Looking like bunches of flattened yellow sultanas hanging down on stalks, the reproductive bodies of the Egg or Knotted Wrack, Ascophyllum nodosum ( Linnaeus) La Jolis, were a very noticeable feature of the weed in April. This picture was taken of the seaweed attached to the limestone of Spaniard Rocks, adjacent to the causeway separating the mainland from Burry Holms, on Rhossili Bay.
Here a detached frond of egg wrack has been washed up onto the sandy beach. You can clearly see the large egg-shaped air bladders spaced along the central olive-coloured frond which lacks a mid-rib.
It is interesting to note the way the Egg Wrack at Rhossili differs in its appearance from the same weed at Ringstead in the same month. The plant and fruiting bodies photographed in Rhossili are larger, more robust, and lacking the attached red seaweed – at least when growing on rocks by the causeway to Burry Holms. Although the Egg Wrack occupied the same approximate tidal position on the shore in both places, the main distinction between the two habitats is the greater exposure to wave action at Rhossili. It looks like the Rhossili Egg Wrack thrived where the sea was rough.
Bladder wrack or Popweed, Fucus vesiculosus Linnaeus, was growing on the limestone Spaniard Rocks right next to the Egg Wrack (there is a small bit of Ascophyllum gate-crashing top left corner of the picture above). You can tell the two seaweeds apart by the mid-rib to the frond and much smaller bean-sized air bladders positioned lower on the blade in Bladder Wrack, and the reproductive bodies are confined to the lighter coloured swollen tips. Bladder Wrack tends not to grow so large as Egg Wrack.
Channelled Wrack, Pelvetia canaliculata (Linnaeus) Decaisne and Thuret, is a much smaller seaweed than the previous two described. It grows in short dense tufts upto 15 cm high attached to rocks just above high water level of neap tides. It is frequently seen dried up and blackened. Black Pygmy Lichen is often mistaken for very small tufts of Channel Wrack.
Pelvetia does not have a midrib or gas bladders; the edges of the fronds tend to curl inwards – creating the groove or channel from which it gets its name – but this is not a reliable feature for identification. The fruiting bodies are irregular shaped, swollen, forked ends to the fronds.
Egg, Bladder and Channelled Wrack are all brown seaweeds belonging to the Class Phaeophyceae.
Revision of a post first published 2 May 2009
COPYRIGHT JESSICA WINDER 2011
All Rights Reserved