Toothed Wrack on Worms Head Causeway

Toothed Wrack seaweed, Fucus serratus Linnaeus, close-up detail showing reproductive conceptacles on the receptacle in transmitted light. Specimen from Worms Head Causeway rocks, Gower, South Wales, UK (1)

Toothed Wrack, Fucus serratus Linnaeus, is a common and familiar British seaweed. It grows on rocks of the lower seashore in the inter-tidal zone. The pictures in this post were taken on the Worms Head Causeway in Gower when the seaweed was exposed at low tide.

This algal plant can reach a length of 2 – 3 feet – that is, up to about a metre. A seaweed is not differentiated into a stem, roots and leaves like the higher plants. However, it does have different parts. The plant body, or thallus, has a branched hapteron or holdfast – a root-like structure at its base – by which it is attached securely to the rocks.  The thin ‘branches’ of the hapteron grow into the cracks and crevices to hold the seaweed into position and make it very difficult for the actions of the sea to dislodge it.

A short cylindrical stalk or stipe connects the hapteron to a flat broad branched blade known as the lamina. In Toothed Wrack the edges of the laminae have an irregular serrated (saw-like or tooth-like) edge from which the seaweed gets its name. 

Reproduction in Toothed Wrack is mainly sexual rather than vegetative. At certain times of the year, the terminal few centimetres of the branched laminae become swollen; and these parts are then called the receptacles. Small cavities named conceptacles sit just below the outer layer of the receptacles and are connected to the surface by minute openings known as ostioles. [Actually, these tiny cavities are found in other places on the seaweed but in these locations they are sterile and only contain hairs. If you look closely at  Picture 4 in this post, you should be able to see regular grouping of these small hairs on some of the laminae.]

However, in the receptacles, the conceptacles are fertile and produce the gametes used in sexual reproduction. Fucus serratus L.  has separate male plants and female plants, each producing gametes that are shed through the ostiole into the sea water where fertilisation and development take place. 

Natural pattern and texture in seaweed: Tooth Wrack, Fucus serratus Linnaeus, detail of the swollen rounded conceptacles containing ripening reproductive products on the terminal receptacles - macro photograph in reflected light showing surface texture. Specimen from Worms Head Causeway, Gower, South Wales, UK (2)

Toothed Wrack, Fucus serratus Linnaeus, showing the branched receptacles bearing the conceptacles at the end of the lamina, blade or frond of the alga. Specimen photographed on Worms Head Causeway, Gower, South Wales. UK (3) 

Toothed Wrack, Fucus serratus Linnaeus, showing branched reproductive receptacles at the end of a flat, tooth-edged lamina. Growing specimen exposed at low tide on Worms Head Causeway, Gower, South Wales, UK (4)

Seaweed of the Gower Peninsula: Toothed Wrack, Fucus serratus Linnaeus, showing branched reproductive receptacles at the end of a flat, tooth-edged lamina. Growing specimen exposed at low tide on Worms Head Causeway, Gower, South Wales, UK (5)

Toothed Wrack and Coral Weed growing together: Olive-green Toothed Wrack, Fucus serratus Linnaeus, growing among purple Coral Weed, Corallina officinalis Linnaeus, exposed at low tide on the lower shore at Worms Head Causeway, Gower, South Wales, UK (6)

Common British seaweeds of the lower rocky shore: Toothed or Serrated Wrack, Fucus serratus Linnaeus, on the lower rocky shore with other common British seaweeds, exposed by a very low tide at Worms Head Causeway, Gower, South Wales, UK (7)

COPYRIGHT JESSICA WINDER 2011

All Rights Reserved

3 thoughts on “Toothed Wrack on Worms Head Causeway

  1. Pingback: Hill End to Spaniard Rocks & Back: Step-by-Step Part 6 | Jessica's Nature Blog

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