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Science, Maths & Technology

Carbon in sea consumers

Updated Sunday 7th May 2000

Fish and mammals need organic matter to keep alive - and that keeps carbon moving.

Great White Shark Copyrighted image Icon Copyright: BBC

Ocean creatures, like those on land, need a regular diet of organic carbon. A little of this carbon is built up into body tissues. But most is broken down to carbon dioxide to give the animal energy.

The familiar carnivores, like sharks, dolphins and sea lions, are comparatively rare. They rely on smaller organisms like krill or small fish. These in turn may graze on plants and animals in the plankton. The animal component of plankton are called zooplankton. They eat phytoplankton, detritus and each other. Suspended in the upper waters, they live amongst their food.

The soaring towers and intricate lattices in a coral reef provide shelter for many creatures. But closer examination reveals that the architects of these fabulous structures are animals too. The framework of coral is secreted by tiny animals which live inside. As the coral organisms grow, they build up skeletons, forming reefs. The skeletons are made of calcium carbonate, which often survives after the animals die.

The vast majority of ocean consumers depend ultimately on photosynthesis. And all of them will eventually die. Detritivores and bacteria go to work on fragments of dead animals, plants and faeces. They respire, and recycle the organic carbon, releasing it as carbon dioxide which dissolves in the water.

Where do you find the carbon?

Marine animals (including zooplankton) and bacteria

What form of carbon?

Organic carbon and calcium carbonate

How long will the carbon remain?

Less than a year on average

What processes will free the carbon?

Less than 1 x 10 12 kg

What processes will free the carbon?

Respiration, dissolution, sedimentation


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