3. Key Features of the Marine Ecosystems in Tai Tokerau

3.2 Physical Characteristics (Continued)

Climate

As mentioned above, vast oceans surround New Zealand. Because of this, all air masses that reach New Zealand must travel several days over water. This process evens out the air temperature and explains why air temperatures at coastal locations do not vary greatly over the different seasons (Fitzharris, 2001). The climate in the Tai Tokerau region is mild in comparison to the rest of New Zealand, with a mean annual temperature of approximately 16 o C (National Climate Centre – Summary Statistics 1985-2000, Kaitaia and Whangarei data). Monthly average air temperatures are typically in the range 19-20 o C in February (the annual maximum) and 11-12 o C in July (the annual minimum) (Harris, 1985; Leigh Marine Laboratory, pers. comm. ). Virtually no frosts occur on the actual coast, or to the north of the region (e.g. Kaitaia). However, some frosts do occur in the lower part of the region (e.g. Whangarei). The region has relatively high mean sunshine hours (approximately 2020 hours per year, National Climate Centre – Summary Statistics 1985-2000, Kaitaia and Whangarei data), and a moderate rainfall (approximately 1412 mm per year) with the maximum rainfall occurring in winter.

Sea Temperatures

Seawater temperature is one of the most important physical properties of the marine environment. The seawater temperatures off the Tai Tokerau coast are relatively warm when compared to the rest of New Zealand. This is because warm subtropical water is forced down both the eastern and western coasts of Northland (as described in the “Major Currents” section above).

Average monthly mean sea surface temperatures recorded at the University of Auckland's Marine Laboratory at Goat Island, Leigh, indicate that minimum average coastal sea surface temperatures occur in August (13.96 o C), and maximum average temperatures in February (20.56 o C) (based on sea surface temperatures recorded from January 1967-December 2000) (See Table 1 below).

Table 1: The average monthly mean sea surface temperature and monthly mean range in sea surface temperature recorded at Auckland University's Marine Laboratory, Goat Island, from January 1967 to December 2000.

Sea temperature changes with distance from the coast. The sea on the continental shelf is often cooler than that seaward of the shelf (Harris 1985, Sharples et al. 1998). Data collated by Harris (1985) for the eastern coast of Tai Tokerau from a number of sources indicate a general trend of decreasing sea surface temperature from north to south. However, in summer, this trend is reversed in the south of the area, as temperatures increase from the region between Great Barrier Island and Bream Bay, towards the south into the Hauraki Gulf and the Firth of Thames. The influence of the warm East Auckland Current off the eastern coast of Tai Tokerau results in mean sea surface temperatures of approximately 1 o C higher on the eastern coast than the western coast at the same latitude (Sutton and Roemmich 2001). The comparatively mild climate and warm water temperatures not only influence the ecology of the Tai Tokerau region, but also make Tai Tokerau an attractive place for marine-based recreation.

Salinity

Salinity is a measure of the saltiness of the water. Salinity is commonly expressed as parts per thousand (ppt), and water in the open oceans away from the coasts around New Zealand normally has a salinity of 34-36ppt. (Harris, 1985). There is a general trend of increasing salinity with increasing distance from the coast. This is because freshwater run-off from the land dilutes the sea near the coast. Salinity may also vary along the coast. Because estuaries are areas where rivers or streams run into the sea, the salinity in these areas is lower than in the open ocean. In contrast, areas of open coast distant from estuaries would be expected to have comparatively high salinity. (For a more detailed discussion of salinity variability in the region, refer to Harris, 1985).

3.3 Marine Flora and Fauna of Tai Tokerau

This section talks about the marine flora and fauna ( flora are plants, and fauna are animals) in Tai Tokerau. Marine organisms tend to be adapted to live in specific conditions, with each organism having its own physical requirements. From the previous discussion about the physical environment you can see that there is a wide range of different marine environments in Tai Tokerau – for example, exposed sandy beaches, sheltered sandy bays, sheltered and exposed rocky shores, estuaries and harbours, and offshore islands. Each of these marine environments is inhabited by groupings of plants and animals that are adapted to live there.

The composition of marine flora and fauna in Tai Tokerau reflects the broad environmental differences of the region. On the western coast, which has lower sea surface temperatures than the eastern coast, there is a dominance of species associated with cooler water. The eastern coast is influenced by the warm East Auckland current, and the associated marine biota ( biota are living organisms) include significant numbers of warm temperate and sub-tropical species (i.e. species that are adapted to living in warmer waters). Offshore islands in eastern Tai Tokerau (such as the Poor Knights and Cavalli Islands) and prominent coastal headlands (e.g. Karikari Peninsula and Cape Brett) lie in the path of sub-tropical water from the East Auckland Current during summer, and are characterised by the presence of algae, corals, mollusca, urchins and fish that are rare or absent elsewhere around Northland and the rest of New Zealand. This is one of the very special features of Tai Tokerau, and attracts divers and snorkellers to the area.

Also associated with the seasonal influence of the East Auckland Current is the occurrence of larger fish species, such as marlin and swordfish, off the coast. These species provide the focus of ‘big game fishing' in the area. Other species that people often find interesting, such as sea mammals, also occur on the eastern coast of Tai Tokerau. These include the regular presence of dolphins in some areas (such as the Bay of Islands, and the coast near the Cavalli Islands), and the seasonal migration of whales, which are frequently seen off the Tutukaka coast and near Rangaunu Bay/Cape Karikari. Brydes whales and orca may be encountered all year round, and minke, sei, pseudorca, pilot whales, humpback and southern rights whales from spring to early summer.

Figure 6: Bryde's whale surfacing.

The more homogenous physical environment on the western coast (i.e. long exposed sandy shores and reefs, plus harbour and estuarine environments) results in less diversity in ecosystems than is present on the eastern coast of Tai Tokerau, which has open sandy beaches, enclosed sheltered beaches, rocky shores and reefs, and estuaries and harbours. This diversity of marine ecosystems within close proximity to many parts of Tai Tokerau (including areas such as the Aupouri Peninsula, where both the western and eastern coasts are in very close proximity) is one of the special features of Tai Tokerau.

In addition to the impact of inherent physical characteristics, the ecology of an area is influenced by the impact of human activity. Much of the coastline of Tai Tokerau is inaccessible, and therefore relatively unmodified by human activity. There are thus many areas of high natural value within Tai Tokerau. Many of these areas, particularly areas of coastline, are protected by regulation as reserves.

Details of the physical environment and marine ecology of specific coastal areas may be accessed by clicking on the links provided below. Figure 7 illustrates the location of the areas discussed.

•  Physical and ecological features of Berghan Point to Takou Bay: BERGHAN POINT TO TAKOU BAY

•  Physical and ecological features of Cape Brett to Taiharuru Head: CAPE BRETT to TAIHARURU HEAD

•  Physical and ecological features of Cape Karikari to Knuckle Point: CAPE KARIKARI TO KNUCKLE POINT

•  Physical and ecological features of Doubtless Bay: DOUBTLESS BAY

•  Physical and ecological features of Great Exhibition Bay to East Beach: GREAT EXHIBITION BAY to EAST BEACH

•  Physical and ecological features of Hokianga Harbour: HOKIANGA HARBOUR

•  Physical and ecological features of Doubtless Bay: HOUHORA HARBOUR

•  Physical and ecological features of Kaipara Harbour: KAIPARA HARBOUR

•  Physical and ecological features of Mangonui Harbour: MANGONUI HARBOUR

•  Physical and ecological features of Ninety Mile Beach: NINETY MILE BEACH.doc

•  Physical and ecological features of the Offshore Islands Group: OFFSHORE ISLANDS GROUP

•  Physical and ecological features of Parengarenga Harbour: PARENGARENGA HARBOUR

•  Physical and ecological features of Rangaunu Bay and the coast from Puheke Beach to Whakapouaka: RANGAUNU BAY AND THE COAST FROM PUHEKE BEACH TO WHAKAPOUAKA

•  Physical and ecological features of Rangaunu Harbour: RANGAUNU HARBOUR

•  Physical and ecological features of Ripiro Beach to Rangatira Beach: RIPIRO to RANGATIRA BEACHES

•  Physical and ecological features of Scott Point to Ohao Point: SCOTT POINT to OHAO POINT

•  Physical and ecological features of the South Head of the Hokianga Harbour to Maunganui Bluff: SOUTH HEAD of the HOKIANGA HARBOUR to MAUNGANUI BLUFF

•  Physical and ecological features of Taiharuru Head to Takatu Point: TAIHARURU HEAD to TAKATU POINT

•  Physical and ecological features of Takou Bay to Taupiri Bay: TAKOU BAY to TAUPIRI BAY

•  Physical and ecological features of Whangaroa Harbour: WHANGAROA HARBOUR

Figure 7: Map showing location of the bounding points of regions for which details of physical and ecological features are provided. Not shown on the map is Aotea (Great Barrier Island) (discussed in the “Offshore Islands” section) which lies at the tip of the Coromandel Peninsula to the east.

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