Physical Environment
Rangaunu Bay is a large, wide-mouthed bay extending from Perforated Point in the west, around to Whakapouaka (Cape Karikari) in the east. The following section of the report contains a description of Rangaunu Bay, including the eastern coastline from Puheke Beach to Cape Karikari (including the Moturoa Islands).
Rangaunu Bay is relatively shallow adjacent to the Karikari Peninsula, being about 15 m deep at distances up the 5 km off shore. The bottom of the bay is covered with clean, well-sorted white sand, with large amounts of shell grit, and very little mud or silt.
Puheke and Karikari Beaches form Karikari Bay, which dominate the northern part of the Karikari Peninsula. These white sandy beaches are 11 km long, and form the southwestern and western shores of Rangaunu Bay. On the western side of Karikari Bay, the north-facing Puheke Beach is backed by a belt of low sand dunes, which are partially consolidated by marram grass and lupins. Puheke Hill (151m high), a dominating feature of the otherwise low-lying area, was once an island on its own before the tombolo was formed. This rocky promontory extends into the inter-tidal area, separating Puheke Beach from Karikari Beach. Backing Karikari Beach is an extensive area of consolidating sand ridges, which impounds Waimango Swamp, a wetland of significant size. North of Karikari Beach is Whakapouaka (Cape Karikari), from which the rocky Moturoa Islands extend in a northwesterly direction. Moturoa Islands comprise three small islands (4.3 ha. - 13.0 ha. in size), and a number of adjacent rocks and stacks. Like the Poor Knights Islands, this island group lies in the path of the warm East Auckland current. Moturoa Islands are of international importance as a nesting area for seabirds, and on account of the presence of rare lizards. They have national importance as rat-free refuges.
Flora & Fauna
Rangaunu Bay supports an abundance of fish and shellfish - there are significant populations of scallops in the Bay, which in the past used to wash up on the beaches after storms (there is concern by local iwi at the depletion of this resource by commercial fishing). Tuatua are abundant at the low tide mark on the sandy beaches. Other invertebrates are abundant and diverse: the starfish Asteropectin polyacanthus ; bivalves - Myadora striata, Tawera spissa, Venericardia purpurata, Notocallista multistrata, and Talabrica bellula ; and the gastropods Zeacolpus pagoda and Amalda australis . Crabs, hermit crabs and polychaetes are also abundant, and sea cucumbers are also present. The invertebrate populations provide food for fish, and snapper are found in significant numbers in the Bay. Rangaunu Bay is also an area where sea mammals are frequently found - Saddleback and Risso's dolphins school and feed in the Bay, and Humpback whales and orca pass close to Whakapouaka (and occasionally enter the Bay) during migration.
The sandy beach behind Karikari Bay is backed by dunes, semi-drained lagoons and swamp margins, which are important breeding areas for the NZ dotterel, bittern, variable oyster-catcher, fernbird and marsh crake. At the western end of this bay (i.e. behind Puheke Beach), the dunes back onto the important freshwater habitat of Rotokawau Lake and adjacent swampland. In this area, four species of shag - pied shag, little shag, black shag, and the little black shag, have all been observed nesting in the same rookery, something that has not been recorded elsewhere (Dept Lands & Survey, 1979).
A rare NZ plant, Lycopodium serpentinium , (a kind of clubmoss) is found along the access road to Karikari Bay Motorcamp, and on the south side of Lake Rotokawau, where there is the largest, and probably the only viable population of the species, anywhere in New Zealand. It is also found in the swampy area behind Waipapa Bay.
The rocks off the Moturoa Islands support dense populations of the kelps Carpophyllum angustifolium, Lessonia variegata and Ecklonia radiata . The very clear water allows these forests of macroalgae to extend down to 30 m in depth off the outer island, Rocky Island. From 25 m in depth down, large sponges such as Iophon proximum and Callispongia ramosa , and the soft coral Alcyonium aurantiacum start to replace Ecklonia . The rock faces also support populations of sea urchins ( Evechinus chloroticus and Centrostephanus rodgersii ) and sea anemones ( Corynactis haddoni and Actinothoe albocincta ). Both spiny and packhorse crayfish are found in the rocky fissures and underhangs.
The fish populations around Cape Karikari and the Moturoa Islands are diverse and abundant. A study done in a section of coast on the eastern side of the Cape, from Black Point (Te Rae o te Rakau) to Pihakoa Point, found unusual diversity (see discussion in the section Cape Karikari to Knuckle Point ), and suggested that (based on records of fish species sighted) the diversity in the area to the north was even higher. This makes the area attractive for diving. Fish species include schools of demoiselles, and pink and blue maomao, and the non-schooling fish: leatherjackets, red pigfish, Sandager's parrotfish, yellow moray eels, porae, red moki, and butterfish.
Due to the absence of rats, the Moturoa Islands are significant for their varied reptile populations, including the gecko Hoplodactylus pacificus, the skinks Leiolopisma suteri, Leiolopisma smithi, Leiolopisma moca, Cyclodina aenea , and Cyclodina allani. C. allani and L. moca are rare lizards. (Internationally, New Zealand geckos are of interest, since of the 600 species of gecko in the world, only the NZ geckos and one species found in New Caledonia, bear live young instead of laying eggs). Moturoa Islands are also an important nesting site for seabirds, including the diving petrel ( Pelecanoides urinatirix urinatrix ) the white-faced storm petrel ( Pelagodroma marina Maoriana ), the fluttering shearwater ( Puffinus gavia gavia ) and the little blue penguin ( Eudyptula minor iredalei ).
References:
Department of Lands & Survey, 1979. Karikari Peninsula: A land use study. Prepared by the Department of Lands and Survey, June 1979.
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