Algae and Seaweed

  • Algae

Algae are found on stones, in water and on tree branches; on coastal rocks and pools.

Sea plants are usually algae – they reproduce by spores instead of flowers. Most of them are tiny but there are many thousands of them. Algae are the basis of all animal life in the sea.

All seaweeds contain chlorophyll. This is a green chemical that turns the sun’s energy into food. Not all seaweeds are green though – some are brown or red.

Seaweeds attach themselves to rock or stones so that they don’t get washed away. The point where they stick themselves is called a ‘holdfast’!

The Brown Seaweeds

On the upper shore you can find the flat wrack. It has short, narrow fronds which can survive out of water for a long time. On the end of the fronds are spotty pods which contain the spores. Because they are small, the fronds aren’t damaged too much by the sea’s waves.

  • Algae

    The middle shore has two brown flexible wracks, bladder wrack and knotted (or egg) wrack. These have bubbles of air called ‘bladders’ along the fronds which help them to float. This way they can rise over the waves and not get damaged. The spores are carried in pods on the ends of the fronds.


  • Algae

    You can find bladder wrack across the middle part of the shore. The bladders on its fronds grow in pairs.


  • Algae

    Knotted wrack has single bladders like knots along a piece of string. It prefers the deeper water.


  • Algae

    The serrated (or saw) wrack grows on the lower shore. Its fronds have spiky edges like a saw, but no bladders.


The Pale Green Seaweeds

Pale green seaweeds like fresh water and diluted salt water.

  • Algae

    Gut weed or tube weed (Enteromorpha). Its fronds look like a mass of tubes. Look at the way they are flowing – this shows you the direction the water is running.


  • Algae

    Sea lettuce fronds are broad and flat. They look like lettuce leaves.


  • Algae

    Hair weed (Cladophora) have fronds that are like fine hairs. It is not as common as the other pale green seaweeds.


The Red Seaweeds

  • Algae

    Red seaweeds aren’t very common on this shore. The one you are most likely to see is Corallina. It is called this because its fronds are hard, like coral. The whitish covering helps to protect the plant and makes it look like a tiny skeleton.