Thongweed, Himanthalia elongata (Linnaeus) Gray, was washed up in moderate quantities on the shingle at Chapmans Pool in June. This olive green perennial alga belongs to the brown seaweed group – the Phaeophyceae. The part that survives from year to year is small, about 3 cm across and looks like a stalked mushroom with a concave top. It attaches to rocks in deep pools or on the lower shore.
The long narrow ribbon-like part of the weed that is found, sometimes in great abundance, on the shore is in fact the reproductive body which is shed by the seaweed in summer. It may be up to 2m long and turns a more yellow-green colour as it ripens; sometimes with brown spots on it.
These long straps of weed wash up in interesting patterns on the beach sometimes tying itself up into complex knots. Where larger quantities occur, it can roll up into a long sausage shape many metres long parallel to the drift-line.
Yellow-green Thongweed reproductive ribbons washed up with Japweed and other seaweeds on a rock platform at Chapmans Pool.
Long narrow straps of Thongweed with a plume of golden Japweed, bright green Sea Lettuce and assorted red algae on a rock platform at Chapmans Pool.
A brown ‘slick’ in deeper water offshore shows where the Japweed and Thongweed are still growing.
In the photograph below, the Thongweed has been washed up in a mass and is drying out on the strandline of a cobble and boulder strewn rocky shore in the southeast part of Chapmans Pool.
Revision of a post first published 1 July 2009
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