Physical Environment
This area includes the coastline from south of Takou Bay to Taupiri Bay, including the Bay of Islands.
While sheltered from the prevailing southwesterly swells which affect the west coast, the east coast is exposed to seas from northerly and easterly directions. Large swells which impact on this coast are generated from subtropical disturbances. The convoluted nature of the coast means that there are changes in the degree of wave exposure over short distances of shore. This results in the range of habitat types characteristic of this shore - from estuaries with mangrove forests and saltmarsh in the upper reaches of the Bay of Islands, through sheltered rocky shores and beaches, to the steep, exposed rocky coasts in the outer Bay and on the exposed east coast itself.
The predominant oceanic current which influences the coast is the East Auckland Current, which flows from the north. There is commonly an abrupt hydrological gradient between the inshore cooler coastal waters, and those of the East Auckland Current which are warmer, clearer, and of higher salinity (Harris, 1985). The position, flow speed and direction of the East Auckland Current with respect to the coast varies over time - at times the Cape Brett Peninsula deflects some East Auckland Current water as a northwest flowing eddy current across the mouth of the Bay of Islands, producing an overall anticlockwise circulation within the outer part of the Bay (Booth, 1974) (see Map 2.4).
Most of the coastline is composed of indurated (hardened) sedimentary rock (greywacke), but the northern part from south Takou Bay down to Black Rocks on the Purerua Peninsula, is igneous rock.
The outer coastline is basically formed of steep eroding coastal cliffs, and associated inter-tidal reefs. While small pocket beaches occur in many of the embayments, there are few beaches relative to the length of coast. In the south, Whangamumu Harbour is a sheltered harbour with a sandy beach enclosed by two long steep greywacke peninsula headlands.
The coast is adjacent to a steep narrow sub-tidal coastal shelf covered with mostly locally derived sediment. The type of sediment along this coast is known as the "Bay of Islands Facies", and the same sediment type is found from south of Doubtless Bay to Ngunguru. This sediment has a high rock fragment content compared to sediments in other parts of Northland. The sand has approximately equal proportions of shingle, quartz and feldspar sand, and shell fragments. The sediment is mostly derived from the greywacke coastal cliffs and reefs, with a small contribution of quartz sand from the north, and feldspar-rich sand from the south. Because of the narrow and steep sea floor, there is little sediment driven onshore from the sea bed. This means that the shore is sensitive to the removal of sediment (Applied Geology Associates, 1982).
The Bay of Islands itself is formed from a drowned-river valley system, resulting from a post-glacial rise in sea level prior to 6500 BP (before present). Although the mouth of the harbour is relatively wide, the numerous islands in the harbour provide additional shelter from wave exposure from the north and east. Seaward-facing coasts on the southeastern side of the Bay of Islands are sheltered from southeasterly to easterly swells, whereas the southeast-facing coast on the Purerua Peninsula is sheltered from northerly swells. Within the Bay, the water is up to 65 m deep, but reaches 85 m at the seaward limit. Much of the terrain surrounding outer areas of the bay is steep and gullied, while inner areas are more moderately rolling.
The Bay has a total surface area of approximately 179 km 2 , of which 8 km 2 are exposed as tidal flats at low tide (Heath, 1976). The shoreline is extremely convoluted, and includes three major inlets (the Waikare Inlet, the Kerikeri Inlet, and the Te Puna Inlet) and many smaller embayments and estuaries. The shoreline in the Bay of Islands is approximately 200 km in length (Heath, 1976). The main freshwater inflows into the harbour are the Kerikeri, Waitangi, Kawakawa and Waikare Rivers.
Flora & Fauna
Due to the differences in physical environment, there are a wide range of habitats in this coastal area, and thus a variety of flora and fauna.
Estuarine areas are sheltered, with water of lower salinity and higher suspended sediment than the more open coast. Many of the estuaries in the Bay of Islands are fringed with mangroves ( Avicennia marina var. resinifera ): In the Te Puna Inlet, mangroves and saltmarsh are found at the head of the inlet, and at Opete Creek, Poukoura Inlet, and Te Tii; the Kerikeri Inlet at Aroha Island, Wainui Island, Rangitane, Pihoe, the Hauparua Inlet, and fringing the Kerikeri and Okura Rivers; the Waitangi Inlet, fringing the Waitangi River, and Hutia and Kaipatiki Creeks; Haumi River; Orongo Bay; Uruti Bay; Te Wahapu Inlet; Pipiroa Bay; the Waikare Inlet at east Okiato, Whangae River, Kawakawa River, Karetu River, Kaurinui Creek, Waikino Creek, Man'o'war Creek, and the head of the inlet itself; Waipiro Bay; and Parekura Bay. Most of these mangrove areas are flanked on their landward sides by salt-marsh comprised of Juncus maritimus var. australiensis , Leptocarpus similis , or a mixture of both. At higher shore levels, the large sedge Scirpus cernuus, Cotula coronopifolia, Muehlenbeckia complexa, and the glasswort Salicornia australis may be mixed in with the Leptocarpus. Samolus repens (the shore pimpernel) and Stipa teretifolia also occur at higher levels, along the shoreline. At Te Tii, there is a bed of neptune's necklace Hormosira banksii under the tall mangrove. The green algae Enteromorpha occurs in standing water near the mangroves at Haumi River, Whangae River, and at the head of the Waikare Inlet. Eel-grass ( Zostera sp.) is also found in some tidal estuarine areas - for example, Opete Creek and Orongo Bay. Dense beds also occur at Parekura Bay, and in the sheltered bays of Urupukapuka Island. Up river, the salt-marsh at the Okura and Kawakawa Rivers, Man o' War Creek, and Parekura Bay grade into freshwater marsh comprised of Typha (raupo) (Chapman, 1978b).
Animals associated with mangrove scrub and estuarine flats include the burrowing crab Helice crassa , the gastropods Zediloma subrostrata and Zeacumantus lutulentus , the topshell Melagraphia aethiops (in shaded places), the catseye Lunella smaragda , the estuarine whelk Cominella glandiformis and the mud snail Amphibola crenata , and the burrowing nereid worm, Nicon aestuariensis.
Fish species in these habitats include mullet, parore, eels, flounder, and kahawai.
The estuarine areas are attractive to coastal and wading birds. Species found here include pukeko, white faced heron (at Opua), reef heron, godwit, knot, white fronted terns, pied stilt, shags (black, spotted, pied, and little shags), oystercatchers and mallard ducks. Rare and endangered species include brown teal (two large roosts occur at Parekura Bay, and another at Mangawaora Bay), banded rail, weka, bittern, NZ dotterel, oriental dotterel, Asiatic whimbrel, Caspian tern and fernbird.
Different habitats occur away from the estuarine areas in the Bay. A comprehensive study of the subtidal rocky reefs in the Bay of Islands was done by Brook and Carlin (1992). They suggested that the subtidal rocky reefs can be grouped into several broad ecological types on the basis of substrate type and topography, benthic zonation sequences and composition of fish fauna: "Five recurrent shallow subtidal benthic zone types characterised by the presence or absence of laminarian and fucalean kelps were identified. A shallow mixed weed zone is present from intertidal to immediate subtidal depths throughout the Bay. Carpophyllum spp. (i.e. Carpophyllum angustifolium, C. maschalocarpum ) are the dominant kelps throughout most of the bay, but Lessonia variegata is locally dominant at exposed sites at Cape Brett and Motukokako Island. An algal turf and paint zone (e.g. Corallina sp.) with sparse kelps (i.e. Carpophyllum spp. Ecklonia radiata ) is present below the shallow mixed weed zone in most areas, but is locally absent in sheltered inner bay habitats, and in some partly sheltered bays on Cape Brett peninsula. A kelp forest zone comprising extensive stands of Ecklonia radiata is present throughout most of Bay of Islands below the algal turf and paint zone. However, it is absent at Motukokako Island and is replaced in some sheltered parts of the inner bay by mixed stands of E. radiata and Carpophyllum flexuosum , or by monotypic stands of the latter species. A deep kelp zone with sparse E. radiata plants is present below the kelp forest zone on deeper reefs, and on some reefs is bounded to seawards by a kelp-free zone in which laminarian and fucalean kelps are absent. Lower depth limits of the shallow mixed weed, algal turf and paint, kelp forest, and deep kelp zones become progressively shallower from outer to inner Bay of Islands, and species compositions of associated non-kelp algal flora, and of benthic encrusting fauna also vary from outer to inner Bay."
Brook and Carlin also found trends in the diversity of reef fish in the Bay of Islands: "A standardised total of 98 species of coastal fish in 40 families, including 29 "subtropical indicator" species, is recorded from the Bay of Islands. Nearly all of those species have been recorded in the area from Cape Brett Peninsula to Motukokako Island (i.e. 92 species in 35 families), whereas a standardised total of 67 species in 33 families (including 7 "subtropical indicator" species) is recorded from the remainder of the Bay of Islands. The overall diversity of coastal fish of the outer southeastern part of the bay is considerably greater than in other areas in northern New Zealand with the exception of Poor Knights Islands, whereas the rest of Bay of Islands has an overall species diversity comparable with some mainland and island coastal areas between Three Kings and Great Barrier Islands" (Brook and Carlin, 1992). (A list of the fish species found in the Bay of Islands in their survey is given in Appendix I). The higher numbers of "subtropical indicator" species out towards Cape Brett are presumably a result of the impinging of the East Auckland Current on the peninsula.
Flora and fauna on the open east coast (the coast outside the Bay of Islands) is typical of most Northland open coasts. A zone of barnacles occurs at the top of the tidal range ( Chamaesipho species, then slightly lower, Elminius plicatus ) along with the barnacle drill Lepsiella scobina , and below this the brown algae ( Carpophyllum species - C. angustifolium , or in less exposed places C. maschalocarpum ), followed by Lessonia variegata in the sub-tidal zone. The gastropods Nerita melanotragus and Melarapha oliveri , and the limpet Notoacmea pileopsis extend through and above the barnacle zone. The limpets Cellana ornata and Cellana radians are found in the mid-intertidal zone. Sub-tidal fauna include kina ( Evechinus chloroticus ), paua ( Haliotis sp.), and rock lobsters ( Jasus edwardsii ).
References:
Applied Geology Associates. 1982. Coastal sand and shingle resources of Auckland and Northland. Unpublished report to the Auckland Regional Authority, April 1982.
Booth, J. D. 1974. Observations on the hydrology of Bay of Islands, New Zealand. New Zealand Journal of Marine & Freshwater Research. 8 (4):671-689.
Brook, F. J. and Carlin, G. L. F. 1992. Subtidal benthic zonation sequences and fish faunas of rocky reefs in Bay of Islands, northern New Zealand. Department of Conservation. 80 pp.
Chapman, V. J. 1978(b). Mangroves and salt marshes of the Whangaroa and Whangaruru Harbours and the Bay of Islands. Department of Lands and Survey, Auckland. 33 pp.
Harris, T. W. F. 1985. North Cape to East Cape: aspects of the physical oceanography. University of Auckland, Physics Department, 178 pp.
Heath, R. A. 1976. Broad classification of New Zealand inlets with emphasis on residence times. New Zealand Journal of Marine & Freshwater Research. 10 (3):429-44.
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