A Blog from the Past 
Kelp with smaller red and green seaweeds washed up on the pebble seashore at Lulworth Cove, Dorset. Kelps are the biggest brown seaweeds with a flat frond or blade, often divided, at the end of a long tough stalk which it attached to a rock or other hard surface by means of an special structure called a holdfast. The variations in the structure of these three elements define the different species. The kelp in the picture above is commonly known as Cuvie and its scientific name is Laminaria hyperborea (Gunnera).
Wireweed is an alien or invading species of seaweed found on the British coasts (its Latin name is Sargassum muticum (Yendo) Fensholt). The species was accidentally introduced from the Pacific to the English Channel on oysters imported for cultivation. It is thought to be a nuisance in shallow water because it grows so prolifically – and also a threat to native sea-grasses by competing for space and resources.
In this close up picture of the Wireweed you can see the gas bladders (which help it float) on the fronds; the fronds can be over a metre long. If you were to hold up the weed horizontally between two hands, all the side branches would hang down in a row.
There are three main groups of seaweed classified according to colour: the brown ones belong to the Phaeophyceae, the green to Chlorophycae, and the red to Rhodophyceae. All three groups possess the green pigment chlorophyll but in the Phaeophyceae and Rhodophyceae this colour is masked by brown and red pigments respectively. All three types are washed ashore at Lulworth – as you can see in the photographs above and below.
The red seaweeds are the most striking in the assortment shown above. A bundle of light-coloured mossy-like Hydroids sits on the top of them. See tomorrow’s Post for details of these Hydroids.
The red seaweeds are more ephemeral. Their presence on the shingle beach provide bright splashes of contrasting colour.
Sometimes the pattern of the fronds of red seaweed are elegantly displayed where they have dried onto flint pebbles on the beach. It should be possible to identify the seaweed to species where this has happened – but I am not a seaweed expert so I am not sure. It looks a bit like Irish Moss or Carragheen (Chondrus crispus Stackhouse) but smaller and possibly less mature than the plants you normally find. Or it might be Laurencia obtusa (Hudson) Lamouroux which is related to the Pepper Dulse. Any help here with identification would be appreciated.
Below, the features of the algae are less distinct where they have dried in the air as a clump. Seaweeds are easiest to identify when they are fresh.
For more information about Lulworth Cove look at the Lulworth web site.