Introduction
Alison MacDiarmid and Franz Smith
Marine biodiversity
New Zealand has a unique and particularly rich marine flora and fauna. There are an estimated 65,000 known and unknown species and the level of endemism—species not occurring elsewhere—at 44% is particularly high, making the New Zealand marine region a hotspot of marine diversity worldwide (see Table 1).
For instance, in the sponges about 95% of the 733 known species are unique to New Zealand, while the bivalves and gastropods are not far behind at 84%, ascidians at 75% and bryozoans at over 60%. While overall only 16% of bony fish are endemic, in some families, like the triple fins, all New Zealand species are endemic and New Zealand is the centre of their diversity. About a third of our seaweeds are endemic. At the other extreme are the highly migratory baleen, beaked, and sperm whales with no endemic species in New Zealand waters. (Note: taxonomic terms are explained in Appendix 1.)
Table 1: Summary statistics of the number of known species and the relative proportion of endemic species in the New Zealand marine ecoregion.
| Entry | Number of known species | Number endemic | Percentage endemic |
|---|---|---|---|
| Oystercatchers | 3 | 3 | 100% |
| Sponges | 733 | 696 | 95% |
| Bivalves & Gastropods | 3340 | 2805 | 84% |
| Ascidians (sea squirts) | 166 | 125 | 75% |
| Diadromous Fishes | 17 | 12 | 71% |
| Penguins | 6 | 4 | 67% |
| Comorants and Shags | 12 | 8 | 67% |
| Jawless fish | 3 | 2 | 67% |
| Bryozoans | 943 | 585 | 62% |
| Albatrosses | 12 | 6 | 50% |
| Brachiopods | 32 | 16 | 50% |
| Fulmars, Petrels, Prions & Shearwaters | 35 | 14 | 40% |
| Echinoderms (sea stars, sea urchins etc) | 618 | 229 | 37% |
| Red Algae | 465 | 166 | 36% |
| Crustaceans | 2731 | 915 | 34% |
| Polychaetes | 828 | 255 | 31% |
| Brown Algae | 160 | 50 | 31% |
| Terns, Gulls & Skuas | 14 | 4 | 29% |
| Green Algae | 130 | 38 | 29% |
| Elasmobranchs (sharks and rays) | 109 | 31 | 28% |
| Octopus and Squid | 119 | 28 | 24% |
| Cnidarians (corals, medusae and hydroids) | 1044 | 218 | 21% |
| Bony marine fish | 1007 | 161 | 16% |
| Dolphins & Porpoises | 17 | 2 | 12% |
| Seals & Sea Lions | 9 | 1 | 11% |
| Zooplankton | 1096 | 23 | 2% |
| Phytoplankton | 963 | 2 | 0.20% |
| Baleen Whales | 10 | 0 | 0% |
| Sperm Whales | 3 | 0 | 0% |
| Beaked Whales | 12 | 0 | 0% |
| Mangroves & Seagrasses | 2 | 0 | 0% |
| Sea Turtles & Sea Snakes | 7 | 0 | 0% |
| Overall Statistics | 14,646 | 6399 | 44% |
Geology and oceanography of the New Zealand marine ecoregion
What has caused this richness in New Zealand’s marine biodiversity? Briefly it has been caused by two forces; isolation and physiographical complexity. The New Zealand continent and its submerged margins have been largely isolated in the southwest Pacific for many millions of years, thus reducing the potential for transport of larvae or adult organisms into the region. Isolated New Zealand populations were thus likely to evolve into new species. New Zealand’s isolation, moreover, has been coupled with a particularly rich and complex seascape; a consequence of its extension over30 degrees of latitude, position on an active plate boundary with all the consequent folding, faulting and volcanism, and its positioning in relation to major subtropical and subantarctic water masses and surface and deep-water current systems.
Figure 1: The topography of the New Zealand seascape. The orange red areas around the main islands are depths less than 200 m while the deep purple in the Kermadec Trench northeast of the North Island is over 10,000 m deep. Undersea New Zealand, NIWA
The geographic isolation of the New Zealand continent since the separation from Gondwana approximately 82–85 million years before present (mybp) has been recognised as being an important aspect explaining the biogeography of the region and the endemic nature of the flora and fauna. During the period from 65 to 35 mybp, New Zealand experienced large variations in archipelago structure, corresponding to the fluctuations in sea-level and tectonic activity and rotational displacements of the landmass. This changing archipelago structure may have played an important role in isolating populations and fostering the diversification of organisms through the creation of new environmental conditions and ecological settings. The separation of Australia and the Antarctic continent in the early Eocene (55mybp) marked a significant event in the distribution of species in the Southern Ocean, with the beginning of the West-Wind drift. This circumpolar current has been thought to have linked species pools within the Southern Ocean, where biogeographic relationships of latitudes from 40˚ to 60˚ S have been documented.
Along with large-scale tectonic activity over millennia, more recent climatic events in the southern hemisphere have also played an important role in determining contemporary species distributions. For example, the Last Pleistocene Glaciation, which occurred from 2.4 mybp, has been considered to be an important event in determining present-day species in New Zealand, as this time period also coincided with intense tectonic activity. The presence of glacial ice masses and altered climatic conditions combined with geological uplift created distinct environmental types and may have possibly created refuges that may have shaped local populations (eg, endemic black coral in Fiordland and southern Stewart Island). The New Zealand region is still active tectonically, with areas of active uplift and subsidence and the formation of deep-sea trenches, active seamounts and volcanoes. As well as influencing the overall biogeography of the region, these processes also create special habitat types that are inhabited by marine organisms, such as hydrothermal vents and cold seeps.
Along with the geographic isolation of New Zealand, several major frontal systems have an influence on marine life within the region with respect to the dispersion of organisms and primary production. The South Pacific subtropical gyre forces a warm current from the Coral Sea into the northeast region of New Zealand, where it forms the East Auckland Current, and this feature—where a major region of continental shelf intercepts a western boundary current in mid ocean—has been regarded as globally unique. This current is inherently variable and forms anticyclone eddies off the northeast of the North Island, which has an influence over primary productivity in the region (see figure 2). The East Auckland Current influences the occurrence of subtropical species in the northeast region of New Zealand.
In the south, New Zealand poses a barrier to the easterly flow of the Subtropical convergence, where subtropical and subantarctic water masses meet. This front intersects the bottom portion of the South Island, is deflected southwards along the shelf edge, turns northwards, following the Otago coast, and extends out along the Chatham Rise. This feature contributes to a change in the biological character of species in these areas. Towards the southern extreme of the New Zealand region, another major oceanic frontal system, the Antarctic Circumpolar Current, flows eastward along the edge of the Campbell Plateau.
Tidal forces around New Zealand include an anticlockwise internal tide, which means that the high and low tides are out of phase on different sides of the two main islands. This feature is expressed in the Cook Strait region, where in the Cook Strait narrows tides can be 120˚ out of phase within a distance of 23 km creating areas of persistent high current. Other regions where this tidal flushing occurs is in the North Cape–Three Kings region, and Foveaux Strait (between Stewart Island and the South Island).
Figure 2: Ocean currents and water mass frontal systems in the New Zealand region. The Tasman Front (TF), the Subtropical Front (STF) and the Subantarctic Front (SAF) approach New Zealand from the west. The STF represents the meeting of Subtropical Water (STW) and Subantarctic Water (SAW), while the SAF is formed by the meeting of SAW and Circumpolar Surface Water (CSW). The fronts contain or generate currents and there are several permanent eddies off the eastern North Island (EAUC, East Auckland Current; WAUC, West Auckland Current; ECC, East Cape Current; DC, D’Urville Current; WC, Westland Current; SC, Southland Current; ACC, Antarctic Circumpolar Current; NCE, North Cape Eddy; ECE, East Cape Eddy; WE, Wairarapa Eddy). There are also areas of tidal mixing in Foveaux Strait between Stewart Island and the South Island, in Cook Strait between the North and South islands, and north of Cape Reinga (Carter et al. 1998). Image provided courtesy of NIWA.
New Zealand’s exposure to the dominant southwesterly winds means that wave dominance in the coastal zone varies around the coast. The most wave-exposed habitats tend to occur in the southwest of the South Island while the more sheltered coasts are found in the northeast of New Zealand, though there is often local protection from wave exposure due to small-scale topographic features.
Habitat diversity
This wide variety in marine seascapes means that New Zealand has a great diversity of different marine habitats. The second deepest part of the Earth’s abyssal ocean is found in the Kermadec Trench, just to the east of the Kermadec Islands northeast of mainland New Zealand. Its fauna is almost completely unknown. The shallow waters around the Kermadec Islands are the warmest in the New Zealand marine region and support our only large colonies of plate and soft corals.
Stony and soft coral colonies at the Kermadec Islands. Photographer Malcolm Francis.
Also part of the ridge extending northeast and southwest of the Kermadecs are many seamounts, steep-sided undersea volcanoes with crests 50–1500 m below sea surface. Some slopes are composed of recently extruded material with little marine fauna, while others have developed unique faunas different from adjacent seamounts. Around active hydrothermal vents can be found highly specialised vent faunas dependent on chemosynthetic bacteria for their energy needs. Seamounts are found around much of New Zealand, though not all have been formed by volcanic action.
Specialised mussels and crabs surround hot sulphur-rich vents on the slopes of the Kermadec arc seamounts. NIWA.
The rich northeast coastline of the North Island has many harbours, estuaries, and sandy bays interspersed with rocky headlands and offshore islands. Along the muddy margins of the harbours and estuaries are forests of mangrove, while in the shallow harbour flats are meadows of seagrasses and banks of filter-feeding cockles and pipi; all rich feeding grounds for coastal fishes and sea birds. The Malborough Sounds at the top of the South Island is another rich coastline, though its channels are deep and narrow.
New Zealand also has a great many offshore islands, some of which are close to the mainland (eg, Kapiti and Little Barrier) while others are well offshore at the edge of the continental shelf (eg, the Poor Knights Islands), or lie well to the east (the Chatham Islands and the Bounty Islands) or to the far south (eg, the Auckland Islands and Campbell Island). These islands and their surrounding shelves act as stepping stones for faunas and floras from the subtropics and the subantarctic that influence the diversity of marine species in the New Zealand region.
The margins of New Zealand’s continental shelf are indented by over one hundred canyons. Some of these steep-sided features are only a few kilometres long while others, like the Cook Strait and Kaikoura canyons, are major features of the seascape and bring deep water close to the New Zealand mainland. Vertical mixing of the water column and associated increased productivity often occurs in and around canyons, helping to sustain a more varied and abundant mid-water and bottom-dwelling fauna than the surrounding continental shelf. This in turn attracts large predators like giant squid and sperm whales.
Sperm whale at the start of a dive deep into the Kaikoura Canyon.. Photographer Rob Murdoch.
Fiordland is a place of land- and seascapes unequalled in Australasia with densely forested mountains flanking deep fingers of ocean. Sheer rock walls carved by glaciers plunge as deep as 450 metres below the surface. A yellow-tinted surface freshwater layer—a consequence of the high rainfall percolating through forest humus—greatly reduces the underwater light except near the fiord entrance. The fiords are strongly stratified by temperature. Consequently, species usually only found in deep, cool, and dark waters can be found close to the surface. Black coral is abundant along the rock walls of the fiords. Colonies may live for over 300 years and reach heights of over three metres. Nowhere else in the world are black corals found as shallow or in such abundance.
Inclusion of the New Zealand Marine Ecoregion in WWF’s Global 200
A global trend in habitat modification and the loss of biodiversity has called for the development of conservation efforts that protect ecosystem components at a scale that enables relevant ecological processes to maintain them
The Global 200, developed by WWF, established a network of 238 ecoregions based on a hierarchy of biogeographic regions and habitat types used to identify representative areas on a global scale. Ecoregions were stratified among three realms, including terrestrial, freshwater and marine, and divided among Major Habitat Types (MHTs), describing different areas around the world that share similar environmental conditions, habitat structure, and patterns of biological complexity. The MHTs were then further subdivided among major biogeographic realms (eg, Nearctic, Indian Ocean) to address global representation of biological assemblages within a habitat type. The identification and evaluation of each ecoregion was based on extensive literature analyses and consultation with experts working in each region. Ecoregion boundaries were intended to roughly coincide with the area over which key ecological processes strongly interact. (For a more comprehensive explanation of Global 200 see Appendix 2.)
Within the scheme of the Global 200, the New Zealand Marine Ecoregion was considered to represent the MHT of Temperate Shelf and Seas, within the major biogeographic realm of the Southern Ocean. The biodiversity features of the region were characterised as being one of the most diverse and productive Pacific south temperate and polar ecosystems and recognised for supporting a diversity of algae, fish, bivalves, seabirds and marine mammals. Selected species included several species of penguins (including some endemic species), albatross and petrels (with some endemic breeding colonies), and marine mammals, including seals, sea lions, dolphins, sperm whales, and southern right whales. General threats to the biodiversity of the region that were identified included overfishing, and environmental degradation in coastal areas due to sewage discharge and agricultural runoff. Additionally, it was noted that for some areas seabird species are under threat by introduced species (eg, cats and rats).
Scope of this resource
This resource reviews and summarises the number of living species across all the major groups of organisms in New Zealand’s marine environment apart from the functional decomposers including fungi and bacteria. Taxonomic and functional groups were selected based on a number of criteria, including the threatened status or vulnerability of the taxa and/or functional group, taxonomic knowledge, and information on the geographical distribution of species, including the level of endemicity or range restriction. In some cases, the functional or life-history characteristics of a group of taxa allowed for a more reasonable assessment of the biodiversity and status within that group.
The degree of coverage varies widely across the groups. For instance the seabirds (class Aves) are devoted six chapters while sea snails (class Gastropoda) are devoted just half a chapter. Likewise, the number of species per chapter is highly variable. The chapter on mangroves and seagrass discusses only two species while the chapter on gastropods and bivalves summarises 3340 species. Obviously the amount of detail afforded to each species is thus highly variable, as are the summary tables that accompany the entry for each taxonomic group.
Taxonomic or functional group entries were constructed through a combination of literature review and contributions from experts working in that particular field. Each chapter has been reviewed by an expert in the field. In each chapter the taxonomic context, morphology, special adaptations, behaviour, diet, and life history are briefly discussed. The special status of species within each group, key locations, threats, typical habitats, state of information, significance for Māori, and key references are also summarised. Finally, in each chapter a table listing the number of species in each taxonomic group is presented. Where there is sufficient space, tables list every species, while in others the total number of species and the total number of species per family or order is listed.
The World Conservation Union (IUCN) threat status and the Department of Conservation threat levels are listed under each heading as appropriate. These species classification systems are summarised in Appendices 3 and 4 from original source documents available from these institutions via the internet and these should be consulted directly for a full detailed description. See:
www.redlist.org/info/categories_criteria2001
www.doc.govt.nz/templates/MultiPageDocumentTOC.aspx?id=42704
Unusual terms are defined in a glossary in Appendix 5 while the location of place names mentioned in the text are shown in maps in Appendix 6
Maps of species distributions are available for three or so species in some entries. These have been reformatted from maps kindly made available by the Ministry of Fisheries from its National Aquatic Biological Information System (NABIS) web pages. These web pages (see https://www.nabis.govt.nz/nabis_prd/index.jsp) contain many more maps of species distributions, especially for marine fishes, and should be consulted. Figure 3 is an example of the maps used in this summary to illustrate species distribution. In the example, hot spots of grey-headed albatross distribution are indicated in dark green, while the area of 90% and 100% occurrence of this species in the New Zealand region are shown in increasingly lighter shades of green. Areas where a species does not occur are shown in white while grey indicates areas for which there are no reliable data.
Figure 3: An example of the maps used throughout the summary.
The summary is targeted at people interested in New Zealand’s biodiversity. It is intended to be in an easily accessible and understood format that allows wide uptake.
Implications for management
Although the summary was not conducted as an exercise for setting priorities, the information contained within the individual entries provides base information that would enable the evaluation of criteria to be able to establish priorities for conservation action. This includes sections on Status and Summary of Threats in each entry. These were compiled bearing in mind that there are both geographic (eg, endemic status or range restriction) and non-geographic (eg, slow growth, low reproduction, exploitation or other anthropogenic sources of mortality) aspects affecting conservation status.
Several themes with implications for management of New Zealand’s marine biodiversity emerge from this assessment. Although these themes are not wholly new, they are worth emphasising in this context. First, the large number of species within the New Zealand marine ecoregion indicates that the management responsibilities for New Zealand’s departments and agencies are also great. Second, the large percentage of still undescribed species in many groups, and the rate of new discovery in others, underscores the need for increased effort to fully document New Zealand’s biodiversity. Third, the high level of endemism means that New Zealand cannot be reliant upon the good stewardship of biodiversity in neighbouring countries or areas to maintain many of the species present in the New Zealand marine ecoregion. This need for self-reliance needs to be translated into policies and strategies that maintain the integrity and long-term sustainability of the environments and habitats in which New Zealand’s marine species occur. Lastly, it is apparent that there are a significant number of highly migratory species within New Zealand waters that are highly dependent on safe access to either breeding or feeding grounds in environments and habitats well beyond New Zealand’s exclusive economic zone; in some cases in the northern hemisphere. For these species, New Zealand’s management policies and actions must include close and continued dialogue with the countries and agencies responsible for management and conservation of these species.