I found three types of kelp washed up on the seashore at Kimmeridge Bay on 15th March 2009. Kelps are the largest of the British brown seaweeds or Phaeophyceae. They are perennials in plant terminology compared with many of the more ephemeral red and green algae that appear seasonally or annually. Kelps all have a flat blade joined to a stalk, sometimes substantial, in turn attached to rocks by a much branched structure called a hold-fast. They live at low water or deeper.
The kelp on the pebbles in the photograph at the top is known as Furbelows, Latin name Saccorhiza polyschides (Lightfoot). It has been washed up onto the shingle complete with the large stone to which it is attached. The holdfast is like a hollow knobbly ball. The stem is smooth and flat, often with a twist just above the holdfast, sometimes with really noticeable wavy or frilly edges. The blade starts off as a single blade but becomes divided up into long straps. The whole thing can reach 4.5m long and 3.5m wide.
The photograph below shows in detail the characters of stem and holdfast by which this species is identified.
Cuvie, or Laminaria hyperborea (Gunnerus) , is another type of kelp found on the strandline (shown below). This one also has a long stem but with a round rather than a flat cross-section; and the outer surface is roughened and not smooth. The blade is divided up into long straps just like the Furbelows described above. The holdfast is not bulbous in this type but simply a complex of ‘rootlets’.
Additionally, it is typical that some smaller red seaweeds are actually growing on the stem. You can see these details more clearly in the picture below.
The third type of kelp I saw was Sea Belt, or Poor Man’s Weatherglass – Latin name Saccorhiza saccharina Linnaeus. This is easily recognisable from the crinkly puckered blade. You can spot it straight away amongst the piles of seaweed on the Kimmeridge strandline shown in the two pictures below. This weed has a thin short stem and a holdfast of branched rootlets.
When this seaweed is dry, a fine sugar-like powder coating appears on the blade hence the saccharina in the Latin name. Because this dried weed becomes limp again in damp air, it is traditionally used to forecast rain.
For more information about seaweeds a useful website is Algaebase which is a data base for all agae including marine seaweeds. For more information on the three kelps illustrated click on Furbelows, Cuvie, and Sea Belt.
For more information about Kimmeridge Bay see the Purbeck Marine Wildlife Reserve Web Site.
COPYRIGHT JESSICA WINDER 2011
All rights reserved