inlet contains soft muds with relatively few species, including polychaetes and the introduced bivalve Theora lubrica.
- To the north of the embankment, shelly sandy sediments occur along the northeast side of Motumānawa / Pollen Island, with higher diversity of marine life. There are extensive beds of small cockles, with associated polychaete worms and large numbers of the small bivalve Nucula hartvigiana. Towards and below low tide softer mud occurs with relatively low diversity of marine life.
View the Monitoring report (PDF, 905K).