The marine environment can be divided into:
New Zealand’s coasts are mainly rocky cliffs, or beaches. The coast is a tough place to live because it is exposed to wind, salt spray, the changing tides, and often large waves.
Plants and animals that live in coastal areas have adapted to live in this ever-changing environment and can cope when the tide goes out. Rock pools provide homes for animals such as cockabullies’, sea anemones and crabs.
Clumps of marram and pīngao survive in the sand dunes. At low tide pipi, tuatua and other shellfish can be found. Crabs, sandhoppers and shrimps live under the sand on the beaches, and come out to feed at low tide.
Various birds use the coastal area. Gulls live up in the cliffs and visit the shore. Birds that come down to feed at low tide include oystercatchers and herons, which hunt for crabs, snails and fish.
An estuary is an area of water on the coast, where fresh water and sea water mix. It often forms at the mouth of a river, with large mud flats where the tides wash in and out.
There are about 300 estuaries around New Zealand’s coastline. The biggest is Kaipara Harbour. Estuaries formed about 6,500 years ago when the sea began to flood river valleys and bays.
Estuary plants are special, they have to survive salt water, storm waves and other tough conditions. Two common New Zealand estuary plants are seagrass and mangroves.
There are a range of creatures, from tiny organisms to eels and godwits. Burrowing mudworms are eaten by birds and fish. Crabs make tunnels or hide under rocks. Cockles help filter the water and are food for birds and humans. Many native fish, including flounder and kahawai, use estuaries for feeding and breeding. Flocks of wading birds such as herons feed on the mudflats, and thousands of godwits and other migrating birds arrive each spring. Swamp birds such as pūkeko and bitterns breed among the mangroves and rushes.
A fiord is a long, narrow inlet of sea, with steep sides gouged out by a glacier. New Zealand’s 14 fiords were carved out by glaciers 20,000 years ago.
A layer of fresh water lies over the salt water, created when heavy rain runs into the fiords. As the water runs down banks it absorbs chemicals called tannins from the vegetation, which turns the water brown. The brown layer of fresh water reduces the amount of sunlight filtering through to the salt water below. This makes the salt water dark, and so many creatures that usually only survive in very deep black water can also live in the fiords.
Most creatures in the fiords live on the underwater rock walls. The top layer of brown fresh water is home to only a few hardy creatures such as mussels, shrimps and barnacles. Just below this layer, the rock walls are covered in huge numbers of sponges, corals, sea stars, sea urchins, lace corals and sea squirts. Further down, sea cucumbers and glass sponges make their homes.
Heart urchins, tube worms and crabs are among the animals that live on the muddy floors of the fiords.
The richness of ocean life is closely connected to the supply of nutrients that fuels growth of microscopic plants called plankton.
Plankton are living organisms that drift in the ocean. They are the base of the food chain: plant plankton convert sunlight into energy and provide food for animal plankton and other creatures. Where plankton flourish, larger animals come to feed.
Animal plankton provide food for ocean fish such as hoki, the most common commercially-fished species in New Zealand waters.
The sea floor that belongs to New Zealand is 16 times bigger than the land of New Zealand. It has three parts:
- the continental shelf, which is closest to the ocean’s surface
- a steep slope, which drops down from the continental shelf to the deep sea floor
- the deep sea floor, which has trenches, ridges, seamounts (mountains), and flat plains.
On the sea floor there are bacteria and worms, anemones, corals, sponges, seaweeds, crabs, sea stars, shrimps, sea urchins (kina) and shellfish.
Where the water is shallower, seaweeds make their own food by absorbing sunlight. Other organisms eat dead plankton or fish, animals’ excrement, seaweed that sinks to the bottom, or other animals living on the sea bed.
Usually, as you move into deeper water, there are fewer animals and less variety of species.