Three brown seaweeds: Furbelows, Sea Belt & Spiral Wrack from Studland Bay in spring

Seaweeds usually start off life attached to rocks. Although Studland Bay is famous for its beautiful fine, clean sand, there are rocks to the west of the bay near Old Harry Rocks, and also the artificial substratum of what is locally termed the Training Bar. The Training Bar runs from the junction of Shell Bay and Knoll Beach (both are parts of Studland Beach) seawards in an approximately south-westerly direction. It is signposted with beacons on poles. Its purpose is to guide boats safely into the narrow entrance to Poole Harbour by the Sandbanks Ferry.

Seaweed becomes detached from the rocks for many reasons but most commonly due to strong wave action in stormy weather. The weed then floats around and often gets washed ashore. Because the weed may have been swilling around for a considerable time, the condition may be poor when it is found on the beach.

Most of the time the quantities of weed are moderate, scattered and impermanent  – it gets washed out to sea on the next tide. Occasionally vast banks of weed accumulate and do not disperse. If this happens, the National Trust (who own the beach) have hit on the novel idea of bagging it up and selling it as fertiliser for the garden. It makes excellent enrichment for the soil. For centuries, people have gathered seaweed for this purpose. In Alderney in the Channel Islands, for example, you can find evidence of the former wrack-gathering activities in the cobbled ramps that lead down to the beaches; these were constructed for the carts to get down to the shore. 

The top picture shows the commonly occurring kelp called Furbelows, Saccorhiza polyschides(Lightfoot) Batters, washed up at Studland Bay, Dorset. It is one of the largest brown seaweeds or Phaeophyceae. It has long strap-like leathery fronds. The stalk is short, flat and typically has a wavy ruff or frill either side of it as you can see in the picture below. Sometimes the stalk is twisted at the base. The holdfast at the base frequently has a warty and bulbous hemispherical appearance as well as rootlets. Lots of plants and animals prefer to settle here on both stalk and holdfast. The specimen below has red seaweeds attached to it. 

Sea Belt or Poor Man’s Weather Glass, Laminaria saccharina (Linnaeus) Lamouroux, is another large brown kelp but is easily distinguished from Furbelows. The frond is often a single blade and is has a crinkly surface that looks like that old-fashioned fabric known as seersucker.

The stem of Sea Belt is short and slender as you can see in the photograph below. There are no lateral frilly edges. The holdfasts are a series of intertwined rootlets and there is no large bulbous structure.

You can find more pictures and information about these two kelps in a previous post – click here for Kelps at Kimmeridge Bay.

One of the smaller brown seaweeds is Flat or Spiral Wrack, Fucus spiralis Linnaeus, pictured above and below. Like Bladder Wrack and Toothed Wrack it has a central midrib – but it doesn’t have any air bladders and the edges of the fronds are smooth. One of its supposed characteristics, and the one from which it gets the name Spiral Wrack, is the tendency of the fronds to twist -but you can’t rely on this feature alone for identification. When the forked tips of the fronds swell with reproductive products, they are lighter in colour and have a granular appearance. However, these swellings have a distinct longitudinal ridge or border around their edge which is a continuation of the blade or frond. This is one of the diagnostic features for the species.

There are more detailed pictures and explanations about Flat or Spiral Wrack click here for Flat or Spiral Wrack from Chapman’s Pool.

Revision of a post first published 4 June 2009

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