Story: Sea floor

Very few people have explored the sea floor – a mysterious world with canyons, trenches, seamounts and hydrothermal vents, and animals ranging from microscopic worms to corals, sponges, crabs and shellfish.

Story by Ashley Rowden
Main image: Life near a hot vent

Story summary

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What is New Zealand’s sea floor like?

The sea floor around 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 and seamounts (mountains).

What lives on the sea floor?

On the sea floor there are bacteria and worms, anemones, corals, sponges, seaweeds, crabs, sea stars, shrimps, sea urchins (kina) and shellfish.

What do they eat?

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 animals living on the sea bed.

The continental shelf

Different animals live in different places on the continental shelf. For instance, corals cling to hard surfaces, while worms and shellfish live in mud and sand.

Where these animals live also depends on the temperature of the water, how salty it is, how much oxygen is in it, how strong the currents are, and how much food there is. Usually, as the water gets deeper, there are fewer animals.

The deep sea floor

The deep sea floor has flat plains, seamounts and trenches. Seamounts can be cone-shaped and rise hundreds or thousands of metres above the sea floor.

The deepest seabed in New Zealand is the Kermadec Trench. There is life in the trench. Scientists have found worms, sea stars, sea snails, shellfish, sea cucumbers, shrimps and barnacles.

Vents and seeps

In the 1970s animals were discovered in places on the sea floor where chemicals flowed out. These were vents (underwater volcanic hot springs) and cold seeps of methane.

At these places, bacteria make food using the energy in the chemicals coming out of the sea floor. This process is called chemosynthesis.

Some animals eat the bacteria, while other animals have bacteria living in their bodies and producing food there.

How to cite this page:

Ashley Rowden, 'Sea floor', Te Ara - the Encyclopedia of New Zealand, (accessed 18 April 2024)

Story by Ashley Rowden, published 12 June 2006