As much as 80 per cent of New Zealand’s total biodiversity lives in the sea. 2409 It is estimated that there might be up to 65,000 different marine species, of which only twenty-five per cent have been described. 2410 Marine research is significantly behind its terrestrial counterpart, making assessment of ecological health and measurement of biodiversity difficult, because information is so scarce. 2411 However, we do know that the high diversity of marine habitats within New Zealand’s waters is critical to the ecological health and productivity of the marine area, and is relied on by an extraordinarily high number of species.
New Zealand is considered internationally to be an important contributor to global marine diversity. For example, endemic species include:
- About 95 per cent of the 733 known sponge species
- 84 per cent of bivalves and gastropods (types of marine molluscs)
- 75 per cent of ascidians (commonly known as sea squirts)
The greatest biodiversity of fish and invertebrates is found along the northeast coast of the North Island, where known hotspots of species endemism and/or species diversity occur at the Three Kings Islands, in the soft sediment assemblages of Spirits Bay (Piwhane) and Tom Bowling Bay (over 700 invertebrate species).
In a recent paper by marine biologist Dennis Gordon, it was recorded that the animal kingdom Animalia
is by far the richest in species numbers with 13,415 marine species, followed by Chromista ( a eukaryotic
supergroup) with 2644 species, Plantae (mostly red and green seaweeds) with 702 species, Fungi with 89 and Protozoa
with 43 species.
Gordon noted that seaweeds comprise approximately 900 species, including at least 109 that are new to science and not yet described.
Plankton comprises the largest group of organisms in the ocean. The term refers to organisms that rely on the movement of the water to carry them around, because the vast majority of the many species of plankton are too weak to swim against the current. There are many species of plankton and they are divided into two basic groups – phytoplankton (or plant plankton) and zooplankton (or animal plankton).
Phytoplankton are the primary producers for the oceans. Around half of worldwide primary productivity is achieved by these microscopically small organisms which grow and divide in the ocean.
The animal components of plankton are the zooplankton. Like phytoplankton, zooplankton are usually weak swimmers and tend to just drift along with the currents. Phytoplankton and zooplankton are key components of marine ecosystems forming the base of most marine food webs.
Specific species of phytoplankton and zooplankton occupy particular marine habitats. Each species is uniquely adapted to factors like light, temperature, turbulence and salinity in its environment. Phytoplankton and zooplankton are sensitive to their environment and a change in concentration can indicate a subtle environmental change. They are often highly responsive to nutrient levels, temperatures, pollution, food that is not nutritious, levels of light and increased predation.
Plankton are believed to be the most important life form on Earth. Through photosynthesis, phytoplankton convert water and carbon dioxide into organic material, or food and oxygen. They are at the base of the oceanic food chain, and without them, few other life forms in the ocean could exist. 2422 Plankton are also responsible for manufacturing a significant amount of the Earth’s oxygen.
Algae and seagrasses
Algae are an ancient group of primitive plants that support major marine food webs. In contrast, seagrasses are flowering plants (angiosperms), whose ancestors once lived on land. One prominent and important temperate zone seagrass is eelgrass which provides excellent habitat for grazing animals. These fast growing plants form the base of a rich and productive food web.
The distribution of algae is generally clearly zonated within the marine environment. Yellow, white and grey lichens (a combination of fungi and bacteria) all live within the zone which is both wet and dry. Green seaweeds are common in the upper intertidal zone, whilst brown algae are found closer to the low-water line. Red seaweeds are found below the brown-seaweed zone and the large kelps are found in the subtidal zone.
This is a highly diverse group of species, including sponges, worms, shellfish and echinoderms. The sessile animals living on rocky reefs harvest plankton and organic particles from passing seawater. They include sponges, hydroids, corals, anemones, bryozoans, tube worms and barnacles.
Hydroids, jellyfish, corals and sea anemones belong to the group Cnidaria and are among the simplest of marine invertebrates. Jellyfish may consist of individual organisms or colonies of individuals, some of them specialised for tasks such as feeding, stinging and reproduction.
The name “coral” is given to a variety of animals which grow in colonies with skeletons made of calcium carbonate or horny material. The largest invertebrate sea-floor species on the planet, the bubblegum coral, lives in New Zealand waters. True (or “stony”) corals may be solitary (cup corals, to which most New Zealand species belong) or colonial (reef-building corals). Their skeletons are made up of calcium carbonate and are external to the body. Black corals, of which there are 58 species in New Zealand waters, belong to a different group than the true corals. They have hard, protein-based skeletons with tiny polyps. Mostly they live in deep water, but in Fiordland, the black coral Antipathella fiordensis can live in relatively shallow depths.
Bryozoans are fascinating creatures, which have been variously referred to as lace corals, moss animals or sea mats. These animals form coral-like groupings on rocky and gravel areas, which in turn provide shelter for other invertebrates and juvenile fish. Nearly 1,000 different species of bryozoans are found within New Zealand’s marine area and most of these are unique to the country.
In contrast to the sessile animals, other invertebrates move around the rocky reef to feed. These include herbivores, such as kina and top shells, which graze on seaweed, and carnivores, such as octopus, starfish, crayfish and crabs. The reef is also home to brightly coloured sea-slugs (nudibranchs), shell-fish type animals which have evolved to live without shells. Some sea-slugs protect themselves with stinging cells recycled from their prey.
There are numerous types of shellfish found in New Zealand’s marine environment. Of these, many bivalves, such as mussels, cockles, oysters, pipi and scallops, feed by straining plankton from the water. Some species of bivalves can reach phenomenal densities at over 20,000 per square metre. Most bivalves are sedentary or slow-moving animals. Some, such as pipi and cockles, spend their life buried in seafloor sediment, while others like oysters and mussels remain anchored to one spot by attaching themselves to rocks and solid structures. 2426 Scallops, on the other hand, can move quickly through the water if they sense danger.
Seamounts can support very large deep-water sponges and corals that may live for hundreds of years. In these habitats, sponges can reach several metres in height and corals have been found growing up to 10 metres tall. Deep-water coral banks, large sea fans, sea pens and sponges are particularly vulnerable as they are fragile and slow-growing. Once destroyed, coral formations appear to need 200 to 400 years to recover to some degree but will never be quite the same if their endemic species have been lost. 2427
Fish are found in all kinds of marine habitats. Rocky reefs support some 250 species of reef fish. Some of these, including parore, silver drummer and butterfish, graze on seaweed. Others including maomao, trevally and demoiselle sift plankton from the seawater. Other fish commonly targeted by fishers, including snapper, blue cod, kahawai, John Dory and moki, predate on smaller fish and invertebrates living in the rocky reef environment or on adjacent areas of sediments. Some unusual species also make New Zealand’s rocky reefs their home including sea horses and sea dragons. The sea horse species found in New Zealand is one of the largest in the world. The sea horses anchor themselves to seaweeds or other structures on the reef with their prehensile tails, and ambush their food, mainly crustaceans. Male sea horses incubate fertilised eggs in a specialised pouch.
Bottom-feeding fish such as flounder, terakihi, snapper, red cod and warehou predate on common residents of coastal soft sediments including a variety of worms, crabs, shellfish, starfish, sea urchins and sea cucumber. Some fish, such as the stargazer, completely bury themselves in the sand and pounce on unsuspecting passers-by. 2428 Seamounts offer a refuge for deep-water fish species including orange roughy, black oreo and black cardinalfish.
Many of the fish found in New Zealand waters are present in other parts of the world. However, there are a number of fish species that are very rare, and found only living in certain habitats, such as the morse-code leatherjacket which is generally only spotted in the Kermadec Islands.
There is a much higher level of endemism in New Zealand rock pool fish which are less mobile. It is thought that 62 per cent of New Zealand’s 94 species of rock pool fish are only found in this country.
Fish are an important food source for marine mammals and birds, as well as for the larger predatory migratory fish species. New Zealand waters are visited by numerous migratory fish and they provide a critical habitat for many of them. Species such as the southern bluefin tuna and striped marlin migrate seasonally across the vast ocean basins.
New Zealand’s seas are a marine mammal ‘hotspot’. It is estimated that just under half of the world’s total number of dolphin and whale species are found in New Zealand. There are five different species of dolphin that live year round in New Zealand’s coastal waters, including the common dolphin, dusky dolphin, bottlenose dolphin, Hectors and orca. There are a few other species living in offshore waters. New Zealand is home to one of the smallest dolphins in the world, the Hector’s dolphin. This species is threatened with just over 7,000 remaining. The Maui’s dolphin is only found along the west coast of the North Island. There are as few as 55 adults of this critically endangered species remaining.
Species of whale, including the humpback and blue whale, migrate through New Zealand waters. Other species such as the Bryde’s whale and southern right whale breed here. A small population of around 40 to 50 Bryde’s whales resides in the Hauraki Gulf year round, with a further 150 visiting seasonally. The species is classified as nationally critical in New Zealand, although there are secure populations overseas.
New Zealand fur seals and sealions are part of the other main group of marine mammals found in New Zealand’s waters, the pinnipeds. It is estimated that up to two million fur seals lived around the New Zealand coastline before humans arrived. Their population was decimated by hunting but is now recovering. The endemic and threatened New Zealand sea lion breeds in the Auckland Islands and can be seen around southern coasts, including the Catlins and Otago Peninsula. Southern elephant seals and leopard seals are occasional visitors to New Zealand beaches, travelling up from subantarctic and antarctic waters.
New Zealand has been referred to as the ‘seabird capital of the world’. This is because more species of seabirds breed here than in any other country. There are thought to be more species of seabirds in New Zealand than land birds. Thirty-five species of seabird only breed in New Zealand.
New Zealand’s seabirds range from the large southern royal albatross, which can have a wingspan of over three metres and which spends most of its time at sea, to the small and critically endangered New Zealand fairy tern, which nests on Auckland and Northland beaches.
Seven species of penguin can be found in New Zealand, with four of these breeding on the mainland (yellow-eyed, white flippered, Fiordland-crested and blue). The blue penguin is the smallest penguin species in the world and can be found along the coasts of the North and South Islands. The largest penguin in New Zealand is the distinctive yellow-eyed penguin, which nests along the south-east coast of the South Island, and on subantarctic islands further south.
Gordon D, 2012
Department of Conservation and Ministry for the Environment, 2000, 57
Ministry for the Environment, 2007
Morrison M, 2005
All animals are members of the Kingdom Animalia, also called Metazoa
Any organism whose cells contain a nucleus and other structures enclosed within membranes
Single-celled eukaryotes (organisms whose cells have nuclei) that commonly show characteristics usually associated with animals
Gordon D, 2012
Gordon D, 2012
Bollmann M, et al., 2010
Project AWARE Foundation, 2009, 2-10
Project AWARE Foundation, 2009, 3-6
Ministry for the Environment, 1997, 7.30
Westerskov K and K Probert, 1981, 74-75
Paulin C D and C D Roberts, 1993
Last updated at 2:11PM on February 25, 2015