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Forming the base of many marine ecosystems, seaweed is an algae and it come in all sorts of sizes and forms. Like land plants, they need sunlight to make their food, in a process called photosynthesis, and this means that seaweed is only found on the shore and in shallow seas. This is their only food source, as they do not have roots through which to take in nutrients from the seawater. 

Kelp - Lawson Wood

Kelp © Lawson Wood Ocean Eye Films 

Different species of seaweed are adapted to living on different areas of the shore, and this can be explained by 'zonation'. This is when the shore is separated into different zones depending on the environmental conditions and the species that live there. For example, the higher up the shore you go, the length of time it is exposed from the sea increases, and different species of flora and fauna are adapted to living with varying amounts of exposure (i.e. have evolved to withstand being out of the water for longer). Therefore the species you find at the top of the shore will be adapted to living in longer periods of exposure than those living further down the shore. 

All plants get their colour from chemicals called pigments. Leaves are green because of a pigment called Chlorophyll, which is used during photosynthesis. Seaweed too has this pigment, however it can sometimes be masked by other pigments, making them appear different colours. Therefore, seaweed can be grouped into three main groups according to their colour - green, brown and red.


Green Seaweed

Green seaweeds are green because their chlorophyll pigments isn't masked by any others. They are usually found higher up on the rocky shore.  


Brown Seaweed

In brown seaweeds, their green chlorophyll is masked by a brown pigment. This group of algae is very diverse, and they cover a large area of the rocky shore. Kelp is included in this category, which is found at the very lowest of parts fo the rocky shore, and can only be acessed at extreme low tides. 

Red Seaweed

Red seaweeds have their chlorophyll masked by - you guessed it - a red pigment. Some red seaweeds are hard and appear fused to rock surfaces.


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